High Idle

[Radioguylogs]

My SF is back from the resurrection, except there is a problem with high idle.

I got it to idle low long enough to set the spark timing, synchronize the carbs , and adjust the idle speed.

Then, when the throttle is revved, it hangs up around 2k every time instead of returning to idle.

First I loosened the throttle cable so there was lots of slack at the carbs- no relief.

Next, I removed the tank and re-installed the snowblower tank so I could get better access to the problem.

I tried sniffing for an air leak with an unlit propane torch. No leaks.

I pushed on the synch screws and tabs while the idle was stuck high. It seemed like the 3/4 junction had almost no effect, same as 2/3 junction, but the 1/2 junction seemed to help it go back to normal idle, but it wasn't stuck because it didn't really move at all and the problem was loosely correlated.

So, I removed the carbs I found evidence of leaking float valves on #1 and #2- there was gas residue inside the intake air-cleaner boots and a little in the coupler to the engine intake. The #3 and #4 have no such evidence. There is a very minor amount of particles in all the bowls, something I'm used to seeing with a first time start-up. Of course I need to clean those float valves.

I pulled the plugs, and they were ugly, sooty black, confirming the rich smell it has while running. All 4 plugs look about the same.

Here's the big question. I put in the jets from a TourMax carb kit. I have read the numerous posts about K&L pilots being too rich, so I know what I have to do-I already placed the order for genuine Mikuni jets.

My questions:
(1) Do you guys think the 'wrong' pilots could cause the idle to hang-up at 2k? Seems like the butterfly's would restrict the air enough to preclude the pilots as a cause.
(2) Could the wrong sized pilot cause the rich mix at idle?
(3) Do you think the high fuel in #1 and #2 bowls cold cause the high idle, unrelated to the rich plugs, since #3 and #4 are rich with normal float levels?

Here are some pictures:

(1) The idle setting- all butterfly's look to be in this same relative position:




(2) The #4 plug looks the same as the others:

[LoHo]

First, look for a vacuum leak...the caps on the carbs and the vac advance hose.

[Radioguylogs]

Forgot an important piece of information: Idle mixtures screws are backed out 1-1/2 turns.

Note: I am thinking I should confirm a 1/16" drill bit does not pass through the idle speed screw jet holes...

[motoman]

Well, you can start by putting in correct Genuine Mikuni main jets #137.5's. Otherwise, I'll get dizzy from posting chasing your tail.

[natemoen]

Don't go sticking drill bits in holes and screwing them up.

This may sound counter intuitive but try turning your idle mix screw out to 3 turns out and see if your hanging idle goes away.

[rover]

idle

Mine did that from time to time, then most of the time. The diaphragm parts were sticking. I could leave it in gear while coming to a stop, until the revs were around 1100 before pulling the clutch, then it would idle normally until I reved it, then would not idle back down. Removed the tops of the carbs, cleaned and freed up everything, now always gets to idle properly. Hope this helps.

[jetmechmarty]

You have some issues for sure. First, I believe the high idle came from improper bench sync. If the bench sync was done properly, the engine should perform in a manner that it appears to not need further sync. Vacuum sync to an improper bench sync could result in the high idle you describe.

Redo the bench sync while you address the other issues.

[WMarshy]

You have some issues for sure. First, I believe the high idle came from improper bench sync. If the bench sync was done properly, the engine should perform in a manner that it appears to not need further sync. Vacuum sync to an improper bench sync could result in the high idle you describe.

Redo the bench sync while you address the other issues.

The bench sync is just to get you in the ball park, vac sync is the end-all be-all. If the vac syns says balanced then your good. However, if you adjust the pilot screws it affects the balance so you have to go back and vac sync again is my understanding. Too lean on the idle circuit can make idle race in 2 strokes, not sure if that is the same with 4 strokes... Color tune if you have one to check idle mix.

One thing I noticed when I recently cleaned a spare bank of carbs was the pilot jet has a very fine hole in the very end of it that was clogged when the other larger side holes were free and clear. I had to use the finest wire I had in my jet cleaning wire kit to poke through it...

