rm 80 won't rev

[flogga400]

I have an '84 rm 80 that won't rev. The air box has had the air filter supports cut out of it. I covered the hole with two layers of low density home a/c filter foam and held it in place with the bolt on support ring. The bike had a new piston and rings, and starts very easily. The throttle can be held below half throttle and it will eventually rev into the powerband. If it is twisted open it just stutters and stumbles. The clip on the needle was in the middle position. I moved it down it got worse. I moved it up it got better. It is now in the top position. I'm afraid it is sucking too much air. The carb is a mikuni I believe it is stock. It has no adjustments other than the idle. The local shop confirmed that it had no exterior adjustments. Is this true? Do I need to re-jet? It seems so, but I am unsure of how it all relates. If it is pulling more air it also needs more fuel right? Is the pilot what needs changed? Someone shed some light in my direction!
thanks

 

[dell30rb]

Your bike's stock jetting is now a piece of crap. The removal of the real airfilter is the cause of your problems. You can tun the setup with the 2 layers of foam, and re-jet, or put the old airfilter back on.

 

[flogga400]

I wish I could replace the stock filter. Someone cut out the supports in the air box. There is nothing to attach a filter with. That is why I had to jerry rig it. Now I need to know what jet to change. Do I need to change the pilot? If so which way, higher or lower number?

 

[dell30rb]

You will need to change both jets.

Probably richer...

If its bogging like that... go richer on the jets

If i Were you I'd find a way to put the stock filter back in there!!

 

[Jasle]

bigger number = bigger jet hole. Before spending too much time on this jerry rigged setup why don't you bug a proper fitting uni-filter. At least that way you can clean and oil it easily and regularly. Also if you didn't oil your foam it will be slightly leaner than with oil. You will most likely need to go bigger on both jets. Basically its trial and error. Go one or two sizes higher at a time and only switch one jet at at time. Keep going up on the main until you can get it to rev out with the needle in or near the middle. this way down the line you can go up or down if need be.