Mis-fire / dead cylinder

[Ron Watson]

 

When I bought this car it mis-fired, idled rough, popped and back fired. I knew it needed some tuning, but it sounded good otherwise. It has never run properly and I can't seem to sort it out. Engine is a 2332cc.

 

I started with rebuilding the carbs (dual weber 44 IDF's). It ran better, but still popping and back firing at low speed.

Tired different pilot jets (currently has 60's) fuel screws are at about 2 turns out.

 

However, #3 cylinder does not respond to the fuel screw. I can turn it all the way in or take it out, with no response.

 

Also, if I pull the plug wire off #3, there is no change in the idle, like a dead cylinder.

 

When I rev the engine running I can see fuel in the #3 carb barrel, but when I pull the #3 wire at the cap,

the spark is very weak. (CDI ignition, not sure of what kind).

 

I have not checked the valves yet or done a compression check.

 

Thanks for any help.

[dunefreak]

Look into that weak spark issue first. Compare the spark to a known good cylinder. Possibly a bad distributor cap or wire. 

[Ron Watson]

I have already installed new plugs and wires, cap and rotor look new.

Does anyone know if a CDI ignition can fail on one cylinder?

I always thought you either get spark or you don't, but that's been my experience on single cylinder 2 stroke motorcycles.

[dunefreak]

I've seen many new caps be bad, usually cheap Auto Zone stuff. You'll need to figure out why that spark is weak. Swap wires with another cylinder just to rule that out. 

 

Are we talking VW here? I'm not very familiar with that ignition, but yes it usually works or doesn't. 

[raspadoo]

You can adjust the valves on that motor in under 30min. Pushrods are prob chromo on that engine so just set the lifters to 0. 

[bp-guy]

Is the exhaust tube on that cylinder hot to the touch? 

Pull the plug and rest it on the exhaust and see if it is indeed getting spark all the way to the plug.

Is fuel getting to the cylinder.

Accelerator pump working?

Check the inside of the cap for carbon tracks or cracks.

With the motor running, spray carb cleaner along the sides of the carb and see if the idle changes- if yes- you have a leak at a gasket.

Swap plug wires and see if the dead cylinder changes.

Clogged jets, suckers get clogged easily.

 

Look into a velocity stack air meter- it is crucial in setting the jets and getting all 4 cylinders balanced.

 

Just a few things I can think of that plagued me when I had my VW motor back in the day.

[Ron Watson]

Thanks for all the suggestions and input.

I had been swapping idle jets, thinking that was the problem, so I'm sure they're clear.

It's getting a weak spark on #3 and that's the dead cylinder. I can not get the carb to respond to the fuel screw, but I do see the accelerator pump squirt.

I don't have any spare "known good" parts, so I bought a (same as I have) 009 ignition kit with a new coil and plug wires. Should be here in the next day or two.

It looks pretty clean around the base of the intakes, but I will check for leaks.

I did the carbs when I initially got the car, so I think there clean, but that will be next, if the new ignition doesn't fix things. BTW, I have a snail type sinc tool for balancing the carbs.

As lousy as it runs, it's got some pretty serious horsepower (VW 2332cc with dual 44 webers). But I'm not going through a lot of money at it though.

I'm hoping to do a V6 Honda swap, after I finish some honey do's.

[Stormin189]

I had a similar issue on a 2054 of mine, what it ended up being was I had a cap from a non doghouse style engine where the oil cooler is in the fan shroud not on the outside, on the older style caps there a built in retard to prevent cylinder number 3 from building excess heat where has the air that cools the cylinder has to pass thru the oil cooler first, I did almost everything you talked about, but a new cap solved my issue

Edited February 13, 2019 by Stormin189
Misspelling

[bp-guy]

You don't need new parts to diagnose this.  you have 1 bad cylinder- so move a plug wire from another cylinder to the #3 position and put #3 where you took that wire from.  If the problem moves away from #3 to another hole- BINGO!