[motoman]

Don't go sticking drill bits in holes and screwing them up.

This may sound counter intuitive but try turning your idle mix screw out to 3 turns out and see if your hanging idle goes away.

Not on the early carbs Nate.........and the ONLY reason your gettin' away with that on those later carbs is your location.....it's called sea level. Your bike, would be all but pukin' fuel anything above 5,000ft........trust me....BTDT....just this past wk.(and I posted referring to just this subject).

[natemoen]

Not on the early carbs Nate.........and the ONLY reason your gettin' away with that on those later carbs is your location.....it's called sea level. Your bike, would be all but pukin' fuel anything above 5,000ft........trust me....BTDT....just this past wk.(and I posted referring to just this subject).

Well the OP's elevation is not much different than mine so your argument doesn't really stand in this situation.

I am not saying that there isn't something else wrong with the carbs, I am just giving other options to try. I personally do not think 1.5 turns out is enough for todays gas that we have, and that is backed by my personal experience with bikes and cars.

[motoman]

Well the OP's elevation is not much different than mine so your argument doesn't really stand in this situation.

I am not saying that there isn't something else wrong with the carbs, I am just giving other options to try. I personally do not think 1.5 turns out is enough for todays gas that we have, and that is backed by my personal experience with bikes and cars.

I'm sure you also know that those mixture settings are also tottally dependant on actual fuel level settings in bowls too. All else closely equal(compression numbers, ect.), and you notice, I say closely, not exact, idle mix settings SHOULD be closely identical also. If not, almost guarentee fuel levels of the four bowls are NOT same levels. You seriously ought to read the thread I posted yesterday pertaining to this, and setting changes I made while at the rally that tottaly back what I'm suggesting Nate.

[motoman]

Blaming todays fuel Nate is a cop-out for incorrectly done or poor tuning procedures...........proof is in the pudding if you'll read what I posted in the other related thread.

[MarkD]

Rlogs-- maybe this will help--- unwanted revving issues

http://www.xs11.com/forum/showthread...ighlight=Markd

[Radioguylogs]

Its' great to have such much support.

Loho: I did try pinching off the vacuum hose to the spark advance, in addition to the thorough propane investigation. I'll double check, but so far I didn't find any vacuum leak.

Rover: I wondered about the diaphragm pistons, because one of the original needles was worn off-center. I dismissed the thought because I expected the slides would fall back under idle, but perhaps I should revisit this train of thought. I CAN say I cleaned them thoroughly, but maybe they have a problem. When operated manually, thy ooze nicely into place. They do pull a vacuum when you close off the intake arched passage, but they do drop in about 2 seconds.

Jet-Marty and WMarshy: I believe the bench sync was surprisingly close. I only had to tweak a tiny bit to get the vacuum syncs to match. I should not discard this thought though. I will be sure to do a meticulous bench sync before the next iteration.

Nate: Making it richer is counterintuitive. I would try it in a minute if the carbs were still on the bike. What are you thinking? I know the 80-81 need more turns, but I should be OK at 1.5 turns unless the idle hole(s) is plugged?


I was happy to see Jet-R-Us had my genuine Mikuni pilots (42.5) and mains (137.5) in the mail this morning. I just ordered them at 5:00PM yesterday. I wish I had an extra 180 pilot air jet for the original one that was bugered. Can't find a replacement to buy.

I read the GLoweVA documentary on pilot jet holes, and I still ordered the pilots that have the holes in the side since they were same as what should have been original. I hope they are the 2-1-2-1 holes, as shown in the picture, not the 2-2-2-2 holes version.

I'm listening to all the ideas. Keep them coming.

[natemoen]

if you'll read what I posted in the other related thread.

Is this the thread you are raving about Brant?

http://www.xs11.com/forum/showthread.php?t=42489

Again, I am not saying you are wrong (except saying that blaming gas is a cop-out cause gas today has less energy than in the past and requires more fuel to produce the same amount of energy than 100% gas) just offering other experiences.

Plus I enjoy arguing with you Brant!