Popping from cylinder#2 only.

Millennium Falcon · Posted: Tue Apr 10, 2007 5:23 pm Post subject: Popping from cylinder#2 only.

1972 type IV, dual solex carbs, stock dizzy.

Here is what I know:

1. A popping (slight backfire) seems to be coming from cylinder #2. When I remove the #2 plug wire from the dizzy cap the popping totally stops and it idles fine on 3 cylinders (idles not too bad on 4 as well).

2. Popping is most prevalent when engine is warm at idle and while bumping the throttle up a little.

3. Valves gaps are 0.15 m.m.

4. Firing order is correct.

5. Each cylinder pressure tests at around 120 p.s.i. including cyl #2.

6. Idle mixture screws are out about 2.25-2.5 turns. (and I have tried much richer and much leaner:still popping)

This is what I would like to know:

Why would this is happening to only cylinder #2 and not #1?
If there was a burnt valve the p.s.i. should not be at 120, right?
Is something plugged?

Cheers.
_________________
"Don't worry, she'll hold together . . . You hear me, baby? Hold together!" -Han to the Falcon

1972 White Campmobile
1700 cc Type IV
Dual Solex 34 PDSIT2/3

MedicTed · Posted: Tue Apr 10, 2007 5:34 pm Post subject:

Check for a vacuum leak on the intake manifold.
_________________
Ted Wojton
70 VW Bus Westfalia camper
2003 GMC Sierra

Millennium Falcon · Posted: Wed Apr 11, 2007 5:12 pm Post subject:

Millennium Falcon · Posted: Sun Apr 15, 2007 6:33 pm Post subject:

Update:

There is no vacuum leak around the intake manifold but I did get the popping to cease by richening the idle mixture on the right carb. I had tried this before of course but this time I backed the mixture screw out a lot, about 5 1/4 turns before the popping stopped. Slowly I will try and lean out the mixture out over the next day or two, a 1/4 turn at a time and see how that works

Still not sure why it was only cylinder #2 that was popping though, I guess it had to start some where. The left carb seems to run nice a bit leaner at 2 1/2 turns out.
_________________
"Don't worry, she'll hold together . . . You hear me, baby? Hold together!" -Han to the Falcon

1972 White Campmobile
1700 cc Type IV
Dual Solex 34 PDSIT2/3

MedicTed · Posted: Mon Apr 16, 2007 7:00 am Post subject:

It sounds like you have a vacuum leak on that bank. Check the throttle bushings.
_________________
Ted Wojton
70 VW Bus Westfalia camper
2003 GMC Sierra

Shaman · Samba Member Joined: October 18, 2004 Posts: 144

I have this exact same problem...

Im running a 78, with a stock 2.0 and Weber ICT 34s..
I have adjusted them to lean best idle, it may not be perfect, but its got to be close.

I get popping out of the right carb AND the exhaust at idle.. Only the right carb.
When I drive it, I get popping and little power. It also gives a SHOTGUN backfire when you shut off the engine once warm.

I can take off the #2 plug wire from the cap and the popping totally stops.
I take off any of the others and the idle drops and the popping continues.

She seems to idle fine when #2 is off, sounds better even..

I have 140 lbs of compression in #2.. The valves look to be even..

I sprayed for vacuum leaks and found none, it seems to me that if I had a leak on the right carb, then I would get the same result from pulling the #2 plug wire that I do with the rest..

What was the solution for you?
Does anyone have any ideas?
_________________
We are not human being having a spiritual experience,
we are spiritual beings having a human experience.

Brew Bus - Volkswagen Campout and Brew Fest
Lazy J Campground - Rosman NC
www.brewbus.net

SGKent · Posted: Fri Feb 20, 2009 4:08 pm Post subject:

put the timing light on that cyl and see if the timing is stable and the same as the others. If it is then you have a problem with mixture on that cyl. I use a bottle of windex or water to spray around looking for a vacuum leak. You can also look at the distributor cap to see if it is carbon tracking. That can cause weird misfires. So can a sticky intake valve or broken spring that is allowing the engine to spit back into the manifold through that valve.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

veg2001 · Posted: Fri Feb 20, 2009 6:09 pm Post subject:

Good thought...

Dude, I was so thinking of your bus as I was reading this, thinking how I needed to send you this link. Too funny Laughing

-Scott

Shaman · Samba Member Joined: October 18, 2004 Posts: 144

Ill check the timing on that cyl. today..

I also wanted to mention that the motor has hydraulic lifters that were adjusted not too long ago..
I might just re-adjust today as well..

If I had a valve sticking open, would I still get such good compression? (140)
_________________
We are not human being having a spiritual experience,
we are spiritual beings having a human experience.

Brew Bus - Volkswagen Campout and Brew Fest
Lazy J Campground - Rosman NC
www.brewbus.net

Shaman · Samba Member Joined: October 18, 2004 Posts: 144

I changed the plug wire, no change.
I then changed the plug, and the popping seemed to stop..

I was able to adjust the carb then and get almost all of the popping to stop.
I drove her and she ran horribly..

However, I might be at least one step closer. When I pull the plug on #2 now, it drops as I would expect.
_________________
We are not human being having a spiritual experience,
we are spiritual beings having a human experience.

Brew Bus - Volkswagen Campout and Brew Fest
Lazy J Campground - Rosman NC
www.brewbus.net


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