 

Remember this- Keep it simple, Start in one direction and and work forward/backwards. Don't jump around or you might miss the problem.  Sounds like the Fuel system is ok, work on the electric side.  Check the cap/rotor, if thats good, move to the wires. If they are good, go to the plugs. Throw in a new set just for added cheap security. 

 

VW's are such a simple motor, I have rebuilt them in my bedroom when I lived at home. Picked the damn thing up out of my 63 and walked it into the house. LOL

 

And as Stormin189 said- #3 is a culprit for less air flow. My sand rail had major overkill for my oil system. Deep Sump + stock oil cooler and a 96 plate cooler with oil filter inline. I had over 6 quarts of oil in my motor. 

[Ron Watson]

Just a follow-up.

After trying to chase down the problem, it seemed to keep getting worse. The spark kept getting weaker.

I finally decided to just replace the whole ignition system. I installed a Pertronix ll ignitor with the matching Ignitor ll coil, along with a new Bosch cap and rotor and all new plug wires. Spark is now strong on all cylinders,

however #3 still did not respond to the fuel screw.

I pulled the carb and soaked in the carb dip again. Now that I have the carb back on the motor, #3 is responding properly to the fuel screw. Except now the problem has moved over to #4.

I"m certain now the trouble was in the carb originally, but I had a failing ignition system making things more confusing.

I have a fuel filter inline, so I'm not quite sure how I'm getting debris in the carb, but I'll keep cleaning it till it works.

[bp-guy]

I did a quick youtube search and found this- This might be your culprit.

 

 

[Stormin189]

I use to love my dual 44s, the buggy ran great, but cheap ethanol gas was always plugging up the idle jets. I started buying ethonol free 88 and that seemed to help but me and a friend noticed after riding the buggies hard then shutting them down, we could hear bubbling coming from the carburaters, like the fuel was boiling. They sell spacers that insulate the carburater from heat sinking from the head after shutoff. My friend uses them now and hasn't plugged a jet in 2 years

[Ron Watson]

I sometimes get annoyed when a thread thoroughly describes a problem and then ends without

a solution. So here's my solution to the  "mis-fire / dead cylinder" issue I was having (after replacing the ignition system), I finally solved the problem.

 

After I got it running again, I still had issues with the fuel screws not having any effect.

All the way in or all the way out made no difference in idle speed and of course ran like s&#t.

I decided to take the carbs off for another cleaning. Starting with the driver side I couldn't see any thing anything dirty, but I put it in the dip.

 

As I was stripping the carb I took the pilot jets out. I noticed when I unscrewed the holder, the pilot jet remained in the body. I remember when I put the jets in the carb, they did not fit snugly in the holder, but I assumed the jet was trapped and being loose wouldn't matter. Just more convenient when you take them out.

 

Last night I was looking a Weber manual and noticed a drawing that showed the pilot jet

and it caught m eye that the jet was suspended in the holder. Then it dawned on me that might be my problem.

 

Sure enough, when I put the driver side carb back together I spread the jet end to make it fit tightly in the holder. Then I took just the pilot jets out of the pass side carb (didn't pull the carb for cleaning again) and tightened the fit on those pilot jets.

 

When I put it all back together and fired it up. At first I worried I hadn't found the problem. When I started adjusting the fuel screws and sync'ing the carbs, the idle started smoothing out and it would rev like a 2-stroke.

No flat spots and no hesitation. It still made a puff of black smoke each time I rev'ed it, so I started backing off the accelerator pumps, until the black smoke went away.

 

Bottom line, my fuel screws would work and then go stop working, for what seemed like no reason. When the problem was the pilot jets did not fit tightly in their holders.

 

I don't know whether to pat myself on the back or kick myself in the butt.

 

They sell spacers that insulate the carburator from heat sinking from the head after shutoff. My friend uses them now and hasn't plugged a jet in 2 years

 

I think I'll add these for cheap insurance.

 

Thanks to everyone for their knowledge and help. Hope this helps someone.

 

[raspadoo]

Thanks for the follow up and nice find