[230tard]

This is driving me crazy!!!!!!!!!!!!!

As some of you know, I installed a 30mm Kehin PD Carb on my CRF230 replacing the stock 26mm PD

It has a 40 pilot, 1.75 turns out on the fuel screw, 37D slide, 85A needle, and a 158 main.

Engine has a 11:1 piston, BBR Cam, BBR Pipe and some mild head porting.

When running the bike at WOT, and then rolling off the throttle (not chopping the throttle) the engine momentarily cuts out, and then recovers.

Not a huge issue when in the dirt, but when mid corner racing SM, it could really ruin my day....can you say highside!!!!!!!!!!!!!!!!

 

[Kwota]

too much fuel in the mix?

 

[Eric Landstrom]

Sounds like you've a rich misfire. You're goal is to determine if you're still on the main jet when this happens or on the pilot get. Either way it sounds like you need to fiddle with jet sizes and/or dropping the needle.

 

[TomCRMI]

Also consider the following:

A carby needs a certain "air speed" to create enough suction at the venturi for a good mixture.
If a smaller engine, like your 230, is fitted with a carb too big for the application it may very well be that at lower rpm the negative pressure, due to lack of wind speed, is not high enough to create a good enough mixture.

Just a thought ... haven't had a chance to find out what the biggest size carby for a certain application may be.

 

[Kwota]

it got me thinking about your exhaust as well.... there might not be enough flow through to suck out the exhaust gasses, which might stay in the cylinder for a little bit longer, especially when you've been throttle happy and then you chop it

 

[230tard]

It has a 40 pilot, 1.75 turns out on the fuel screw, 37D slide, 85A needle, and a 135 main now.

Holy smokes she rips. I went up to a 138 just for kicks, but the hickup started to rear it's ugly head....ever so slightly. She really pulls up top now. It's a good thing I ordered the rev box...I need it!!

What was screwing me up was the fact that with the OEM carb and the "power up needle" (C30f) you could run as fat of a main as you wanted....because the needle has almost no taper at the end. You really don't get anywhere near the main jet with it.

The 85A needle in the 30mm carb has a much more aggressive taper to it...so you actually get to use the main jet to it's full potontial.

 

[sumo bill]

with that large of a carb you dont have a strong enough "signal' to properly atomize the fuel at lower rpms.I suggest that you try a smaller pilot jet (prolly a 32 or 35).your mix screw should be set at around 2-2.5 turns.