Nearly stalling after rev. Misfire at speed.

[Rizz280s]

Hi all,

1970 280s, aftermarket double barrel Holley carb

1. I adjusted the carb this morning (idle and mixture screws) and now it idles nicely and spits out less fuel from the exhaust while warming up, but a new problem has become more apparent.
After revving and taking the foot off, the revs drop and the car nearly stalls. Any ideas what it could be?

2. The other thing is a spluttering and lurching when cruising. It runs as smooth as a new car when accelerating, but when I reach speed and hold my foot steady, it feels like it's swaying between having too much fuel and not enough - sort of spluttering and lurching and almost dropping out. This means I have to constantly let the car slow down and then accelerate harder back up to speed, slow down, accelerate etc.
The same sort of splutteriness can happen if I accelerate too gently from a stop, so I make sure to put my foot down firmly when I accelerate too.

Any help would be very very much appreciated!

-Rizz

[CraigB]

So it is a SOHC 6? And just one holley? Interesting what they used as a manifold. I had a later W116 280s with DOHC M110 with a holley on it, but that replaced the original Solex that usually give trouble and just bolted up in its place. It might be relevant though because i messed around trying to get it to run right and the conclusion between experts etc. that it just wasn't the right carb and was wasting my time trying to get it to run right. What model holley too? There is something called an economiser (something like that) which is what i had and they are a bit of a disaster or at least not suited and lack of adjustment. The double pumper models have all the adjustment but probably a bit big for the application. Just going by memory - i think that was the conclusion. For me i went to a straight LPG conversion and with rebates at the time was cheaper than a new carby and it all worked great.

Depends on how much you want to stuff around and at what point you value your time into the equation, but for SOHC W108 the only really successful carby outcome i have heard of is the Weber conversion sitting on standard manifold. A kit is around the $1000 mark but once fitted all the problems go away by the sound of things.

See what other responses you get but i think you will need to identify what Holley it is you have.

[Rizz280s]

It's a W108 280s with the M130. I'm not game to have a look under the rocker cover just yet to tell if it's SOHC yet, but I will next weekend to inspect the valves.

Update:
I was looking through the nice, new, clear fuel filter I put in the other week and noticed air bubbles coming through with the fuel. Not a good sign right? I inspected the hoses and although they were old, looked ok. The hose clamps were loose however. I replaced the section of hose and tightened the clamps - no more bubbles, slightly nicer idle and easier start - but still gurgling when cruising (though significantly reduced from what it was).
I'll inspect the lines a bit more - I recall the line directly from the fuel tank was a bit shabby, so Ill check that out - it might clear things up even more.

I don't think that I need a new carby. I'm not sure how they adapted it to the old plate and I don't know what model it is even, but I don't think it is the problem. I'm starting to think it could be a timing problem - maybe the vacuum advance? I noticed that the distributor has a line from the carby going into the back, but has a nipple at the front (vacuum retard?) with nothing connected. I also thought it might be a timing issue because it is sluggish off the mark and, if it was too retarded for example, might explain the rev drop on take-off when combined with fuel starvation?
Lastly (sorry to drag on), I noticed that throttle linkage (a cup-and-ball linkage at each end) at the carb has a bit of play - as if the cup has worn down.
Another thing to add to this is that I have upgraded to pertronix electronic ignition - if that is a factor at all.

So some new questions:
1. Is the vacuum advance/retard necessary or is it one of those emissions-and-performance limiting things?
2. Is there any way to measure the function of the coil?
3. Any tips for identifying the model of carby?
4. Is the bit of play in the throttle linkage (guessing ~1 - 2mm) normal and could it be contributing to any of these symptoms?

Thanks for replying Craig!

[merc-304]

Carb housing should have a number stamped on it which you can check thru uncle google Holley and the linkages should no play in them or a very minor amount - They are cheap to replace
Do you have any play in the throttle shaft..the one which runs through the carb ?
Replace all your fuel hoses .

[CraigB]

If its m130 and engine number starts with 130, then it is SOHC. They came with dual 2 barrel carbs so that's interesting how they went about all that - sounds like a lot of work!

