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gs750 cylinder 1 not firing and gas in the airfilter

  • Thread starter Thread starter franchizai
  • Start date Start date
F

franchizai

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hey everyone

been using this site for a year now since i bough my gs but haven't posted anything as the searches helped when i needed it, i got a little problem now though and i hope someone can
point me in the right direction. i'm from denmark so please excuse the language :)

i bought a 1977 gs750 last year and it was running o.k. i thought, i started the general maintenance tasks as i didn't know when it has last been serviced correctly.
i found that cylinder 1 had some problems firing , at least that's what i though since it was colder than the other cylinders.

the last time i really took it for a drive i came home and gas was seeping out the airbox.

the only modification is a 4-1 exhaust everything else is original as far as i know.

up to this points i have done all regularly maintenance task.
oil filter change
2*valve shims adjustment
point adjustment (i had a little weird thing here the 1-4 was spot on the 2-3 was spot on but not everytime)
cleaned out the electrical system.
new sparkplugs
new kn airfilter for the airbox.
sealed airbox with weatherstrips.
new o-rings between carb and engine
carb rebuild with every part ultrasound cleaned sprayed (used vm carb rebuild by paul musser) as instructions.
new o-rings/gaskets in the carbs from keyster but used the original screws and jets
bench synched
synched with carbtune pro
idle adjusted using highest idle method

and here is where the problem comes in it seems that after my efforts i still have the problem
i can get cylinder 1 to fire in choke, and when i close the choke it'll have combustion for a little while, i used colourtune to verify this.
so basically it runs for a little while and then combustion stops.
i tried fiddling around with the pilot fuel screw / air screw but it seems it has no real effect.
i still get gas in the airbox especially if i rev it a few times.

any ideas as to what im missing ? im mostly concerned about the same problem persisting on the same cylinder which makes me think it related to the engine itself
and not the carbs as i started out thinking, since its apparantly the exact same problem as before i did all my maintence tasks

i tried switching the ignition cables as well with no difference

DSC_0006 (1).jpg
 
Did you check to make sure the pilot fuel screw tip isn't broken off in the carb body? How many turns open are you on the fuel and air screws? Most GS's run best with the fuel screw at about 3/4 of a turn, and the air screw about double that. Also make sure the pilot jets are clear by holding them up to the light.
 
went and took the float bowl off carb 1
unscrewed pilot jets to check it but no visible clogging, compared to new one from the keyster set and it seemed fine,blew it through with
compressed air and put it back in.
rechecked the fuel screw tip and it was fine


back on with the float bowl and it fired ? so maybe it just was something cloggin up my system, gonna start fine tuning the vacuum and pilots once more to make sure its right
and hopefully the problem will stay away.

the engine still seems to have an occasional misfire and with the colortune in cylinder 1 i can see a very yellow combustion everytime else its fine and blue.
i dont know whats causing this and im pretty sure it was the same thing i saw when setting my points. where the 1-4 was spot on but the 2-3 was flickering as if every other spark on the 2-3 was off.
any ideas to whats causing this is very welcome.

im guessing maybe the points need changing other than that i have no idea
 
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