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This is sort of going to be a continuation of a thread that I posted here last winter. https://xs11.club/forum/idle-talk-fo...aphragm-issues. Other things came up and I decided to put this bike on the back burner for a while. Well...now it's time to fix this bike for real. Bike sat for years before I acquired it, cleaned it up, etc. Cleaned the carbs. No holes in the diaphragms and they all rise and fall smoothly with applied air pressure. The bike idles smoothly and runs just fine on light throttle apertures. HOWEVER....once you apply anything over 1/3 throttle (basically running on the main jet) it starts loading up and running rich. It happens at highway speed, 1st and 2nd gear, etc. Basically the problem manifests itself via throttle position.
Some basics about the bike: The bike does NOT have the stock vacuum operated fuel pump. I simply have it set up for a typical gravity feed (there are no vacuum leaks either). Compression is excellent and even across all 4 cylinders, 170 psi. No oil burning, no piston slap, no rod knock, etc. I checked the valve clearances, all perfect. Vacuum advance is fully functional, ignition is spot on. It does have an aftermarket exhaust system. It is a 4 into 2, something like a MAC or an old Kerker. It is louder than stock but tolerable and the baffles are intact. It has a stock air box that I removed and replaced with pods (I hate pods) but it made no difference in how it ran or it's performance envelope. I'd like to go back to the stock airbus. I also checked the float height, it appears to be good also. Throttle sync was also good.
In getting into the carbs, I noticed it had stock main jet and pilot jet sizes, 137.5 and 42.5. I also noticed the needle had the numbers "Y265" (it was also shimmed). I got to poking around on the internet and discovered that this is NOT the Mikuni number but the number that is commonly used in the K & L kits or even the cheaper Chinese kits. I even saw a comparison photo of the stock Mikuni and the K & L. The Mikuni is obviously much larger dimensionally and a totally different needle in general. I know that with all things Mikuni every thing is flow rated and often dimensions themselves may have no significance. I was also able to measure the orifice to the main jet and it was 0.055"....measured with two instruments to insure continuity.
So......my best guess is that someone MAY have put an aftermarket jet/rebuild kit in there. In rebuilding other carbs, I have never noticed aftermarket kits like K & L being THAT far off. The larger Mikuni needle and smaller K & L needle style could possibly account for it running rich in the 1/3 throttle position range but once you go with full throttle it should therefore clean up and rev to the moon. (Right?) This bike does not. Full throttle just burbles along for a few seconds or longer until it fouls a plug.
I will include a few photos.
Some basics about the bike: The bike does NOT have the stock vacuum operated fuel pump. I simply have it set up for a typical gravity feed (there are no vacuum leaks either). Compression is excellent and even across all 4 cylinders, 170 psi. No oil burning, no piston slap, no rod knock, etc. I checked the valve clearances, all perfect. Vacuum advance is fully functional, ignition is spot on. It does have an aftermarket exhaust system. It is a 4 into 2, something like a MAC or an old Kerker. It is louder than stock but tolerable and the baffles are intact. It has a stock air box that I removed and replaced with pods (I hate pods) but it made no difference in how it ran or it's performance envelope. I'd like to go back to the stock airbus. I also checked the float height, it appears to be good also. Throttle sync was also good.
In getting into the carbs, I noticed it had stock main jet and pilot jet sizes, 137.5 and 42.5. I also noticed the needle had the numbers "Y265" (it was also shimmed). I got to poking around on the internet and discovered that this is NOT the Mikuni number but the number that is commonly used in the K & L kits or even the cheaper Chinese kits. I even saw a comparison photo of the stock Mikuni and the K & L. The Mikuni is obviously much larger dimensionally and a totally different needle in general. I know that with all things Mikuni every thing is flow rated and often dimensions themselves may have no significance. I was also able to measure the orifice to the main jet and it was 0.055"....measured with two instruments to insure continuity.
So......my best guess is that someone MAY have put an aftermarket jet/rebuild kit in there. In rebuilding other carbs, I have never noticed aftermarket kits like K & L being THAT far off. The larger Mikuni needle and smaller K & L needle style could possibly account for it running rich in the 1/3 throttle position range but once you go with full throttle it should therefore clean up and rev to the moon. (Right?) This bike does not. Full throttle just burbles along for a few seconds or longer until it fouls a plug.
I will include a few photos.
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