Mikuni without accelerator pump?

I have a mikuni 35mm flat side carb, but it doesn't have the accelerator pump, like the 33mm and 36mm versions have. Think it will be a waste to try and mount this up, or will it be a decent upgrade from the CV carb, but a step below the comparable version with an accelerator pump? I have this in the garage with a throttle and cable left over from an older xr250. It was an aftermarket carb available for that bike at the time, so i figure i can machine a few parts and make this work on the klx300 to get a little more performance than the stock CV style carb.

I guess my main questions is...what exactly does the accelerator pump do and why is it important for four strokes to have them versus the non-accelerator pump version?


Its like the power jet on 2 strokes. It directly squirts fuel into the stream going into the motor to give it instant throttle response.

Don't waste your time installing it. It's likely from a two stroke. The accellerator pump shoots a small stream of gas just as you crack the throttle off idle so that the engine won't bog after you lift the slide. The stock CV carb uses engine vacuum to lift the slide.

How did it work on the XR? If you liked the throttle response on that bike it will probably be ok on the 300.

the stock CVK doesn't have an accelerator pump, right? So i guess this will offer similar characteristics, but since it uses a cable to lift the slide, it will have quicker throttle response than the CVK. At least that is what i am hoping for.

Right. The CVK has a delay in lifting the slide because it's vacuum operated. Your carb won't have that but it may have a bog due to no accel pump. Again: did it work on the XR?

it was a long time ago when this was on the xr250, but i believe it worked well. i am not sure how much tuning it got, but it did had a lag/bog when the throttle was cracked, but after that it would work great. i may just run it and see how it turns out. there is no harm in trying.

A loooong time ago I use to have a XR200, that was before they upgraded them to 250's. They had the dual carb and exhaust system and 4 valve head for a single cylinder. I must say they ran pretty decent. Or at least to me it seemed so at the time. I was pretty young then too.

Are they still like that? I've been a MX bike rider since so I don't know what they are like now.

And, is there really a bog? I think people get so into this stuff they describe the lack of throttle response as a bog and thats confusing. If your carb truly has a bog its jetted improperly. Just because a bike with an accelerator pump goes faster than one without, doesn't mean the one without is bogging. It just doesn't accelerate AS fast. I think people need to change they way they talk about things.

I mean a momentary lean condition when you wack the throttle open caused by the low air flow through the venturi. If it didn't exist the accel pump wouldn't be needed.

There's no harm in trying to fit the old XR carb. As long as it's not too much of a hassle, it may be worth experimenting. The XR 250 and the KLX300 are pretty close in engine size, so hopefully the jetting will in the ball park. You'll have to clear the cross beam between the upper frame rails, make sure the carb fits the boots for intake and airbox, and route the cables without binding up or being too short during lock-to-lock. I'd go for it.

As for the accelerator pump/bog condition, my guess is that a properly set up non-pump equipped four stroke might work fine, but not as good as one with a pump. The momentary lean condition can cause the bike to stall at the worst possible time. Also, the stock CVK with dynojet kit probably works as well or perhaps even better in some circumstances than a regular, non-pump carb.

Out of curiosity, I'd still try to see if it works. I'd also like to know if all the above theory is bunk or not.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now