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missing around 4,000 rpm

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motomensch:
Hi, 1982 FT500, bought with wires  hanging our t all around. got it together and took a ride. Starts nicely, minimum choke, carb was re-jetted (145) for my 6,200 foot elevation. Out on the road runs good till around 4,000 rpm and then breaks up. Does same in all gears. Re-jetted to a larger size  (160) and same problem, checked spark and it was black, sooty, dry so I must be quite rich. Going back to last jetting and wonder if it could be the CDI as someone suggested to me??
Any help suggestions or advise appreciated.
Thanks,
Motomel

scottly:
Hey Mel, how about some more pics of your bike? :) What gas tank is that?
What air cleaner are you running? Be aware that once a spark plug has been fouled, you can fix the rich issue that caused the carbon, and the motor will still run badly until the plug has either been cleaned (my preferred method is to burn the black off with a propane torch) or replaced with a new one. I doubt that the ignition is the cause of the carbon: no spark=no fire=no soot.

thumperdh:
I'm with Scottly here, new plug. they're cheap and good insurance.

If i'm not mistaken, shouldn't you go down in jetting size for higher altitude? The RAD (Relative air density) will be less and therefore require smaller jets to compensate for the change in density associated in altitude?

But aside from that. Pretty sweet fairing set up you got going on there.

wrk2ride_ride2wrk:
Fun bike you have there! I have just changed out my CDI, & regulator, very similar symptoms. Lets see what happens withy rejettiing & plug change, you might also check the coil lead & cap

motomensch:
OK Scottly, here are a few more pics,  the tank is a Suzuki GS450 around 82-83. Saw a pic of one on an Enfield 500 and started looking for he tank. I found one at the junker in Albuquerque but he wanted lots of $$ and it needed cleaning and coating and a couple of dents fixed. Gave up on him and in the next day or two E bay had a new old stock tank  from east coast for a good price. Not many of them out there. The red pic is what the bike looked like when I bought it in Phoenix. Lots of loose wiring and rigged items, missing lots of lights, etc.
Took the seat to House of Covers in Albuquerque and had them work on the original seat pan and do the bump stop seat for me, Rick the Painter in Albuquerque did the colors. The tail light is a HD aftermarket and the brake light is the led bar under the plate. I have a bad left foot (drop foot) and can  not lift the shifter with my toe so a friend in Santa Fe welded up a heel shifter for me, also did one on my KZ1000ST side car rig.
I re-jetted from the 138 to a 145 for altitude and had the breaking up and a magazine tech guy recommended the 160, which was the same problem of breaking up at 4,000 rpm so I'm going back to the 145 main jet. Also need to look over the CDI before replacing it, have to check it and need a bit of info on that. Could use a loaner for a day to see if the problem goes away. Anyone in the Albuquerque area have one I could borrow for a day or so?
Anyhow that's where I'm at now. tomorrow is the Pediatric Brain Tumor Ride for Kids and they predict rain, but I think I'll take the hack and give a kid a ride anyhow.
MotoMel

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