Intermittent acceleration issues

[shaffermd]

I have a 99GL1500. I rebuilt the carbs about 2 years ago. 30% of the time it runs great. The other 70% it doesn't want to accelerate or will even just die barring emergency adjustments.
Interestingly, engaging the 'choke' fully for 4 or 5 seconds seems to fix the problem for 3 or 4 miles or 30 or 40 miles. I've been looking for vacuum issues to no avail. Covering the carb throats immediately fixes it but not necessarily with enduring results.
I'm perplexed. Any word of wisdom?

[Swagonmaster]

Will the engine idle ok when this happens? Have you checked the fuel vacuum hose at the fuel shut off valve inline from the filter(and the filter itself as well)? Just by the sound of it trash in the carb is likely but other weird things happen also.

[WingAdmin]

Does it run at constant highway speeds OK? Does it only have a problem on acceleration?

What happens if you accelerate very gradually as compared to sudden acceleration?

I'm thinking accelerator pump/jet here. Sudden acceleration causes a lean mixture which normally is compensated for by the accelerator jet introducing extra fuel.

The "choke" doesn't actually choke like most engines, it "chokes" not by restricting airflow, but instead by adding more fuel, thereby enrichening the mixture - which might explain why it helps your acceleration/lean problem.

[shaffermd]

When it is wrong, it's wrong. Cruising, idle or acceleration. If it were not for the momentum, the engine would stop turning before i could choke it. I have been stuck at a light a couple times as well. Humbling...
The accelerator pump seems consistent. I have observed a lot of different scenarios with the breather off. I have watched it struggling to accelerate while fuel was spraying into the manifold. I'm sure I've screwed something up somewhere. Everything was perfect before the float valve stuck and I got the bright idea to just rebuild everything while I had it apart. I've been a professional auto mechanic (when cars still had carburetors) and addressed many an issue but this had me feeling like an amateur.

I'm aware of the choke method (similar to throttle body injection). It seems to have an affect on the vacuum as well. That's the part that has me curious.

By the way, I would like to take this opportunity to say thank you for your tireless efforts maintaining this forum. I've benefited may times from the wisdom and experience of you and the other members.

[Swagonmaster]

That reminds me, these are diaphram carbs, what if a slide is sticking/hanging up? I've had scooter carbs drive me crazy and all of the parts are there in the right place (sort of). Since you took the pair apart the only likely suspects are in the carbs and the hoses and whatever that attach to them.

[WingAdmin]

That reminds me, these are diaphram carbs, what if a slide is sticking/hanging up? I've had scooter carbs drive me crazy and all of the parts are there in the right place (sort of). Since you took the pair apart the only likely suspects are in the carbs and the hoses and whatever that attach to them.

That could definitely be an issue, for acceleration, and it would explain the intermittent nature.

Does it feel like it's affecting all the cylinders equally? Or just one? Or perhaps just the cylinders on one side of the bike?

[shaffermd]

I have observed the carbs with the air filter off and both slides are functioning identically. There are some functions that are vacuum controlled and that's been a consideration but I haven't isolated anything yet. If I have a vacuum leak it's well disguised. I have tried to determine if there's a difference in the cylinder banks but can't determine right now. I'm in the process of taking down the carbs again and very carefully reassembling.

[Swagonmaster]

If the problem continues after the rerebuild see if you can shut off the engine and check the sparkplugs on each side to see if they are very rich or very lean. While I know that might be rather hard since the problem won't show up at any predictable time but it would aid the diagnosis. (I hate intermittents)