I was wondering in anyones past experience which main jets work best with a slightly modded f3 engine. I purchased a spare race motor and the guy that had it before me was in the mountains of north carolina. I put the motor in my bike and it is running very lean. (I am in florida) It has been about a year since i dropped the motor in, and i am not sure what the main jets are anymore.

It was suggested that i go 138's on the outter two cylinders and 140's on the inner two. Does that sound about right to anyone?

The motor is as follows: PnP head, intake and exhaust pathways. 3 angle valve job. The second owner put in a mild cam, dont remember the specs, I am at work now.

Anyways, does that sound about right for the main jets?

Also i want to go up a few teeth in the rear sprocket for better off the line acceleration, should I go +1 +2 or +3. I dont wanna kill my topend at the expense of acceleration. Any suggestions?

Thanks
Steven


[Modified by cbrman, 11:39 PM 2/5/2002]

 

wow, no suggestions at all.

 

sorry man. we dont have any F3 pros on here. if you need to know about Keihin 32mm CV carbs for any Kawasaki KZ750 bikes, let me know!

 

Why not take the carbs apart and see what's in there. Is it running lean throughout the rev range?

It's also possible that old gas in the carbs have gummed up clogging the jets.

I suggest a carb clean and rebuild, get them syncro'ed too if possible.

Go +2 on the rear.

 

I think they were 138's all the way across, but i cant remember i had them apart and cleaned/synched them over a year and a half ago.

It is running lean how can you tell if it is running lean through the whole rev range???? It pops and throws flames out the exhaust when decelerating, and sometimes when I am riding it sounds like it does when you are running out of gas and need to put it on reserve, that gurgling sound and slight hesitation. It was jetted for the nc mts and i am running it in fl. One f3 racer suggested 138 on the outside two cyls and 140's in the center for a slightly modded f3. I however have more motorwork done to my bike than he does.

Steven

 

Assuming the carbs are still in sync I'd check the spark plugs to see where it's running lean.

If anything my off the head recommendation is to go 140's all around and go one notch richer on the jet needles. Bike jetted for altitude do tend to be leaner.

 

so what are some signs that a certain cylinder is running lean? Is there any way to tell at what points it is running lean or rich????

I am gonna yank the carbs off the bike this week. I wanted to wait till the car was straight after the swap, but had another incident with the bike, which causes it to be non operational at this point.

I snapped the DID gold X ring chain going across the bridge at 2:30am. I pushed the bike the rest of the way across the bridge and loaded it up into my sisters truck and took it home.

Soooo.... As I wait for my new chain and sprockets I may as well adjust the jets.

Thanks
Steven

 

do you know what caused the chain to fail? did it tear up both sprockets? sounds like no fun

 

Don't know what caused the chain to fail... Never found it. It must have fallen off the bridge. both sprockets are fine.

when it went it slapped the tubular frame for the tailsection, and broke a chunk off the case where the front sprocket is.

Either the riveted master link, or another link broke and the chain uncoiled after tearing some $hit up.

The chain had ~4k miles on it. It was properly adjusted, not too tight, not too loose. The chain was not rusted up, bike stored in the garage, the only time it saw water was getting washed. It was lubed after each wash/chain cleaning.

Oh well.

Back to the jetting, I yanked the carbs, and I think I know my problem. Cyl's 1&4 have 130 mains cyl's 2&3 have 132 mains. Stock is 135 mains. I contacted factory pro and explained to them what my config is. They tech recommended 138/140's for my ride. So i went to buy some 138/140 jets. They didnt sell them individually, they said i have to buy them in a 5 pack.

Each 5 pack comes with 1 each 130/132/135/138/140
At 18.95 per 5 pack, it was tooo much. That would be 40+tax for 4 jets??? Lockhart phillips has em for 3.50 each, so I am gonna order some from them tomorrow.

Steven

 

Chain sounds like either crap make or over tight. Most CBR's have alot of travel at the rear and prefer a bit more slack. As for the jetting you wont get into too much trouble going up two sizes but be carefull. It is better to start rich and work back than to 'nibble' a piston. If you are unsure then i would use a Dynojet kit and RR to set it up as you will always be wondering 'is it right' when you are flat out. Also it wil show you what the mods are doing and if they are woking to give you a ref. to start from. MOst bikes are set up woefully lean as stock anyway to get henm through the emmission regs. Good luck.

 

If the spark plug is white, it's lean.. if it's black, it's rich. Normal is a tannish brown.

Rev the engine to around where you think it's leaning (for main jets it's upper third of the rev range) then kill the engine and check the plugs.

Since you took apart the carbs and figured out the jets were too small that's probably not necessary.

I'm surprised your shop won't sell you single jets. Most shops sell main jets at ~$3 each... if anything you can have them order the jets from a parts unlimited catalog or any other street bike parts catalog. I recommend you stick with OEM jets, aftermarket non-OEM jet sizes seem to differ.


[Modified by redblues, 4:41 AM 2/16/2002]

 

Well really the spot it has no response is low/mid range revs. Would adjusting jet needle clip height fix this? It is in the middle 3 of 6. I was thinking maybe moving it up once to see how that goes?

Steven

 

The lack of drive in the mid-range is due to the emmission testing constraints. Free-er flowing can and Dynojet will give you big gains.

 

My error, the needle height was at 4 of 6. I moved it down to 3, and synched the carbs. Got the 14t front sprocket and 43 rear, along with a new x-ring chain.

I have yet to take it out.

as for a freeer flowing exhaust, I have a two bros complete race exhaust, carbon can.

K&N 7 jetkit. I thought it was a factory kit, but now I am not so sure, factory jet needles have 8 positions, mine has 6 positions.

Thanks for all your help.

Steven

 

Well i took it out the other day, midrange is alot better. With the gearing change and the adjustments to the jet needles it is screaming. I can roll the throttle at 6k and bring it up in first 1.

steven