I don't think they had any sort of vacuum retard and just he one hose. Later M110s had that sort of thing. Maybe a later distributor added? Maybe other markets like US had stuff like that? Not sure about coil but doesn't sound like the sort of thing you describe. As said, there will be a stamping on the carb somewhere. Play in linkages not ideal but i can't see how it would affect he running.

Especially being not standard, my suggestion would be to get it on a dyno and see what the mixture is like throughout the rev range. That sounds concerning to me what you said about spitting fuel out of exhaust. I'm pretty sure overfueling can cause damage to bores etc so worth checking out - that stuff is expensive.

[Rizz280s]

Thanks for the promt responses Craig and merc-304 - it's so refreshing on a forum like this!

Ill definitely look or a stamped code and google it (unfortunately it's dark now and I don't have a garage to work in anymore) so that will be another one for next weekend. I'm not sure which linkage you're referring to, but I'll have a play and look for play everywhere I can.

Honestly Craig, the more I get to know this car and, now that I have a Haynes manual, get to know what things should look like it's becoming more and more apparent that this car is just one quick fix after another. The last inspection was 2003 according to my DOT account for the car, which makes me think it was probably off the road for a while, and there's receipts for all sorts of major work going back a little further. I don't have the money to do a proper job of it yet, as I'm still in uni, so I'm just trying to keep her alive until the time that I finally do have some cash to splash.
There's hoses cut and plugged everywhere (and a vacuum nipple of some sort on the back of the carby), wires ending abruptly, and all sorts of filler in places I'm certain shouldn't need it - and Im not talking about body filler, though there's evidently a little of that too!
I still don't regret buying it - it was cheap, I've learned a lot, gained an immense respect for car history and Mercs in particular and it's so beautiful to drive when it's running nicely

The distributor is stamped with "Bosch 231116062" - not sure if that's original or not, but the first hit on google suggests that it is.
The fuel spitting was before the carby adjustment and I haven't checked for it since, but from listening to it drive, it sounds like it's missing ignition intermittently on some strokes. It even backfired once today (when I was giving it a good high-rev run on the highway), which suggests to me that it's still running rich or not burning all the fuel on all of the strokes.
I think the previous owners rich carb adjustment was probably to cover up some other vacuum problems (eg the almost completely sheared brake booster hose). The bloke I bought it from said he mostly runs it with the choke out a little all the time and recommended I do it too, but I figured that couldn't be good for her - which lead me to the hose.

I like the idea of the dyno run. Maybe I can use some of the uni's resources on this one. They love inter-department collaboration and all of that kind of stuff and it would be a great little educational tool for some engineering students to see something that isn't injected and supercharged.

[merc-304]

Its dark outside ...slip outside and fire her up..lift the bonnet ..just wondering if youll see any bright blueish flashes from plug leads coil or anywhere

If you can post some pic of the carb and inlet manifold conversion would be gd and some engine bay pics of what hoses are blocked off etc.

[CraigB]

Where are you located? If you could put even just a city in your profile it just makes things easier. If it was mine I wouldn't mess with it and would be looking for a local source of the right bits. There has been a lot of rusty 108s wrecked and you can probably find stuff fairly easily once you know where to look. That brake booster hose leak or any large vacuum leak into intake will cause your sort of problems - having the choke on would suggest that too. It sounds right about quick fixes. Often people will find a cheap or free carby and then spend huge amounts of time - depends if you value your time and you have to consider that it might never work right. Agree in the dark is best time to find and earthing ignition problem. Pull your plugs too and have a look because if its not running right they can get fouled. filler sounds like chasing vac leaks. You can spray aerostart around these places and see if revs increase - confirms an air leak. But that booster hose sounds like a good place to start.

[Rizz280s]

Mmmm I've tried that test not long ago - the flashes in the dark - but didn't see any. The leads are all quite new too, so I don't think thats the problem, but I will give it a try. Ill get some fresh pics of the engine bay next weekend (tomorrow is a full day unfortunately). This is exciting! Getting the ball rolling!

Im in Perth mate. Ill update the profile now. I replaced that brake booster hose a little while ago and it instantly made a massive difference - I really wish I could drive it when I first bought it and then again now to be honest.
I've been meaning to do the fog machine vacuum test for a while now. I've sprayed 'Start ya bastard' around the carby before and didn't notice any change in revs or anything, but that was last year and there's been a fair bit of mucking around in there since then. I'll give it another shot.

