Factory Idle Screw Settings

It is assumed 2-3 turns get you in the ball park but the correct setting can be a long way from there. I just rebuilt the carbs on a 1982 650 Maxim. Very low miles and still had the factory caps covering the idle screws. The factory settings were 2 5/8 4 1/2 3 1/2 1nd 4 1/4. The moral of this; don't get worried if you have to turn them out to 4 or 5 for best idle.

 

Those screws with the caps covering them are the mixture screws, used for setting the petrol and air mixture, and they would have been set all the same in the factory.
I reckon a previous owner has removed the caps and adjusted them.
The idle adjuster screw is a single, long screw located under the bank of carbs.
Read the manual and it will tell you how many turns out for the mixture screws.

 

Not necessarily; they could have been all over the place.

The factory used an EGA, hooked up to the little ports on the bottom of the exhaust system, to adjust the mixtures, and then capped them. It's not unusual for "factory original" mixture screws to be set at some pretty odd-seeming positions.

That being said, a PO (or dealership service dept.) could also have re-capped them, it's not out of the realm of possibility.

Once you've serviced your carbs and adjusted the valves on a motor that now has a few thousand more miles on it than when it left the factory, those initial settings have been invalidated anyway.

The factory "base" 650 book doesn't admit to a setting; the factory 650R supplement (and the 650 Seca had the same motor as the early 650 Maxims) gives 2 1/2 turns out as the starting point.

 

--and that could be an indicator that the factory didn't take as much care in putting the carb/exhaust system together as we originally thought. It COULD be an indicator that they could tend to just slap the carbs together, then adjust the mixture to suit the situation.

OR......it could indicate that our own adjustment window is actually greater than we have believed.

Or........it could be just that way that particular pipe/carb/mix needed to be set.

just playing devil's advocate for a minute......................

Dave F

......................
Not necessarily; they could have been all over the place.

The factory used an EGA, hooked up to the little ports on the bottom of the exhaust system, to adjust the mixtures, and then capped them. It's not unusual for "factory original" mixture screws to be set at some pretty odd-seeming positions..
.........................

 

The carburetors/intakes etc. cannot be made precisely uniform. That's why the carburetors have adjustments. If everything was repeatable (and didn't wear) the carburetors wouldn't need adjustment screws.

On the 650 they changed the pitch of the mixture screw in 1982. 3 turns on an 82 is a lot less open than 3 turns on an 81.

Get them set so they're right for your bike as it is today. Of course if you back them out so far there is no spring resistance on them you need to look at your other work.

 

It ia a lot easier to adjust the mixture screws accurately than it is to set the float level. I think the factory presetted the floats but not with the effort we do. Float level variation was then corrected by the mixture screws and an exhaust analyzer. More variance in the float level would yield more variance in the mixture screws.

My bike has only around 7000 miles and was in storage all but it's first few years. I believe that was the original adjustment with the original caps.

 

I don't believe the float level has anything to do with the mixture screws and exhaust temps. My experience has been that the float levels need to be set so that the bike doesn't stall upon either launch--fuel starvation........or hard braking----flooding via fuel surge. But that's my own experiences.......

Dave F

 

Float levels don't effect fuel mixture, except for the reasons that Dave F pointed out. Both float levels and mixture settings have to be correct.

 

Float levels CAN affect mixtures, if they're far enough out of spec.