Slight Hesitation off idle, but smells rich

[Snap]

I have recently rebuilt a 34-PICT 3 for my bus with a S.B. DP case, 1641 P & C, w/ Scat C25 Cam, & stock heads. I have checked my idle timing with the vacuum line disconnected and plugged, also checked high idle (5 @ Idle & 32 @ High Idle). I have lowered the fuel pressure down to 2.5 psi and checked the float bowl fuel height.

When I first got the carburetor installed and started driving, it had a horrible hesitation off of idle and accelerating under load. The weather was quite cold and dry at the time, so I assumed that it may also be affecting the hesitation problem. Before I could get jets, I increased the accelerator pump throw and increased the idle mixture to make it driveable. To remedy the problem, I stepped up my main jet from a 127.5 to 130 and leaned the mixture and it runs good. However, when the engine is idling after its warmed up it still smells rich. I still have a slight hesitation off idle and was wondering if I should go to a 132.5 and lean the mixture out more. I also have a larger pilot jet I was thinking about trying as well. Right now I am running a 55 and have a 60. The head temps are not getting close above 275 or so, but I don't trust the temp thermo-couple VDO gauge because its just a variable indicator and not a measuring instrument.

How can I lean the idle mixture and still get rid of the slight hesitation?

[hambone]

Make sure your timing is spot-on, and dwell if that's your trip. It can cause all sorts of weirdness. Are you sure the hesitation is fuel related?
Yeah I noticed you were running rich.
I don't have a book right now, but isn't the fuel pressure 3.5? If it is then I need to go lie down, what a waste of a human life.
I run a stock Brazil Solex in my single port 1600 and I have been very happy with it's performance. Of course I run a stock cam. With the Scat cam you may need to check with the high performance folks for workarounds. Right now the only answer for you may be trial and error. Or try a new stock carb and see if it has the same symptoms. I have one you can try, but it may need rebuilding. I have a kit, maybe I should just do that.

[Amskeptic]

I have recently rebuilt a 34-PICT 3 for my bus with a S.B. DP case, 1641 P & C, w/ Scat C25 Cam, & stock heads. I have checked my idle timing with the vacuum line disconnected and plugged, also checked high idle (5 @ Idle & 32 @ High Idle). I have lowered the fuel pressure down to 2.5 psi and checked the float bowl fuel height.

When I first got the carburetor installed and started driving, it had a horrible hesitation off of idle and accelerating under load. The weather was quite cold and dry at the time, so I assumed that it may also be affecting the hesitation problem. Before I could get jets, I increased the accelerator pump throw and increased the idle mixture to make it driveable. To remedy the problem, I stepped up my main jet from a 127.5 to 130 and leaned the mixture and it runs good. However, when the engine is idling after its warmed up it still smells rich. I still have a slight hesitation off idle and was wondering if I should go to a 132.5 and lean the mixture out more. I also have a larger pilot jet I was thinking about trying as well. Right now I am running a 55 and have a 60. The head temps are not getting close above 275 or so, but I don't trust the temp thermo-couple VDO gauge because its just a variable indicator and not a measuring instrument.

How can I lean the idle mixture and still get rid of the slight hesitation?

Step 1.
Make sure that the heat riser is hot at both ends at operating temperature.

Step 2. If it is rich, going up a size with the main jet makes absolutely no sense.
The main jet is only the foundation under the idle circuit, it is not a cause. Main jet sizes are only to be monkeyed with if your *sustained high speed mixture* is a problem as in white spark plug insulators and hot CHTs.

Step 3. Pilot/pilot air bleed jets are the low end players.

Step 4. How do you know that you are not actually drowning the engine with the accelerator pump?

[Snap]

I have recently rebuilt a 34-PICT 3 for my bus with a S.B. DP case, 1641 P & C, w/ Scat C25 Cam, & stock heads. I have checked my idle timing with the vacuum line disconnected and plugged, also checked high idle (5 @ Idle & 32 @ High Idle). I have lowered the fuel pressure down to 2.5 psi and checked the float bowl fuel height.

When I first got the carburetor installed and started driving, it had a horrible hesitation off of idle and accelerating under load. The weather was quite cold and dry at the time, so I assumed that it may also be affecting the hesitation problem. Before I could get jets, I increased the accelerator pump throw and increased the idle mixture to make it driveable. To remedy the problem, I stepped up my main jet from a 127.5 to 130 and leaned the mixture and it runs good. However, when the engine is idling after its warmed up it still smells rich. I still have a slight hesitation off idle and was wondering if I should go to a 132.5 and lean the mixture out more. I also have a larger pilot jet I was thinking about trying as well. Right now I am running a 55 and have a 60. The head temps are not getting close above 275 or so, but I don't trust the temp thermo-couple VDO gauge because its just a variable indicator and not a measuring instrument.

How can I lean the idle mixture and still get rid of the slight hesitation?

