anyone get a weird idle after a cam/piston install??

[cals400ex]

i have had this problem for a while now. i installed a 10.8 compression ross piston with a stage 2 cam. i get a fluctuating idle. when the bike is still cold, it is just fine. when it gets hot, the idle starts fluctuating. it will even die sometimes. i am running a 42 pilot with 2.75 turns out on the fuel skrew. i think i am a little rich at idle so i can try to turn the skrew in a bit to see if that fixes it or not. i don't know, it may be from the more aggressive cam than stock. any ideas??

[carlj75]

I had the same problem when I installed a 11.1 426 piston and stage 2 cam. While it was apart, I removed my choke and installed a #42 pilot. Sometimes it would idle really fast and then it would slow down and sometimes die. I messed with the mixture screw. I ended up turning it all the way in and now it idles fine. I know it shouldnt be screwed all the way in, but I can't figure out what the problem is....I'm thinking the pilot jet is too big.

[carlj75]

If you figure it out, let me know.

[MIKE400EX]

Sounds like a vac/air leak between carb and head on both bikes. An overly rich idle circuit will mask the problem some.

[PHIL_B54]

mine does that just alittle, i figured i was alittle fat in the idle and it was loading up then clearing

[400exdad]

i'm with Mike... sounds like a vacuum leak somewhere.

[cals400ex]

the vacuum leak is exactly what i thought at first too. however, i don't think that is my problem. the reason being is because i have had my airbox, carb, and the boot connecting the carb to the head off numerous times since the rebuild. i have cleaned all of the surfaces and made sure all skrews or bolts are tight. i even have a good gasket in the boot that connects to the head. so, i don't think this is my problem unless the leak could be somewhere else. i also have had my exhaust off so i don't think the leak is there either. also, i would think it should run with a weird idle when it is cold or hot if i had a leak. mine is just fine when it is cold, but problems emerge as it warms up ( which makes me think its ok jetting for the cold, but as things heat up it becomes too rich). i first had a 45 pilot jet in and i let the bike sit and idle for a minute, then shut it off and checked the plug. it was pretty rich. i turned in the fuel skrew and it seemed to get better but was still rich. i then put in a 42 pilot jet and the fuel skrew was set at 2.75 turns out and it seemed a little better but the problem still persisted. now i am at 2.25 turns out with the 42 pilot and i will let you know if that helps out or not. i havn't got to check yet.

[carlj75]

Yeah, I also checked for vacuum leaks....Didn't find any. I might put my stock pilot jet back in and see if that works.

[jshtex]

We have the same problem with our 416, 11:1 with Stage II hotcam and head porting. Ours speeds up every so often never dies though. I actually just took ours to a shop for Dyno tuning yesterday (to verify that the jetting is correct) and I mentioned it to the guy there. Once he gets the jetting dialed in I will let you know if it helps any.

[cals400ex]

i am going to go mess with it for a bit now. who knows, i may even be a little fat on my needle. i am running it in the 4th position with my airbox lid on. i will perform more tests.

[cals400ex]

well, i think i have it figured out. i went out there and drove it with the fuel skrew out about 2.25 turns. it still idled weird. i turned it in some and still a little wierd. turned it in more and it seems to be fixed. i am not positive, but i am probally only between 1 to 1.25 turns out on the fuel skrew with the 42 pilot. the plug looks just like i prefer. i like it when it turns colors right on the bend. with the fuel i use, it changes from gray to tan. this is how i check the mainjet too. however, i let the bike sit and idle for this test, instead of doing a full throttle test, because the pilotjet/fuel skrew controls the fuel between idle and 1/8 throttle. i have no clue why i needed to lean my fuel skrew out after putting in a cam/piston. here is my only thought: i bet i was rich on the pilot/fuel skrew before i did the piston and cam (but i never realized it), but since the stock cam is not aggressive and doesn't have any lope, it idled just fine. now, with the more aggressive cam, it lopes more thus making the idle more irratic and the rich air/fuel mixture was enough to make it want to die. however, you can still tell this is a more aggressive cam than stock by the idle, but at least it doesn't die (or hasn't yet!!!). i imagine a 40 pilot would be just fine. heck, i am wondering if the stock pilot would work if you are out 3 turns or so. i don't know. all i know is my 42 is just fine where it is at (i am guessing somewhere around 1 turn out. i turned it a couple times so i am not sure.) my headers are not glowing either, so i must not be lean. my stainless steel sparks headers tend to glow if it is even a little lean. good luck everyone!!

[carlj75]

Yeah, mine runs fine when the screw is all the way in...probably going to try a #40 pilot.