My CB750F Supersport 1982 wont pass 6500rpm.

[gkmaia]

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[TOOLS1]

 The CV carbs on these bikes will only operate correctly with the stock air box, so put the stock airbox back on, and it will run properly.
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[gkmaia]

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[TOOLS1]

No harm, but it is a band-aid fix. Also you will notice he still had problems. One thing you need to look out for is a lean condition, which will burn up an engine.
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[gkmaia]

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[TOOLS1]

Those are all pretty good ideas, but have been tried before with little success. Some people have had good experiences with the Dyno Jet kit, you might want to try that. My best suggestion for you if you are set on pods, would be to adapt a different type of carb to the bike. There is a thread on here somewhere where a guy adapted a set of 77-78 keyhole carbs to his DOHC. Worked pretty good if I remember.  
TOOLS

[gkmaia]

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[TOOLS1]

There is more to the stock air box then restricting air flow. It actually does not decrease air flow by very much. The thing about it is that it creates a venturi effect, and vacuum that makes the CV carbs work with the differences in atmospheric pressure. Also the Dyno Jet kit is more then bigger jets. Hell if bigger jets were the answer every one would have pods working on the CV carbs, and they DON'T.
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[gkmaia]

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[gkmaia]

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[gkmaia]

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[Re-run]

Now if things work out, you will have to drop in a set of cb900 cams.

[gkmaia]

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[Re-run]

Basically be like putting hotter cams in essentially.

[Roadracer22]

Consider this when tuning your bike. Removing the airbox while changes resonance does affect the amount of air entering the engine. Although there maybe more entering the engine with pods that air isn't always streamlined and can be affected by things such as a cross wind or your leg.

Now changing idle mixture screws have little to do with the top of the RPM range and is mainly for the lower end of the RPM such as idle and off idle running. Idle mixture screws do work in conjunction with needle height and the two overlap. Needle height is mainly for the mid range RPM tuning. When you are at wide open throttle the needle height is taken out of the equation and tuning is all reliant on the main jet.

From stock tuning with all the stock components idle is typically set o be lean allowing a little easier time passing emissions. As the RPM rise the tuning is typically set to richer up. Removing the airbox will change all this. Equalizing carb synch is another process all in itself and can be mechanically set based upon the opening of the butterflies.

[gkmaia]

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[shinyribs]

The porcelain is the area to look at. The plug on the left has a nice semi-dark tan color to it. I'd call that perfect. The lighting might not be just right in the pic,but the plug on the right looks a little rich.

Both of them seem to have a fair amount of soot build up around the base of the threads which might just be from extended idle time. But that plug on the left looks perfect. I definitely would not go any leaner according to that plug.

[gkmaia]

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[LukeM]

Plugs 2 and 3 look about the best to my eyes.  Maybe a little bit rich, but close enough.  You're looking for a very light brown on the insulator, and a light rust color on the center and side electrodes.

If you do a Google search for "spark plug color chart" with or without "motorcycle" in the bar, you'll find lots of images of what different conditions look like from a spark plug standpoint.

Also, almost every Haynes manual has a similar chart in there somewhere, mostly in the car manuals.  I'll have to check my CB750 manual to be sure.  Based on what I saw, they don't look too bad.

The best way to check the health of your motor is to put in a set of plugs, then run a "plug chop".  This is done by revving the motor to redline in each gear, and when you max out in top gear, pull in the clutch, switch off the motor, and brake to a stop.  This exposes the plugs to everything from idle to WOT (wide open throttle) in lightly loaded and heavily loaded conditions.  You can search our forum for "plug chop" to see how it's done.

Hope this helps.
Luke M

[gkmaia]

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