round slide or flat slide? 2 stroke

[Tri-valleyracin]

round slide or flat slide? i have a carb off my pe250 that is a 34mm and my 86 lt250r is a 32mm and my lt is flat side and my pe is round slide. what would be better? the pe is 1977 but the carb is good and the bike runs good with it. idk if the jets are interchangable but i have have a baggy with lt jets. my lt has a fmf pipe and silencer for mods and its bored to the max (255cc). i have a hole pe to use the parts off of if needed.im using the kicker off it know. for a 1986 lt250r. im goin to be racing mx.

[GPracer2500]

Flat slides are generally a superior design. I'm less familiar with Mikunis but for Keihin:

First there was the PE--round slide.
Then there was the PJ--oval(ish) slide.
Then there was the PWK--oval on one side, flat on the other ("D" shaped).

AFAIK, the only reason Keihin didn't go to a true flat slide right after the PE was due to patent reasons.

In your case, flat slide vs. round slide isn't the whole story because they are different sized carbs.

[mic 902]

I dont think that your engine is bored out enought to need a bigger carb yet. You are probably better using the flat slide. :D

[wilkin250r]

I don't know, 32mm is pretty small. The TRX250r came stock with a 34mm, and it's generally regarded as too small, most people upgrade to something between 36mm and 38mm, depending on their applications.

A little on the theory of carburetors.

In order to accomodate a "round" slide, the air passage cannot be smooth where the slide moves. This area of discontinuity in the wall of the carb causes turbulence in the airflow. Also, at anything other than WOT, the incoming air must encounter the round slide face and it's intersection with the carburetor walls. This causes a lot of turbulence right at the jet, causing poor fuel atomization and inconsistent fuel metering.

A flat slide is better in both respects. The carburetor walls can be made smoother with less deviation from a perfect wall, and the turbulence at the area of the slide at half throttle is much less severe. This gives much better throttle response, and also improves airflow overall.

However, in this situation, I think the round-slide 34mm is going to be the better choice. The 34mm is already going to give you good throttle response and low-end power simply because it's still a small carb, you don't need to improve it further with a flat slide. At the same time, the 34mm is going to give you MUCH better top-end performance over the 32mm simply because of size.

[Tri-valleyracin]

i might put the dirt bike carb on my lt after i get it running and break in the motor. its goin to be raced mx so i need a decent carb.