Rejetting the VF500F

Well, my bike's 1986 VIN is PC1201GM200503, which makes it a 49 state bike. Disclaimer: There's no telling what previous owners have done to it over the last 24 years.

 

How true!

On a side note, I am a bit puzzled by Factory Pro's jetting spec's. Have you contacted them about this?

 

Nope, but the date on the sheet is 7/23/92. I think they've had time to fix it if there was an error! Hell, it's quite possible they're right on the money.

In the meantime, I was going to sync the carbs this evening but it requires a 90° screwdriver which I do not have. Those adjustment screws are buried! I'll have to hit up my local Cycle Gear or find someone in the area who's got one I can borrow.

 

Or you can do the home made approach:

http://vfrworld.com/forums/1st-2nd-generation-1983-1989/30292-homemade-carb-sync-tool.html

 

If I could ask, would you be able to scan a copy of the Factory Pro instructions and post in this thread? This would be a great reference to have. Thx!

 

Hey guys, I think we discussed the main jet differences in another post but here it is again:

The different size main jets have nothing to do with running temperature of the engine or anything like that. The reason they are different is because one bank of cylinders has downdraft carbs and the other has sidedraft carbs. I've found it best to run one size larger jet in the rear carbs. Being one size off probably isn't a big deal though, unless you plan a lot of long-distance full throttle runs (not reccommended!).

 

No problem. Here it is:

http://www.superhawk996.net/Other/'86 VF500F Factory Pro Sheet.jpg

 

Factory Pro '84 and '85 Specifications:



Factory Pro '86 Specifications:



Interesting to note:

• The main jet sizing is much larger on the '84/'85 with #108's front and rear with the stock exhaust vs. #95F/#92R (Is this a typo?) for the '86.
• The jet sizing is the same front and rear on the '84/'85.

 

The main jet size difference between the years is due to the direct relationship between the amount of air the larger 32mm carbs can flow on the 84-85. Even with heavy engine modifications and a full exhaust, the size of the venturi will be a limiting factor. Thus if you can only put so much air through the carb, to maintain the proper air/fuel ratio you must limit your main jet size. Note that idle jet size, mixture screw turns, and needles are all the same between the years. This shows that even with a larger diameter venturi the airflow at lower throttle positions is similar for 30 and 32mm carbs. Only when the butterflies and slides are wide open will you be able to utilize the larger diameter carbs and increased airflow. Doesn't the '86 have a lower redline? This is probably the reason for the smaller carbs. If you're not pumping that much air then it's just not needed. The smaller diameter venturi will give higher air velocity, more complete combustion, and better throttle response.

 

Thank you for the post.

Re. my question on whether the '#95F/#92R' was a typo - I am wondering why FP has larger mains in the front. This is opposite of the '84 which has larger mains for the rear cylinders (#102F/#105R).

Also, from what I've read (and per Jamie D's post #46) these engines do better with larger mains for the rear cylinders - based on the different carb design.

Any thoughts on this are welcome!

 

See posts #12, 15, and 17.

 

Thanks for the post.

Not sure I am articulating my point.

The Cali '86 is 95F/92R. The 49 State '86 is 90F/90R.

The '84 is 102F/105R, the '85 is 90F/90R. The 32mm can handle 102F/105R with the '84 needles and emulsion tubes - the Factory issued it this way so we know it works.

Since all of the 49 State models are either the same main jet size for front and rear or larger jet sizes for the rear why would Factory Pro select a larger main jet size for the front on a 49 State bike?

 

Beats the hell out of me. I'll email them and ask. Maybe we can get an answer straight from the source.

 

Sounds like a good plan, I am curious to know their thoughts on this. Hopefully the engineer that designed the kit is still on staff...'92 is a few years back.

 

Here's a couple more threads on the subject just for kicks

http://vfrworld.com/forums/1st-2nd-...52-1986-vf500f-main-jet-sizes.html#post238164
http://vfrworld.com/forums/1st-2nd-...995-vf500-carb-differences-between-years.html

The bike is running great and the weather is cooling down. I'm going riding! I'll email FP when I get back.

 

Good deal! Ride safe and I look forward to reading what FP says. Thanks for taking the time to write to them.

 

The bike runs great! It idles super smooth and doesn't hang when blipping the throttle. Idle speed is a steady 1400 rpm. Low end power is significantly improved. Mid is about the same, maybe a little lean if anything. I'll have to play around with the choke a little to troubleshoot that. There is a nice rush of power at about 7500 rpm all the way to redline. It's no rocket, mind you. It's a 500 after all, but 8-10k seems to be the sweet spot in the twisty stuff. I'm don't normally rev the motor that high because I normally ride literbikes, so it's taking some getting used to. Overall, I'm very happy with the results. Yeah, adjusting the valves and jetting & sync'ing the carbs was a pain in the ass but it was definitely worth the time and money.

Final settings:
Idle jets: stock #38
Main jet: 95r/98f
Needles: clip 2nd from top
Mixture screws: 2-3/4 turns out
Bike specifics: foam air filter, Cobra F1 slip-ons, sea level

I wrote Marc Salvisberg at FP. Hopefully he will roger up with a reply soon. I'm pretty sure he's been with the company since the beginning, so the only limiting factor is how well his memory is and/or how well he keeps his records.

 

Thanks for the post. Glad to hear that the Factory Pro jet kit is working well!

 

You might want to be careful there. I advise that you observe a 9000rpm max engine speed to avoid dropping valves. That means running through corners at considerably less, something on the order of 6000-7000rpm - basically one gear higher (at least).

I'm glad to hear that it's running well for you!

 

Generally, I've been keeping it below 10k. I don't think I've run it up to redline even once since I've had it running. Yeah, I've heard about the valve drops and yes I'm a bit careful because of it. The motor looked really great when I adjusted the valves so I'm a bit more confident in its abilities now.

Jamie, any news on the fork tubes?