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Idles great, no power under load

  • Thread starter Thread starter ttfraz
  • Start date Start date
The bike will start without any air filter and using stock jetting. You will need more choke (enrichener) than normal but it will start and idle. Problem is, when you try and drive it off the kickstand you will have to slip the clutch a whole bunch to get it moving and it will feel almost like the clutch is slipping. It won't transition through the gears well nor pull anything like redline. The 26s on a 750 are stupid-lean to begin with. The 115 mains are ok. The pilots should be swapped for 17.5s. Jet needle is OK on 4th clip slot. Plug chops for anything other than main jet sizing are... well not all that helpful. Your bike transitions off pilot jet at about 3500 rpm to the jet needle/needle jet and stays there until wide open throttle. The main jet size determines how much gas the jet needle/needle jet have to deal with and the pilot jet is still kicking in a dribble of gas the whole time as well. The only possible reason for a plug chop is to determine if the main jet can let you pull to redline. You will likely NOT want to try this in top gear if the bike is running decently as you will be riding faster than safety dictates. Do a plug chop by driving to somewhere where you are the only one who will get killed if you crash. Take a BRAND NEW SET OF PLUGS. Stop by the side of the road and swap plugs and take it to redline or as close as you can get in say, 3rd gear. Ride for a 1/2 to 1 miles and hit your kill switch. COAST to the side of the road so you other circuits don't affect plug burn and remove plugs and look at them.

If you don't like messing with this plug chop thing (and I think it is a waste of time personally):

Rev the bike out in 3rd gear. If your bike bogs, it may be rich. If you pull up the choke all the way, it was lean, not rich. If it makes it worse, well your main jet was too big. 115 you started with is right in the ball park so don't worry about plug chops till you get the bike to run half decent through the rpm range.
 
A lot of bad information here. Read the Mikuni tuning manual for the VM carbs, it is NOT like the CV carbs. You can tune the pilot circuit and the needle without the main jet even installed, it has no effect on the low power circuits unlike on the CV carbs. Most of us use the stock pilot jets for pods and pipes, some try one size bigger and usually go back to stock. You can read plugs for low power, it just takes a lot longer to get the color. Ride a while at the throttle opening you want to look at, kill the engine and pull in the clutch so the color doesn't change as you slow, and look at the plugs. Old plugs work as well as new ones, it's the color of the carbon that you look at. No carbon = no color. Just don't use plugs so old they aren't staying clean. The only circuit that is stupid lean is at idle and at very low power, that's the only place the EPA tested. And stupid lean at idle is fine, as long as there is good throttle response when you open the throttle.
 
So I dialed the pilot back to 7/8 on the fuel side and ~1 on the air side. But I think I may have found the problem.... I believe it may have been the clutch. I noticed the lever was a little tight so I loosed the cable so there is a little bit of play just in case it was slipping a bit and it seems a lot better. I'm glad I didn't go far with it like that.

Im not sure how it got so tight on the stock handlebars but oh well

now it's time to do actual plug chops do you guys can stop shaming me haha:encouragement:
 
tkent02 said:
You can tune the pilot circuit and the needle without the main jet even installed, it has no effect on the low power circuits unlike on the CV carbs.
Click to expand...

You can do the same with the CV carbs. They will start and idle on the pilots just fine without main jets in place. As soon as you start getting up into the needles much it will bog, though.


Mark
 
A lot of good information here. I don't mind doing the plug chops but I wanted to get it some what decent enough to ride it long enough to do the chops.

How cold hearted are these bikes when I got back from a lil ride it was idling significantly higher than when I had set it before. But that could have just been because it was finally warm and I had adjusted somewhat cold
 
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