Motorcycle Repair: 1984 VF700C, v45 magna, wire colors


Question
QUESTION: I have a V45 magna that I have been redoing the last two years. Its complete and put back together. The bike has good fire and the carbs have been thoroughly cleaned. The fuel pump seems to be working. The bike simply will not start, it cranks over but all to no avail... Please help as I am dying to ride this damn thing!!!

Motorcycle Repair: 1984 VF700C, v45 magna, wire colors
VF ignition  
ANSWER: Hi Jeremy,

I am not sure exactly what you have done on
the bike so far such as was the engine
rebuild or not. There are a few things
that can cause problems but some might
be related to things that could
be affected by a rebuild such as camshaft
timing etc.

Just going from a general no start condition
here are some things to check.

First off is engine compression as
it will never start if this is too
low. Being a multi-cylinder bike increases the
chances that at least a few of the cylinders
would be okay. When new the cylinder pressure
is about 188 psi but 150 psi is okay to run.

If you have cylinder pressure or compression then
move on to the fuel system. Is there fuel in
the carbs? Are the spark plugs getting wet at
all when you choke it?

Will it run if you spray starting fluid
into the carbs?

If it fires on the starting fluid it means you
still have fuel problems.

If it does not fire the starting fluid (with dry plugs)
then your spark is messed up for some reason.

It might be the coil wires are mixed
up somehow.
The yellow coil wire is for plugs 1 and 3.
The blue coil wire is for plugs 2 and 4.
The black/white is power to your coils from the kill switch.

Check that the coil wires are going to the correct
plugs.

Number 1 plug is the left rear (sitting on the bike.)
Number 2 plug is the left front.
Number 3 plug is the right rear.
Number 4 plug is the right front.

If the coil wire colors and the plug wires
are on the correct spark plugs then
that is done.

Now with any luck you should have spark at the correct
time and can see if the bike fires on the
starting fluid or not.

If it will run temporarily on the starting
fluid then you have to find out
why it has no fuel.
Is there a fuel filter?
Have you checked for air leaks
around the carb mounting rubber tubes?

If it sucks air or vacuum it will not get fuel
into the engine. Make sure you have
no leaks around the intake where the carbs
hook up. Even a vacuum hose off might cause
problems.

If your spark plugs are wet it might be
the engine is flooded.
Turn off the fuel and blow out the cylinders
with compressed air or leave the plugs
out so fuel can evaporate.
Use some dry plugs and try again.

Is your fuel fresh and free of moisture?
Moisture in the fuel can block carb jets.

Use a fully charged battery as transistor ignitions
can cut out on low battery voltage.

If your compression seems low check your valve
clearance. It may be hard to start if the
valves are tight, not enough clearance to close
fully.

Camshaft timing off may be indicated by low
compression if you had the engine apart at all.

So you need compression, spark at the correct time
and fuel/air mixture in the right amounts to make
this thing run.

If you have any more information to add please send
it in a follow up.

Good luck,
Wayne S.
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---------- FOLLOW-UP ----------

QUESTION: Ok, after doing a compression test everything checked out fine. It still wouldnt start. It had been backfiring thru the carbs so we got the idea maybe it was out of time. We have the thing wired completely backwards from how it should be and it runs. Im guessing someone at some point in time has replaced the stator/pickup coils and wired them wrong. Also I had to buy a different set of carbs and they are a little bit different than the ones that were on it. They have an extra vaccum line coming off of the throat of all the carbs and hook together. This bike was a complete basketcase and is making me a basketcase. Thanks again for all of your help!!!

Answer
Good job! I suspected something
was making it fire at the wrong time.
You never know what previous owners
have done, that makes it hard to
troubleshoot.

Some carb tubes are just air vents
but if they have any vacuum they
should be plugged to prevent lean
fuel mixtures or overheating.

Good luck!
Wayne S.
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