I cleaned the plugs fairly recently (as the car completely stopped running a month or so ago) and regularly clean and tighten the most obvious electrical connections (including the leads to the distributor). The plugs were quite fouled the last time I got it running after it hadn't been running for a while, but the reason was that I was trying to crank on a near-dead battery. So far, 90% of the time the bad running has been battery related - since I only drive her on weekends and, having been either sick or busy, have left it longer than a week to run her.

Again, thanks for the help guys :occasion5:

[CraigB]

Lots of good people in Perth. I can't think of an obvious person with W108 M130 bits. There are finnie people and V8 W108 I can think of. Giles has wrecked a few cars, not M130 but then he knows lots of people and i think is in the club so he could be a good person to ask. Also there are a couple of facebook pages that could pick up more people - Ozbenz facebook and australia/nz mercedes benz buy, sell and swap.

Thinking about it more I had a cranky M130 that was giving me grief and running erratically and backfiring at times. I put a distributor in from another known running car and it solved it. I figured it was sticking weights or something like that. But weight of springs etc, sliding plate can all effect the advance curve. More than anything i am thinking putting the right distributor in it would be a good start if it is running erratically.

[Rizz280s]

I drove it again today, after I managed to fit in a very rushed replacement of the bit of hose from the tank to the fuel lines, soaking my jacket and eye with fuel in the process, and decided that it just feels like it is too rich - It basically didnt need the choke to start up, it's sluggish off the mark (which could be too rich or too retarded), but accelerates strongly when through after 55kph and it still sounds like it's still not burning all the fuel at idle (put my hand in front of the exhaust, hand smelled like fuel).

I am thinking now that the carb adjustment I did with my Dad might have gone too far the towards rich.
I'm also thinking that there is a problem with the distributor.

I'll start from scratch and use my manual to the tee to reset the timing and tune the carb. Hopefully that should smooth things out.
If not, then Ill start looking more closely at the distributor - check that the weights inside are moving freely, but not too freely and make sure that the vacuum advance (or retard?) is able to move the plate and return to position smoothly.

I noticed another thing the other day when tuning the carby with my Dad - the choke doesn't return to fully open when pushed back in. You push it all the way in and it goes 95% of the way and you have to physically push the choke butterfly valve to the point that it pops to full open. Ill try to sort that out. Dad didnt seem to think it was an issue, but it could still affect the fuel/air ratio a tiny bit right?

Another thought - is it possible to have a carburetor that is simply not compatible a given engine? Say it is able to deliver enough fuel under low revs (idle), is it possible that it isn't able to deliver enough fuel at higher revs?
Assuming your vacuum and timing are perfect, is it possible a carby isn't able to deliver enough fuel for the car's needs only within a certain power range, while being able to deliver enough fuel under another range? Or should a carby be able to always deliver fuel at the required amounts - with poor performance within some power ranges being entirely the result of a bad tune (fuel/air ratio)?

[CraigB]

Yes that was my point originally, if you are starting with non-original parts then I think you are pushing the proverbial uphill. These companies make a huge investment developing the carbies to work on a particular car. You can swap but best to something that someone has done before and done all that development work, like the Weber kits sold to suit your car. If you look at the range of jets, chokes, air thingys, whatever they are called - tubes with holes in it to suit say a DCOE weber, it is mind boggling. It all has to match the cam on the car, when it needs more or less fuel, porting etc as to how much velocity of the air passing the jets and sucking the fuel in etc etc etc. When the Chrysler factory built their E38 Chargers with triple webers, the story was that they had every engineer and expert in to try and make it run right, including communicating direct with Weber. In the end they shipped a whole car to Italy and in no time they had it running perfect. And the story goes they were really impressed with the car which is high praise from a company that set up Ferraris etc.

And like i was saying my M110 engined car had a particular model Holley that i tried to make work but was advised it was basically impossible to do that given the amount of adjustment available on that particular model. If you have more time than money at the moment, I would be putting out a call for a set of the right carbies, which I would hope someone will sell you cheaply and you can pull down and clean up and see how you go. They are not the greatest carby and lots of people hate them (although i have had a pretty good run) and that's why the best way to sort it is to spend around $1k and fit brand new downdraught webers especially set up and jetted etc for your car.

