bad engine misfire...tried everything

[ClareSutton]

My '73 standard beetle is misfiring badly and will periodically backfire out of the exhaust if pushed hard. I have replaced the points, plugs, condenser and the coil. I have checked and re-checked the timing (7 deg btdc with vacuum hose off). The distributer is about 2 years old and is a single vacuum unit. The carb is also about 2 years old. The car was running like a dream for the last two years and has suddenly started this. I checked the psi compression on all cylinders:
cyl 1--100,95,100, 95
cyl 2--100,100,100
cyl 3--110, 115, 110
cyl 4-- 110,110,110

I think these look fine and should not cause this kind of issue. The only thing I have not adjusted is the carb. I can't see how it would go out of adjustment all of a sudden. I have scanned the Samba forum search engine and I don't see anything that I haven't tried. Any other ideas??? Thanks.

[oceanair]

Adjust the valves -- do it stone cold. .006 all of them.
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[Starbucket]

If you don't have an inline filter or its clogged its crap in carb. How old are your plug wires one might be leaking and shorting out momentary. When was the last time you gave it a good long 65 mph drive, you might be spitting out small pieces of carbon that hold the exh. valve open till it spits it out.

[Danwvw]

Adjusting the valves is always a good step before trying to tune the carb. However popping is usually mixture related. It could be it only pops when the engine is not good and warm. Someone may have removed the thermostat or the warm air to the carb or something is making it run very cool. Case should reach a temperature 180' F to be warm enough to tune.
It could be the carb choke opens too early. You also have it over advanced, timing it that way, but I don't think that is causing the popping. The Stock DP should static time at 5' ATDC with the stock distributor and carb. But most old PICT 34 Carbs are too leaky at the throttle shaft to idle anymore with the timing set so retarded. Do you have the retard vacuum side hose connected between the PICT 34 Carb and the Distributor? It may run better with that retard blanked off. Metal shavings in the points are really hard to clean out and they cause really bad random back-firing too.

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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[Danwvw]

Just re reading the first statement here, It's What engine? That is a Single Port Distributor. Does this 73 Beetle have a Single Port Engine in it? Like in Europe and England you see a lot of late bugs that have the PICT-30 Carb Perhaps you have one. I have seen them pop a lot when too cool! Perhaps the pre-heat manifold clogged up, if so you will sometimes see the manifold below the carb white with frost!

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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[67rustavenger]

[Multi69s]

I tend to agree with 67, I have encountered more then a fair share of bad new condensers. If you have any other condensers laying around give it a try, it doesn't matter model of distributer, they will all work if you can get them to fit. Bad running and backfiring are "usually" caused by ignition or air leaks. So also check that no hoses or carb plugs have fell off or cracked.
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[ClareSutton]

I have already replaced the condenser (today). I have also replaced the ignition wires. I adjusted the valves last summer. I'll check them again. I am also wondering if one of the new spark plugs might be faulty. Maybe I should buy four new plugs. Thanks for the tips. I'll let you know what I find out. Also, it is a basic dual port carb that has been running great for the last two years.

[67rustavenger]

What brand of condenser have you installed?

Seriously! Stop throwing parts at it and diagnose the problem.

Follow what I posted above and you'll likely arrive at the condenser again.
Yea, I know you just installed a new one today. But as shitty as they are these days, it's likely you have another bad one.

My buddy was convinced that it was something deeper in the engine. When It turned out to be the condenser after all.

I had a condenser fail 10 minutes after installation last year. And it was new.

Good Luck.
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[mukluk]

Step one for any rough running or tuning problem on a VW engine that the cause isn't immediately apparent: check your valve lash and adjust as required. Once that's done, check the plugs are gapped correctly, set the point gap, and then basic ignition timing.

Grab a stroboscopic timing light, connect it and start the engine up. Aim the timing light at your pulley and activate it, taking note of whether the light pulses are consistent or if they have a stutter -- repeat the check for all four spark leads, verify the advance is also functioning properly throughout the rpm range. Whichever leads have a stutter, those are the cylinders that are misfiring due to an ignition system problem. If none of them stutter yet it is still misfiring, the problem is due to a fuel delivery problem.
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1960 Ragtop w/Semaphores "Inga"

[ClareSutton]

I'm going to check the valve lash again and see if I can find a good BOSCH condenser from a supplier in London Ont. The condenser I put in has been around for a few years in my parts supplies but has never been used. Not sure of the brand. I'll let you know the results.

[Randy in Maine]

Is that picture of the iced up intake/non working carb heat from your car?

[gt1953]

Cannot be that serious the condenser's do fail. Doubt if its plugs or wires. Like 67rustavenger has is a complete known good function distributor. When you swap that out it is like changing five items. Points, rotor, cap, condenser and the dizzy itself. That has worked for me as well eliminating those components.
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72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold})

[sb001]

[Starbucket]

Test your condenser using a DVOM. Connect the leads to the condenser and set the DVOM to the 200 OHM scale and watch the numbers rise until you reach overload then switch the leads. The scale should climb back down, if not you have a bad condenser. Quit guessing and always carry a spare that you have tested.

[richardc]

check firing voltage at coil wire, does it jump a good 1/2 inch and if it does hold coil wire over distributor rotor and see if it jumps to rotor while cranking ( if it does you have defective rotor).

Rich
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1970 Ghia vert

[ashman40]

Please provide specific details as follows:

Make/model of your carb?
Make/model of your distributor? (use a mirror to see stamping on distributor body)
Spark plugs make/model?
Spark plug wires... solid wire core or suppression core? What brand?
Tune-up (replace cap, rotor, points, condenser) when was it last done?
Where you able to do the valve adjustments? Were any valves tight or loose?
While you are adjusting the valves for each cylinder in turn, confirm that the distributor rotor is pointing to the spark plug wire that runs to the same cylinder you are adjusting the valves on (valve adjustments are done when the cylinder is at the end of the compression stroke so the rotor should be nearly in position to deliver a spark to the same cylinder).

Report back with your details.

I suggest you read thru Speedy Jim's page on Engine No start troubleshooting. Walk thru his troubleshooting steps and they may help you isolate something that is not right.
http://www.speedyjim.net/htm/eng_strt.htm
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[ClareSutton]

My distributer is an SVDA vacuum adv which I bought new from CIP in June 2015 (part no. VWC-043-905-205). My carburetor is a Euromax 34 PICT-3 bought new from CIP in 2013 (part no, C24-113-129-031K. The SVDA is supposed to work well with a 34 PICT but not a 30 or 31 PICT. This combination has worked extremely well up until now. I would have to pull my plugs to check the exact numbers but they are NGK and were purchased at NAPA as designated for my car. The spark plug wires are NAPA brand premium. I adjusted the valves last summer and replaced the air filter at the same time. The condenser that I just installed has never been used but was in my parts supply for a few years. I'll try replacing with a new one. The dist cap and rotor were also changed with new un-used parts from my parts supply but are at least two years old.

[vamram]

[ClareSutton]

Ok, I took a quick look under the air cleaner today to see if the accelerator pump was squirting fuel into the carb......and it wasn't. I didn't think to check that earlier since the carb isn't that old. So I guess there may be a fuel clog somewhere in the carb (fuel pump is working well because there was pressure in the line) or there is something wrong with my accelerator pump. I'll have a closer look tomorrow.