1991 FJ1200 idling problem

[Jocko]

I just purchased a 1991 FJ1200 from the original owner. I love the
bike and have been busy detailing it.
I have discovered an idling problem that I need some help with. When
the bike is first warming up the choke must be on. Once it has warmed
up the choke is shut off (pushed in) and the bike idles down to around
1200 RPM. The problem occurs when the bike has been run for a while
and you come to a stop. The engine will not idle correctly and
fluctuates between 1800-2500 RPM. I have checked to see if the choke
was sticking and it doesn’t appear to be. Any thoughts or advice?
Thanks in advance....

--
Posted at author's request, using moderated http://www.MotorcycleForumz.com interface
Thread archive: http://www.MotorcycleForumz.com/1991-FJ1200-idling-problem-ftopict165375.html

[som...@some.domain]

In article <7807426_9de48ea0c5ca...@motorcycleforumz.com>, Jocko <no...@000.com> wrote:
>I just purchased a 1991 FJ1200 from the original owner. I love the
>bike and have been busy detailing it.
> I have discovered an idling problem that I need some help with. When
>the bike is first warming up the choke must be on. Once it has warmed
>up the choke is shut off (pushed in) and the bike idles down to around
>1200 RPM. The problem occurs when the bike has been run for a while
>and you come to a stop. The engine will not idle correctly and
>fluctuates between 1800-2500 RPM. I have checked to see if the choke
>was sticking and it doesn’t appear to be. Any thoughts or advice?
>Thanks in advance....
>

use a cigarette to dribble smoke around all the fittings to see if there is a
leak. also, have the carbs been cleaned recently? do the need rebuilds?
google up the shop manual and do all the carb maintenance normal to a big tune
up. if you're mech inclined, check it all out. if not, bribe a buddy.
if all else fails, pay a pro.
oh yeah, stomp the butt out and don't smoke it!
let us know how you make out or ask if you need more help.

[The Vicar]

Hi, You could check the carb diaphragms for pin holes or splitting.

[.]

On Jul 29, 2:22�pm, Jocko <n...@000.com> wrote:
> I just purchased a 1991 FJ1200 from the original owner.

He probably drilled out the EPA anti-tamper plugs and turned the idle
mixture screws two or three turns counterclockwise.

The idle mixture screws are a slot headed screw that may be under the
carburetor ahead of the float bowl, or on top, forward of the
diaphragm cover
on the top of the carb.

If you see a slot headed screw in either area, you can be sure the
previous owner has screwed with the idle mixture and made a mess of
it.

> �I have discovered an idling problem that I need some help with. �When
> the bike is first warming up the choke must be on. �Once it has warmed
> up the choke is shut off (pushed in) and the bike idles down to around
> 1200 RPM. �The problem occurs when the bike has been run for a while
> and you come to a stop. �The engine will not idle correctly and

> fluctuates between 1800-2500 RPM. �

This is typical of how an engine idles when the idle mixture screws
are turned too far out. The mixture is actually *too rich* at idle, so
the idle RPM slows down.

But, to compensate for having made the idle mixture too rich, the
previous owner turned the idle *speed* knob clockwise, and this
uncovers a triangular pattern of acceleration transition ports just
downstream of the throttle butterflies.

They aren't supposed to be uncovered until you are trying to
accelerate away from a stop.

So, the solution to your idle mixture problem is to turn the master
idle knob between the carburetors down to the specified RPM.

Then turn all four idle mixture screws clockwise a quarter of a turn
at a time, and, as the idle *speed* increases, turn the master idle
knob counterclockwise to get the idle RPM back to spec.

Then turn the four idle mixture screws in another quarter turn and
turn the idle speed down again.

You'll know when you've turned the idle mixture screws in too far.
When your idle mixture becomes too lean, the engine will start idling
rough.

It was a lot easier to do this idle mixture adjustment on a two barrel
carburetor on an American V8 engine, as there were just two idle
mixture screws instead of four.

When you turned one of the screws in too far, the engine would start
idling rough, so you just turned that screw back out a quarter of a
turn, revved the engine up twice, said, "She's a-taking the gas now,
Joe Bob," shut the engine off, slam the hood, and go get a beer from
the icebox.

Nowadays, shop manuals recommend using a sensitive tachometer and
turning the idle mixture screw in until the idle speed decreases by 50
RPM, then turning the screw back out until it picks up 50 RPM.