But dyno for WOT fuel mixture

Its not practical to hold your bike at top speed WOT throttle on the street so you can get a plug chop and check the color. You can spend the money for a air/fuel ratio tool and software but you have to mount it on the bike. So what I just did is richen my main jets until it just start to miss at WOT in 2nd gear. For the 33mm FCR carbs this was 150 main jets. Then I leaned them out until it just started to miss by easing it up to about 4500 RPM at partial throttle and then giving it a short 3 second WOT burst (you don't want overheat the pistons) - This started happening with 105 main jets. I changed it to 128 main jets which is the mid point between 150 and 105 and I'm calling it good. Another way is to simply jet it rich till it misses and go down 20 from 150 to 130 which is what I used to do.

Sounds like a solid plan as log as you are saying it. If I said it, the dog pile of you're doing it all wrong would start up. lol

Or you can go pay $140 bucks for a dyno run round here and chase the AFR numbers, which may or may not be any better in real world use on the street than a butt dyno.

What mains do the 33mm FCR carburetors come with from your source? 35mm FCRs come with 150 or 152. No bogging or miss firing with my engine. 140 said to work by a member or two here was too lean, so I went back to what they came with new from SUDCO.

Schwany said:

Sounds like a solid plan as log as you are saying it. If I said it, the dog pile of you're doing it all wrong would start up. lol

Or you can go pay $140 bucks for a dyno run round here and chase the AFR numbers, which may or may not be any better in real world use on the street than a butt dyno.

What mains do the 33mm FCR carburetors come with from your source? 35mm FCRs come with 150 or 152. No bogging or miss firing with my engine. 140 said to work by a member or two here was too lean, so I went back to what they came with new from SUDCO.

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I've been sending the 33 FCRs out with 130s but may change that to 125s (they come supplied with 125s). My 750 is ported and a little thirsty. Some customers find 130s too rich but its safer.

Do wot in a lower gear.

jseng1 said:

I've been sending the 33 FCRs out with 130s but may change that to 125s (they come supplied with 125s). My 750 is ported and a little thirsty. Some customers find 130s too rich but its safer.

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Yep I have a ported head blah blah yadda yadda racy this racy that.

My P11 750 likes the accelerator pump functional and the 150 mains. Needle at 4 down from the top with a 1/2 step shim under it. However, I'm fairly certain a stock 750 wouldn't respond well to that setup. They don't breathe as well as my engine does and they are spinning more rotating mass weight and possibly a big fat guy in the saddle. Oops, that could be offensive.

BTW, I foolishly put the 140 mains in before I first installed the 35mm FCRs. That's what I get for reading stuff in forums. lol The 150 mains were an instant improvement. Although they might be 152. I didn't write it down when I had them apart, and I do not want to take the float bowls off again to find out. Friggin rubber gaskets expand and I have to wrap them in blue paper shop towels for a day or so before I can reuse them.

I thought your featherbed was an 850. Is your test bike a 750?

Never mind you probably need to get back to work and make you some money.

jseng1 said:

Another way is to simply jet it rich till it misses and go down 20 from 150 to 130 which is what I used to do.

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That's what I did because my bike had 240 main jets installed in my amal 930's, and it would just not go past 83mph. I read somewhere that if you hit the wall like that approaching WOT, if the engine seems to surge slightly as you back it off, that it means that you have the wrong main jet installed. My commando actually did just that so I put the 220's in and it zoomed right up to 100mph. I probably should have tested 230's too since it's safer to be on the rich side of things (as Jim mentions above) but the 220's worked fine and I'm not really riding around above 85mph all that much. (except flying up one stretch of the hiway near my house )