Back for more help *eye roll*

[JonathanPD812]

Hi all, back at it. I'm going to try to keep this short (as short as possible)... About a year ago, my brother rode my bike, stalled, then put it down on the ground (idk why, it has TWO kick stands).

Got it home, the pin in the carb was stuck in the venturi part so I took apart the carbs. They were gross.. cleaned them (ultrasonic in carb cleaner) re assembled with new rubber.

Doing some PM, I installed new points, regapped them, checked the timing (perfect!) And put it all together.

Checked the valves, perfect clearance, good pressure on each side (150 PSI).

Bike will start okay when cold. Runs decent (other than hesitation at 3-4k) but solid in the other RPM ranges. Once the engine warms up it dies, and is tough to restart.

My plugs keep carbon fouling. If I let it cool down and clean the plugs it will run again until again it warms up.

This is the loop I'm stuck in. My research leads me to believe I have a float height issue. It has been tough to find the actual float height for BS34 carbs, but what I am set at is 27mm from the gasket surface.

Please help, this bike means the world to me, I need to ride it again! Thank you

[Rob S.]

What bike (year, model)?

[Rich82GS750TZ]

There are factory service manuals for many GS years and models on BikeCliff’s Website. The info you seek will be in there.You don’t mention your year/model. That’s the kind of thing that’s good to put in a signature. Yes measure from the gasket surface.

[JonathanPD812]

Excuse me! I keep forgetting to add that to my signature. 1977 GS400

[Gorminrider]

The Clymer manual is probably at the link above. It's not the best manual and a bit odd about float heights: it says 25.6 to 27.6mm for "all bikes" in it's purview EXCEPTING the 450 which it says are 21.4- 23.4..small diff suggesting the older bikes like it a little richer. Likely these decimal mm are converted from inches...but a float level just below the gasket on LEVEL carbs (not the bike!) should work well enough.

It's very noteable that bikes with the same problems all show up together. Nowadays, it's "bikes that die when warm" so the Mass Brain should have this nailed by now.Look at some recent threads in other mechanical sections...aka ignition, petcocks and all that.

I expect we are nearly ready to troubleshoot SKYNET at this point...

[1978GS750E]

This may help....... Suzuki Carb Specs.jpg

[Rich82GS750TZ]

This may help more:



This is from the Carb Specs/Cleaning file link found on BikeCliff's Website. I did not compile this data. If I recall correctly, there have been errors found in the table.

[JonathanPD812]

This may help....... Suzuki Carb Specs.jpg

I actually found this chart when looking for more information today... the 27mm I referenced before was from a Clymer's guide and It had called out for 25.6 to 27.6. I went on the high side, my exact height was 27.2.. If I refer to the table I should be at 26.3 +/- 1. I will set them at 26.3 this afternoon and try again!

Does my diagnosis / conditions sound like a float height is likely to blame...?

[zed1015]

Sounds like wet fouling due to an over rich mixture.
Could be too high fuel level ,float valves sticking , blocked pilot air bleed passage, blocked main air jet passage etc.
You should also check that the choke plungers are seating fully when closed.

[JonathanPD812]

Sounds like wet fouling due to an over rich mixture.
Could be too high fuel level ,float valves sticking , blocked pilot air bleed passage, blocked main air jet passage etc.
You should also check that the choke plungers are seating fully when closed.

It definitely seems over rich. I just finished reassembling with a float height at 26.2 on each side, and cleaned everything while I was in there. Same deal, runs decent initially, run it up and down the driveway a few times and same deal. I will say that the 3-4 k issue seemed.. better .. as in less stuttering until I stalled it in the room range and it was all over .. if I wanted to lean it out with the float height I would go large correct? So instead of 26.2 I go to the max of 27.6? Or should I go the other way considering that the max is similar to where I was before and it didn't work? I guess I just don't know what to try next

[JonathanPD812]

I feel confident that the floats are set as they should be, so now I feel like I need to focus elsewhere such as mentioned above: float valves sticking , blocked pilot air bleed passage, blocked main air jet passage.

I did try my darndest to clean all those locations which carb cleaner and compressed air... The float valve sticking seems like it may be a culprit. I noticed during bench testing of moving the floats up and down occasionally one of the valves would stick up, I kinda figured with any sort of gas flowing it would drop back down as it did when I blew air into the fuel inlet but perhaps not?

[rphillips]

You haven't raised, or changed, the needles, in any way have you? Whatever is wrong with one carb has got to be wrong with both. Doesn't seem to make sense that both floats are sticking, both air jets stopped up, both choke plungers, naw it don't have a choke cable.... Just thinking out loud.

[zed1015]

both choke plungers, naw it don't have a choke cable.... Just thinking out loud.

It does have two choke plungers operated by a single pull bar which if not returning will soot up both plugs when the bike has warmed up.
Also with it being both cylinders suffering the issue it's possibly an ignition issue , weak spark , ignition coil breaking down etc.

[Gorminrider]

Once the engine warms up it dies, and is tough to restart.

My plugs keep carbon fouling. If I let it cool down and clean the plugs it will run again until again it warms up.

...I wouldn't think a float level within a millimeter would cause this problem....to be plainer: possibly because the ignition is failing while the gas is continually being sucked in.... or less likely something else like fuel supply failing...

[rphillips]

Just thinking the manual choke would be manually pushed completely closed as opposed to a cable that may not be adjusted correctly to push completely tight... I dun'no.