Which Carb???

[Kirt13]

I currently have a Keihen 38mmPWK.
I am looking to get a Keihen 38mmAirstriker or 39mmPWK.
Which one do you thing I should get, and why?
I have also seen the 40.5mm from ESR. I know that this is a 39mm that has been bored and re-shaped.

Thank you for your input.

[wilkin250r]

The Air Striker will have a couple fins that are designed to improve low-end response.

Personally, I don't think a couple fins are worth the money and hassle of upgrading to the same size carb. If you are going to get a new carb, go bigger, get an actual performance upgrade out of it. With a 39PWK, you'll notice improved top-end performance.

Of course, this is assuming you WANT more top-end. If you ride a lot of WOT, like dunes or desert, then the 40.5mm wouldn't be a bad carb either. That 330 will pull a lot of air up at the top of it's game.

[Kirt13]

I do want more top end.
Thanks for the info.

[Kirt13]

Has anybody used the Keihen 40.5mm? How is it compared to a 38mm. Also, how is the 39mm compared to the 38mm. Can you really tell any difference?

[ESR350r]

where would you suggest starting on the jets with a 40.5 on a 330?

[wilkin250r]

Originally posted by ESR350r
where would you suggest starting on the jets with a 40.5 on a 330?

You're asking the wrong guy.

For some odd reason, jetting specs don't "stick" in my mind like other people. Probably because I don't focus on jet sizes, I focus on whether the quad is lean or rich.

It has been so long, I can't even tell you what my OWN jetting is, but I can tell you it's just right in the midrange, but slightly rich up top.

My philosophy on jetting was always to throw something really big in there, and work my way down. Depending on what I saw on the plug, sometimes I go down 5 sizes, sometimes only 1 or 2 sizes, but my starting point was never a "number", it was "something big".

If I was jetting your bike, I'd probably start something like 185-190 on the main, and 55 on the pilot, and work my way down from there.

I'm sure somebody else on here can get you closer.

[jcas]

You will feel the difference. I have both carbs and an ESR 310 kit. The 40.5 will give you noticebly more top end, but struggles more than the 38 at lower rpm. Open riding area=40.5, woods/trails=38.

[Kirt13]

Originally posted by jcas
You will feel the difference. I have both carbs and an ESR 310 kit. The 40.5 will give you noticebly more top end, but struggles more than the 38 at lower rpm. Open riding area=40.5, woods/trails=38.
Thanks for the info. I appreciate it.

[doc-bones]

I run my 40.5 Keihen 350 and 330 powervalves with 52 pilots, 182-185 main, DGH needle middle clip. I am at sea level with temps between 40-70 degrees. So this should give you a good starting point.
Good luck,
Doc

[ESR250R]

My stock ported cylinder with a 38mm airstriker is running a 190 main, neddle in the middle and a 52 pilot. just start your jetting out rich and make sure to adjust according to the plug.