Jetting experiments

[Dave T.]

Since I owned my V I have tried many things to improve performance only to realize stock almost the best option. I thought I'd share my experience with the rest of the group.

First off, I have a very loud MAC exhaust system. I figured that this bike would need more air and fuel to run with higher performance. So I rejetted my 1982 model to a 127.5 front and 132.5 rear main jets. I wondered why it started backfiring more ever since I did this (and synced the carbs). I also disconnected the crank vents from the airbox to get more fresh cold air into the airbox and put a little breather filter on for both cylinders. Next I put in a UNI foam air filter and drilled ten 1/4" holes in the top front area of the airbox to get even more fresh cold air. I thought all these mods would help.

Over the last year I have gradually gone back to stock jetting and it's gotten better and better as far as throttle response and performance. With the overly rich jetting I got a lot of buildup behind the exhaust valves and burbling and coughing in the midrange rpm's. Most of all was poor fuel mileage.

Today I put the 122.5 and 127.5 jets back in and covered up all the holes in my airbox and the backfiring reduced by 50%. It still does a little. Now it doesn't burble as much and performance overall improved. Temp today was 53 deg F and sunny. I am not in a high altitude area.

Next I may go to a 125 or 122.5 rear main jet and see if the backfiring dissapears and performance doesn't suffer. Throttle response is a big thing for me and I will keep you guys informed.  8)

[Lucky]

I have allways felt that the R&D people have a pretty good idea what they are shooting for then they design & build a car, bike, toy radio, what-have-you.  in most cases the product will perform properly if it is returned to "as new" condition.  even when there is a problem with a product such as our 'flat spot' there is usually a factory fix or recall to eliminate the problem.

I think if a jetting change is done on our bikes, it should be done only after all other vaviables are returned to spec, and tthere are a lot of them on the V: Valve adjustment, carb sync, pilot adjustment, properly working airbox flapper, clean carbs, charging system, tight & sealed exaust. just to name a few

changing the jetting on an 82 to match the 83's isn't particuarly the answer either. the 83 has some major carb changes.

i think returning things to stock is the right thing to do. it's a lot harder to find a problem when several changes are made at once.  a great rule of thumb is 'change one thing, then try it under varying conditions, then move on to the next adjustment.

--Lucky

[Dave T.]

Update time. I put in a 125 rear main jet yesterday and just got back from a ride tonight. It was about 58 degrees here and a nice night for a ride. I have to say, this is the best my V has performed yet. The burbling around 4-7K RPM's have reduced even more. I assume that the jetting is very rich. I have a 120 jet, so now I have to try the 120 front, 122.5 rear combination to see if this gets rid of the burbling in the midrange.

The backfiring went down a little also. When I fire it up cold, it doesn't burble or hiccup at all, so I assume it is still rich. Other setup tidbits, I have the vacuum operated flapper with no nickels epoxied on, and the 120 F, 135 R air jet combination

Just a FYI post for your people out there who are curious.

THE MAD SCIENTIST.... ? ;D

Update time again, next day:

I put the 120 main jet in the front and the 122.5 main jet in the rear this morning and now my V runs like it should. Still a little burbling, but a longer stroke  on the accelerator pump helps some, by this I mean backing out the limiter screw. The rod is set at around 65 mm from hole to near side of pump arm connection.

The moral of the story, if your V burbles when you give it gas, it's probably too rich. You can try my above recommendations and see it throttle response improves. I also have my YIKES! unit capped off at the ports and have the nice chrome piece for an attractive sporty look.