Carbs: To pull or not to pull

[RustyTank]

Gents, I find myself in a pickle. I'm the owner of a 1979 GS850G. The carbs were rebuilt by the PO, a good friend of mine who's a motorcycle and auto mechanic. He didn't rebuild the carbs to sell the bike, he rebuilt them to ride it, and that he did. So as I said, the carbs were rebuilt, stock jetting, O-rings replaced, the boots look new and it's still runnin with the stock airbox. The engine ran great when I bought it a year ago. I recently made some changes to the exhaust. I cut off the old exhaust and welded on a new set. The bike is still a 4 into 2, but with slightly shorter pipes. Since making the change to the exhaust the bike doesn't idle well, lots of popping and when I give it gas it bogs down. I've been reading a lot on this forum lately about the order of operations in regard to making sure your bike runs well and pulling the carbs, also been reading some things off Bikcliff's website and some stuff from bwringer. But, If I know the carbs were rebuilt a few years ago by someone I know does good work, should I still pull em? Would it not be worth it to unwind the pilot screws a bit and see if that helps? I'm specifically thinking the pilot fuel screws but I'm open to suggestions.

[Big T]

The pilot screws only control idle mixture. If you want to make the idle mix richer, turn the air screws in.

Your current bogging problem is more likely solved by raising the needles. If you can find a way to remove the needles for adjustment without pulling the carbs, please document that with photos.

[RustyTank]

The pilot screws only control idle mixture. If you want to make the idle mix richer, turn the air screws in.

Your current bogging problem is more likely solved by raising the needles. If you can find a way to remove the needles for adjustment without pulling the carbs, please document that with photos.

Your sarcasm is noted Bit T
I appreciate the info. Carbs are a mystery to me, but I'm learning. Probably wouldn't be such a mystery if I pulled em and cracked em open

[LAB3]

My impression is that most people here would tell you that an exhaust change won't require any major mods to be made to your carbs. There are those who will say that adjusting the pilot screws won't help either but the way I see it, what do you have to lose other than some time?

[allojohn]

If it ran fine before the exhaust changes, there lies the source of your problems. Do the "new" pipes have any baffling? Were the pipes you cut off factory standard?
Other questions: Exactly how many years ago did your buddy clean the carbs? Have you/he been running ethanol free gas?

[RustyTank]

If it ran fine before the exhaust changes, there lies the source of your problems. Do the "new" pipes have any baffling? Were the pipes you cut off factory standard?
Other questions: Exactly how many years ago did your buddy clean the carbs? Have you/he been running ethanol free gas?

The new pipes do have a baffle. The pipes I cut are factory standard.
The carbs were cleaned within the last 5 to 10 years, but I'm not sure exactly when.
No, I've not been running ethanol free gas, I'm sure the PO wasn't always running ethanol free either.

[Tom R]

If you let them sit over the winter without draining them, the carbs could be gummed up. Rebuilding carbs is a bit time consuming, but doesn’t require any special tools or skills. As you’ve seen, there’s lots of info and step by step instructions on how to rebuild. That said, it’s not best practice, but my first course of action would be to pop them off, look for anything obvious, check float heights and blast carb cleaner and air through all the ports, especially the pilot system. I have pods on my bike, so I could prob have them off and on in 30 min doing that, it’s harder with the air box, though. Maybe you’ll get lucky.
We’ve had ethanol in the gas here for at least 30 years and I’ve never had much trouble with it, but others seem to hate it.

[rphillips]

Can't imagine ex. mod changing anything at idle & just off idle. Can you think of any other change, other than the ex. mod when this problem started? Anything at all, even anything very minor? I've always thought easiest & cheapest first, then deeper & deeper till problem is found.

[bwringer]

The GS850 is one of the easiest models to pull the carbs out of. Seriously, it's, like five minutes.


Yes, you changed the exhaust by some unknown degree, so you'll need to adjust carburetion. Making the idle mixture a little richer and maybe raising the needles a wee bit would be a place to start, but no one here knows exactly what you did so it's hard to be more specific.


But I'm mostly wondering whether you have an air leak.

1) What's the state of the boots between the airbox and carbs? If these are hardened, it's damn near impossible to re-install the airbox correctly and you can get air leaks. They're still available from Suzuki and they're fairly cheap. The boots between the carbs and engine are also still available but less cheap.

2) The top of the air filter and the airbox sides must be sealed so that air can only enter the airbox where it's supposed to cannot bypass the filter. Most of us use foam weatherstripping. And also make sure the filter foam isn't deteriorated. Carefully review the intake air path.

3) Also, if you removed the exhaust at some point but didn't replace the exhaust gaskets when you reinstalled it, that can lead to an exhaust air leak and unpleasant popping.

[RichDesmond]

In my 30+ years of perusing motorcycle forums, email lists, BBS's and usenet sections, reading in the course of that time probably many tens of thousands of carburetor-related posts, it has been my experience that any time the first post in a thread is, "do I need to pull my carbs", the answer is always "yes".

Always. 100%. Not 99.9%. Never "no". Always.

You're welcome.

[Big T]

Your sarcasm is noted Bit T
I appreciate the info. Carbs are a mystery to me, but I'm learning. Probably wouldn't be such a mystery if I pulled em and cracked em open

Lots of pops points to clogged pilot jets
So, I recommend pulling the carbs and cleaning them per the VM tutorial.
If your O rings are that new, check their pliability and they may not require replacement. Modern gas only needs a few weeks to cause problems

[RustyTank]

Ok, ok, ok...I'll pull em, probably start a thread in general maintenance or the projects area of the forum.

This is the slap in the face I needed. Thanks guys.

[Big T]

Just go here https://www.thegsresources.com/_foru...ers-CLICK-HERE!!

and spend some time reading. The Top 10 Newbie Mistakes, consider that your checklist. Go to BikeCliff site and download a factory service manual and the VM carb cleaning tutorial.

[rphillips]

Yep Rich, I've read the same stuff, & yes, it seems from the % of opinions the proper way to find a carb. problem is to remove, completely tear down, properly clean & rebuild with new correct parts. I've just not been able to do it that way. I've got to start with the simplest, easiest, cheapest first, then go deeper from there. Just the way I was taught & just my 0.1% opinion.