Mixture Settings on the Track

hobot said:

Duh dudes even I know at WOT near top speed if applying the choke helps then its sign of way too big a carb not Lean-ness. .

Click to expand...

Thats a new one to me. Jim

Well I've never heard of closing choke at WOT to diagnose a lean condition, only ease off og throttle itself. I take choke remark as a spoof until someone puts their name on actually doing this to for usable fine tuning indicator other than misfire and power drop. As kids we found too big a carb on too small a car could be made to work better if choked down some but not all the way.

Perhaps a little more detail

You dont close the choke. You apply just a little cutting back the air supply a small amount. This richens the mixture. If the bike increases speed then the mixture was too lean at wide open throttle.

Perhaps this hasnt made it to Arkansas yet but a standard tuning technique in road racing and also used at the Isle of Man where there are significant changes in altitude and temperature in one lap. - Duh

johnm said:

Perhaps a little more detail

You dont close the choke. You apply just a little cutting back the air supply a small amount. This richens the mixture. If the bike increases speed then the mixture was too lean at wide open throttle.

Perhaps this hasnt made it to Arkansas yet but a standard tuning technique in road racing and also used at the Isle of Man where there are significant changes in altitude and temperature in one lap. - Duh

Click to expand...

It has been a standard tuning technique here for as long as I can remember also. I have also been known to turn off the fuel to see if the motor picks up a bit before the carb runs out to see if its rich. Jim

Ok I must of mis-read - mis-understood the comment about applying choke, instead of just backing off throttle a bit to sense for leanness surge. Locally our air density only ranges from 500-2000 ft. Jim's home has like 3x's higher variations. My Peel project's gravity fed fuel injector self adjusts to attitude changes because they don't depend on venturi suction, just air density and flow to draw proper fuel to air ratio, after base line tuning done. I'm stuck w/o dyno so must learn the temp, time, speed methods plus opening and looking in. My dream would be get Peel ok enough to travel to comnoz and optimize by dyno expert. Then hope it still applies back home. Some carb engines that change elevation a lot like snowmobiles use an extra Power Jet tapped off fuel that can feed fuel on descents to make up for leanness of tune needed at high elevations.

BTW do ya ever look up tail pipe or take a finger swipe to monitior that end of mixture? I don't know how various fuels affect this.

Hi

I used the mixture readings on the dyno a lot in the beginning when I was learning how to set up the bike. Now I have a table of data (track, temp, humidity, pressure) and use that guided by the plugs and lap times.

Cant really see inside the exhausts without dismantling them. We have very tight noise control especially at one track and I have big silencing cans on the ends of the megaphones which dont let you see the colour in the pipes. They run grey without soot when I have seen them. I use either leaded race fuel 100 octane or 98 standard pump gas. Sold as Mobil 8000 down here. Both fuels give the same performance and the pump gas is half the price.

Now Im on methanol so everything is different.

Yes, a lot more than simple elevation above mean sea level. Barometric pressure, temperature and humidity; ask any pilot.

They run grey without soot when I have seen them. I use either leaded race fuel 100 octane or 98 standard pump gas. Sold as Mobil 8000 down here

Click to expand...

Thanks johnm for this report as wasn't sure if well tuned race engine on hi octane would leave dry gray or more sooty dark. Its too crude a sign but for oil burning or way off mixtures of course but nice to know what it can be.