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Fouling #1 plug

  • Thread starter Thread starter jbthomp
  • Start date Start date
J

jbthomp

Guest
Ok guys 1980 GS550L keeps fouling out the #1 spark plug. Here is what i have done to this bike so far

-Carbs stripped and dipped.
-New orings on carbs and rubber plugs on bottom of pilot jet hole
-New intake boots on engine
-New boots on air box
-Factory air box sealed and new foam air filter.
-Valves adjusted
- New spark plugs
- Coil relay mod
- Carbs synched and mixture screws set to 1.5 turns out
- Pilot jet 40 and Main jet 92.5

I am running factory pipes and air box. Nothing is changed from stock. I have checked spark and have sufficient spark on all cylinders. I have verified that the float level is correct with the float level tool. Plug does not look oil fouled it is fuel fouled for sure (dry black soot). I have switched the plug wires from 1-4 and #1 still fouls out. Tonight i leaned the mixture screw out on #1 1/4 turn and took it for a short ride around town. I pulled the plug out when i got home and it was already all black and sooty. Should i lean the mixture screw more and see what happens? How far can i turn it in before tearing anything up? I think it has something to do with the pilot circuit because i mostly just ride around town at 1/4-1/2 throttle all the time. Should i try a hotter spark plug? Im just not sure what my next step should be.....
 
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One of the first things that I would do is to move spark plugs. Move #1 to any other spot, it doesn't really mattery where. If the 'new' #1 plug still fouls, you at least know that it's not a faulty plug. :-\\\
However, if the sooty plug moved, I'd say you have a bad plug.

When you cleaned the carbs, did you verify all of your jet sizes? It is not inconceivable that a previous owner might have installed an incorrect jet.

.
 
Yeah i have replaced the plug a couple times with a new one and it will still foul. I never actually checked all the jets to make sure they were the same although i probably should have :(. It would most likely be the pilot jet that is incorrect right? If so maybe i will just order a new one and see what happens.
 
Still might be a float problem. I've had several that would hold a good level and then start the leak. If the float is leaking faster then the engine is consuming fuel then that cylinder will run rich. I've had one so bad that fuel would on occasion pour out the vent line when the engine was running. If it were me I'd take the carb down and verify jets as Steve said. If all checks out then I'd replace the float valve on that carb.
 
JTGS850L do you know of a good source to get good inlet valves that are reasonably priced? I replaced all of the needles but the seats are still original so maybe it is just worn out. I might just replace the jets and inlet valve so i don't have to pull the dang carbs out 2 or 3 more times :mad:. Is jetsrus.com where everyone gets their jets from?
 
Have you checked the fuel level while the engine is running? If the fuel level is right you are wasting your time fixing imaginary problems with the needle valves. If the level is too high find out why, the float is probably getting caught on the gasket.
 
I have not check the fuel level with the engine running. I just checked it with the engine off and let it sit for several minutes. I will check it with the engine running today. Thanks for the tip!
 
So I pulled the pilot out of #1 and sure enough the orifice hole in the end of the jet is HUGE :eek: so i guess someone jammed something in there at one point in time. Put a new pilot in and it seems to have cured my problem, no more black spark plug :clap: Thanks guys!
 
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