Coil failure, dual or single fire coil still has to fire 2 units, if one side is getting weak, voltage may be low enough below 1/4 throttle to not fire and fire at higher engine rpm's because the charging system is producing more volts to the coil, this is the same thing my Ultima coil did when it failed.

A module failure on a dual fire wouldn't run because only one signal wire is sent to the coil to fire both coil outputs.

Sounds like you eliminated mechanical failures with a known good compression test, a collapsed lifter will produce a VERY noticable clacking sound as I have a few of those lifters in the cabinet from a Woods cam and rpm's, they will still hit at idle with a collapsed lifter but a bad sound is present.

 

Did you look in the holes in the coil where the wires go? They can go bad and burn out.

 

ok this is what i know, have 165 both holes er very close i have spark out of both holes and both r blue seem strong. i clean all gounds checked voltage reg. at 13 er so check timming rebuilt carb two new sets of plugs,changed gas change wires switch them around with very little if any change have checked for intake leaks none present, the rear cyl. drops out until 1/4 throttle then it takes off like it a two stroke. all sound until 1/4 throttle comes from the front pipe. also new battery today,their is no unusal noises from the engine. could it be that little ventura box on top of the carb? i'm grasping at straws oh and the rear cyl actully builds to 165 in two chugs the front in three not bad i wouldn't think. and oil press is good so i think that answers all the questions

 

Spray some carb cleaner on the rear intake gasket while she's idling and hitting on one. If the rear fires up when you do that, pull the intake and replace the gaskets.

 

The way your describing it dropping off at 1/4 throttle it makes me think it has to do with timing staying retarded and not advancing.
Not questioning your mechanical abilities but when you did comp test was bike warmed up and throttle held wide open?

 

You'd be hard pressed to get much over 100 psi if you didn't open the throttle or warm it up first .
165 is great

 

That should be a dual fire ignition system, switch the plug wires to the other cylinders with them staying in the same spot on the coil and if the dead hole switches to the other cylinder, you have found your problem. If it doesn't, then you have a mechanical failure but it is going to be the coil.

Note: dual fire will be ok to switch wires, single fire has to go to designated cylinders.

 

Anything mechanical issue would make a lot of noise,like push rod coming oUt of adjustment, or a bad lifter. A comp,test would show that too.

I don't think there is an intake leak. That would run like shiz from the get go. Check for a snow white plug any way, and do the spray test. Not feeling that though.

I believe a set of wires and a coil are needed as bagger says. might as well,upgrade to a single while at it. A spark doesn't mean you have a good spark!

 

well i took everyone's input and then started over from the begining,and low and behold i found it and i feel stupid but it was a intake leak. the first time i checked for it i didnt hear any difference in the idle but this time it was apparent went from regular idle to about 1000 rpm's with just alittle shot of starting fluid. thank you too all that chimmed in to help. i got to ride it to work today and it ran like a dream. to bad it took over a month to find the problem but atleast its fix and is running great again.

 

Glad to hear another EVO was resurrected!