Mod. Yamaha (slight bog and surging) !!

[Jeff "Yammer"]

Att. ...........
......... need to get rid of my 2000-2500 rpm surging problem . It's only when coming off plane . The motor seems to have a slight bog ( even with a 24" Chopper ) when coming out of the hole ( when stepping on the pedal hard ) ???????????????
The carbs are Nikki 34's bored out to 36's with 184 main jets . !! .

Thanks :p
Jeff

[Nosubforcid]

Call Bob Kottman.

[Markus]

If you need more gas in that range, which is the area where the main jets have just taken over from the idle circuitry, you could try:

1. Bigger main jets, but compensate in the high-end with bigger air jets

2. Bigger pilot jets or smaller pilot air jets. To see if the idle circuitry makes any diffence, I would screw out the pilot screw to some insanely rich setting to see what happens. I know that I have been able to create a lean hesitation at approximately 1700 rpms by screwing them in.

By the way, Jeff, how much difference did 36 mm carbs make over 34 mm? I have changed from 32 to 36, but have not had the opportunity to make a test run. How much did you need to change the jetting? Did the lean/rich areas move when you changed?

[Nosubforcid]

The problem is undoubtedly in the transition circuits, crutching it with a main jet change is stupid! You can't buy hardly any of the brass tuning components for the transition circuit so Kottman scrounges them out of various carbs and makes what he can't find. Call him and save yourself a lot of wasted time.

[Ray Neudecker]

Email me for cure.

[Markus]

Nosubforcid, all you need is a reamer and a soldering iron. Then you can make idle jets and idle air jets any size you want. Based on what I have heard about Kottman's personality, I would do that rather than dealing with him.

Ray, if you have a cure, please email it to me, too, since I am always curious about Yamaha carburetor mods. I would suppose that the cure is reaming the pilot jet, though.

[Nosubforcid]

ALL OEM Yamaha metering components are sized to a tolerance of 2 x 10^-3 mm good luck duplicating that with a hand reamer. Kottman is alright you just have to make it worth his while to help you. If you want a bunch of tech for free call somebody else. The best isn't cheap and damn sure isn't free.

[Markus]

There is no need for that kind of tolerances in the metering system.

First of all, you still end up on the rich side to be safe.

Second, two-strokes are not that sensitive to being on the rich side.

Third, the biggest variance in the idle system comes from the pilot screw anyway. 2 and a quarter turn, or whatever it is is not exactly micrometer precision.

[Travis Fulton]

[QUOTE=Markus] Based on what I have heard about Kottman's personality, I would do that rather than dealing with him.




Marcus, i wouldent say anything about somebody that YOU dont even know!?!? you know what they say about glass houses! bob is a good friend and very smart! one of the best!

[Dingie]

Nosubforcid,Sounds like Mr. Nuedecker knows what to drill to what size to cure your sick 34mm carbs. You should give the Doc. a call ! FEAR THIS ''the over the hill gang"from Tenn.