26mm to 28mm oval bored carbs........

[REV-I-DOO]

I picked up a nice set of 28mm oval bored carbs off Ebay. They came with 25 pilots and 390 mains.

 

So far, I had to go with 30 pilots for it to idle right and I had to go back to the longer needles with the clip in the second notch from the top. It still stumbles a little and then it cleans up.

 

My question is.........

 

Doesn't 390 main seem a little fat?

 

Can a main that is to fat cause it to stumble or load up a little just before the pipe hits?

 

I was running 25 pilots, 300 mains and the clip in the third notch on the stock carbs.

 

I have no room to do a good long run to get a good plug chop.

 

What do ya think?

 

My mods are listed below.

[REV-I-DOO]

[itsaripper]

Lets see if I can give you some idea of what I think is going on with your carberation. First your motor is a air pump, keep that in mind when you are jetting any bike. Then when it is running great it is a combination of all the componants working together.

This answer is going to sound like I am all over the place, going in different directions. But anyway, you have had your motor ported, improved the air flow, now your pipes should work better. After the port job you can rev higher, more air flow, so put on bigger carbs. That improves mid and top end but the low end is sluggish. You have created a condition in the intake that is like you trying to suck water up a 5/8 heater hose instead of a straw. The valosity at low rpm's is low. The only way to get that back is to go back to the smaller carb or put more compresson in the motor to creat more suction. Get the head decked .030 or a cool-head type head with 20cc or 19cc domes. Watch those carbs start worken. But you will have to start running a 50/50 mix of reg and some higher octane.

The 390 main seems a little rich. I hesatate to say put this size jet in, it will fix the problem. But take it back a couple of points and keep watching the plugs. Watch for any backfireing that is a sign of a lean condition you need to go richer.

Hope this helps, Good luck