For the last few nights the temps have been near 50 or colder, and when I start my bike after work and leave it pops sputters and backfires.......But when it warms up after about 1/2 mile, it runs fine.
Seams to be happening only on the rear cylinder.

Question is where do I start to figure out where to begin?
A friend said it may be sucking in air through the intake seal or plugs/ wires......

What do I do?

 

Does it do it while you are running it with the enricher on? I'd say let it warm up a bit longer than normal. My 92 Fatboy did the same thing when temps dip in the 30's or 40's in the fall. But a little longer warm up solved it. EVO's are cold blooded......

 

I let it warm up for 15 mins and left with the enricher **** out and it did it for nearly 3/4 mile then clared up......

 

I would go with plugs and plug wires first, and then since it only does it when cold, I would try spraying the timing sensor with cold circuit board spray after it is warmed up and running OK. I would not think it was the ign. module since it would not warm up that much. You might also spray the coil with the cold spray. Just a few things to try.

 

Where can I find that stuff?

 

Driving with the "enricher on".

Does that mean you have the choke on while attempting to drive down the road, and that makes it run better?

Sounds like intake gaskets to me. Once they warm they seat completely, cold they become unseated, perhaps due to age or warped due to the heat that builds up between the cylinders.

Running with the choke on to keep it running smooth means too much air, not enough fuel is going through the intake with out blocking the main air flow into the carb by using the choke to meter it out to run.

The intakes are where the carb attaches. They then attach to each cylinder behind the carb. Not too bad of a do it yourself repair.

 

Sounds fuel related to me. Intake leak is a good place to start looking. Then clean out the carb well. Jets could be plugged up some.

 

He did say it still did it with the enrichner pulled out for 3/4 of a mile. Could still be intake gaskets, as you say when it warms up they expand and seal. I still think I would go with plugs and wires first as they are cheap and simple to do. You can get circuit spray coolant at most electronic supply stores. Comes in a spray can.

 

Thanks guys for your advice. I'm starting to check things out. I will let you know what I find.

 

Well, I changed plugs and wires to no avail. Then I changed out the car. seal ring. Seems to run beter but, I'll see how it works tonight after work.