Air control valve/ '87 xr6 ??

Can sombody give a quick explanation of the ACV and how it might affect jetting? I've been playing with the jetting the last few WEEKS and it still is running lean (grey plug color). I'm currently @ #48 pilot and #128 mains, and I've got a stock motor with a TRAPP & K&N, and I'm @ sea level.

Muchas Gracias

Gray isn't too too bad. When my bike was lean, my plug was blistered white.

Lean where? At idle, mid-throttle, WFO?

How many discs in that trapp of yours? Opened-up airbox?

The mixture screw should be adjusted to the point where the engine is running fastest but smoothest. A good starting point is to turn the screw in until the engine begins to die, then turn the screw out until it starts to run roughly. The ideal setting will be roughly between these two points. You'll have to tinker with it a bit probably, however.

My Set-up:

stock motor

Uni-Filter (stock airbox)

Primary carb: #45 pilot, #128 main

Secondary carb: #130 main.

8 discs in the trapp

My plug is a light tan color and the bike runs really strong.


I've been trying different settings with the mixture screw, and it seems to run best @1 turn out. I also found a pin hole in the ACV, and I'm wondering if that may be leading to a lean idle/off idle. Mid throttle sems pretty responsive, but just into the throttle @1/8 it is "missing". The popping/miss is almost gone with the airscrew @1 turn. From what I've been reading the airscrew should be somewhere near 1.5 turns +/-.

8 discs in TRAPP, and the airbox is open on top but not drilled out.

What clip position are your needles? On my '87 XR600R, stock motor, UNI filter, White bros E muffler with 8 discs (used to be a supertrapp with 8 discs) I am running the following:

Stock Jetting:

Main Jet's (both carbs) #122.

Slow Jet: #45

Primary carb neeedle in 4th groove, secondary carb needle on 2nd groove.

My bikes jetting:

Primary carb main jet: #125. Secondary carb main: #135

Slow Jet : #45 (might need to go up to a #48)

Primary carb needle in 5th (bottom) groove.

Secondary carb needle still on 2nd groove.

The bike runs real strong, nice tan plug color and gets great fuel mileage as well - 45mpg. I am at 2500ft.

Needle positions are still in stock settings (4th/2nd). I have thought about lowering the clip in the primary carb, but I thought that adjustment was more for adjusting midrange.

StevePSD...what is the benefit of running such a large jet in the secondary carb? Also, how do you have the timing of the opening of the secondary carb set up? AND, where is your airscrew setting?

The dealer wants $130 for a new ACV. This includes the cover/spring/diaphram. All I need is the diaphram! :applause: Bike bandit has the same "kit" for $85......such a deal....

Anyone know where I might get just the diaphram (new, not a used one)? JCWhitney has one listed for a '83 GOLDWING that looks the same in the pic as mine, and it's only $20

Dual carbs....ARGGH!

The larger main jet was the result of long runs at 3/4 throttle and above....this eliminated the bike's tendency for overheating, especially when it's over 100F outside, while maintaining great throttle response, and optimium plug color indications. The carbs are setup to slightly delay the opening of the secondary slide; I have no 'bogging' issues with this setup. The air screw is in the factory position. I normally run at 2000-3000ft and have done long trips at 7500ft with no ill effects.

I found having a smaller main jet in the primary carb, but the stock needle raised made throttle response much better than having both carbs jetted the same (i.e both big main/stock needle or stockish main and raised needle).

Also, my airbox is drilled for more airflow (5 1" holes) with the intake snorkle removed.

There is a new air cutoff valve on ebay for .99 right now:

Thanks for the link! I checked their normal price and it's only $17.50 for the kit, so I'll just order it up!

Put the clip in #5 last night, and it runs better. I put the airscrew @ 1 1/4, and it's not popping as much. When I get the new ACV, I'll play with it some more.....till then it's rideable....

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