JE High Compression Pistons / Jet Kit
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Squid
Joined: Mar 2005
Posts: 11
From: Stockton, Cali
JE High Compression Pistons / Jet Kit
I have recently installed some JE High Compression pistons and definately need to rejet. Does anyone have good info on what jet kit and possible starting point? Exhaust is still stock but debaffled and probably will remain that way for a while till I can scrounge up some cash for the Jardine High mounts. K and N filter installed but i cannot decide if I should go with the Factory or Dyno jet kit. Any suggestions would be helpful but preferrably based on experience if possible. Thanks in advance!!
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Re: JE High Compression Pistons / Jet Kit
I'd say 180's front and rear w/ .030 shims under the needles and the air mixture screws out 2 1/2 turns would be a start depending on the altitude where you live until you can get a jet kit and pipes .
Just remember a severely rich set-up will tend to detonate as much as a lean mixture will .
After messing with my engine I'd say the choice between the Factory and Dyno Jet kit depends on how the engine is modified .
Pistons , cams and head work and non stock air filter I'd choose the Dyno Jet .. FWIW
Just remember a severely rich set-up will tend to detonate as much as a lean mixture will .
After messing with my engine I'd say the choice between the Factory and Dyno Jet kit depends on how the engine is modified .
Pistons , cams and head work and non stock air filter I'd choose the Dyno Jet .. FWIW
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SuperSport
Joined: Mar 2005
Posts: 758
From: Laurel, MD
I like the Factory stuff myself but "6 of one..."
You're into what's commonly referred to as a Stage II kit, engine-wise the K&N may do you some good. I don't really know how the modified stock exhaust will play out. And you'll need some EGR-equipped dyno time to really answer your question. Look for one with an old guy attached to it so you get some actual carb experience. ;-)
But it would be a shame to waste this cool and substantial mod on budget tuning.
You're into what's commonly referred to as a Stage II kit, engine-wise the K&N may do you some good. I don't really know how the modified stock exhaust will play out. And you'll need some EGR-equipped dyno time to really answer your question. Look for one with an old guy attached to it so you get some actual carb experience. ;-)
But it would be a shame to waste this cool and substantial mod on budget tuning.
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From: Ottawa
the dynojet and factory kits are meant for stock bikes with pipes, and that is about it.
your best bet is to take it to a dyno shop and have it tuned properly.
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Squid
Joined: Mar 2005
Posts: 11
From: Stockton, Cali
Re: JE High Compression Pistons / Jet Kit
Well I was hoping to do it myself , like the rest of my mods but it sounds like it would be best to take it to a shop and have it dyno and jetted. If that's the case, I will definately wait till I can come up on some exhaust. Anyone got some cheap highmounts for sale..... 
Thanks Everyone
DameDiggler
Thanks Everyone
DameDiggler
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Re: JE High Compression Pistons / Jet Kit
If I read your mods correctly " pistons and a KN " it's the KN that hurting you w/o a jet kit .
If you have the stock filter still just slip it back in and try .030 more shim and step up the mains one or two steps. It will run good till you get a jet kit and exhaust .
Pistons alone won't change jetting that much . It's wild cams " stage II Moriwaki and larger " along with free breathing airfilters that makes for different specs over stock with slip-on's.
If you have the stock filter still just slip it back in and try .030 more shim and step up the mains one or two steps. It will run good till you get a jet kit and exhaust .
Pistons alone won't change jetting that much . It's wild cams " stage II Moriwaki and larger " along with free breathing airfilters that makes for different specs over stock with slip-on's.
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Yours sounds like a "partial" stage 1 build to me. I did the full stage 1, which includes cams, porting, lightened flywheel, etc. I have a Dynojet kit installed. I started with it when I had stock pipes and have been tweaking it for a couple of years as I have added modifications to my engine, exhaust system and going from altitude to sea level, etc.
The jetting really doesn't change as much as you might think. Stage 2 cams would probably make a bigger difference. Higher exhaust flow is also a factor.
You can do a very effective job of main jetting with the "***-dyno" method. Find a low-traffic, straight section of road. With the bike in 4th gear (to put a load on the engine), it should pull hard and linear from say 5000 rpm all the way to the rev limiter. I would start with the main jet size that is recommended for a stock engine/exhaust (170F, 175R, I believe). If the mains are undersized, the engine will fall on its face at high RPM. If you start out with mains that are oversized, you are likely to run rich and not know it. Better to start on the lean side IMO. See other posts for needle adjustments and low RPM tuning. Good luck!