Same goes for the distributor though. If it has a vacuum retard set up on it then i think it is out of a M110 or something else. Distributors are set up with a particular 'curve' that suits different engines so it will advance at the right rate at the right time.

With so many W108 bodies rusted away over the years, I would have thought somebody locally is sitting on a stash of parts that they would part with. I have stuff here but it is a long way from you and i couldn't guarantee any particular part. If you were local i would swap bits over but freight would be an issue. We can talk later if you draw a dead end, but i think you need to find my equivalent local to you and i would be surprised if there isn't someone.

And I should have said at the beginning, have you compression tested the motor? Such an easy thing to do but if you have a bad sealing valve, broken ring etc then it is also basically impossible to get it to run right. If it starts good and doesn't blow smoke then it is probably fine - if it doesn't do those things then it could still be fine - but buy or borrow a gauge and you will soon know. And buy one gauge and it will last you a lifetime. Even proper leak down testers can be had for $40 or so on ebay, but need a compressor to work with those.

That choke butterfly wont cause the problems you are having but particularly and high revs its best to have straight, but like i said, i think you are possibly on a road of frustration and grief without the right carbs. And also by the sound of things you have one 2 barrel carb, which must have a fairly long runners to get to cylinders, where there were 2 x 2 barrel carbs - hard to imagine that can deliver the same sort of air flow at the right speed. Not saying it is impossible for an expert to get to run right but starting from scratch i imagine the labour charge would be far beyond what you paid or the value of the car. and of course these are just my opinions but based on 20 or more years of 108 ownership.

[merc-304]

Jam Eng have the Weber kit to suit - approx $US 630 plus shipping.

[Bartman4800]

That was the kit that I was going to suggest.

I guess someone slapped a Holley on, and it is not suited for that engine with the CFM it pulls.

The Jameng kit is plug and play, look here:

http://www.jameng.com/products/Mercedes ... -DGEV.html

A few more things to check: There are 2 pieces of fuel hose just above the prop shaft (in the finnie and I think in the W108 too)
They join the fuel lines and are often overlooked

Other tip: buy a cheap diagnostic vacuum gauge from Supercheap auto or such. It is amazing what you can tell when looking at the vacuum of a carburetored engine.

https://www.youtube.com/watch?v=SdlNwm8OHco

Start with the basics:

-Get your ignition sorted (8 deg btdc with vacuum blocked) at around 800 rpm
-Make sure you have great spark (breaker points not pitted, capacitor in good condition, rotor and cap in good condition, breaker points set correctly) or install a pertronix or even better a 123 replacement distributor
-Adjust your valve clearance (0.08 on the inlet 0.15 on the exhaust), adjusted cold
-Make sure your brake booster is not shot and it looses vacuum through that
-Make sure the fuel pump is working properly

Good luck!

I am in Perth too

Bart

[Mercmad]

I'd love to know what the manifold looks like or what it is Off , the only single carb manifold I have seen on a M180-M114 Six were the 220a of the mid 1950's and the 220B of the early 60's .The 220a used a three bolt carb the same as Ford V8's (lots of the 220a's were converted to Ford carbs to cure solex problems. ) and the 220b used a single barrel carb. Both are rare. So i am thinking, is your carb a two barrel or four barrel? There were thousands of four barrel holley carbs sold in Australia in the 1980's to fit all sorts of things and most were 650 CFM carb,I have worked on 110 DOHC engines fitted with this carb and it is totally wrong . The ideal is the rare and expensive 350CFM four barrel or the common 300CFM two barrel. The problem with the 650 carb ,besides being far too big is that it cannot be tuned like the double pump carbs . So a lot of them were fitted with things like screws to stop them opening up under full throttle etc etc . Yours sounds like you need to get a tune up specialist with experience on old carbs who can set the float level and swap the jets to get the mixture right at idle, mid range (where you drive the most ) and full throttle . I would also replace the power valve . One back fire through the carb and they are history. This is a power valve. once, you could go to any repco store and buy these off the shelf, but today, go on line and check out holleys own forums on what carb you have and start looking for a smaller one. And while you are it, consider buying a pertronix in=gnitor to make sure you are getting a good hot relaible spark .


https://forums.holley.com/entry.php?430 ... lve-Tuning

[Mercmad]

