Engine pops and bucks at low rpms 69 Camper 71 dp

[thesamwise4]

Greetings all,

A little background. I will try to be concise.

I was very excited to take my bus (provisionally named Gimli) out for a short ride today after torquing the CV joints. I had not driven the bus since last fall, when I pulled the engine to install a new transaxle.

Colin came around about three weeks ago and helped me put the engine back in. While doing that, we adjusted the valves and the timing. We started it up and it sounded just great at idle (CV joints not attached, so no test ride). It was running really advanced before, so it sounded like a kitten purring compared to how it was before.

Anyway, on my drive today, it was not running well at all. It was about a ten minute drive, and it was not better at the end than it was at the beginning. Basically, the engine runs *terribly* at low rpms. It bucks, it pops, feels like it's going to cut out, and it stutters and hesitates all through the low RPM range. Once I get past what I would guess is about 3000 or 3500 rpms, it runs like a champ (accelerates smoothly and with a good deal of power), but anything below that is bad news.

Even after a shift at decent rpms (say, into second), it just feels like it drops off a cliff and then I have to push the clutch in again and give it gas to get past the low range. If I let the clutch out without revving, it will sputter and hesitate and shake.


I will again proclaim my newbie status here.

Any ideas on what's going wrong? The idea that it just needed a little more time on the road since it hadn't really been put through the paces for six months occurred to me, but it was just running terribly and I had to get to work.

Thanks in advance. I really appreciate it. If I could help by clarifying or answering any questions, just let me know.

[steve74baywin]

Intake leak? Timing/ignition? Bad gas

[sped372]

Adjustments don't just go bad quickly... things like crud getting into a passage do. If it was running great and suddenly changed behavior you'll have to try to narrow down the culprit. Start with the main things, verify you have spark to each cylinder. What carb do you have on there - 34-3?

[thesamwise4]

Thanks for the two quick answers.

Adjustments don't just go bad quickly... things like crud getting into a passage do. If it was running great and suddenly changed behavior you'll have to try to narrow down the culprit.

Thanks, Sped. It was not running great before, but the problem was a little less noticeable (maybe b/c it was running at a much higher idle?). It was still unsteady at low rpms, and I had to give it a lot of gas to get through.

I did not mean to imply that this is a sea change from how it was running before. I just did not get into it (the low RPM problem) last year because I was dealing with the trans. I guess I was hoping that adjusting the timing and the points and the valves would help out a bit. No dice, it seems.

What carb do you have on there - 34-3?

I believe that my carb is the 34-3.

Unfortunately, my bus is about 30 miles away right now. I am hoping to compile a checklist for the next time I get up to see it, which should be in a few days. So thanks--now I have a few things to check.

I will keep you posted. If anything else comes to mind, please let me know.

[steve74baywin]

I mentioned the bad gas because you said something about it sitting for six months.
I have found lately it only takes six months now, some thinks it has to do with the ethanol in the gas. You didn't mention if you drained the gas or added a bunch of new gas recently.

[Amskeptic]

Remember how we found the timing to be criminally over-advanced? Someone was hiding something. Your lousy driveability at low rpm and your *good driveability* at high rpm, totally removes "bad gas", "bad timing", "bad coil", "bad spark plug wires", etc.
It leads us to clogged idle jets/disfunctional idle cut-off/varnish, and I would even say Steve's mention of a vacuum leak is a possibility UNLESS it still idles as well as it did for us.
Overhauling and cleaning a carburetor is easy.
Colin : )