My 89 misses at about 2000RPM. I have looked for shorts, poor connections. Replaced voltage reg, spark plugs and wires, went to a CV carb. Any ideas? If i get it above about 2500 is is just fine.

 

I'm not sure if your year had a voes, but if you do, check to see if your not advancing the timing due to a vacuum leak, or defective switch.,,

 

Should have a VOES. Above the carb with a vacuum line running off the carb or intake manifold as well as a 2 wire harness. Also look for a vacuum leak on that hose.
You might also have a blockage in your mid stage fuel system blocking a jet. might have to pull the carb & give it a good cleaning.
Hatch.

 

It looks like ignition problem. My EVO did this same when the ignition timing was wrong. It just missed at below 2500RPM, something like a small backfire or something.

Also If you give too much gap at the plugs she will do this same. I`ve found 0.9.mm is the perfect spot on Champion plugs.

 

Removed double post sorry guys.

 

Intermitent problems are difficult to diagnose in person, let alone "second person cyberly", but here goes. First check for a vacuum leak by spraying all around the manifold, carb, and VOES to include the vacuum lines and petcock. Be careful to keep away from the filter area as it will give you a false positive reading. If a leak is found/suspected, fix it. If not then we will look farther.

We could probably rule out the carb as it did it with the original, but you could check the jets for size, diaphragm to ensure it is correctly installed and has no holes or tears. Does the slide hang up, has it been modified or drilled out?? Does it have the original, unmolested spring?? Is the enrichner cable fully seated?? 2,000-2,500 is where the CV carb is transitioning from the idle circuit to the main circuit so you could look there too.

Because the problem is only in a 500 RPM range I wold suspect a "harmonic" problem. An engine creats different vibrations at different RPM's. So what might be happening is it causes a connection or perhaps a bad wire to disconnect/short intermitently at that RPM range. So I would go over all the wires in the handlebars, under the tank and any other place that you don't normally look at. Pay particular attention to grounds and connectors especially the "crimp on ones as they will corrode where they crimp and have a bad connection even though they are tight. It could also be the first sign of a failing ignition module. As previously mentioned try a set of fresh, properly gapped plugs.

Sorry for the long winded reply, but there was a lot of ground to cover. Hope this helps

 

It sounds like your not getting any spark advance. My vote is for a non functioning VOES.

The RPM range is where the timing shifts when the VOES engages from higher vacuum.

I hate to say this but that could be the ONLY problem you had...

 

Forgot to mention that I put on a new VOES also. The only place to attach it is to the back of the carb. Enough vacuum there to accuate it?

 

id lookinto ign.module and cam sensor. check the wire coming out of the nose cone.

 

My experience with a failed VOES vacuum hose was that the bike ran like a real bitch. It was not rev related, the darned thing didn't run right until it was travelling at a steady speed. Doesn't sound like that to me, but check it, for peace of mind.