throttle problems

Hey gang,

working on my '83 Honda VT 750C Shadow, I had problems with the fuel
acting like it was not flowing about half way thru the throttle in all
gears. I've changed the fuel filter, air filter, and some of the fuel
line. I also broke down the carbs and cleaned them, although they
didn't look bad. However, now I can't even make it a quarter way thru
the throttle without it giving out. I'm going to check the throttle
cables, make sure they are set properly, the fuel pump and recheck the
carbs. Any other ideas what might be the source?

 

BTW, I would roll the throttle til it hit 4000 rpm, then it would choke
out. now, i can't get it above 1300 before it tanks. it dies like it is
choking, almost an instant cut-off.

 

If you can ride your Honda with the "choke" on and it quits every time
you turn the "choke" off, your problem is probably plugged up idle
jets.

Constant vacuum carbs run on the idle jets up to 1/2 or 3/4 throttle,
and if the idle jets and ports are plugged, the motorbike just won't
accelerate...

Constant vacuum carburetors don't usually have a real choke plate, they
have a tiny little bypass carburetor built into the side of the each
main carb, and when you turn the "choke" on, you're opening up a rather
large jet in the float bowl.

The main carb can suck gas right out of the float bowl through this
large jet, so the engine will start and run. But. as the engine heats
up, you have less and less control of the engine speed since the
mixture becomes far too rich when you're running on this bogus
"choke"...

I've explained how to clean them about a bazillion times. You can
google up "kaybearjr@aol +idle jet" or "spectraltarsier@aol +idle jet"
to see how to clean the carbs out and readjust them...

 

I haven't needed the choke to start it since I put in the new battery.
I dismantled the carbs and cleaned all the jets, even the choke intakes.
I followed the fuel line up past the fuel pump, which seems to be
working fine. I didn't actually measure output, just kind of eyeballed
the output into a jar. I did find the line from the three way split was
kinked. The hose I replaced was a very hard type of line, whereas the
replacement line was too flexible, and kinked when bent at a 90 degree
angle. So apparently the rear cylinder was starving. However, this
doesn't explain why it was having problems before all this. There was a
slight cut in the old line, but I don't know if that was prior to or
after taking it off. I'm going to get a 90 degree elbow and see if that
will eliminate part of the variables, then look to see if there are any
more.

 

I didn't say anything about STARTING your Honda...

What I said was, " If you can RIDE your Honda with the "choke" on and
it quits every time you turn the "choke" off, your problem is probably
plugged up idle jets."

Try riding with the choke on and see if it doesn't run with more
throttle until it gets hot, and then the RPM is uncontrollable. That
indicates plugged up idle jets and idle ports and plugged up idle
mixture screws...

If the fuel pump will supply 12 ounces of gasoline in a minute, the
pump is OK...

If you have fuel supply problems to the carbs, the engine will suddenly
start running on only one cylinder. But it will take a while for that
to happen, you might have to ride for miles and miles...

I bought a set of used racing carbs from a friend and he had been using
thick walled automotive fuel hose. When the hose was connected to the
petcock it was slightly kinked, retricting fuel flow...

My friend had the same motorcycle that I did, but he never had the
problems I ran into. He was drag racing the motorbike and drag racing
requires full throttle running for short distances. I was riding out on
the open road, using lots of throttle for a mile at a time, and I was
having fuel starvation problems. The engine would start running on 3
cylinders, and then on 2 cylinders...

The fuel starvation problem got so bad from the hose kinking I couldn't
ride over the hills to get home, so I started taking the gas tank off.
I had the rear bolts of the gas tank out and lifted up the gas tank and
the engine started and ran. So I finally realized it was just a kinked
hose after about a month of wondering what the hell was wrong. I stuck
a beer can under the gas tank and rode home and then I cut the fuel
hose half an inch shorter so it wouldn't kink anymore...

 

my mistake about misreading your comments on the choke, i'll give it a
try. we looked at the fuel pump again, and it runs great, so it is
something after that.