I'd love to know what the manifold looks like or what it is Off , the only single carb manifold I have seen on a M180-M114 Six were the 220a of the mid 1950's and the 220B of the early 60's .The 220a used a three bolt carb the same as Ford V8's (lots of the 220a's were converted to Ford carbs to cure solex problems. ) and the 220b used a single barrel carb. Both are rare. So i am thinking, is your carb a two barrel or four barrel? There were thousands of four barrel holley carbs sold in Australia in the 1980's to fit all sorts of things and most were 650 CFM carb,I have worked on 110 DOHC engines fitted with this carb and it is totally wrong . The ideal is the rare and expensive 350CFM four barrel or the common 300CFM two barrel. The problem with the 650 carb ,besides being far too big is that it cannot be tuned like the double pump carbs . So a lot of them were fitted with things like screws to stop them opening up under full throttle etc etc . Yours sounds like you need to get a tune up specialist with experience on old carbs who can set the float level and swap the jets to get the mixture right at idle, mid range (where you drive the most ) and full throttle . I would also replace the power valve . One back fire through the carb and they are history. This is a power valve. once, you could go to any repco store and buy these off the shelf, but today, go on line and check out holleys own forums on what carb you have and start looking for a smaller one. And while you are it, consider buying a pertronix in=gnitor to make sure you are getting a good hot relaible spark .


https://forums.holley.com/entry.php?430 ... lve-Tuning

[CraigB]

His original post starts by saying it is a double barrel holley and the second one says he has fitted pertronix.

I was thinking maybe someone had adapted an M110 manifold, but that is 4 barrel so maybe it is an earlier one.

And when i decided what to do about the Holley i had, a big factor was calculating the real cost to get it running and so i went down a different road when i knew exactly what it would cost me - and i never looked back. Taking it to a specialist it won't take up much time at $100or so per hour to start adding up. It might work but i'm not much of a gambler so i would be thinking about the only set up that i have heard people rave about how good it is.

[Mercmad]

A lot of the two barrel holleys are pretty much non tuneable too , and his might be a common 500CFM 2Bbl which was fitted to a lot falcons in the early 90's to try and improve performance, John Cain In Newcastle sold hundreds of them along with his manifolds to holden and Falcon owners, which did little but make them use more fuel .. . The Weber two barrel wont work as it's too small, OK in a twin carb set up. The ideal was the Weber dual throttle carb as fitted to Fords V6 in the 60's . Impossible to find in OZ unfortunately.

[Rizz280s]

Hey all!

I've finally gotten around to having a proper play again. I reset the ignition timing according to the spec in my Haynes manual, (4-12 deg BTDC, vacuum disconnected) and retuned the carb. Two things were very obvious. The timing was way out. I mean really, embarassingly far out (too advanced). Im surprised it wasnt pinging to be honest. With the new timing set, the revs were much lower. Previously I hadnt been using a timing light and had gone by ear.
I had a test ride with my dad after that and it was nearly stalling at idle, when in reverse or drive, but not in park or neutral. We raised the idle a little and readjusted the mixture. I turned the mixture screw to the left - the revs rose - and I could continue turning left with no further change to the revs or sound of the engine. It sounded smooth. I turned to the right (about 2 turns from the start of the higher rev, smooth spot) and it began to run rough. My dad said to just set it at the point where the revs were highest, but I thought you were supposed to set it between the two points - so I did.
We also adjusted the throttle linkage - shortening it to cut out some of the slack I mentioned earlier. There is still some slack, but that is because the ball-cup joints are old and worn.

I also sprayed some 'Start ya bastard' around the manifolds, listening for changes in revs - no change (thankfully).

Anyway, the end result is that it now idles beautifully (with nearly no evident misfire ~say one 'fluff' every 2 minutes), acceleration is a bit stronger and it cruises beautifully - none of the spluttering I was initially talking about. It feels like a whole new car! Im a happy chappy!

Lessons to other beginners: Get a Haynes manual. Get a timing light. Do things properly (not by ear!).

Ill post the pics of the holley and the mount in a sec.

[Rizz280s]

These are pics of the carby.





And this one is a question from my dad. Shouldnt this filter be basically full? I wondered this too - how the hell does enough fuel get through that filter to the carby - it's not even half full!


