I was just curious how large you could bore a 38mm Mikuni flatside out to, and what you think it would cost. Its for a 87 Quadracer 500. Thanks.....

 

I charge $60.00 to do that for that carburetor .

I think back in the day the happiest folks had changed that carb to a Keihin 39 . That was a long time ago , and I don't recall what the complaint was off of the top of my head with the stock carb .

Take care ,

Rick

 

Rick,

I can tell you why I went to the 39mm Kehin, it simply flows better than the 38mm Mikuni. With the 38, I was getting a flat spot around 3/4 throttle where the carb wouldn't flow any more. This is gone with the 39mm Kehin. It flows very well all the way to WFO. I would be afraid of going any bigger for fear of losing what little low end I have. I do know that some people do bore the 38 mm Mikuni to 42 mm, but that seems a tad excessive to me. Unless you're running in the sand, and have a top end pipe or an enormous overbored motor it seems redundant to me to bore the 38 to 42mm. Now the Suzuki Quadzilla might benefit from it, but the Polaris I have probably wouldn't.

 

The carb on that bike is a 38TM , not a 38TMX . It had metering problems of some sort on that bike although I can't recall exactly what it was.

It can be bored properly ,unlike a TMX, which you can't really do correctly. I am just hesitant to advise doing it on a 87 500 Suzuki .

I have seen the taper bored 38 TMX otherwise known as a 42mm taper bore .The carb is not bored all the way through , but tapered to the widest point (42mm) at the engine side of the carb , the venturi is still 38mm. I have tested a 39PWK , a 38TMX , and a 42TMX taperbore on a flowbench .

The results were interesting . The 39 PWK comes out on top , and the 38 and 42 taperbore flow identically . I believe the difference was about 7% flow at WOT between the Keihins and the Mikunis .

Carb makers should follow automive leads , and rate the carbs by flow rate , and not diameter . It makes selecting carbs hard , when the numbers may , or may not mean a thing . Example , I have seen a aftermarket that was a 28 , that was for replacing a 26 on an older quad , suprise, the 26 outflowed the 28 .

I suspect the folks taperboring the 38TMX into a 42 are doing so as to send a stronger pulse to the jets , to make the metering sharper .

PS Hi Mike , it's been a while , how are ya ?

 

Ok, thanks alot. I was kinda leaning towards a new Keihin 39 PWK anyhow, but I was just wondering about gettin' the stock one bored....

 

Rick what is the addy to your web site i can,t find it ????

 

It's www.rittercycle.com

Rick, I have a question at Jack's forum pertaining to porting if you can spare a few minutes?

 

Hey Rick,

I'm doing pretty good. I ran my right hand through a pane of glass yesterday and with qualification (handgun and shotgun) coming up it might be a little difficult, thank goodness I can shoot lefty. My next project is steel braided brake lines for the 400. If they work well I'm going to put them on the 250 as well. I have the lines (from the local Polaris dealer), but I really hate playing with brake fluid. Oh well the nature of the beast and all that...

On another note, I just read an article in the latest issue of Dirtwheels dealing with the LT500. Guess what carb they put on it. Yep, the 39mm Kehin PWK.