Main jet adjustments

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goatman

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I am still trying to sort out my 91, and I wondered if anyone that needed to change their main jet size can tell me how it ran before they sorted it out.
My bike runs uneven and at higher rpms, 7k on up it runs very poorly, but sometimes picks up around 8500 rpms and takes off. Does this sound familiar to anyone who then went up a main jet size and it helped? My carbs are just cleaned and carb boots are new. I'm thinking something electrical, but thought I'd ask about the main jet. I have Morleys kit with 160 main at the moment and Marks 4-2. Thanks.
 

one2dmax

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if it occasionally takes off it almost sounds like something other then carbs??

Sean
 

goatman

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Thats what I'm thinking too. I'll start swapping out electrical parts when I get your box
of goodies. Thanks.
 

4gasem

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WOW! 160's huh? I think I have 155's in mine and it runs rich... Every so often if I slowly run through the gears it will miss a beat right at about 7000 RPMS's.

I was going to go down to 152.5's but didn't want to mess with it.

Chris
 

gamorg02

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162.5s here actually put my 7k and above right about 13 a/f. i went down to 160s but i still dont' feel too rich above 7/8k rpms.
 

4gasem

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Funny how different bikes need totally different tunes. You're sitting in Franklin at roughly the same altitude we are here...

Chris
 

gamorg02

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not saying i couldn't do leaner, but i'm at a point where i just want the needls a little richer (they drop to like 8 or 9 a/f) and i'm done with it. it is what it is.
 

goatman

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Update....Sean sent some electrical parts to swap out and try to fix this bike, but nothing made any difference.(Coils, CDI box, plug wires, misc. relays).
I have 13.9 volts at the battery at idle and it falls to about 13.6 when revved up. My regulator/rectifier already has an added ground wire, and it all looked pretty clean, no corrosion anywhere. So, I thought I'd change the main jets from 160's to 155's to see if that would help. It seems to run a little better under 6k, but worse than with the 160.s above that. I noticed that if I slowly run the bike up to redline, it does fine, but if I whack open the throttle, it stutters and coughs above 6k. So maybe I do still have a carb issue, or at least a fuel delivery issue. Anyone have any ideas? Do I need to go up on the main jet size? Thanks.:ummm:
 

veebooster

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Bigger main jet! Stock needles need big mains in the Morley kit.

Dale #2592
 

Elimax

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I think I'll disagree with the advice to go to bigger mains...I'm down in Phoenix AZ (low elevation) and have Morley kit with with 4-2 Holeshot exhausts.

My bike's problem when I bought it was same as goatman's...really crummy acceleration from about 6,500 rpm and up. EVERYTHING was clean in the carbs, though, with 160 main jets in it.

So, I removed carbs, repaced 160's with 155's, and now the bike kicks ASS!

No problems with acceleration...smooth as hell. Great top speed too.

Just my 2 cents.

Elimax
 

goatman

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But that is exactly what I did Elimax, replaced 160's with 155's and it still sucks, even worse at high rpms. I have Marks 4-2 exhaust, so we have similar setups.
 

ace16a

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Yeah, I had to go to 167.5 mains and two shims on the needles to get morley's kit to work good on my bike. Haven't dyno'd it yet but it's real strong all the way to red line with no sputtering at all.
 

1967vmax

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I have an 02 and had the same problem i tried every jet size in the kit. I ended up sending my carbs to Sean and the problem was the way my jet blocks were casted, I think but you better ask Sean . I know he replaced the jet blocks and i ended up with the 160 mains it runs great now. JIM
 

veebooster

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I had the same issues....mine's a 2002. Shimmed stock needles....went up on the mains 1 step at a time ended at 170's. BIGGER MAINS. Sounds like you were pretty close tho. Try one size bigger.

Dale #2592
 

goatman

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Thanks for the replies. I'll try bigger mains and see what happens. Strange how different bikes with basically the same setup respond to such a variation in jetting. Sounds like a shim on the needles might be a good idea too.
 

1967vmax

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Paul Czernics sells the shims 1/2 and 3/4 shim. I also used the 3/4 shim running dynojet adj needles also. JIM
 
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