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Everyone's running the wrong size main?

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150 and 230 riders, Here's something to think about. note: I'm a 150 rider.

When I first installed the powerup kit, I ran a 118 because a few cutting edge guys with 150's were running that. Fine. Since then, I haven't put much thought into it. The bikes run great.

Then I got to thinking after I read a post about everyone running the wrong size main on their 230's. Everyone was running it too large (and most are still running it large. I think it was the 132 was too large.). According to the post I read, it basically said the HP would be higher if everyone went down in the main. I don't recall the sizes off hand, but. . .

Now let's cut to my 150. The engine is basically stock, but I did have it ported, which might be the major factor for me. Either way, my bike (I thought) runs good. The plug looks good. It's all good. I, however, have to ask myself, "why not try a 115." What will happen? That's what everyone is running, right?

I haven't heard of ANYONE, running a 118, except for the guys I ran into. They were flying too. Totally pulling my on the uphill straight. And yes, they're engines were stock at the time, like mine.

Anyone? Anyone have any thoughts on this? My bike doesn't bog. Is there any possible thought that a smaller 115 could do anything positive?

fyi - I'll still try it since it's cheap, but I was curious if anyone had anything to say about it.

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Check the main either on a dyno with an O2 sniffer....then go up one size, or do a WOT plug check.

IMO each bike is different, what works well on one may or may not work well on another.

Ya wont hurt anything by playing with the jetting. I ran my bike lean on the main for a LONG time with no ill affects (135 main). For ultimate power on my bike, a 138 main works the best. For a little added reliability, I went up to a 142. A 145 is too fat, unless I run some VP U-4.

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Toneconsultant,

I agree with Toast. Every bike is different. Try the 115 and see how it runs. The difference in jet size is not that great, and you may or may not be able to tell any difference.

If there is a clear improvement, you did the right thing. If that is the case, you might then even try a 112 to see if there is further improvement.

Obviously the reverse could also be true. A bigger main may bring improvement. Test, test, test.

Just a tip. The 188 with mild cam I dyno'd a while back made 18 HP with a 110 main...

Stock carb, std. pilot, std. needle.

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Toneconsultant,

I agree with Toast. .

You can't do that! :D I didn't say anything. :D

Hey! Is that what you meant? :) Wise guy! :p

:)

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.

Anyone? Anyone have any thoughts on this? My bike doesn't bog. Is there any possible thought that a smaller 115 could do anything positive?

Bueller is out sick today but I have a thought on this. Best thing to do is try it out.

A dyno would be best but if not handy a quick & easy test to see if the main jet is on the fat side is to go wide open throttle & quick let off. If it pops a little out the back of the tailpipe it's on the fat side. These are the some of the excess fuel particles that couldn't find 13 or so air particles during the burn but were able to find them at the end of the pipe & igniting. This popping decreased with each smaller main jet I tried. On "my" 230 the popping stopped completely when I stepped down from the 125 MJ to the 120 MJ. I'd prefer an infrequent fat pop to make sure I'm not too lean. IMO that would be close to perfect on the MJ.

Don't get this confused with the popping you get on deceleration when the slow circuit is too fat. That's a constant popping while decelerating. The MJ fat popping is 1-3 cute little pops & its over.

I'm hoping for some better gas milage from this! :)

Thanks again Coeshow for posting your dyno results! :p

cdaledh,

Is there a Dyno in the Portland area? If so how much is it?

Thanks!

:)

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Gentlemen, FYI I am running with a 110 main in my 150 and I get no popping at all whatsoever out my exhaust. My bike runs well, the plug looks good, nice and brown in colour, not a hint of black nor white deposits.

Cheers, :)

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Thanks folks. This is all good info.

I like the wide open test. That sounds funny. My bike doesn't pop after it's warm though. I'll go to the shop and get some main jets.

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