Jetting for VFR700F with supertrapps?

The original owner of my '86 VFR700F swapped in supertrapps and removed a bunch of the smog equipment. Now, roughly 20 years later, I'm trying to figure out why it runs roughly at idle (surges), cruise (surges), and if the top-end running is lean/rich.

With the supertrapps, I can swap in/out baffles to lean/richen the bike, but that's not quite as fine-tuned as the jets are.

One thing I wanted to get was just a ballpark expectation from the guys that have tuned a number of these bikes as to what sizes jets I should be expecting to find when I dig into the carbs to clean/sync/inspect/rejet/etc.

Here are the general issues with the VFR:

- hard to start when cold (75 degrees F). Needs full choke to start if the temperature gauge isn't off the C.

- with the choke applied, as it warms up, it will suddenly ramp up to 2500-4000 rpm, and then I back off the choke, and let it sit at 1500-2000 rpm for a while, and this repeats 2-3 times until it's warm, or I get tired of waiting for it to warm up, and head out.

- Without choke, if still not off the C, it will stumble on opening up the throttle (nearly dropped it a few times without it being warm enough).

- once hot, it might be surging lightly at freeway speeds (6Krpm), but usually not.

- I've set idle for around 1500 rpm, because anything less than that and it constantly bogs and tries to stall.

- idling when hot, with it set for 1500 rpm, every few seconds it stumbles, bogs to 1000rpm, pops up over 1500 rpm, and settles again at 1500 for a bit. Gets annoying in a hurry.

Thoughts?

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What makes me think it might not be properly jetted (aside from how it's running) is how my wife's HawkGT had been "rejetted" when it's Muzzy was put on many years ago. All they did was turn out the pilot screws a full turn and shim the needles with a washer. Still had stock size main jets all around. With a factory pro "stage 3" jet kit in there, it's much happier. Hord Power gave me a guesstimate for starting jets and needle clip position that makes it run really well. It needs fine tuning, but went from running worse than my bike to much better.

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I plan on following these instructions to "street tune" both, as I get time:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Will be interesting, I don't have a lot of places to safely run WOT, and no easy access to a dyno and tuner that I'd trust, either.

 

Jetting

I have tried every combination known to man....and have settled on stock needles shimmed 0.020, stock jets , stock air box with snorkel and one turn on air fuel screws. Not very wild but it does run well with no flat spots ,burps or farts. No Dynojet kit I have ever dicked with worked without major issues and just a little goes a long way with jetting on gen 2......a little is alot.And make sue your pilot jets are very clean , sounds more likely to be the issue.

 

If all it takes is cleaning and a small shim, I'm happy. Is that a supertrapp on your gen2? and if so, is it 4-2-1 or 4-2-2? and how many baffles are you running?

 

Too many

I have too many baffles on mine......just to be a butthead.....drowns out he harley's. 4 into 2 exhaust and it really is quite obnoxious, but alot of fun.

 

Just finished cleaning up the emissions equipment. A previous owner did some creative things to it. With things all capped off correctly, it's running MUCH happier. We'll see how a ride does it.

 

Cleaned the up emissions equipment and synched the carbs. That pretty much solved the hunting idle. It still wanders slightly (I'm guessing some light vacuum leaks or will need to clean out the carbs fully at some point). But it's sounding SO much better than it ever has. Starts instantly, but still wants a bunch of choke to start and run until it gets warm. Then it's happy as can be.

I had a big stumble at 6K rpm for a bit, but that was due to how I routed the float bowl vent line into the clean side of the air box. There was enough vacuum in the air box to interfere with venturi effect drawing the fuel out of the bowls. I disconnected the line from the airbox, capped the airbox's nipple, and the problem went away (revs to redline without hesitation in the garage). Now to just wait for the rain to stop and the roads to dry out enough for a safe ride. Probably won't be until thursday or so.