If none of those images uploaded, these are the links.
https://imgur.com/ZcqYAQ6
https://imgur.com/KHSupmV
https://imgur.com/ZPAxmoY
https://imgur.com/6wIDvUu
https://imgur.com/RiGuz42

[merc-304]

So your carb is a Holley 350
Yes your fuel filter should have more fuel in it than that...does it have more in it while the eng is running ?
Homemade card to manifold adaptor i think ?

[Rizz280s]

Hmmm interesting.

I couldnt find any hits for the specific carby model when I googled the stamped numbers "6392-3" and "6R1919B" but got plenty of hits for other forums with old Fords and Holdens). I think you're right that it's a 350 though. It looks most like the Holley 2300 350 CFM Performance 2BBL carburetor.

The volume in the filter didn't change when the engine was running and that picture was taken just after shutting off the engine.

More beginner questions, if you'll indulge me:
1. Slight leak from the base of the idle screw - I just read that this can happen when the O-rings or something like that are lost when replacing the screw. Is this likely to be a problem?
2. Float level. This one is adjustable and quite easily I think. What happens if the level is too low? What about if it's too high?

Thanks again guys! Im loving the support here!

[merc-304]

I put - Holley 6392 -3 into google.
Also try Holley float level adjustment.

[Tony From West Oz]

With the fuel filter:
As you most likely have a fuel pump and accumulator at the tank, you could just loosen the outlet hose clamp on the filter, angle the filter so the outlet is highest, then wiggle the fuel line to allow the air to leak out, with fuel filling the filter. Re-tighten the hose clamp.

OR

Just leave it, you are getting plenty of fuel to the engine. The only thing I would check for, would be air bubbles in the fuel line coming from the accumulator resulting in the filter accumulating air. Was ti full when you started?

[CraigB]

I have to eat my words and my thoughts! Seeing those photos of what looks like a botched together manifold but it works and you can't argue with that. Just because something looks rough it doesn't mean the person didn't know what they were doing. Mind you, if you drove another 280s in good condition it is hard to imagine you would get the same performance as having what looks like about double the carbie volume right above the inlet tract, but if your happy with performance and economy then who cares!

And those filters, i don't think i have seen them without some air in them, but that does look like a low amount of fuel. Being a 280s that should have a mechanical pump off the front of the motor but no reason why you can't just replace that with a cheap 'facet' style pump if the old mechanical is tired. Bubbles could be a leak in diaphragm, valve etc or even the cam that drives it could be worn i guess.

[Rizz280s]

Double the carby volume? Do you mean the carby is much bigger than it needs to be?
I'd considered a new fuel pump, but then... if it ain't broke, dont fix it right?

I still dont know how the 280S really should feel to drive, so you could still definitely be right for bashing the set up haha. All I know is that it is slowly getting better and better.

Tony - I dont think this one has an accumulator? Is that just for the injected models? This one has a mechanical fuel pump, just out of view in the last photo. I can follow the fuel lines all the way to the tank and there doesnt seem to be anything else attached.

I was reading yesterday about the windscreen washers in the W108s and apparently they mostly had foot pumps with a rubber bladder underneath the wiper switch? Anyone have the manual foot pump washers here or is it a US/Euro thing? I think it is so cool!
Mine looks like it has some sort of old electric pump in the washer reservoir, but I dont know what activates it or how to test it. Ideas?

[Tony From West Oz]

OK, I don't know the model well.
Could the air in the filter be the be cause of:
Your engine nearly stalling? - Possibly!
Misfire at speed? Quite likely!

The only obvious thing left to check is: Why does the fuel filter have so much air in it?
Was the fuel filter full of fuel when you started ?
Do you see any air coming into the fuel filter when the engine is running?
Does the fuel filter fill up again at idle?
There could be an air leak into the fuel system before the fuel filter. Please check / replace all flexible fuel hoses between the filter and the fuel tank.

[CraigB]

Standard is 2 x 2bbl carbs that look similar in size to yours - yours has 1 x 2bbl carb. Should be a photo or pic of the set up in your haynes would have thought. And only mentioned fuel pump due to reason for air in filter. But if its working and including being under load then i agree, just enjoy it. I think Tony that his earlier post suggests he doesn't have any more problems with how car running.