That carb is probably a year and a half old. The float bowl is clean as a new one. I have been switching around intermediate and main jets for a few days now. Still doing the same thing but, sometimes not as bad. When I installed the 72 main it was the worst. The thing that really bothers me is how at about 50 - 65 MPH roll on the throttle and it coughs and pops etc.. Doesn't seem to matter if the intermediate is the 031 or the 29.5. And same with the main, I've tried 68 - 72, same thing. I know on a car if it does that under load it's likely to be a distributor cap/rotor button or plug wires. I've got it apart in the garage. I replaced the coil and wires today. When the VOEs switch gets here I'll replace that. I put the 70 main back in and I'm going to stay with the 29.5 intermediate and test it. It's a stock EVO, stock ignition, freeflowing mufflers, iridium plugs. I live 1000 feet above sea level. So, no extremes on that.

 

Unplug the voes electrically and take it out and see if it coughs at 60. If it does, a new voes will not cure the problem. Sounds like it is starving for fuel.

 

When I put the 72 main in it really ran bad. I'm kinda stuck. There's something weird going on. It ran good with the 031/70 jets for a year. Maybe it was a little rich but, ran good all the way to as fast as I had the nerve to go. Now all of the sudden it's acting up. If the voes, coil, spare ignition module and wires doesn't cure it I'm pulling that carb and going all the way through it. Maybe there's some crud in there. Wonder if I got some bad gas??

 

Bad gas usually make the engine hard to start. Hesitation and loss of power are also symptoms. I doubt that is your problem.

 

Got it fixed!! I am bloody thrilled!! It's 39 degrees out. I hit the starter and she fired up, no enricher. I added some enricher and set a high idle. I reinstalled the seat and lids on the bags. Then I pushed the enricher off and set the idle with the throttle screw and let the bike warm up. Once it was warm I noticed that the throttle response is instant and crisp. I went for a ride and holy cow this bike is running amazing. It pulls smooth to red line easy and a 70MPH roll-on is smooth and making great power. I really didn't think this old bike was even capable of running this good. I would have settled for less. I'm thrilled right now.

 

Thats great. Can you tell us what you did to fix it???

 

I feel real comfortable in saying that it was the VOES switch. Although it may, skinney chance, have been the coil. I had a new coil I bought a couple of years ago, some new NGK spark wires and a used ignition control module. I realize this isn't the best idea for diagnosis but, I replaced the coil, wires, VOES and ICM. The old VOES switch was delaminating across the bottom where the wires go in. I think it either had a leak or the diaphragm was busted. I'm going to tear into it and see what's in there.

Anyway, my theory is that when I was twisting the throttle the carb was dumping gas, the cylinders were sucking it in but, it created an instant very rich condition since there was no spark to burn off the fuel/air mixture or, the spark was so late. So, it stumbled, coughed, fouled plugs, and backfired. Now it runs like it should.

 

When you throw that many parts at it at one time, its hard to say what the issue was. It does sound like you may have had a vacuum leak in the voes but, it could have been anything. Next time, try replace one part at a time and when you have these issues again, you'll have a better idea of how to diagnose it.
By the way, when you twist the throttle, the voes causes the timing to retard for more power. When the voes fails, the timing stays retarded and the bike will run fine although fuel mileage will be reduced. If your voes diaphram was leaking, that would cause a vacuum leak which in turn will cause a lean running condition. My guess is that you had a bad coil or wires. The voes certainly needed to be replaced if it is as you describe so, I doubt that you installed any parts that you didnt need anyway. Glad you got it running well. Its always a good feeling!

 

Everybody says this, but when MY VOES failed the switch appeared to stick in the "advanced" mode. The bike ran well, but pinged terribly on acceleration.


Glad the problem is fixed. The VOES is pretty reliable as a rule, but the rubber diaphragm will dry rot with age and heat.

 

I can see where that could happen.