Step 1.
Make sure that the heat riser is hot at both ends at operating temperature. Check

Step 2. If it is rich, going up a size with the main jet makes absolutely no sense.
The main jet is only the foundation under the idle circuit, it is not a cause. Main jet sizes are only to be monkeyed with if your *sustained high speed mixture* is a problem as in white spark plug insulators and hot CHTs. It did not make sense to me either, that's why I wrote this thread.

Step 3. Pilot/pilot air bleed jets are the low end players. Will try the 60

Step 4. How do you know that you are not actually drowning the engine with the accelerator pump? I have cut back the accelerator pump back and advanced the throw until the hesitation was minimized.

So far I drove it this morning to operating temp, got to work, leaned the mixture a bit and advanced the timing a smig. I'll see how it smells/ drives when I get home and check timing.

I will follow this post as I fiddle with adjustments and results... Next will be the pilot jet after I feel I am done with timing and idle mixture.

[Amskeptic]

I'll see how it smells/ drives when I get home and check timing.

Tell me more about this ..... fragrance.
Colin

[Snap]

It just smells like un-burnt fuel. I would expect some fuel smell due to the lack of emission systems and being a carbureted engine but smells stronger than I expect. The tail pipe has black soot on the inside but I have not cleaned it to so see if it is new or left over from the last monstrosity of a carburetor. I guess the real question would be what the plugs look like after I run it a bit. Actually, I need to change them since since the last carb was running so rich they were black, but not burning oil black, the last time I inspected them. (The last carb was an e-bay special that I could never seem to get tuned. It had excessive throttle shaft bushing wear (would not idle), the throttle plate was clocked 180 out so the small holes were not lined up with the throttle plate notches, and it was missing the accelerator jet.)

I leaned out the idle and advanced the timing. I checked the timing last night with the vacuum line disconnected (SVDA) and held the rpm's at about 3000-3500 and found it is advanced to about 32-34 degrees. I drove it this morning and did pretty well! The smell is still there, but does not seem to be as strong. It does seem to hesitate a little bit, but not nearly as bad as it was. I think I had a timing issue, but I am still curious to see what would happen if I continue to lean out the idle more and replace the pilot jet with the 60 from the 55.

[SlowLane]

Dumb question: are you using a stock air filter?

[Snap]

Dumb question: are you using a stock air filter?

No, I converted my oil bath to adapt a K&N pleated filter inside the oil bath housing.

[Snap]

I read through this articlehttp://www.vw-resource.com/34pict3.html and realized I was twisting the volume control the wrong direction (now I understand what you were talking about at the lab last summer).

After realizing my mistake, I actually leaned it out last night, drove to work this morning, and it ran great. I don't know how many times I have read that in the Bentley but it never really set in until I read the article above.

Even though I am happy with the way it is running now, I still want to see what happens when I increase the pilot jet size.

[ruckman101]

I like that site. Used it to walk through complete tear-down and rebuild on the 34 pict 3 feeding the recently demised dual port that was in Bertha Bus. It was also a 1641. A flat spot off idle and a propensity to die coming to a stop light plagued me for longer than I care to admit. Careful tuning/adjusting of first engine and then carb eventually did the trick. I guess my skills are growing.


neal

[Snap]

A flat spot off idle and a propensity to die coming to a stop light plagued me for longer than I care to admit.

I had the same problem with the engine dying at stop signs for years. I kept rebuilding and replacing carbs until I found a good body in that box before I gave you the remaining parts. I was talking to Hambone at the lab on week and we were discussing the erratic idle I had (because I turned up the idle up) and told me that was a problem he ran into and the throttle shaft bushings were shot. What do you know, that was the problem with all my previous rebuilt crap.

The flat spot has been minimized, but I know that Cam has a big influence on the flat spot. We had a Manx buggy growing up with an 1835 and duel dels running the 009 and that thing had a huge flat spot. However, it wasn't as annoying as driving in traffic on a daily basis.

... Careful tuning/adjusting of first engine and then carb eventually did the trick. I guess my skills are growing.

I know I will get it tuned and the weather will change. I also feel that my skills are being honed. The more I play, the more I will learn!

[ruckman101]

Throttle shaft bushing wear was my bane until I got a new carb, every used I tried was pretty darn tired. I didn't ever change a jet, so whatever is stock is what I worked with. Cam was stock, also.


neal

[hambone]

Next set the volume of gas available at idle speeds. This is done using the Volume Control Screw. Please note that the Volume Control Screw controls the AIR volume, not the fuel volume. Screwing it in reduces the air and makes the fuel/air mixture richer. And of course turning the Volume Control Screw out increases the concentration of air and makes the mixture leaner.

I've been doing it backwards too. But for some reason, the car runs right? Intuition trumps logic.

[Amskeptic]

Next set the volume of gas available at idle speeds. This is done using the Volume Control Screw. Please note that the Volume Control Screw controls the AIR volume, not the fuel volume. Screwing it in reduces the air and makes the fuel/air mixture richer. And of course turning the Volume Control Screw out increases the concentration of air and makes the mixture leaner.

I've been doing it backwards too. But for some reason, the car runs right? Intuition trumps logic.

Where did you get the above quote?
It is totally wrong.
Colin

[Snap]

Its off from the website link I have in my previous post.