sounds like its running rich, have you tried driving it with the air cleaner off? if your bike runs worse when its hot out that usually means the air molecues expand so your carb is getting less air, if your bike is running rich to begin with it will be worse when its warm outside. a good test is to take the air filter off and run it around, let it get hot and see if it still happens, if it does that aint the problem. If it takes care of it, you might need to adjust your carb to run right with your new pipes, or change your air filter if its chuck full of dirt.

 

Logically speaking, it is either the spark or the fuel. Only two possibilities. Spark / timing problems are worse at high RPM, not better. So, this is NOT a spark issue since it runs fine at 80.

Fuel problems can be at any rpm. If going up a hill, probably gas restriction of some kind. If elsewhere and not uphill, probably too much gas not enough air.

That leaves wrong jets or enricher full on, bad air cleaner or ..... something else getting in beside oxygen laden air. i.e. backfeed of engine exhaust. Do these bikes do that like a car for emmission control? Something like a PCV valve?

My bet is on the jets being too rich. This will also eventually screw up your spark plugs and the bike will run awful period or not at all.

 

I may be way off here but, have you checked your V.O.E.S.? Has it been tampered with or "adjusted" or damaged? If I am correct, the VOES (Vacuum Operated Electronic Switch) at higher PSI (under throttle load) sends a signal to your ignition module that "retards" your timing to give you better MPG and EPA. Sounds to me like the switch could be damaged or not functioning and it is screwing up your timing at higher RPMs.

There is a hose coming off the back of your carb that attaches to the VOES. The VOES itself is screwed to the backside of your enrichner mount. It is located right under your gas tank. (oh joy) There is a silicone plug in the bottom of the switch that conceals a screw that adjusts the PSI. If this switch is defective or there is a vacuum leak in your system, this could definitely cause your problems.

The reason I know, is that last night.... this happened to me. New VOES and Hose on the way. I will let you know how mine turns out.

 

Hello from hot & hummid florida.Being an old hot rod mechanic sounds like you have a puddle of water inside one of the carburators passage ways. Could allso be a float needle worn out or sticking or leaking past. Could allso be a carb. float with a leak were the float is heavy & not regulating the flow of fuel throu the carb.I think every one will agree, its real tough to diagnose without being in front of the bike.Good luck, one of us is going to nail your problem.tom

 

A serious vacuum leak would bugger the performance on cold days as well as hot. Timing is advanced with rpm, not "retarded" however it is not advanced as much if the engine is under heavy load (vacuum switch).

"In 1982 The V-fire III ignition made its debut. This system is completely contained in a black box more commonly known as a module. We actually get rid of the advance unit because the module has a couple of advance curves built in. Triggered by a rotor cup and a hall effect transducer this system requires no maintenance. Due to the different ignition requirements presented by a light (Sporty) or a heavy (Dresser) motorcycle a Vacuum Operated Electric Switch (VOES) that can be set at different vacuum level handles changing the advance curves. Under heavy load conditions the ignition is retarded. This ignition soon proved to be very reliable but not the absolute best for performance. "

Originally, ignition retardation at very low RPM was employed to kick start the V-Twin. It is employed today to make starting it easier, and is a function of the low load advance curve.

Operating on the wong curve for RPM and Load could certainly rob power.

Is it backfiring?

But why would this respond to temperature I wonder? That still sounds like fuel.