'81 550T…idle

[Buffalo Bill]

I can't get it to idle below 2000, but I have a theory.
The intake and carbs are all stock. I've cleaned the idle circuit thoroughly, and checked the jets with a magnifier. Backed the air screws out as far as 4 turns. Not enough to make it work.
It will idle with a little choke richening it up. I think it's the MAC 4-1 that's leaning out the mix.
Do you think I need larger pilot jets?
Where can I buy a larger size air and fuel pilot jets?
Thanks!

[Nessism]

Did you change the intake pipe boot O-rings yet? That's a common leak source.

Dennis Kirk sells Mikuni jets. Not sure if the pilots would cause the problem you describe.

[tkent02]

Are your fuel levels correct? Z1 has real Mikuni jets for 2 something each, go a size bigger on the pilot fuel jets and see what happens.

[Buffalo Bill]

I'll describe it more fully…

I think I've done everything on the check list.
Yes all new intake O-rings.
Can't find any air leaks in the boots.
Air filter in all proper.
Float levels are normal, if they were low that would cause it to stumble during acceleration, but it runs up fine.
Let me describe it again. It starts up strong and normal with full choke, I ease it off as it warms up. Fully warmed up it will die unless I keep revving it up to 2000 before I ride off. Rides normal on the road until I come to a stop, then I have to keep it revved. That's about it. I can adjust the fast idle up but it's rather high at 2000. Bring it down to 1500 and it will slowly die out.
Can you think of anything else it might be?
Thanks.

[Nessism]

I think I've done everything on the check list.
Yes all new intake O-rings.
Can't find any air leaks in the boots.
Air filter in all proper.
Float levels are normal, if they were low that would cause it to stumble during acceleration, but it runs up fine.
Let me describe it again. It starts up strong and normal with full choke, I ease it off as it warms up. Fully warmed up it will die unless I keep revving it up to 2000 before I ride off. Rides normal on the road until I come to a stop, then I have to keep it revved. That's about it. I can adjust the fast idle up but it's rather high at 2000. Bring it down to 1500 and it will slowly die out.
Can you think of anything else it might be?
Thanks.

Going up on the pilots may help. Just for kicks I'd try shimming the carb needles first so see if that has any effect, although technically it shouldn't.

[tkent02]

Going up on the pilots may help. Just for kicks I'd try shimming the carb needles first so see if that has any effect, although technically it shouldn't.

Man, that's the hard way round. It runs well at part throttle?
Just take five minutes to pop in bigger pilot jets, that's the jet that's in charge with a closed throttle. It will either help or it won't. Either way you will learn something.

[Buffalo Bill]

I got my kicks already…

I tried the needle shim trick for awhile, but the plugs looked blackish. So I went back to stock. I was working on a top end studder when I tried the shims. Based on the bore/stroke ratio I decided that this engine likes to be shifted on the torque peak, and revving over that is futile.
Changing the pilot jets is worth a try.
Are there numbers stamped on the pilot jets?
Thanks!

[Buffalo Bill]

Thanks, I'm on my way…

I just ordered a set of #45 pilot jets. The stock size is #40, so I figured that 45's will provide 12% more fuel flow. Just a guess.
Thanks for the source info.
Bill

[Buffalo Bill]

Bummer, no change…

I put the #45 jets in, stock is 40. But no change.
It still dies if adjusted below 2300 rpm.
I will try spraying ether onto the intake boots to detect an air leak. If that doesn't have any affect then I guess I'll have to go all the way to disassembly, cleaning and dipping.
Bill