The jetting really doesn't change as much as you might think. Stage 2 cams would probably make a bigger difference. Higher exhaust flow is also a factor.
You can do a very effective job of main jetting with the "***-dyno" method. Find a low-traffic, straight section of road. With the bike in 4th gear (to put a load on the engine), it should pull hard and linear from say 5000 rpm all the way to the rev limiter. I would start with the main jet size that is recommended for a stock engine/exhaust (170F, 175R, I believe). If the mains are undersized, the engine will fall on its face at high RPM. If you start out with mains that are oversized, you are likely to run rich and not know it. Better to start on the lean side IMO. See other posts for needle adjustments and low RPM tuning. Good luck!
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Squid
Joined: Mar 2005
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From: Stockton, Cali
Re: JE High Compression Pistons / Jet Kit
Man I love msg boards. Thanks everyone for all the feedback. My friend who I got the bike from changed the stock jetting a little. From what he says he went up to 180(from stock 178) and then took that 178 and replaced the 175. No other changes other than the needles being shimmed a little but not exactly sure how much(if memory serves, I think 2 or 3 washers). While riding the other day, I noticed in top gear at about 60mph(rear sprocket is 43) or so if I just whacked open the throttle to W/O, the engine totally bogged down. Also, on the freeway in top gear at about 6K if I whack it, W/O, kind of mushy pull until 7k and then revs pick up really fast up to 9k, yet pull does not increase with revs....hmmmm kind of like... when a clutch is slipping but not that. Motor screams but power does not increase....hmmmmmm. Hopefully someone can make since of all this jibber jabber. Until next time,...keep the rubber side down!!! DameDiggler Out!!
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Hmmm... A couple of things. From what I've learned, a K&N filter gives an increase in HP at the top end, but with a severe hit in the midrange power. Midrange is why we love these big twins, so I've stayed away. If you aren't feeling a miss at about 3-4k needle position is probably ok. Maybe on the rich side shimmed that much. You might try leaning it out a bit with less shim under the needle. Too lean causes a 3-4k stumble.
I think you are right, Dynojet baseline main jets are 175F, 180R. I'd start with that.
It sounds like your clutch may be slipping. I installed Moriwaki clutch springs to handle the extra torque of the "built" motor.
**I had it backwards on the needle shims.
RC
I think you are right, Dynojet baseline main jets are 175F, 180R. I'd start with that.
It sounds like your clutch may be slipping. I installed Moriwaki clutch springs to handle the extra torque of the "built" motor.
**I had it backwards on the needle shims.
RC
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Squid
Joined: Mar 2005
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From: Stockton, Cali
Re: JE High Compression Pistons / Jet Kit
I did the whack in 4th at 4k test and it pulls linearly, but not strung at all....this weekend, I think I'll get that astock airfilter and try and sort things out. I just can't figure if too rich or too lean yet but will prob have to resort to the spark plug test or take shims out ..... but will keep you all informed- thanks for all the info everyone and keep it coming if you think of anything else to try.
DameDiggler
DameDiggler
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Re: JE High Compression Pistons / Jet Kit
Yeah it sounds like your at the point where it would take a main jet change to know is fat or lean but since you know how it pulls up top merely changing to a stock airfilter will tell you .
If it runs better it's lean , worse it's too fat on the mains .
Do same day testing though .
If you are going to have to buy a filter to try this I'd suggest just buying a jet kit instead . They will run good with a DynoJet kit and KN filter .
BTW , you can buy stouter clutch springs from Barnett for cheap cost .
If it runs better it's lean , worse it's too fat on the mains .
Do same day testing though .
If you are going to have to buy a filter to try this I'd suggest just buying a jet kit instead . They will run good with a DynoJet kit and KN filter .
BTW , you can buy stouter clutch springs from Barnett for cheap cost .
Remember stock is BAD!
SuperSport
SuperSport
Joined: Jun 2004
Posts: 760
From: Jacksonville FL
Re: JE High Compression Pistons / Jet Kit
If it helps. My shawk (bone stock at the time) ran fine with one spacer in it.
With 2 spacers in it: I ran too rich. Rich enough that I would have fowled out spark plugs on the expressway.
My altitude, I live at sea level with the ocean 10 min away.
With 2 spacers in it: I ran too rich. Rich enough that I would have fowled out spark plugs on the expressway.
My altitude, I live at sea level with the ocean 10 min away.
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