Question Dear Chris,
I have a 1996 Shadow VT1100C.
Was getting terrible gas mileage so with my brother-in-law's help decided to do a carb overhaul.
First time off the bike replaced floats and float valves and seat. Set floats as per manual. Cleaned carb. But didn't take out vacuum slide or pilot screw. Put back together; drove home, parked, etc and couple days latter found crankcase filled with gas. Got beyond that.
Took to mechanic to have him check floats and clean carb. He didn't remove vacuum slide.
No improvement in mileage. Decided to take carb off again. Third time. Got into vacuum slide, needle jet. Removed and cleaned air cutoff valve device too. Diaphragms torn on vaccum slide. Decided to try NAPA Plastic Dip to try and repair them. Put carbs back together and then took ride. No top end power. Figured slide wasn't moving up enough to allow flow through main jet. Figured one of two things was happening with slide; 1) diaphragms didn't seal properly against cap or 2) repair changed dynamic of diaphragms causing slide to stick. (Repair area was stiffer than original rubber and may have caused slide to cock to one end or the other.)
Removed for fourth time. Decided to buy new vacuum slides, needle jets, and just to be sure new pilot jet screw sets. (Previous owner had needle jet kit; want to return to stock.)
My question is how do you get those diaphragms to seal properly against the cap? I figured that if I turn them inside out that will give me the best chance of getting a proper seal against the cap. Maybe the new diaphragms will seal more easily than the old ones I had.
My original problem with mileage was a too rich mixture. (That's what I can determine.) I was blowing black smoke out the exhausts with heavy throttle. Exhausts were blacken pretty good. The exhausts have been drilled out or otherwise gutted. Were standard exhausts. The previous owner gutted the exhausts and then probably installed the needle jet kit.
I think I have found the mileage problem with the diaphragms being torn now I just want to make sure I get them in right this time.
tincan53@hotmail.com
AnswerHi Steve.
Put the diaphrams in as recommended by the manual. Make sure that they are seated properly before closing everything up and you should have no problems because of them.
The whole crux of your problem was the mixture due to the aftermarket rejet that had previously been done. Running rich was the big indicator. I would have looked elsewhere for the problem if you hadn't mentioned that the previous owner had rejetted the carbs.
Any time that a set of carbs is rejetted, the entire system has to be retuned to accomodate the modification. The problem is that the factory settings are always optimal for the bike and changing it only serves to mess things up. The one exception is when a bike is being set up for a specific purpose (i.e. racing) where the milage is not important, but performance is.
Ninety-nine times out of a hundred, the guy thinks that changing the jets is the answer to his problem when the real solution is to get a bike better suited to what he wants to do with it.
Good luck and ride safe.
FALCON
