I just posted this over on Dan Moore's site but figured I'd bug the folks over here with it too:

This past weekend I performed all the mods in my signature line that relate to air intake, exhaust, and jetting. Since today was a great riding day after work, I took the bike out to do a speedometer calibration check (posted that in the General Discussion section) and also to see how it performed on the open pavement a bit.

This may have been a characteristic all along but I'm not so sure: at highway speeds of 55 mph or so with 6500 rpm (stock speedometer setting was inaccurately high reading), I get a 'surge' or miss, or something. It's like once in a while I miss a power stroke or else have a weak one. Bike runs stronger with more authority in all the other ranges of operation since the mods.

Some things come to mind:

1. Float level--Before reassembly of carb, measurement of the floats was within service manual specs. Note: I didn't do the clear tube thing after installation. Maybe reset the float levels to the maximum limit for flow into the bowl?
2. Fuel screens--I doubt that is the case but I may check it out anyway.
3. Air buildup--This one may be a long, long shot. Since I have the windscreen installed, could air be building up a little in front of the screen and then 'releasing' after a certain point, causing surging of some sort? If so, I'll live with the problem. Out here in these open spaces I want all the wind protection on me that I can get.
4. Ignition--This is my first motorcycle ever but I have lots of time with automotive and aircraft piston engines and this just doesn't make me 'feel' ignition spark problems are at play here. Just wanted to throw it into the mix and see what anyone else may think. Maybe I'm wrong.

My elevation is 1600 ft and I use 89 octane fuel.

Any guidance or suggestions are welcome.

 

Lean surge. Raise needle one clip (lower clip.)

 

+1 on raising the needle.

 

I have it too. It seems to buck a little at around 7,000 rpm which is about 65 mph. I think on MY bike the slide is sticking. I am not sure. Its a intermittent misfire. I tried a new plug with no change. I moved my needle up one (clip down) it helped, built is still there. Got a mikuni 36-68 on its way. I will let you know if this gets rid of it. Bike has done this since I bought it 2,000 miles ago.

David

 

I'm running the stock needle shimmed by .030". On needles with clips what does one notch equal in terms of shim thickness?

Thanks for the replies so far.

 

Add another shim the same (.060"/1.52 mm.) I've used a 1.5mm on the stock needle and the result is good.

 

My next attempt was going to be back to the stock needle with a shim, but I went for the new carb instead.

Still not sure if its carb related, but will find out.

The day I test drove the bike it had a few misfires. It was bone stock.
I wrote it off as old gas. It had been sitting for a while. It has done it ever since, so it may be ignition related.
Its an 09 SF and had 2400 miles on it when I bought it used.

I was told in college (30 some years ago) most of your carburetor problems are in the distributor. Usually its true.

David

 

Dudes this happens to me at abourt 8000rpm
Bill blue sz I need to go up one size on the main jet. In one of his TM33's
He's not sure which he put in so I'm going to the "0.142.5 Mikuni Large round head main jet"
Right now the float iis stuck any ideas with out removing the carb? They are a chore to take out and put in...say no more say no more.
Thanks Marc

 

I have the same problem after the mods in my signature. Around 7000 rpm I get a quick lag in power. I have my needle set on the highest notch(first one) from top. I tried putting the needle down one more but the bike wouldn't run. I assume it is because I still have the factory exhaust and can't move the exhaust out quick enough for the amount of fuel. I am waiting to get my after market one then adjust the needle again to see if it goes away.

 

Some on here have complained about the stock needle saying that the DynoJet needle or N1TC or "49 state" are better. Could the needle also be causing problems, even if clip adjusted to the best position?