85 VF700F Tuning Questions

Hello Everyone! New Member. I just completed restoring a 85 VF700F Interceptor and was looking for some guidance with the final tune up. I have the bike on the rode and about 100 miles on it and this is what I am noticing.

1. A slow response to the throttle. Better when warm but shouldnt it be almost instantaneous?
2. When I am crusing say at 40 on flat ground it seems to hunt between accellerating and decellerating instead of staying constant.
3. The bike is loud. Could be because of the pipes, no backfires or pops.
4. The engine speed wanders. I mean to say hard to maintain a contant rpm, it will wander higher or lower.
5. Bike idles smooth and stable.

Hope my descriptions make sense.

What I have done.

1. Adjusted valves, inspected plugs
2. Cleaned carbs. Blew out every opening. did not replace anything. Inspected, cleaned, adjusted. Did not touch pilot screws, yet.
3. Did sync with a homemade manometer.

All suggestions welcome.

Jim

 

Good morning, and welcome to the forums.

The slow hesitating throttle could be any number of things... including (but not limited to), Air filter dirty, Air inlets clogged, or dirty, dirty jets in carbs, weak or stretched throttle cable, too much play in the throttle barrel to linkage, worn fuel pump seals, dirty fuel filter, leaky boots in carbs, too low backpressure from exhaust...)

Your "hunt" of a consistent power speed is a bit more indicative that you may have either a fuel delay of some sort. What do you see at higher speeds? say... 65-70MPH? (trying to eliminate potential air shortage variable, by assuming somewhat "ram air" scenario.)

Those bikes are loud. But, have you checked for exhaust leaks? What kind of pipes do you have on it?

I think your item 4 is a by-product of 1, and 2.


Hmm, the more I think about it, If this were my bike, I may start looking at the exhaust first. Sorry to repeat my question, but what exhaust do you have?

 

You might need to play with the mixture screws a bit trying to eliminate the hesitation and flat spots. Did you check float levels and check that the spring-loaded plunger parts at the bottom of float needles are working OK ??

Cruising at very low throttle like around 40 mph does involve the idle circuit, jets and mixture screws, so play around there and see what happens. Typically, i'd suggest going 1 turn counterclocwise on all screws from where you are now as an experiment.

Real tuning requires a few plug inspections to check A/F ratio by plug color unless you have access to a dyno.

Photo shows plug color on a VFR that was running perfectly, and you'd need similar for best performance. When inspecting plugs, first focus on any plug that doesn't match the others.

 

If I access the pilot screws, is it neccesary that I re[;ace the plugs when tuning is complete?

 

NO ! Those caps were required by the US government, so F* them.

 

I pulled the pilot screws and cleaned and blew them out. Reinstalled and set each to three turns. I them played with them while idling the bike. Three of them clearly influeneced how the bike was idling. If you turned it all the way in the bike died. But the fourth one seemed to have no influence, in or out no change in quality or idle speed. This carb just happens to be the front right carb, the one with the idle speed adjusting screw. Is that a coincidence?

Bike seems to runs better, but only took a short ride.

 

No clear response to closing the mixture screw suggests that the idle jet is not as clean as it should be or that the overall carb synch needs improvement.