Poor idle when hot

[inthedirt]

2006 Sportster 1200 Custom - 5700 miles

Bike runs fine when cold but when it gets warm out (80s and warmer) and it has run for a while, it idles poorly and will stall occasionally.

My thinking is plug wires or coil. Since this only happens when hot, how can I test these parts?

I have checked the carb jets and they are clean.

 

[Breeze3at]

What is your idle rpm's? Cold engines usually idle a little faster.
As the parts expand there's more friction and they slow down. If your idle is slow cold, maybe setting it a bit higher will help. Of course there's all the other "maybes", like intake leak, etc.

 

[inthedirt]

I'm not sure what the idle is but I have turned it up a bit to try to help out.

I might add that the bike has a 170 main jet in it and seems to run rich. Not sure if this is the stock jet or not but I believe that it may have been changed when the previous owner put the Rinehart slip-ons on.

I'm considering putting the stock exhaust back on to see if it makes a difference, but I doubt it.

 

[Hoople]

I'm considering putting the stock exhaust back on to see if it makes a difference,

I wouldn't expect to see anything changing the exhaust.
Under steady hard acceleration in a tall gear (3rd gear 40 mph roll), does it pull smooth and hard without any sign of a miss. I would perform a compression test when hot to see if cylinders are even.

 

[inthedirt]

She runs great all the time except while idling when it is hot out. Pulls plenty hard in all gears. Problem is only when run for a while, half hour or so, and hot outside. If it is cool out, there is no issue with idling.

 

[Hoople]

My thinking is plug wires or coil. Since this only happens when hot, how can I test these parts?

High engine loads place the greatest demand on secondary electrical parts. If it doesn't miss under hard acceleration & load while it's hot, it's probably not the coil/wires/ignition module or plugs.

This problem just started one day on its own. Was running fine, then started this? Just out of storage or anything unusual? Have you filled up more than once since this problem started? Possible bad load of fuel or stale fuel?

 

[inthedirt]

I just got the bike last year after it sat for about a year. It did the same thing last year too so it's not the gas.

I have a new idea..........

What if it is running lean? This would make it run hot and could result in insufficient fuel to keep it idling when hot - kinda like a vapor lock condition.

I'm going to remove the plug for the fuel mixture screw and take it out a half turn to see if that helps. I have seen some threads that claim they are jetted lean from the factory (aren't they all these days). It will be in the 80's today so I can test it out.

 

[Bodeen]

If its really lean it will certainly make it run hot. If the plug hasn't been removed then it is stock. Does it also have an aftermarket air cleaner on it? If so then it is definitely lean. Pull the plug and give it a shot. If you have a good breathing air cleaner and new exhaust you may need to go up to a .046 jet but try the adjusting the screw first.

 

[inthedirt]

Stock air cleaner...........

I assume you mean the pilot jet on the jet size.

Rinehart's web site claims no jetting is required for the slip-ons (have done many rejettings on dirt bikes and quads so I understand the concept).

mtc......

 

[inthedirt]

After an adjustment on the needle, it seems to be better although we were not out in the real heat of the day. No stumbles at idle and I got to turn it down a bit after an hour's ride.

Ooooops, mean idle mixture screw. It is now 1.5 turns out.