T500 Carburetor Jet Info Needed

TLRam1 · Post by **TLRam1** » Sat Aug 08, 2009 7:47 pm

74 T500 sounds like it's running rich.

Right off idle seems okay, full throttle seems okay to a point, in-between is not so good, sounds like blubbering, open full throttle for a steadier pull. Seems the right side is having more issue than the left side, if the left has any, I don't know.

Synced the carbs, timed the bike a little while back with a dial gauge, new points about 400 miles on them.

The left head feels hotter to the touch than the right as I was riding. When it ran out of gas from the regular tank the bike Really picked up where I had to let off the gas. All of this appears to confirm a rich running bike. Plugs are on the darker side but not wet like one side does not fire.

Spark, compared to modern stuff looks weak, compared to vintage stuff I would need to pull one out and check, just seems weak though, might be good enough. Bike starts easy.

I am at 600 ft above sea level in Texas.

Air screws are 1 1/2 turns out on both sides.

Stock setting on needle jets are 3 from the top and that is where these are.

What I have done;

I changed the condensers

Points reset to .014 from about .012

What are you running on your needle jet position and what altitude, temps where you are? IIRC the rest of the jetting is stock, Mains 97.5 and I would have to look up my Pilots, needles are 5FP-77 or 17?

I don't know if the condensers will help, seems I need to lower my needle jet except normally in my area stock works okay.

I have not put this back together yet as I want to get ideas and limit my RR times.

TLRam1 · Post by **TLRam1** » Sun Aug 09, 2009 4:18 pm

I lowered the needle jet by one slot. Helped quit a bit, runs much better. I get some preignition or knocking but the timing should be on, I will have to check that again. Might be able to lower the needle jet another notch.

When I let off the gas a bit the motor stumbles a little than clears up. Maybe the stock air filter media breaths better than the Uni Green media I made?? Not sure if I open the air screws further if that would help this.

skids · Post by **skids** » Thu Aug 13, 2009 9:24 am

The base specs were:

T500K to GT500B
Main jet: 97.5
Needle jet: P-4
Needle: 5FP17 3rd position from top of clip
Pilot screw turns out 1.5

TLRam1 · Post by **TLRam1** » Thu Aug 13, 2009 9:37 am

Thanks Tim for posting, not sure if I had stock parts & settings or not, especially the Needles.

There is the Main Jet and Needle itself.....What are you calling the Needle Jet?

Wayne Meuir · Post by **Wayne Meuir** » Thu Aug 13, 2009 10:12 am

Terry, the needle jet is the part the needle drops down in to when the throttle is closed. The main jet screws into the bottom of it.

What you need to do is back one idle screw off until the engine is basically being supported by the other cylinder, then turn the air screw SLOWLY in and out on that cylinder until you find the highest idle speed. Then repeat for the opposite cylinder. That will get you the optimum setting for the air screw. That setting will also tell you if the pilot jet is the correct size. After that is done, readjust the idle screws and recheck the carb sync.

You really need to know at what throttle position the flat spot resides. (Throttle position, not RPM) To do that, put a piece of masking tape on the switch housing and mark it off in 1/4 throttle increments, closed, 1/4, 1/2, 3/4, open. Then stick a straight pin in the rubber grip adjacent to the closed position mark on the tape. Then ride the bike and see at what throttle postion the flat spot or bog is detectable. That should tell you what needs to be done. Most likely the bog exists at a specific throttle setting, regardless of what gear you are in or how fast the engine is spinning.

You could just drop the needle another slot and see how it runs, but if it is pinging like detonation already, I would be careful leaning it out much more or you could sieze the engine.

Wayne