Jetting a TM34

I got the TM today and need some help jetting it. They shipped it with a 280 main, 50 pilot, Q2 needle jet and a 5FP17 needle. And no air jet at all. It's not an oversight, that's how they list it. The needle jet, needle, and main are very rich, so it makes a certain amount of sense. I'll order up the parts below tonight, but It's hard to figure out what they were thinking, except that it's best to come at the right tuning from the fat side.

I went back to the thread from April of this year and have the spec's that Chip used:
Main Jet: 240
Pilot Jet: 35
Needle Jet: Type 389, Size P-0
Needle: 6DH3
Airjet: 2
Slide: 4
Would this also apply to an 850 w/ balanced pipes and Beancans?

I could not get my 34tm to run with the 6DH3 with the 389 needle jet. You need the 159 type needle jet. Here is the trick. The only way to fit the #159 type needle jet was to change the main jet ring (VM36/17) from a vm carb, along with the needle(6DH3) and needle jet #159 p2, you will blow the door off twin carb setups.
I believe that these three item could be a standard set up for Norton. The Main jet (280)and pilot jet (40) are good starting points for any particular need. Pop in a 300 or 330 and feel the excelleration. Leanness and richness will have little effect. Carry a set of mains 280, 300,330, a 17mm for the bottom plug and a 8mm for the jet. 280 is good for mileage 330 great for kicking ass. For the price of the mains you can't go wrong.

Hi bpatton & pvisseriii,
I've read lots of different postings regarding Mikuni set-up and it seems like no two are just the same. I visited Chip in Florida and heard his bike start and run, it seemed fine although I believe it may have been a little fat just off idle (he was using a hotter heat range plug as the normal heat range had loaded up somewhat)(sorry if I am wrong about that Chip).
I played with my personal 34mm TM a lot this spring (74 850 non balanced pipe peashooter), I had a heck of a time getting it to run lean enough. I ended up with a #15 pilot and had to go down to a O-6 needle jet (I have an extra if you want to try it). Presently it seems very good, although the enrichener is way too rich and I will soon be fixing that.
Apparently there is no one size fits all, fortunately jets and needles are cheap, but needle jets $15 each, and slides $70 (ouch). Good thing the Norton/Mikuni set-up is quick and easy to access and alter. If you have deep pockets a trip to the local dyno/exhaust gas analyzer will set you back about $300.
Good luck on your bike, could be it will be just fine the way you get it.

GB

GB, did you install an air jet? It would have an effect on everything past the pilot. I still can't understand what Mikuni is thinking going with such rich jetting paired with no air jet to compensate. There must be a reason they chose this route, or not.

bpatton said:

I went back to the thread from April of this year and have the spec's that Chip used:
Main Jet: 240
Pilot Jet: 35
Needle Jet: Type 389, Size P-0
Needle: 6DH3
Airjet: 2
Slide: 4
Would this also apply to an 850 w/ balanced pipes and Beancans?

Click to expand...

Just a note about my setup...it's for a 750 Combat.

geo46er said:

I've read lots of different postings regarding Mikuni set-up and it seems like no two are just the same. I visited Chip in Florida and heard his bike start and run, it seemed fine although I believe it may have been a little fat just off idle (he was using a hotter heat range plug as the normal heat range had loaded up somewhat)(sorry if I am wrong about that Chip).
GB

Click to expand...

GB's absolutely right about this. I was running a bit rich despite dropping the needle all the way down. Switched from the BP7ES to the BP6ES NGK's and the bike has been running perfectly ever since. I know the plug switch only dealt with the "symptom" and not the problem of running rich, but the switch resulted in nice tan plugs and she starts first kick EVERY time. Once the TM is dialed in, or you adjust as I did, I can't say enough about this carb. Idles perfectly, fantastic mileage and no loss in acceleration when compared to the dual Amals...heck, I even kept up with Windy (aka "Bill" on this site) the last time we rode together!!