Engine won't hold idle below 1100 rpm?

WD-40 · Post by **WD-40** » Fri Jan 28, 2005 11:12 pm

Quick version:
Specs: 1600DP, Monza 4-tip exhaust, 009 dizzy, Solex 34pict3
Problem: engine idles at ~1100rpm, but regularly dips to ~400rpm and barely keeps running... will recover and rev back to ~1100, but repeats. This is not while driving, just letting the car sit and idle. "idle" is stable if I put it in the 1300rpm range.

Long version:
After 3 years in the garage (you know how the restoration process goes), I've been driving my car again for about a week now. I've put approximately 175 miles on it (including a 2h, 130 mile trip to school), and the engine was running pretty good. The problem was that the idle was high (1200-1300 rpm), and it was noticeably rich (you could smell it). I averaged 18.75 mpg on my long trip. I didn't adjust the idle speed because of the weather (below zero on some days), and didn't adjust the mixture as I didn't want to risk running lean for a long trip. The engine was running nice and cool, so no problems there.

Now, I'm at school, and I attempted a tuneup. This is the procedure I used, which roughly follows the advice at vw-resource.com:

1 ) held choke fully open, set adjustment screw so it just hit the fast-idle cam.
2 ) adjusted choke so that throttle arm sat on the highest step of the cam.
3 ) drove around for 15 mins or so to make sure engine was warm & choke fully open
4 ) car off- turned the volume (small) screw in until it bottomed, then out 3 turns
5 ) put bypass (large) screw at roughly it's half way point
6 ) started engine, adjusted bypass so that engine idled as slow as possible (about 1100 rpm)
7 ) adjusted volume screw out until idle was as fast as possible, then turned back in until RPM dropped slightly.
8 ) attempted to tone idle back down with bypass screw.

Now, this didn't quite work- the idle would "calm down" to the magic 1100 rpm, but only with the bypass screw turned ALL THE WAY IN. It ran OK, but I found that if I turned the volume screw out a good 4 or 5 turns, and the bypass out a turn, the engine ran significantly smoother. By just playing with the two screws (within a turn or two of where it was at), I could get the engine to not visibly bounce around when it was idling... previously, if I tried to slow the idle down, the engine would act unbalanced and shake a bit as it slowed down, but it was fine at >1100 rpm.

But... I still couldn't get past that problem... anything below 1100, it would be running fine one second, then it would just load up and slow WAY down.... I'm surprised these engines can run at 400rpm, but this one does... and it pulls back out of it!! But it's certainly not drivable when it hunts around like that.

As a troubleshooting test, I adjusted the screw on the throttle lever in a few turns. I remember reading somewhere that this has to be in slightly to allow the idle jets to work. This did seem to wake the engine up a bit, but it only ran faster- I had to turn the bypass/volume screws in more to slow it back down, and that only aggrevated the idle problem.

Manifold icing is not the problem- I've modified the exhaust so the right side port is blocked, and I've hacked the right side of the manifold heat tube off, and routed a new pipe down and out under the right side tailpipes... so the manifold doesn't "shuffle" heat, it just flows out one direction. Works VERY well.

I'm tempted to blame the 34pict3 / 009 combo, but in all of the things I've read, I see a lot of the "hesitation" complaints (which I definitely do have), but never any reports of unstable idle conditions.

I don't have a timing light with me here, so I haven't checked that yet, but the car only had ~25 miles on it since the last tuneup when I parked it to work on it, so I don't think it would have moved. The carb definitely needed adjusting because of the weather change (80+ degrees F last time I drove it, 0 to 20 degrees now), but I don't think the timing would have moved.

Plugs have no more than 200 miles on them.

If anyone has any thoughts on this, I'd love to hear them. The car is fine now with a 1300rpm "idle"... so I can get around, but it certainly isn't ideal.

Thanks
- David

TWD · Post by **TWD** » Sat Jan 29, 2005 8:14 am

I suspect a vacuum leak. Don't forget to check the throttle shafts.

mharney · Post by **mharney** » Sat Jan 29, 2005 9:00 am

Three years with junk sitting in the carburetor.. what do you think might be in there now??

Have the carb rebuilt.

2332 baja · Post by **2332 baja** » Sat Jan 29, 2005 9:01 am

I agree with TWD. Check the rubber intake boots that connect the intake manifold to the end castings for cracks. Also, if it sat for 3 years, you could have bad gas. Open the tank and take a whiff,,, does it smell like gas or does it reak?

Guest · Post by **Guest** » Sat Jan 29, 2005 10:49 am

Thanks for the replies.

With the vacuum leaks-
Other than visible play, how do you check the throttle shafts?

With the gas-
The car had the fuel treated with STA-BIL before being parked, and it was run/driven for several days to ensure that this was mixed in and had made it to the carb.

The gas tank was only in the vehicle for a few months, however, as we needed to remove it to replace the steering linkage. (replacing the steering box and rebuilding the front end was one of the major reasons I quit driving it). It has since been replaced with a fuel cell, and I've run a good 10+ gallons of good gas through it.

So I don't suspect crud in the carb, but I could take it apart and clean it all up easy enough. I'll have to order a rebuild kit for that.

Thanks for the replies
- David

2332 baja · Post by **2332 baja** » Sat Jan 29, 2005 12:36 pm

2332 baja wrote: Check the rubber intake boots that connect the intake manifold to the end castings for cracks.

TWD · Post by **TWD** » Sat Jan 29, 2005 5:14 pm

Not foolproof, but spray starting fluid or WD-40 around the throttle shaft while it is running. If there is a noticeable change in RPMs you are likely sucking air around the shaft. If they are leaking, you can have them re-bushed. I would just buy http://www2.cip1.com/ProductDetails.asp ... %2D031%2DK

Xyclone · Post by **Xyclone** » Mon Jan 31, 2005 8:41 am

I wouldn't go with the NEW carb, with my experiance, those new carbs are crap, you loose about 4-5 mpg (without rejetting) and after awhile some of them start to leak. Maybe others have had good luck with them, but I would use that money to buy an armload of carbs that have tight shafts at a swap meet.

Just my 2 cents

Pete

TWD · Post by **TWD** » Mon Jan 31, 2005 9:59 am

Xyclone wrote:I wouldn't go with the NEW carb, with my experiance, those new carbs are crap, you loose about 4-5 mpg (without rejetting) and after awhile some of them start to leak. Maybe others have had good luck with them, but I would use that money to buy an armload of carbs that have tight shafts at a swap meet.

Just my 2 cents

Pete

Are you speaking of the Kafer carb that I linked to or the Brosal?

Guest · Post by **Guest** » Thu Feb 03, 2005 7:35 am

woop's my bad, definetly the brosal crap, I'm sorry I just looked at the link real quick and thought it was the brosal. That'll teach me to rush through a post

If you're in the market (have the money) for one of the kafers, I would say go for it,, but I'm cheap and prefer grabbin an orig 34 for 5 bucks at a meet, but thats just me