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Hesitation, bogging while riding

  • Thread starter Thread starter oldgsfan
  • Start date Start date
O

oldgsfan

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I'm having a problem with hesitation while the bike is running at speed.

It's a 1980 GS850G and although I had cleaned the carbs before, I had always bench synched the carbs. The bike ran fine, but about two weeks ago I got a morgan carbtune and, for the first time ever, I vacuum synched the carbs.

When I rode the bike on the freeway I began experiencing some hesitation while the bike was running at freeway speed. It felt as though the bike wasn't getting a steady flow of gas.

I had installed a new inline fuel filter when I did the synch because I had to replace the fuel line (it had broken).

So I removed the fuel filter.

The problem persisted.

I pulled the carbs, took them apart, cleaned them though they didn't really need it, and cleaned my gas tank with evapo-rust.

When I put them back in, I synched the carbs again.

The problem persisted.

I did some GS Resources forum reading and thought the problem was the air-mix fuel screws, which I had set to about 2 turns out. I adjusted them out to three full turns each.

The problem seemed to go away and, in fact, the bike rode really well during my 35 mile commute this morning. I was really happy.

I thought the problem was resolved.

But on my ride back home the problem returned with the hestitation while riding, kind of like a bogging. It almost felt like the bike did when it had a bad petcock a couple of years ago.

The bogging/hesitation wasn't as bad as it had been, but it was still there.

I played with the air mix screws a bit but I haven't been able to resolve this issue.

I've checked to make sure my airbox is well sealed, my intake and airbox boots are all tight, and the hoses are where they should be. I also checked to make sure those brass screws in the intake boots were tight and that I hadn't accidentally left them loose.

The spark plugs are new. The intake o-rings are two or three years old. I replaced them shortly after I got the bike. The petcock, as I said, is new. The tank's been cleaned.

I'm not sure what to try next but I'm thinking I need to start over - reset all the air mix screws and re-synch the carbs.

But I'm beginning to think I'm reaching the definition of insanity - trying the same thing again and again and expecting a different result.
 
Two things.

First, where is the throttle when it hesitates? That will tell you what jet circuit to focus on.

Second, how are the valve clearances?
 
Usually, the bogging happens when I'm at about 4,000 rpms.

Does this sound like a problem with the jets? I haven't changed anything on the bike -- it's a stock exhaust.

Last time I adjusted the valves was two years ago.
 
I can do that, but why would valve clearances cause this problem?

Is this a symptom commonly associated with poorly adjusted valves?

One thing that really puzzles me is that the bike ran so well this morning and then like crud on the way home.

One bummer about a valve job - the shop that let me buy individual valve shims last time moved from two miles away to about 15.
 
Adjust your valves per the Suzuki manual recommendation otherwise you can damage the engine. Regardless of whether or not that is the problem at hand, it needs to be done. Once you take an inventory of all your various shims then you can order extras from Z1 Enterprise for $5 each and have everything you will need going forward.

As for the problem, you might want to try shimming the needles. Tons of threads in the archives detail what to do.
 
Well, I checked my records and last time I adjusted the valves was nearly 14,000 miles ago! OK. So, yeah, guess I'd better do that. I hadn't realized it had been so long.
 
oldgsfan said:
Well, I checked my records and last time I adjusted the valves was nearly 14,000 miles ago! OK. So, yeah, guess I'd better do that. I hadn't realized it had been so long.
Click to expand...

The service interval is 4000 miles.
 
Adjust your valves. Don't think it will solve your current issue but it'll help and should be done as stated above. Another thing to check is your slide diaphragms. Check for tears/pinholes etc. if they've gone south, they'll not work as they need to. Other than that it sounds like shimming the needles is going to help. Although carbs dont care so much about rpm, cruising on the highway is early in the needle usually. Pilot/needle transition area. And you're sure you've set your float levels correctly?
 
I'll definitely be doing the valves this weekend. One thing i remembered was that when i inspected the carbs the rubber ring in one of the air mix screws seemed flatter than the others.
Im getting a new exhaust system with my tax tefund and planned to attempt my first ever rejet. Ill replace the carb orings at the same time.
 
Last edited:
Word of advice. Don't replace the exhaust (requiring rejet) until you figure out this current problem first. Otherwise you'll be chasing your tail trying to figure out why the bike won't run right.
 
AFRetired said:
Word of advice. Don't replace the exhaust (requiring rejet) until you figure out this current problem first. Otherwise you'll be chasing your tail trying to figure out why the bike won't run right.
Click to expand...
This ^^^^^^ is good advice
 
Hi,

I just thought I'd mention to check your carb vent tubes. They should be laying over the airbox with the open end hanging on the back side in relatively still air.

Even with my carb vent tubes properly positioned, on very windy days riding in a cross-wind I can get some hesitation. It's momentary but it makes me check my vent hoses when I get home. :-s


Thank you for your indulgence,

BassCliff
 
Try resetting your mix screws. Set them to two rotations from fully seated. Too much fuel can also feel like no fuel at all. You can know for sure by opening up the choke when you are bogging down. Does it make the problem go away, or no effect? No effect means you are running rich.
 
I don't know if this helps, but I recently tuned some Flatslide carbs on my bike. When I went up a size in pilot jet I got a similar problem to yours - idle was good, acceleration fin for the first 1/8th of throttle but at around 4000rpm or 1/4 throttle the nose dived and it bogged down horribly. After about 4500rpm it was fine again.
It was too rich at that point. I moved the needle jet clips up one notch and everything was perfect. It really surprised me that moving the clips on the needle jet one notch would have such a dramatic effect.

With my bike, hesitation and carb farts seem to indicate I am running lean, and bogging down with occasional very loud backfires too rich. It really helps to put some tape alongside your throttle so you can mark where open, closed and 1/4 increments are. It makes it a LOT easier to work out what you need to do. RPM varies depending on the gear, so knowing the throttle position really helps.
 
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