jet for 39FCR w/HMF [Archive]

hotex28

03-09-2003, 10:27 PM

Does anyone run an HMF full system with a 39 FCR carb on their 400 EX? I have a big valve ported head and need to know an idea on where I need to start with jetting. I just switched to this pipe from a Yoshi full system, help please!

shamisc

03-09-2003, 11:13 PM

What main jet do you have in it now? These carbs are very forgiving as far as jetting goes. I would start around 165 or 170 main. Did you have the large valve ported head w/ the Yosh? If so the jetting would prob be about the same.

hotex28

03-10-2003, 03:16 PM

bump

hotex28

03-12-2003, 09:31 PM

I have a 165 main with the yoshi, but the HMF has way bigger headers. It calls for a 200 main jet with the stock carb, but I don't know what to put with this FCR. Ran good with the yoshi and a 165, I started it with the HMF same jetting and It is throwing fire out of the pipe!!!

hotex28

03-13-2003, 04:24 PM

bump

NTPRacing#19

03-13-2003, 05:12 PM

if its throwin fire out of the silencer then i think it would make sense that its gettin too much fuel

400exRacerX

03-13-2003, 07:01 PM

Yeah if its throwing fire, i would have to say that its too rich. This meens that there is raw fuel in the exhuast and it is igniting in the pipe.

hotex28

03-13-2003, 08:36 PM

I was able to get the jetting right today.The flashes of flames were only mill oil burning out from the pipe manufacturer.I started with a 180 to be safe,but I worked my way all the way down to the165 I was using with the yoshi.the headpipes are huge on this HMF,so Iwas a little worried Iwould lose a lot of bottom end power.Just the opposite!It has better bottom than the yoshi,way better mid-range,but not near as much top-end as the yoshi.with the yoshi,it would easily get all over the stock rev-limiter.Now,I have to try to hit it intentionaly before i can.It now has a completely different powerband.