Honda Nighthawk question

1985 Honda 450 Nighthawk.
Rebuilt carburetors, adjusted valves etc. etc.

Cleaned fuel petcock (strainer) and noticed that I cannot blow air through
it. Read in the manual that vacuum from the engine opens the port and
allows gas to flow. Does this mean that I will have difficulty with initial
starting since my craburator bowls are empty? Should I manually feed gas
into the carburator prior to starting?

Advice appreciated.

Ivan Vegvary

 

You should not have a problem. There will be enough vacuum created when
the starter cranks the engine over.
Bruce

 

YMMV. While the above is probably true, it WILL take longer than "normal"
to start. May take 15~20 seconds (of cranking time) to get enough fuel in
the bowls. Battery needs to be fully charged and shouldn't crank for more
than ~5 sec. continuously, IMHO.

Is there not a PRI (prime) position on the petcock lever?
If there is, that position by-passed the vacuum cut-off and lets fuel flow.
Set it there for a couple of minutes and check for leaks B4 cranking.

 

I agree with Ken. On some bikes, cranking will supply enough vacuum to
turn on the petcock, on others it won't, even continuously spinning
the starter beyond the point of abuse. My '81 CB900C was one of the
latter. Most of my Kawasakis had a PRIme position on the petcock that
would fill the carb bowls without needing vacuum. The CB900C didn't, in
fact it had a conventional manual ON/OFF/RES petcock in series with a
separate vacuum operated valve mounted on top of the carbs.

If you don't have a PRIme position on your vacuum petcock, a handheld
Mityvac vacuum pump is the slick way to fill the bowls without making
your starter motor work overtime. You may also be capable of sucking
sufficiently to actuate the petcock by mouth...

 

Agree absolutely. My Triumph 1200 Trophy started quicker and easier if
I switched it to Prime (especially if it hadn't been used for a
while). Ditto my old Z650, now disposed of.

That CB900C system sounds like an absolute abortion, btw.

I've never seen a vacuum tap without a Prime position, actually. I
suppose there must be some somewhere....

 

There is not a prime position on Honda petcocks. A small amount of
vacuum should be all that is needed. Of course the petcock could be bad.
Bruce

 

Bruce Farley schreef:

Mine are a Honda VF400F's. They have ON, OFF, PRI
ON=open when vacuum, closed when no vacuum,
OFF=tap closed, independent of vacuum.
PRI=tap open, independent of vacuum

For the rest, the advices are correct. If you have a PRI
position, then use that after your bike has been left
alone for a long time and wait a few seconds to let the
bowls fill up, else use ON and be aware that starting takes
a while.

Rob.

 

Thanks everybody for the sage advice. I'll use my hand vacuum pump and
spill a little gas into the carb bowls prior to starting.

Thanks again.

Ivan Vegvary