TheSamba.com :: View topic - Bad idle and hesitation at cruise

Mon Jun 05, 2023 10:33 am

So, car was running reasonably well but one carb had an air leak at the base that was standing in the way of tuning in really well, so I took my carbs (Solex pdsit 32-34) off and reinstalled them with new base gaskets. I went for a drive to warm it up, sync the airflow and then come back to set the CO (all per the ultimate guide here on the forum).
However already when driving around I felt a pretty apparent hesitation when cruising, stumbling when acceleration at lower speeds (not so much stumbling under acceleration at higher speeds) and a pretty rough idle.

When I came back I synced the carbs but it really wasn’t running well, hooked up the 4-gas meter and got the results as per first photo attached.

Then I unhooked the retards and the central idling solenoid to set the CO at the carb bases, which I reset both to 3 turns out. It turned out the right side was 6 turns out :shock:
When I then started it and checked the difference between the two sides the right was almost not contributing: taking the power to the left solenoid killed the engine, taking the power from the right side only lowered it a tad. Second photo is the gas analysis in that end state.

I really don’t understand what’s going on! :( Does anyone have an idea? Should I take the right side off again!?

Mon Jun 05, 2023 11:54 am

That second pic is way too lean, is that with the CIS disabled?

Mon Jun 05, 2023 2:01 pm

Yes, that's with the CIS disabled. But both have way to high HC values which points to unburned fuel.

At the same time I'm wondering if the hesitation at cruise and the bad idle could be caused by a clogged idle jet? But why would a clogged idle jet lead to high levels of unburned fuel? #-o

Mon Jun 05, 2023 3:02 pm

HC's can also be caused by a lean miss, that's why it's higher on pic #2.
An idle jet isn't going to have much effect on cruise, what's the float level like in that carb?

Wed Jun 07, 2023 7:25 am

Quote: HC's can also be caused by a lean miss, that's why it's higher on pic #2.
Right, I took the right carb off and flattened the mating surface to the manifold, blew compressed air through the idle jet (solenoid) and the hole it sits in, and now remounted I do get a much better contribution from the right side (HCs down to 50, CO up to ~3%).

I still hear the stumble at slightly open throttle and 'cruise' RPM (2500-3500RPM). About the float level, these carbs are not the original ones to a 72 but from a later model, they have the warm up element and cold acceleration enrichment things. Do those still need to have 1.2mm float needles and 12-14mm float level, or are they okay with 1.5mm needle and 16-17mm float level?

Wed Jun 07, 2023 8:02 am

Those numbers sound much better.

Niels911SC wrote: About the float level, these carbs are not the original ones to a 72 but from a later model, they have the warm up element and cold acceleration enrichment things. Do those still need to have 1.2mm float needles and 12-14mm float level, or are they okay with 1.5mm needle and 16-17mm float level?
I'm not sure, bigger needles can't hurt, or change performance all that much. Since it's a bit of a mongrel setup I'd start playing with float level and get it high enough to climb a big long hill hard, yet not overflow when shut down hot.

Bet you're getting good at pulling carbs by feel, or does your bus have the trap door in the roof of the engine compartment?

Wed Jun 07, 2023 9:12 am

:lol: yeah I could never butcher my car like that, installing an access hatch in a 72 :shock:

I'm a sucker for originality, so much that I bought a set of original 72 carbs and had them rebuilt, but there's something wrong with them because it ran even more crap then it does with this later year setup (I at least know that the float bowl mating surfaces are crooked because I could get a feeler gauge in between the carb halves so they definitely weren't flattened by the rebuilder). But that's another story.

I can post some pictures later, even the 'mongrel setup' looks pretty much stock :wink:
I'll start working with the float levels. To be continued.
And long answer short; yes I'm getting pretty good at removing and mounting stuff through the back engine lid :twisted:

Wed Jun 07, 2023 10:39 am

I find it's not too bad if you jack up the back of the bus first, then you can sit on a short rolling stool and reach in comfortably.

I wonder what the jet sizes are, particularly the main air correction ones, and are they matched?

Sun Aug 06, 2023 1:38 am

The last time they were out I check all the jets and they are matched left to right. I’m not entirely sure about the main jet size, I think it was 127.5 or so. Air correction maybe 140? I didn’t write it down though so I could be very off.

Picture of the engine so you can see it doesn’t look too weird :)