Best Carburator for CR125?

John Denman · Posted: Wed Aug 08, 2001 5:03 pm Post subject: Best Carburator for CR125?

Technical stuff is getting a bit dry here lately.

So how about those carbs? I am guessing that 38mm is about right for most sprints and about 40 sounds good for road racing right? Then there are different brands like Kiehn, Mikuni, Delorto, Hudlett Pumper, PSI/Big Air,and now Edelbrock.

What seems to be the best on a Sprint Track?

What seems to work best on a Road Course?

I will be testing three carbs over the next month, maybe 4. Help me choose which ones to try first!

Marc Miller · Advertiser Joined: 18 Jul 2001 Posts: 1834

John-

I have run the same 38mm Keihin PWM carb road racing as I have run on the sprint tracks.

You should not need a larger bored carb for road racing. You do however jet a little different. (usually richer)

MM

Charlie Tackett · Posted: Wed Aug 08, 2001 5:35 pm Post subject: Best Carburator for CR125?

John, that's like asking which pipe will work best on my motor! Depends on a lot of things.

Have run many differnt size and kinds of carbs. GOing to depend on your porting and rpm range of the powerband and also on the type of track you are running and where you want the most performance.

I would disagree with your speculation about sprint vrs long track carbs. We have found just the opposite to be true. On a long track, because of the gearing, it takes longer to pull thru the rpm range. YOu also need a strong low-midrange because of this. THe smaller venturi has a higher flow velocity and is more efficient in this situation.

With sprint gearing, you pull thru the rpm range so fast that this is not as critical as on the long tracks and big carbs work better. We have a 36PJ and a 38+PWM and have run both on the long track, depending on which track and where we feel we will make the most time. What little you may give up on absolute topend with the littel carb, we can more than make up for in getting out of the tight stuff adn working up thru the gears. Just another tuning option.

BTW, I'll give you a really good deal on a 41mm Boswell if you really want to try a big carb

Chad Stapleton · Joined: 19 Jul 2001 Posts: 4403

Why are these (ex bike) float bowl carbs preferred over adjustable jet diaphram carbs (IE Ibea or Tillotson etc) as used on Direct drive or clutched 2-stroke kart motors ???

Brian Kay · Posted: Thu Aug 09, 2001 6:41 am Post subject: Best Carburator for CR125?

Marc,

Can you expand on that? (to clarify things for those of us who do not posess your technical genious)

BTW - Love the new SKI cover shot. Very Cool!!!! (congrats)

Buh,

Brian K - T2R

Bob Chiras · Joined: 30 Jul 2001 Posts: 198

I'm with Charlie we often change port height (replace the cylinder), the pipe and the carb when we sprint versus road race. The road race is always a smaller carb.

Andy Szyszkowski · Joined: 01 Aug 2001 Posts: 149

John,

Run the smallest carb that will yield the best lap times in either venue. Use your stopwatch. Smaller the carb, the easier to tune from higher velocity; i.e. responds better to jet changes, atomizes better, circuit response is better, driveability is much improved. Just some things to consider.

Andy