weird surge problem recently noticed

[GS750]

I havent been riding my GS750 much lately but took it for a run yesterday and again today, I noticed that it seemed to be slightly mis-firing, and surging when cruising

I last rode it 6 weeks ago because Ive been too busy over christmas and new year.

It is really hard to explain but basically, it does what happens when its running out of fuel and it surges then settles, until it runs out of fuel.

I was thinking about it and I figured it is probably a fuel issue, checked the fuel flow and its fine so the in tank filter is not blocked up.

Is there a filter in the carby or carbys?

Any other ideas or suggestions? Ive checked all electrical connections, plugs, wires etc and ensured that all connections are fine, and nothing else has been altered, changed or tampered with, so I am pretty certain its fuel related.

[tkent02]

Are your spark plugs white???

Burning lean?
My 750 was the same, turns out the fuel level in the float bowls was too low, even though the float measurement was set perfectly.
Check it out, it's easy to do. Just involves a tube connected to the float drains, search here for more info.

[Dave8338]

Could also be a slightly plugged fuel vent in the gas cap, old gas (but not likely) or the ever dreaded lean conditinon as a result of one or multiple air leaks. I'm going with the last one...

[nabrams]

Yeah, that's a typical "minor air leak" symptom. When they're very minor, it can be very hard to detect exactly where the leak is. The "spray mist on all boots" test doesn't always expose the location of a very minor air leak.

[Pearson]

Could also be a slightly plugged fuel vent in the gas cap....

I was thinking gas cap too. I had mine torqued way down and the engine starved and quit on me. I thought of the forum a few minutes, loosened the cap and haven't seen the problem again (course it's about 0degC here in the US right now and I'm not riding) :shock:

[argonsagas]

Starved sounds right, and my first thought was the gas cap.

You would not see this when checking the fuel flow with the bike parked, as there would be no vacuum build-up.

You might find it when it occurs by stopping the bike, shutting off the engine, and opening the cap immediately. If you hear a small hiss, you have identified the problem.

[bradleymaynar]

Not that this is your problem, but when I first got my 1100 it wasn't running on all 4. It would run decent, but had a tendency to give me a head-jerking ride when I would open the throttle. Turned out that one of the carbs was completely clogged from old fuel.

If none of these other suggestions cure your problem, maybe a carb rebuild is in order. It solved my problems.

Brad bt

[GS750]

Starved sounds right, and my first thought was the gas cap.

You would not see this when checking the fuel flow with the bike parked, as there would be no vacuum build-up.

You might find it when it occurs by stopping the bike, shutting off the engine, and opening the cap immediately. If you hear a small hiss, you have identified the problem.

Well It isnt the gas cap, Even though the last few times I filled with the bike on the centre stand, and then stupidly parked up on the side stand after a short run home, resulting in masses of fuel sploshing out the vent, I figured as I saw the posts indicating that it was a possibility, then I should check it
Its fine.

Not that this is your problem, but when I first got my 1100 it wasn't running on all 4. It would run decent, but had a tendency to give me a head-jerking ride when I would open the throttle. Turned out that one of the carbs was completely clogged from old fuel.

If none of these other suggestions cure your problem, maybe a carb rebuild is in order. It solved my problems.

Brad bt

Thanks for the posts, I will endevour to check it over for airleaks, and then may have to strip them and rebuild them anyway. At least it will give me a good opportunity to clean the internals properly with my new ultrasonic cleaner, and also to clean the paint from the outsides of the carbs from a previous owner.

[tfb]

You don't have an inline fuel filter installed, do you? If so, you might like to check the many posts on the subject of "vapor (or vapour) lock" on the GSR.

Inline filters can cause fuel starvation when a bubble lodges in the fuel line at the filter, and then expands under heat to slow the fuel flow.

Try pulling on your choke a bit when the surging starts... if the surging disappears, then you have a fuel starvation problem for sure. Take it from there.

[Road_Clam]

I havent been riding my GS750 much lately but took it for a run yesterday and again today, I noticed that it seemed to be slightly mis-firing, and surging when cruising

I last rode it 6 weeks ago because Ive been too busy over christmas and new year.

It is really hard to explain but basically, it does what happens when its running out of fuel and it surges then settles, until it runs out of fuel.

I was thinking about it and I figured it is probably a fuel issue, checked the fuel flow and its fine so the in tank filter is not blocked up.

Is there a filter in the carby or carbys?

Any other ideas or suggestions? Ive checked all electrical connections, plugs, wires etc and ensured that all connections are fine, and nothing else has been altered, changed or tampered with, so I am pretty certain its fuel related.

Sounds to me like the classic rust sediment inside your fueltank. The most common culprit of high end intermittant lean out's. Look inside your fuel tank, if you see rust, thats your issue. Rust sediment momentairly clogs the petcock strainer choking off fuel flow, after the bike sits, or is leaned over hard in a corner it tends to run better, than the issue comes back....

[GS750]

You don't have an inline fuel filter installed, do you? If so, you might like to check the many posts on the subject of "vapor (or vapour) lock" on the GSR.

Inline filters can cause fuel starvation when a bubble lodges in the fuel line at the filter, and then expands under heat to slow the fuel flow.

Try pulling on your choke a bit when the surging starts... if the surging disappears, then you have a fuel starvation problem for sure. Take it from there.

Well I seem to have found the problem!

It seems to have been caused by the inline filter.

I removed it and placed a new filter of a different type and it has not occured since then.

My compression is getting low and Im thinking that I will need to re-ring by the end of the upcoming Aussie summer.

Thanks for all the suggestions, it is really great to have a large gathering from around the world, all willing to offer their help when something is wrong!

Im off to bed now @ 23:30

Thanks again to all!

[tfb]

Excellent news. The daft thing about the inline filters is that they are just about the last thing anyone every suspects... :shock: