Engin Doing Something Strange

Hi, my engine runs somewhat erratically after about 7000rpm. It's a
GPZ600R (1986). Fine otherwise. I've asked a friend and he thinks it
may be a dirty air filter, valve clearances or carb balancing issues.
I would be surprised if it were any of these as it had a service only
a couple of months ago.

As it only seems to be loosing power in the high end of its range I
would imagine it's an air or fuel supply problem, or ratio problem;
most likely lack of air perhaps. But I dont' really know what I'm
talking about.

Does anyone have any ideas how I might remedy this problem?

Thank you for your time.

Dylan

 

There could be any number of things causing this.

One possible cause that's easy to look for is clogging
in the fuel delivery system. You've likely got filters in
the tank above the petcocks. If these get clogged,
it slows delivery of fuel and can cause high RPM skipping.

Similarly, if the tank isn't venting you can get a vacuum
buildup which can also slow fuel delivery. You can check
for this by loosening the tank cap to allow venting to
see if the running improves.

Symptoms of a problem like this would be a skipping problem
that goes away if the bike is stopped or run at low RPM for
a while then returns after a minute or two at high RPM. On
an older bike, crud in the tank is not an uncommon problem.

Good luck

 

High speed misses are often a result of a weak spark.

How old are your sparking plugs? Conventional plugs (not platinum,
palladium, or iridium tipped) will last about 8,000 to 10,000 miles,
while
the more expensive precious metal tipped plugs will last three times
as long.

Since each conventional plug now costs $3 to $4, I recommend pulling
them
out and cleaning them and filing the center electrode *flat*, so it
has a sharp edge all the way around before regapping.

Also, check all the connections in your ignition circuit from the
battery, through the ignition switch, kill switch, fuse box, and all
the wire harness
connectors in between.

The ignition system needs the full 12 to 15 volts that the charging
system puts out to provide the best spark the rather small ignition
coils are capable
of producing.

If the problem isn't with the ignition system, you might have a dirty
fuel system. Clean out the fuel filters, wherever they may be.

Engines with electric fuel pumps will have a seperate replaceable gas
filter and there are probably fuel filters in the gas tank. You have
to drain the gas tank and remove the petcock to clean those filters.

Some carburetors even have tiny gas filters just above the float
valves in each carburetor.

You can find out where the fuel filters in your specific motorcycle
are by
looking at the parts diagrams at www,powersportspro.com

Another possible source of high speed fuel starvation is a plugged up
carburetor.

You can add four or five ounces of Berryman B12 Choke and Carburetor
Cleaner to a full tank of gas and just ride the motorcycle to dissolve
the
gum and varnish buildup in the jets, ports and passages.

You can also use GumOut or STP carburetor cleaner, by I like the
Berryman
B12 because I can buy it in liquid (non-aerosol) form at Wal*Mart.

None of the above carburetor cleaners will dissolve *rust* or calcium
carbonate buildup inside a carburetor.

There are gas tank cleaning and recoating kits like Kreem that solve
the rust problem.

Calcium carbonate builds up inside carburetors when hard water gets
into gasahol. The alcohol in the gasohol emulsifies the water so it
stays in suspension in gasoline and the calcium carbonate (a hard
white substance)
plugs up the jets and ports and passages.

Disassembly and cleaning is the best method for getting the calcium
carbonate out of the carburetors.

 

Pretty obvious, that is.

Take it back to the place you had it serviced.

Since you don't seem to be ready/willing to take advice offered by others,
why should we bother ??