Jets for an '84 vf750f

Hey guys,
I've been thinking about re-jetting my bike. I have a full kerker exhaust and a K&N airfilter. Any recommendations for what jets to use in this bad boy? Thanks.

 

I have the same setup. Go one step up on the slow and main jets. You have different sized front and rears, so IIRC, the fronts can be used on the rears so you don't have to order 8 new jets, only 4.

I had to turn my pilot jet in one full turn from stock because I was getting popping on decel and the exhaust smelled rich. Been getting 37 mpg and carbs still need to be synced.

 

Awesome, thanks for the advice.

 

Factory Pro only - stay as far awat from Dynojet as you can get.

 

Hi Jamie,

Does the Factory Pro kit include a range of jet sizes? couldn't find detail on their website.

thanks

 

They normally include a couple of different jets to suit your configuration. You'll need to contact Marc at Factory Pro directly for a kit.

 

You can buy main jets at the dealer for two bucks each, the slows are less than five a piece. Paying 80 bucks for a factory pro or dynojet kit is ridiculous.

Here are the stock sizes for a 1984 VF750F:
MAKE SURE YOUR CARBURETORS ARE CORRECT! they change from '83-'84.

Carburetor model:
49 state VD52C
California VD05A

Main:
49 state 1&3 (rear) #110 2&4 (front) 112
California all four #128
I didn't misread the information, nor was the manual mis-printed. You probably know, but just incase you're wondering... the front carbs run richer than the rear, instead of the other way; this is due to the front carbs being down-draft, and the rear carbs being side-draft. This is also the reason the bike will sputter if you slow down really fast, or push the bike off the centerstand while it's running.

Slow:
50 state, all cylinders #38

the initial setting for the pilot screw is 2.5 turns out. Then you need to perform the ridiculous adjustment procedure some crackpot thought up (anybody that has done it before knows what I mean).

These carburetors have non-adjustable main jet needles. If you can find matching needle retainers with adjusting clips, use those.(I did a rejet on another VF750 a few months ago, and had another set of Keihin carbs that I could take parts from). Bumping up the main jet one size is usually lean a high rpm, but more than that loads it up at lower speeds. The solution is to increase the jet size three sizes up, and move the needle down one position. The slow jets were adequate with this setup, and the AFR was as even as it could get with these carbs (I checked it with a dyno test to be sure). The dyno made me realize the job couldn't be done to the degree I felt safe with without modifying the jet needle position. A stiffer slide spring can make up for adjusting the jet needle, but you have to be careful with that.

This bike was an '84 VF750F with a Kerker 4-1 and a UNI filter. The uni filter is slightly more restrictive than the K&N, but it shouldn't be enough to matter. You'd think the float vents would be between the filter and carbs, that way an air filter won't affect fuel mixture.

 

fabinator, you really seem to know your stuff. Thanks for the reply. I'm interested in the fix you made to optimize performance with the +3 size jets. How can I make the needle position adjustable? What did you do?

 

I used the needles and retainers from another set of Keihin carbs that happened to have the same bore. Unfortunately, they were just a set laying around in the shop, and I have no idea what they were originally from. All I know is they were from a Honda or Kawasaki.

Basically, if you found different jet needles that fit the slides, you just want the jet needles to be 1mm longer than stock... but make sure the taper is correct, you don't want to use straight needles in place of tapered, etc.

Since these carbs are a real pain to remove, it would be best to get it right the first time, but incase it's not, don't just let it be. Use a dynamometer equipped with EGA hardware to check your AFR throughout the RPM range. You'll probably have to remove the carbs to tweak things a couple times before it's spot on. You're looking to achieve a 13.4-14.9 AFR at all times. Just don't let it run lean, they tend to do that around 7K, which just happens to be really close to normal freeway speed.