So I originally started with running a bit rich, not being able to idle below 1700 without stalling easily eith slight throttle and no power with full throttle. 331 no lid with hmf exhaust. Tm36 stock except pilot changed to 17.5

Installed a p6 needle jet, 125 main, y-51 needle in 3rd slot

Now it starts a bit better, idles better, doesn't seem to be so rich. Though, 1/8th throttle has a stumble/miss. Not horrible but its there. Full throttle is still funny. If chugging at lower rpm full throttle will maybe stumble at first, then yeilds no acceleration when half throttle will accelerate. In higher rpms, if I back off from full throttle I can feel more power and the exhaust note also sounds louder/more powerfull.

The only thing I can think is to drop the needle to the second clip to hopefully take care of the stumble, no clue as to what to do to fix the full throttle issue. I almost want to say its behaving the same as when I had the 130 main, though the engine cut out completely if I tried to chug it at lower rpm.

 

I'd try a 15 pilot jet?

Main jet size shouldn't affect carb below 3/4 throttle or so. Something I read yesterday said in fact you should be able to take the mj out and run fine until about 3/4 throttle

Try turning off the gas and see if it runs better in the rpm range it's running bad in now.

Is the spark plug looking rich?

Going WOT when chugging at low throttle might be tough if you are on pavement and not running gearing more for dirt.

 

Dropped the needle one clip and 1/8th got worse, so we'll try once in the other direction. I put a 127.5 main in to see how it behaves. Wont know for sure till I get to faster roads to really test, still has more power as I roll off otherwise. I think the roll off might have been less pronounced when I had the 130 in. Would it make sense that I'd have to throw a 132.5 in there only running a331? Most setups I've seen are usually fine with 130 and that's on a 351.

For clarification, the needle jet itself generally alters 1/4-3/4 right? That range is spot on currently.

 

If I remember correctly, if the engine picks up when rolling off of w/o throttle to say 7/8th that is an indication that the main jet is to small. try this pdf for some tuning info- http://www.smellofdeath.com/lloydy/o...uni_tuning.pdf

 

Alright, so I raised the needle to the 4th slot. Aside from forgetting to take the choke off, most of the lean stumble seems to be gone. Full throttle is still a bit funny with the 127.5, but doesn't give so much of a feeling of lost power. Sounds better and feels like it may actually be gaining power from 3/4 throttle. It still wavers a bit oncd first opened up till it seems it settles itself shortly after.

Bike definitely seems a bit cold blooded still. Heading home from work the bike was still sputtering a bit at part throttle but seems to have stopped that once it was fully warmed up. Warmdr weather should leave it running even better, though I'm considering throwing a 130 main back in to see if full throttle feels a bit better yet.

 

Alright, jetting is pretty good off idle. Idle is smooth. Starting, however, is a chore. Itll start easy enough on choke but it'll die out after 15 seconds or so unless I bump the idle up till its warmed up. It used to run high idle on choke then I could gradually push the choke back in as it was warming up. At least its good other than that for the time being.

 

I see 3 or 4 different jetting setups with this carb where the P6 and P8 are being used. In those cases did you guys try the P4 to start with? Mustang and Dan Moore settled on the P4 for their big bore applications, and I did too on the 300. Subtle changes on this carb can make a noticeable difference. I only had to change the air pilot jet from a 1.0 to .9 to get perfect throttle response.

On the cold start idle, I find that if you have the carb jetting right at the leanest but proper settings, you will usuallly have to turn the idle **** up just a bit for warmup unless the temps are well up in the 80's or warmer. Frankly, this is a good sign. You probably have it too rich if you can just fire up the bike and quickly be off choke and have a good idle. That's why there's a big, easy to reach idle **** on the left side of the carb.

 

Definitely cold blooded. I just went to tick it over to see how it started. Instant start to high rpm, only needed choke for 10 seconds. Though it settled at 1700 rpm when warm that idle would be 2100-2200. Seems bumping the idle temporarily is the trick. It's running well enough now I don't want to mes with it much more.

I went with the p6 needle jet as it was running pretty strong with the p8. Smell and signs of running rich so I decided to try one step down on the nj and swapping out the needle to the y series. Coincidentally, its behaving better ekth the 127.5 main now then it was with the 130. I also had the original needle in second position. It seems to me that needle position may have some effect of what happens full throttle on these carbs. Main may still be just a tad lean for sub freezing, but good otherwise, felt strong with 35deg today. 3/4 may be a tad rich still, p4 could possibly fix that. But I think that jump would be too big.

Once it warms up a bit more ill see how its really running. I'm expecting 58 or so mpg as it sits.

 

Alright, can anyone actually tell me what the needle jet does? I'm thinking 1/4-3/4 throttle which I think is still rich. Main is just barely lean, not so bad once the bike is fully warmed up. 1/8th throttle is still jist a tad lean, again gone once warmed up.

Oddly, it still won't start up perfectly. Itll start right up on choke with high idle and all then slowly drop idle speed and eventually cut out. If I start it up using a little throttle it'll idle fine without choke. I leaned out the pilot screw and it started popping on decel so turned it back a little richer than before. No popping on decel but its still funny starting when it wasn't before.

Just too cold to be doing all this jetting!

 

Actually it appears that the needle jet affects about 1/16th to 1/4 throttle. The needle takes over more control as it leaves the mouth of the needle jet. Now, one might say that's not a big influence, but IMO it's possibly one of the most critical points that affect off idle performance where you tend to get irritating stumbles and such.

Have you read the HS40 Mikuni tuning manual? The 36 is basically identical to the HS40, so don't get concerned. However, note that some descriptions are specific to a Harley which is mainly what the HS40 goes on, but the principles of tuning are applicable to our carb exactly. Their comment on the needle jet on the HS40 as it applies to a Harley is an example of what I'm talking about.

On this issue of a 351 or 330 or a 340 or a 300, frankly it doesn't appear that this makes that big an issue on the jetting. I've had extremely good results with the P4 which is what Mustang and Dan Moore finally settled on. And I believe Dan Moore use a fuel/air ration meter during his research. Still, I wouldn't be surprised to see that some other combinations could work if balanced properly.