TheSamba.com :: View topic - HELP! - Backfiring through carb, rough idle, car dies

Sun Jun 10, 2012 10:27 am

***Please see most recent post below for up to date symptoms. **

Hello all, this is my first aircooled VW and my first post! Need help...

1970 Ghia , 1600 single port

Car ran fine for past few months since I got it (even though I had only a few hours of drive time on her)

- Installed new exhaust and J tubes.
- Car ran fine, I had it idle for 15 minutes or so while the low temp paint was burning off
- Made it a block and upon accelerating the car dies
- Backfires up through carb
- Have to manually open up butterfly to keep it running, even so it backfires upon "acceleration" and wants to die. Dies within seconds if I let up

What could cause this sudden change? I tightened down everything exhaust the best I could, and even put some hi temp gasket sealer around certain points etc.

Adjusting idle speed and carb screws seems to do nothing. I have sprayed WD40 on certain points to see if it runs better (leaks) and so far no luck.

Help!!! Thanks in advance, if any info is needed I can provide (video, pictures, info etc)

Sun Jun 10, 2012 11:06 am

It sounds as though you may have knocked off you vacuum advance tube
Thin pipe running to distributor. Or you timing is out

Sun Jun 10, 2012 11:11 am

Thank you for the prompt reply.

- Can the timing just change or would you need to adjust or change things for that to happen?
- I did notice that just under the carb there was a cable with a "ball" on the end that had popped off. Would that then cause the timing to be off for whatever reason?
- Could a spark plug or wires cause such symptoms? Normal for a wire boot to be melted?

Thanks again, I will investigate the vacuum advance tube.

Sun Jun 10, 2012 11:48 am

Everything appears to be hooked up to the distributor.

Tue Jun 12, 2012 4:17 pm

Got engine to keep running, but when I attempt to accelerate is when it surges/backfires from carb and dies. I checked the rotor and valve positions...seemed ok. Clogged jet? Fuel pump? I do have an inline filter that seems to get nasty at times

Just trying to figure out why this would suddenly change. Bolt on lower pulley was slightly loose as well. I will get a test light to at least static time it

Tue Jun 12, 2012 5:27 pm

The backfiring definitely sounds like a timing problem. Exhaust leaks can sometimes make a snapping sounds but that's usually during deceleration.

All the plug wires stayed on? (nothing crossed up there?)

Did you maybe bump the distributor when you were doing the rear exhaust bolts? Try to rotate the distributor back and forth with low/medium force to see if it's not tight and you could have bumped it. Definitely get a timing light on it to make sure.

Usually if a vacuum advance line is off you're going to have a very slow acceleration but no backfire because the distributor isn't even advancing.

I doubt the cable with the ball-end is the problem.

Quote: - Could a spark plug or wires cause such symptoms? Normal for a wire boot to be melted?

is there a boot that's melted?

if you're not firing on a cylinder you might get some backfiring when it dumps non-ignited gas-air into a hot exhaust. It would run pretty rough at idle though..

Thu Jun 14, 2012 4:59 pm

I static timed it to 7.5 degrees past TDC (Is this correct?) and it seemed to run better, but then eventually went back to doing what it is doing on acceleration. I attempted to adjust the two carb screws numerous times...any tricks for this?

PICT 30 - 3

Backfiring through carb, power surging, some backfiring through exhaust. I somehow managed to drive it around the block and it especially wants to die/power surges once I get into 2nd.

Here is a link to a quick video I took. Can you also tell me if it appears to be idling too high? I feel it is and I do not have a tach

[url] http://s41.photobucket.com/albums/e289/thelaststrum/?action=view&current=VIDEO0037.mp4 [/url]

Thank you all so much for the help, I need to get this thing running accordingly asap!

Thu Jun 14, 2012 6:44 pm

sounds like an issue with the carb..(too lean). http://www.vw-resource.com/34pict3.html

Thu Jun 14, 2012 7:25 pm

Did you remove the dizzy while working on it? IF so, did you make sure it was completely seated when reinstalling? I thought so to once when I had the same symptoms. turns out the dizzy wasnt fully seated and would move. check it out. Definetly sounds like a timing issue.

Thu Jun 14, 2012 9:22 pm

EPETREA wrote: Did you remove the dizzy while working on it? IF so, did you make sure it was completely seated when reinstalling? I thought so to once when I had the same symptoms. turns out the dizzy wasnt fully seated and would move. check it out. Definetly sounds like a timing issue.

The dizzy?

I had similar symptoms and think it might have been one or both of the filters; either the tank or in-line filter.

If the tank has a brand new filter, is there really a need for the in-line filter?

Thu Jun 14, 2012 11:03 pm

Check that the accelerator pump is working properly. If it isn't working right the motor will hesitate and can backfire when the throttle is opened - the resulting lean condition causes hesitation and often backfiring. The condition is temporary - once the carbs main jet catches up with the demand put on the motor to accelerate under load the motor will run better. Improper timing will make this condition worse.

You need to give us the distributor (dizzy - ugh - hate that term) and carb model so someone can supply the proper timing information. Many distributors have very different timing requirements.

Fri Jun 15, 2012 12:06 pm

Since this started with exhaust replacement,does the new setup have provision for the heat riser?

Fri Jun 15, 2012 2:38 pm

The cap is on tight as is the actual distributor.

It is a solex pict 30-3 carb, the distributor is a single vacuum line one , not 009...

The new exhaust is the black GT exhaust and does have the same tubing for heat risers. Would that be addressing it?

Thanks again everyone

Fri Jun 15, 2012 5:24 pm

YOU ARE TOO LEAN ! see the link I posted earlier. You took off a somewhat restrictive exhaust and installed a free flowing one. Usually the people who do this are doing it to a BIG motor with dual carbs already and they are re-jetting them to suit their motors. Pull a sparkplug and look at the color and you will know if it is lean or not. The exhaust is flowing faster than the intake. IMO

Fri Jun 15, 2012 5:47 pm

Ok I gained some ground...

I yanked the carb off and found that the accelerator pump holes (with the balls) were gunked up. I cleaned and put everything back on (forgot one gasket, DOH!) I will put back on tomorrow. The area by the diaphragm is now leaking fuel...will try to readjust and tighten.

NOW...it still has some issues starting up, but once I do get it started the acceleration is smooth with no backfiring at all.

BUT...

It dies as soon as I let off the throttle. I attempted the standard adjustments as listed in the link above. It still dies... I will post a video tomorrow morning. Is there an accelerator pump adjustment that would cause too much fuel to be dumped thus causing it to die? Would a vacuum leak from that missing (one of two) gaskets cause this?

I am learning a whole lot, and thank you again for keeping up with my first thread. I am almost there!!!

Fri Jun 15, 2012 7:14 pm

Make sure you don't have a intake to carb leak. You might be sucking air.

Fri Jun 15, 2012 9:36 pm

MKEVW13 wrote:
BUT...

It dies as soon as I let off the throttle.

Adjust the throttle screw up a bit. If it won't idle without opening the throttle more than the adjustment allows then you still have something plugged up in the carb. Find the idle jet and pull it out - probably what is plugged.

Sat Jun 16, 2012 11:44 am

Took off carb. Cleaned up everything I could. Also found the electromagnetic pilot and choke weren't working. This changed everything. The car starts and idles. Has smooth acceleration when in neutral. Somewhat in 2st, but then once in 2nd it surges and has poor random acceleration. I believe I made rich carb adjustments too. I.think.this is my last hurdle....