GS450 Runs rich at low throttle

[Guest]

I'm working on a GS450TX for my daughter. At low RPMs it runs excessively rich, to the point of stalling. I have checked and double checked the floats, float level, needle valves, pilot mixture screws to no avail. Pilot mixture screws have no effect on the way it runs. Any thoughts or ideas on what the issue may be? Once you get the bike past about 1/4 throttle it runs strong.

 

[Rijko]

Welcome. Please tell us more about the bike.
How long have you owned the bike, have the valves been adjusted, have the carbs been properly cleaned as in completely disassembled and dipped and orings replaced, jets and passages checked. Has the bike ever ran ok. How did you determine it runs rich as low rpm. Electrical gremlins plague these bikes because of corroded connectors and the igniter box may have failed. Spark plugs new ? What color are they ? Get good spark ? Age of battery and charging properly ?
Etc etc. What is your wrenching experience level ?

 

[Rijko]

Oh - we like pictures. Any help may just be suspended until we see proof

 

[Gorminrider]

You didn't mention it so Perhaps the choke is stuck ON....symptom will be an easily starting bike that gets progressively worse ...and I wouldn't expect the idlemix screws to overmaster that.....are you familiar with the 'choke" on these carbs? There's no butterfly plate as a "choke"- on these, the starting mixture is enriched by opening a vacuum passage that sucks a large amount of fuel from the carb bowls. I call them 'enrichers" for lack of a better term.

Be sure yours is working*

You might say more about symptoms and things you note especially if there's smoke, if compression is good, if the bike starts easily.
Assuming your floats and valves are actually keeping fuel level in spec, and the extra gas isn't bubbling into the throat of the carb,
The symptom of idlemix adjustments not working is usually blockage in the jets and passage. I'd expect leanness not "richness-to-the-point of stalling". Perhaps the throttle has been adjusted to compensate for no idlemix supplied.

*( if disassembling BE Careful- removing the rod that lifts the valves might allow tiny ball bearings and springs to escape (on mine anyways) (On mine these are "detentes" to apply friction- i expect you have the same)

 

[Cipher]

Does it have an accelerator pump?

 

[Guest]

I've had the bike about 5 years. Originally bought it as a project from a guy who was trying to get it working. He had rebuilt the carbs and top end, but couldn't get it started. I went over the top end and confirmed everything was good - valves, compression, etc. While checking the timing, I discovered he had run the spark plug leads to the wrong plugs (he had reversed the mounting of the coils.) After correcting this the bike started and ran in the condition I described above. It then sat until recently when it found it's way to the top of my priorities.

I have dismantled the carburetors several times: Choke plungers are intact and fit properly, all jets and passages are clean and clear, gaskets are intact. These Mikuni's seem to have overly complex passages. I have not checked the jet numbers. I have not weighed the floats (soldered brass, not plastic). Does anyone know the correct weight?

From basic principles of CV carb operation, overly rich conditions at idle to 1/4 throttle should be caused by the choke, pilot circuit and/or float level, and I have checked all these. I have pondered blocking off the enrichment circuit to see if there is some fault there that I haven't noticed.

 

[Gorminrider]

What year is this 450? I think "TX" can be a little confusing. In Suziki-speak it means "a 450 T ("traditional" )model made in 1981 (= the "X" ) or (I recall) a 450 T ("traditional")X ('special") made in 83? and until when they began to put out the entirely remodelled 500 based on the same engine .

The carbs are still basically the same Mikunis throughout but enricher has various pull knobs, levers and cables among them pulling that bar across the carb bank. to me. the floats being brass suggests older 0n the scale or not original ?.. my nearest bike-a very very similar 81 GSX400TX with mikuni cvs has plastic floats. ....jets might vary through years but maybe especially where someone has done a "rebuild"

If it's not carb,(enricher, fuel levels, petcock, jets, air filter , or even a nest in the airbox ) you might consider timing. Older, it's weights moving sensor coils for the black box (a TCI) centrifugally at the crank, newer, Suzuki began to integrate advance in the "black box". There are no 450s with points I know of.

 

[tom203]

“….Perhaps the throttle has been adjusted to compensate for no idlemix supplied. “

Very possible….if carbs were cleaned poorly, a clogged idle system might encourage you to raise idle stop spot as compensation. The bike needs to transition from idle circuit properly.

 

[zed1015]

.

I have dismantled the carburetors several times: Choke plungers are intact and fit properly,

From basic principles of CV carb operation, overly rich conditions at idle to 1/4 throttle should be caused by the choke, pilot circuit and/or float level, and I have checked all these. I have pondered blocking off the enrichment circuit to see if there is some fault there that I haven't noticed.

Even if the chokes are sitting properly the rubber seals in the end of the plunger degrade with age and ethanol fuels and will leak redardless and cause your issues.
With the age of these n bike it is becoming a widly known issue.
If you can''t source OEM replacements your original plungers can be repaired with new VITON seals.

MIKUNI Choke plunger seat replacement and Air corrector jets for GS fours VM's - The GSResources Forums

 

[Guest]

What year is this 450? I think "TX" can be a little confusing. In Suziki-speak it means "a 450 T ("traditional" )model made in 1981 (= the "X" ) or (I recall) a 450 T ("traditional")X ('special") made in 83? and until when they began to put out the entirely remodelled 500 based on the same engine .

.

Sorry, should have put the year in. It's a 1981 "Commuter"

 

[Guest]

Even if the chokes are sitting properly the rubber seals in the end of the plunger degrade with age and ethanol fuels and will leak redardless and cause your issues.
With the age of these n bike it is becoming a widly known issue.
If you can''t source OEM replacements your original plungers can be repaired with new VITON seals.

MIKUNI Choke plunger seat replacement and Air corrector jets for GS fours VM's - The GSResources Forums

Good point! I will double check those. It's possible that the PO didn't put them in and I missed them.

Thanks!

 

[Gorminrider]

Here's an idea that's a bit wild- the metal carb floats? Still seems odd to me they aren't plastic like my '81.of course it doesn't matter if they keep the level and seal the needle in it's place (do check for a functioning float needle-it must be able to stop flow when floats at level, however well petcock is working)....but is it possible the bike has carbs from say, an earlier GS425 or GS400?
You can't trust previous owners. Old bikes can go pass through the hands of many.