4/6 Won't Idle

[mswyka]

Good afternoon.  I need a sanity check here.

Our 4/6 will not idle.  I have pulled apart and checked the engine in its entirety - re-building with new gaskets, crank seals and NOS 4/6 head gaskets.  Carbs have been completely pulled apart, cleaned and have had all the jets replaced - every passage is clean as a whistle.  Oh, yes, new carb boots also.  Running stock airbox.

Now, with that said, she fires right up on a prime will rev to about 4K, nudge the primary, and then settle back to 3K for 10, 15 or 20 seconds and then die a slow death.  Add a prime and she picks back up to 4K, nudges the primary and settles back to 3K. 

Open the enrichener, she will idle at about 2.5K but bog considerably on acceleration.  With the enrichener off, she is slow on the pick up but will absolutely fly.

To me, the way she behaves it suggests that we have a problem in the pilot circuit - but with the carbs checked now about a half dozen times I don't see any problem in the pilot passages and as I said, all the jets are new Mikuni jets.

What do you think?

[Interceptor398]

Perhaps the primer sucking air??

[mswyka]

Perhaps the primer sucking air??

Good thought.  I will give that a try.

[Checkmarks]

Mark,

It sounds like a pumping problem.  Swap a fuel pump in there.  Check the lines.  MUST identify if the problem is fuel or spark!  Get a timing light on it and check the blue flowing of the strobe.  When your sled is peetering out is when to watch the strobe hard. 

Pumping my first guess.  Lord knows how I hate to guess.  Could be stator, coil, CDI the list starts endless but you can eliminate about half with the timing light....

Please report back fuel or ignition. 

[mswyka]

Mark,

It sounds like a pumping problem.  Swap a fuel pump in there.  Check the lines.  MUST identify if the problem is fuel or spark!  Get a timing light on it and check the blue flowing of the strobe.  When your sled is peetering out is when to watch the strobe hard. 

Pumping my first guess.  Lord knows how I hate to guess.  Could be stator, coil, CDI the list starts endless but you can eliminate about half with the timing light....

Please report back fuel or ignition.

Thanks Mark, good thoughts, I will check these out.

[ltdman]

My 4/6 has a similar problem. From idle to around 3,500 rpm's, it bogs, but from there up it's a beast. Could it have to big of jets? Carbs were cleaned up this past fall before I started riding it. All seals were recently put in along with new fuel lines, screen in pump was cleaned. I have the oil pump cable coming on as soon as throttle moves, mainly because I just rebuilt the the motor and I wanted good break in lubrication. Could it be to rich or maybe carb jetting. It used to have individual filters when motor went down. Since it's been rebuilt I went back to the original airbox. What do you guys think??? Thanks.

[gixxer6]

What RPM is your idle set?  The manual shows 2500rpm.  My 4/6 is ported with Aaen pipes, it likes to idle around 3200, if I don't have the idle screws turned up and it drops below 3000 it is real boggy. 

[Checkmarks]

Ltdman,

What pilot jet do you have in the carburetors?  Your idle mixture jets may be set incorrectly.  Idle jets control idle and transition to needle jet/jet needle.  Just because the starting point is 1.5 turns out does not mean they are correct.  In your specific case you may need to 2 turn out the screw in the mixture screws.  Maybe even 2.5 turns out.  When you get to 3 turns out then you go down one step in the pilot jet.

[mswyka]

Ltdman,

What pilot jet do you have in the carburetors?  Your idle mixture jets may be set incorrectly.  Idle jets control idle and transition to needle jet/jet needle.  Just because the starting point is 1.5 turns out does not mean they are correct.  In your specific case you may need to 2 turn out the screw in the mixture screws.  Maybe even 2.5 turns out.  When you get to 3 turns out then you go down one step in the pilot jet.

Mark, isn't the initial setting on the 4/6 supposed to be 3/4 of a turn on the air bleed screw?

[ltdman]

gixxer6

I have the idle set at around 16-1800. As for air screw setting, the shop manual calls for 1.5 turns out from the bottomed out position. I had it set at 2.0 and no help at all in bogging. I'm going to try moving idle up to 2,500 and give it a whirl.... Ltdman

[mswyka]

gixxer6

I have the idle set at around 16-1800. As for air screw setting, the shop manual calls for 1.5 turns out from the bottomed out position. I had it set at 2.0 and no help at all in bogging. I'm going to try moving idle up to 2,500 and give it a whirl.... Ltdman

Are you looking at the manual for the 4/6 or the stock Invader?  In my 1980 manual the stock Invader lists 1.5 and the 4/6 in the appendix lists 3/4.  I want to be sure I am looking at the right settings.

[ltdman]

I have the shop manual for the 4/6. That's what it calls for. Could they be to far out?   Ltdman

[jimvw57]

Carb adjustments are mostly a starting point. Depending on local conditions, elevations, etc you may have to change them. I have had sleds that would only run with air screws just barely cracked open. My guess is that someone over tightened them and damaged the seat on them.

With idle set at 1800, you will get a bog. crank it up to at least 2500 or more. clutch engagement is around 4000 so as long as the idle is below that, you should be OK.

My 4/6 fought me for a long time until I figured out it was a spark issue and not the carbs.

[Lloyd (ljm)]

 My 4/6 starts and idles pretty good, But I have a Liquifire that is hard to start and idles like Mark's 4/6

 Jim on your 4/6 what was the spark issue and how did you get it figured out?

 Lloyd

[jimvw57]

after a lot of carb cleaning and such, I found that the coils were heating up and one would work cold, one would work hot. they never both worked at the same time. It gives you a terrible bog and then when they both started working, it would scream!!!  I finally changed both coils and it ran much better.  About drove me crazy when one plug would work, then the other (on each cylinder)