1975 GPX 433 - Mikuni Carb setup ?????

S

ss433

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Jan 22, 2005
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I have a GPX 433 that I'm restoring and as much as I like to keep everything original I'm thinking of leaving the Keihin's on the shelf and go with a set of Mikuni's (as it seems that everybody who drove on in the seventies did)

Out of all the GPX parts machines that I've purchased I have a couple of sets of Mikuni carbs. One set are some 36's with some type of adjustment screw on the float bowl (maybe these are the power jet ones I've heard about?) and another set of traditional 38's

This is one of my restoration projects that I actually plan on driving so I would like some input into a starting point (jetting) on either one of the carbs that I have.

Thanks
 

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38's
360 main
40 pilot

This should get you up and running. Then do plug chops and look at the piston wash and precisely dial it in. Should be too far off tho.
 
Yes - the Mikuni float is better carb - but we ran up front with stock carbs no problems. Except - 1/16 of a turn too rich would take you from 1st to 5th.
 
took my 38's apart and they have 340 and 380 mains and 35 pilots. So I will try the 40 's with some 360 mains as a baseline.

There is also a slotted jet in the bottom of the float bowl (looks like 150) never seen carbs like this.... any thoughts?
 
YES, THEIR POWER JET CARBS. DON,T RUN THAT. BLOCK IT OFF. RUN THAT EXACT SET-UP SANKA POSTED. VERY NICE SLEDS BY THE WAY. 3:16 (yammie tony)
 
blocking off power jet?

Should I just disconect the line going to the bottom side of the float bowl and let it hang and then plug up the jet inside the bowl

Thanks for the feedback.
 
OR YOU CAN PLUG UP THAT LINE. EITHER WAY WILL WORK, IF ITS PLUGED OFF IT CAN,T DRAW. THAN YOU CAN RUN A LARGER MAIN JET. ALOT MORE TUNER FRIENDLY. 3:16 (yammie tony)
 
New question

Checking some old racers around here (arctic cat guys) and upon mentioning a setup that I want to go with for my Mikuni's they told me to ask a few more questions.....

What needle jet

What jet needle

and what slide cut away?

Thanks
 
ss433 said:
Checking some old racers around here (arctic cat guys) and upon mentioning a setup that I want to go with for my Mikuni's they told me to ask a few more questions.....

What needle jet

What jet needle

and what slide cut away?

Thanks
Click to expand...
here is where i'm at with a set of 38's on my gpx 433
370 main jet
166 QO needle jet
6dh3 jet needle
pilot jet 25
2.5 cut slide. it has been 10 below zero and my plugs look fine,does have a bit of a bog,i'm going to drop the slide to a 2.0....been told by a few to actually run a 1.5.
clip position is in the middle.
 
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