Jets and Needles for TM34 on 71 stk750?

I recently acquired a MAP single carb manifold and have been searching and reading about jets and needles for the TM34 . I am on a tight
bugit since retiring and hope someone can suggest the best setup for a 71 stock 750 engine. My exh is the reverse cone peashooters from Comdo Spec. All I have found mentioned so far is a combat commando 750 and the 850. Anyone done this for the 71-72 750 commando? My altitude here is from 8ft to 150ft at the most so Oxy is fairly high.

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 type #p2, you will equal or exceed twin carb performance.
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.


main jet ring (VM36/17)
needle jet type159 - p2
{needle and needle jet are key }
Main jet (280) (very variable as noted)
pilot jet (40)

Hi Seaguy,
There are several members of this forum who presently run 34mm TM Mikuni carbs and it seems that each ones settings vary a little bit.
If you purchased yours from Sudco as a kit I believe you will get:

Main Jet 240
Pilot Jet 35
Needle Jet type 389 size P-0
Needle 6DH3
Air Jet #2
slide 4 (I think)

This proved to be too rich for my bike especially during idle and just above idle (I have to admit that my bike was always too rich even with the stock twin Amals, and when I ran a single Amal, and when I tried a 34mm VM Mikuni). I was determined to get this straightened out and eventually dropped down to #15 pilot and O-6 needle jet and I am quite satisfied with the way it is running (I have an extra O-6 if you want to give it a try let me know). However, starting is another matter I am still working on the choke setting, as it is it runs way too rich on choke, so I end up flipping the lever up and down up and down till the engine gets warm enough to run. I down sized the starter jet in the float bowl, I thought I had it, but last time I tried I couldn't start it. It was getting too cold to ride here in Massachusetts so I pickled it and put it away till next season.

GB

Thank you for the replies friends. At present my engine is completely apart so I won't be testing for a while. I plan to get the TM setup put together for installation. I have been working on 2 other bikes so the Norton is on hold. Only recently got a deal on the "Single" manifold so thought I would search others' advice on the single carb setup. Since the TM 34 is touted as a significant improvment over the VM I figured I would go that way if others found it to be so.

I have my new TM34-2 with the standard jets and needle they come with being: 280 main,50 pilot,389/Q2 needle jet, 5FP17 jet needle and a 4.0 throttle valve.
I would appreciate any others mentioning their final setup and the type air filter they chose. Please don't be bashful.

in my stock 850

tm4 34mm single

Main Jet 240
Pilot Jet 30
Needle Jet type 389 size P-0
Needle 6DH3 ( 4th notch down)
Air Jet #2
slide 4

for air filter i use a unifilter - not sure of size but was same as one i used for my VM

in my stock 850
tm4 34mm twin carb setup

Main Jet 240
Pilot Jet 27.5
Needle Jet type 389 size P-0
Needle 6DH3 (middle)
Air Jet #2
slide 4

2 uni-filters

i would say that single setup similar to mine would get you started and running - you will have to adjust a bit for 750 and individual bike requirement

I am really surprised at all the different combinations of needles and needle jets I am finding being used successfully with the TM34. Pilots and mains show the least variations.

Dont be surprised seaguy, this is just testament to what really good carbies do. They will run well when they are still a bit off, but dont stop there, because when you hit it right, they are fantastic. Cutaway can be finicky. It's times like these when you need a friend, mate, local agent or dealer who will let you try before you buy, other wise you end up with a lot of bits that are really of no use. It's all good exp.

geo46er said:

Hi Seaguy,
There are several members of this forum who presently run 34mm TM Mikuni carbs and it seems that each ones settings vary a little bit.
If you purchased yours from Sudco as a kit I believe you will get:

Main Jet 240
Pilot Jet 35
Needle Jet type 389 size P-0
Needle 6DH3
Air Jet #2
slide 4 (I think)

This proved to be too rich for my bike especially during idle and just above idle (I have to admit that my bike was always too rich even with the stock twin Amals, and when I ran a single Amal, and when I tried a 34mm VM Mikuni). I was determined to get this straightened out and eventually dropped down to #15 pilot and O-6 needle jet and I am quite satisfied with the way it is running (I have an extra O-6 if you want to give it a try let me know). However, starting is another matter I am still working on the choke setting, as it is it runs way too rich on choke, so I end up flipping the lever up and down up and down till the engine gets warm enough to run. I down sized the starter jet in the float bowl, I thought I had it, but last time I tried I couldn't start it. It was getting too cold to ride here in Massachusetts so I pickled it and put it away till next season.

GB

Click to expand...

Geo46er stopped by my place on his Florida vacation and we took my TM34 apart to diagnose its components. His list above is what we found, but that MAY NOT be what you get if you order direct from Sudco. I got my TM from a guy in Florida who's partnered with Sudco and this was his set-up. As Geo46er says, it is a rich set-up. Everything was great, tan plugs after thrashing days in the hills, but I was fouling plugs when doing the lazy beach crawl at 30 mph. Adjusted the needle and couldn't get any leaner, started thinking about pilot jets etc. to cure the problem. On a whim, I tried NGK BP6ES plugs instead of the BP7ES I had been running....and perfecto! Nice tan plugs for the last 3000 miles.

Thanks Cemessenk. Which hole in the front is that #2 airjet in? It looks plugged. Is it screwed in from the back so that the slide cover will have to come off to get to it? Also ....which needle notch are you using? Are you using an electronic ign?

Well I finally got around to installing my new jets and needle in the TM34. Really simple to do. Didn't even need the diagram until I started to put the slide spring back in. Mikuni dropped the ball on that spring. It sort of wads up to go back in. Double checked the diagram to make sure it was in correct and no parts missing. They should of spent the extra 5 cents and had a "contour correct" spring designed for it so the throttle cable wouldn't rub on it. That size 2.0 air jet screwed right in. I swear I couldn't see any threads down in that hole :lol: Now I have to get off the TV and get that engine back together :roll:
For those that want to know " How to" ,what comes off and what tools are needed here you go: 1/4" nut driver (for Main jet) #2 phillips for top and bowl....I used a switch tip driver handle. The end is 1/4" for the tips and fit the Main jet. Small phillips for the cable connector inside the slide and a small flat blade for air and pilot jets. ....Loosen the 4 top plate screws then hold it down while removing them (it's spring loaded). Pull out the slide parts and replace the needle putting the C retainer in your chosen needle notch ( I"m starting with the middle notch). Leave slide assembly out until all else is done. Now remove the 4 phillips on the float bowl and ease it straight off(tap it's side to loosen from the paper gasket). Floats remain in the bowl. Now remove the hex end main jet and lift off the plastic jet ring. Now you can get to the pilot jet. Replace it with the new one ( 27.5 to 35) I got a 30. Now you can push the needle jet up through the slide cavity. You may have to tap it with something plastic to get it out. It's top notched area faces the engine so when you install the new one start it in oriented that way . Make sure it seats as the original was then put on the jet ring and screw in the main 240 (or what you chose). Replace the bowl carefully guiding it on straight (watch the little brass tubes!). Install the slide ( all parts only go one way ), install a 2.0 air jet in the bottom front and your done.