High Idle With Choke On

[Chief]

I have an '01 rm 250 with a pwk Keihn Carb. I pull the choke out before I start it and it always starts on the 1st or 2nd kick. It immediately revs very high. I push it in as fast as I can, it idles down, and I let it warm up. Everything works fine, but I always wonder why would it idle so high when the mixture is supposed to be rich with the choke pulled out. Anyone have an idea or similar experience? I'm thinking about pulling the choke out once it's fully warmed up to see what it does.

Joe Chief

 

[jboomer]

My Kx does the same thing. I'll start it, then quickly push the choke back in (before it really screams), wait about 2 seconds, then pull it back out again and let the bike warm up. I have no clue as to why it revs like that though.

 

[RM_guy]

Joe,
Your bike revs so high when you first start it because it knows that's the only time it will get the chance :p

 

[Nevada Sixx]

yea, that is strange how a bike revs high like that, doesnt the choke cut off the air? i heard that your bike stills needs choke after 30 seconds, then your jetting is too rich.

 

[atc3434`]

Nevada, I'd say you've got that backwards. If you still need choke after 30 seconds, your too lean, at least on the pilot. The bike likes to rev, because its got a mixture that is burning well. Its not too rich, and not quite lean. If your pilot was richer, it probalby wouldn't idle so high on the choke, but you'd end up too rich for normal use, and maybe fouling plugs. That initial high idle is a sign of pretty healthy, to maybe a tad lean pilot jet.

 

[jboomer]

I resemble that remark RM_guy!

Does everyone pretty much agree with atc? That we may be a tad too lean on the pilot? I'm curious because I rejetted back in January or February (40-60 degree temps) and haven't rejetted since (currently high 80's to low 90's). My pilot dropped from a 52 (stock-lots of drool and smoke) to a 45. That seemed lean to me, but the bike runs great with it, awesome throttle response and ZERO spooge and smoke (except when I first start it for the day). I'm a lugger anyway (especially in the woods). I've got a step richer pilot, but haven't taken the time to give it a try.

 

[atc3434`]

A tad lean at best. I'd say your pretty close to perfect if your running good with power good on the bottom, no bogging. IF your not fouling plugs, and your making good power, I wouldn't step up. Maybe when it gets cold again...

 

[RM_guy]

You won't seize it with too lean of a pilot jet unless you ride around at no more than 1/4 throttle all the time. I have a 40 pilot in my bike and it is real snappy now.

The modern day choke doesn't block the air flow to richen the circuit, it opens up an orifice that allows more gas through. I'm not totally sure why it idles high when you first start it but I suspect it's because it's just getting so much more gas and the engine isn't hot enough for it to burn correctly yet.

You can use the choke knob to see if your jetting is too lean by putting it on but only after the engine has been totally warmed up. If it runs better then the jetting is lean and visa versa.

 

[merlinnn]

My YZ does the same thing. I read this somewhere on this website and it works for me. Before you start the bike lean it over until fuel comes out of the vent hose, and then with the choke on kick the bike over once or twice with the kill switch on. My bike then starts straight away with no high revs. Give it a try, and thanks to who ever posted this info the first time.

 

[Chief]

Originally posted by RM_guy
Joe,
Your bike revs so high when you first start it because it knows that's the only time it will get the chance :p

See What I Smart Bike I Have ? :laugh:

 

[Chief]

Ok Guys/Gals,

Thank you for the replies. At least I have some ideas now and know other bikes run this way too. To me the choke is only a starting aid and it works. I have a 50 pilot in mine now, and it still surges if I tightnen up on the airscrew. Being that RM_Guy has a 40, I'm beginning to think that maybe the A.S. and pilot do not work exclusively as one. Also going to go a bit leaner on the main to see what that feels like. I have a 158 main in and it pulls well, but there is a bog/delay at low rpm WOT. I'll try the next smaller size to see what happens.

Sincerely,

Joe Chief

 

[atc3434`]

A bog, then power, usually is consituting a lean condition, you get too much air and not enough fuel initially when you snap open the throttle. Try a leaner main if you want, but I think you'll find the bog will get worse. What you might try is raising the needle a spot or two. It'll slid out of the mainjet quicker when the thorttle is opened, allowing for more fuel, and hopefully getting rid of the bog. You may need more main too, but I'd try the needle first. Just some thoughts. I'd just play with it, try different things, and learn from it. Thats how I do my learning!

 

[RM_guy]

Joe,
I have Eric's porting and V-Force reeds that work better with the smaller pilot. I also have the needle at the middle position and a 158 main. Don't forget you have a fatter needle than I do that could be giving you the lean condition.

You should go ahead and try the leaner pilot. It may be that you are so rich that it is bogging even though that is normally an indication of being lean.