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jetting question for my 434cc BB and keihin 39mm FCR

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Just finished this winter rebuilding my drz400sm. As everyone knows the carb is a must! So I installed a 434cc big bore and hot cams in and exhaust. 39mm carb and a new air filter, plus an oversized 3x3 air box mod and fmf exhaust soon to change exhaust but.

Bike runs great but at stop lights she just wants to rev really high so i turn the idler down a little. Next light bike dies, so i turn it up a bit and it revs high.

Now i have a little grasp on the hole fuel to air for this bike. So if the bike is doing this i'm leaning out???? and i have a 165 in the main and a plug that does not seem to be overly dry and white. I ordered a 168, 170 and 172 main jets to see if these solve problem.

I'm i going to have to start playing with my main air now? or any of the other jets? I don't think I will have to but i really do not know.

By the way I live around Sault Ste. Marie Ontario at about 180 feet above sea level. It is not a humid place but it is normally about 20-30 Degrees Celsius during the summer.

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If your issues are with fueling at idle and low revs then the main jet has very little to do with it. However if you have a 165 MJ then it's probably running to rich anyway. You may have an air leak from a bad seal somewhere which will cause the engine to rev high. The other areas to consider are the pilot jet and mixture screw, if there to rich it will choke the engine meaning you'll need to have the idle stop screw wound in further which lifts the slide higher. This will make the bike idle high briefly, it will be worse when the engine is hot.

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The fcr came from detroit with a 162 in the main, now i have have a JD jet kit it came with a high humidity and a low humidity needle so i inserted the low one on like the 3rd or or 4th position what ever the paper work said to do.

How can the big bore need less fuel then when it was the 400cc. wouldn't that lean it out even more.

My dad is a class A mechanic and he says that the float bowl is half full when riding maybe and when i stop less and that is leaning the motor out. But i have no clue,

Now there is no way for me to trouble shoot that. Im lost and don't want to burn out my BB

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Pretty sure it came from a 03 DRZ but not Positive. when it was shipped to me it came with every jet recorded on a piece of paper. But i am not at home so it is hard to remember them all.

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i would look very close to make sure the throttle cable and throttle linkage isnt binding somewhere.

BTDT.

Frank

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Now there is no way for me to trouble shoot that. Im lost and don't want to burn out my BB

Bin, don't worry. You're not gonne burn your motor on jetting. That is on the very extreme. There is a lot of jetting info here on TT, so punch in your trouble and something will pop up. If Eddie or any moderator is asking you questions do your best to answer them because they know best. Jetting does take skill, so be patient. And I would not touch that float bowl ever, unless you are very skilled at carbs. BTW (as many of us do), I have the same set up as you do, but I got my carb from TT.

Do your best.👍

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I have done a fare share of looking for the carb set up and that is why I am lost, when I get home I'll be sure to punch in the carb jets and what not to see what eddie or anyone else who has some thoughts on my set up.

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Ok so the carb right now has:

main jet 165

pilot jet 45

starter jet 62

main air 200

pilot air 100

Then the JDJETTING Blue marked needle (low altitude/cool temp) and c-clip is on the 4th from the top, just like the old one.

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that jetting should be real close.

is it haveing a specific running issue?

big bore need leaner jetting because when the bigger piston pulls more air it also pulls more fuel.

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ok so thats good. And thank you for the BB explanation eddie, that makes a lot more sense now.

It runs like a champ, smooth even when Im playing down low in the rpms and no problems at the top end just at idle.

Some one looked at it and said the vacuum on the fuel pet cock might be what is interfering. So I will try to make a new Vacuum Nipple since it was a home made one to start with. But the one now is showing lots of pressure but its just not a steady vacuum/ suction.

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Ya, pretty sure.... had my old man over my shoulder the hole time i didn't miss a beat.

He has been working on my klx400 since 03 and a mechanic since 1985, almost positive we didn't miss anything.

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