Idle jet problem, rough running, rough acceleration, carb problem

Started by David Allaband, April 06, 2014, 11:57:46 PM

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David Allaband

Long story short, I figured out that piston #1 isn't pulling it's fair share. Ruled out compression and spark. #1 and #2 share the same pod air filter so it's not that. When I throttle carb #1 by itself that one piston will pull and accelerate the engine. When i screw the idle needle at the top of the carb all the way in or out it changes nothing.

So I pulled apart carb #1 and shot carb cleaner through the whole thing, especially the idle circuit. Did the same to carb #2 just so I could see that the carb cleaner was flowing the same through the same orifices on the different carbs. Put it back together and the problem was not solved. (Maybe I should have switched internals to see if the problem migrated to piston #2?)

I got into carb #1 again, but this time only took out the idle adjuster screw and the one jet that points at the air filter. Used the rest of the can of carb cleaner in the circuit. No improvement. One other thing I noticed is that if I cover carb air intake #1 and #2, #2 pulls at my palm a lot harder then #1. Not sure if that's a symptom of the problem or a side affect.

I did float the floats and submerge them in gas for 5 minutes to see if they had a leak and I didn't find one.

I'm not a novice, i've been rebuilding carbs for years and I completely rebuilt these carbs 5 years ago. Anybody have the solution for me? I gave the throttle adjustment a little twist so the engine is running a little more even now but I don't like it this way. This is my only transportation and I want it running right.

Thanks!
----------------------
Sometimes the fear won't go away, so you'll have to do it afraid.
Los Angeles, CA
1/3 1987 - 1/3 1989 - 1/3 1993 FJ1200

aviationfred

Quote from: David Allaband on April 06, 2014, 11:57:46 PM
One other thing I noticed is that if I cover carb air intake #1 and #2, #2 pulls at my palm a lot harder then #1. Not sure if that's a symptom of the problem or a side affect.


I am far from a carb expert.... In fact they pretty much scare me.   :unknown:

Concerning the above quote. Have you checked the rubber cap over the intake boot vacuum nipple on the #1 carb for cracks or a poor seal?

Fred
I'm not the fastest FJ rider, I am 'half-fast', the fastest slow guy....

Current
2008 VFR800 RC46 Vtec
1996 VFR750 RC36/2
1990 FJ1300 (1297cc) Casper
1990 VFR750 RC36/1 Minnie
1989 FJ1200 Lazarus, the Streetfighter Project
1985 VF500F RC31 Interceptor

Pat Conlon

1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

andyb

Carb is fine.

Do a compression check, and at best get ready for a valve adjustment.

David Allaband

Thanks for the replies.

Fred, good catch, I did check the rubber cap over the intake boot vacuum nipple but forgot to mention it. Took them off and ran the bike with my finger over them with no change too.

Pat, I synced the carbs about a week before this happened. Now it's impossible to sync them because of what I wrote in my post.

Andy, I'm curious, what in my post lead you to believe the problem is compression related?
----------------------
Sometimes the fear won't go away, so you'll have to do it afraid.
Los Angeles, CA
1/3 1987 - 1/3 1989 - 1/3 1993 FJ1200

Bminder

Doesn't that year of bike have the vacuum operated petcock? Is it possible that is bad and causing the poor running problems?
Billy Minder
92 FJ1200 ABS

rktmanfj


David, just to clarify... you used the late-model (pump) carbs on the early model (gravity) bike?   :scratch_one-s_head:
Randy T
Indy

Blessed be the LORD my strength, which teacheth my hands to war, and my fingers to fight.
Psalms 144:1

'89 FJ1200
'90 FJ1200
'78 XT500
'88 XT350


Pat Conlon

Quote from: David Allaband on April 07, 2014, 02:18:44 PM

Andy, I'm curious, what in my post lead you to believe the problem is compression related?

The weak cylinder could be due to low compression from tight valves (not closing all the way)
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

andyb

It concerns me that you've got a hole that isn't providing as much suck as the rest.  That's not a carb issue (unless the synch is way, wayyyy off!)  With luck, you've got some tight valves, staying open and reducing compression/efficency.  Without luck, you've got a crushed ring land or holed piston or other horrible thing.

Dan Filetti

Quote from: andyb on April 08, 2014, 09:53:25 AM
It concerns me that you've got a hole that isn't providing as much suck as the rest. 

Happens to the best of us.
Live hardy, or go home. 

Lotsokids

I'll be watching this post closely. Mine seems to act the same way. Mine coughs and chugs during throttle roll-on at less than 2,500 RPM. But wide open throttle, it produces enormous power and rotates the earth. Is that what yours does?
U.S. Air Force sport bike instructor (initial cadre), 2007-2009

I'm an American living & working in Hungary

FJ_Hooligan

Quote from: David Allaband on April 06, 2014, 11:57:46 PM
Long story short, I figured out that piston #1 isn't pulling it's fair share. Ruled out compression and spark. #1 and #2 share the same pod air filter so it's not that. When I throttle carb #1 by itself that one piston will pull and accelerate the engine. When i screw the idle needle at the top of the carb all the way in or out it changes nothing.

How are you "throttling" carb #1 independently of the others?  Are you reaching in and lifting the slide with your fingers?

You're saying you can completely shutoff the idle mixture screw and it makes no difference at all?  If so then something is seriously screwed up.
DavidR.

Bminder

Quote from: FJ_Hooligan on April 08, 2014, 04:01:35 PM
Quote from: David Allaband on April 06, 2014, 11:57:46 PM
Long story short, I figured out that piston #1 isn't pulling it's fair share. Ruled out compression and spark. #1 and #2 share the same pod air filter so it's not that. When I throttle carb #1 by itself that one piston will pull and accelerate the engine. When i screw the idle needle at the top of the carb all the way in or out it changes nothing.

How are you "throttling" carb #1 independently of the others?  Are you reaching in and lifting the slide with your fingers?

You're saying you can completely shutoff the idle mixture screw and it makes no difference at all?  If so then something is seriously screwed up.

I'm confused too. If you've ruled out compression and spark, how do you know that #1 isn't pulling its weight?
Billy Minder
92 FJ1200 ABS

novaraptor

1990 FJ1200
Ride fast, live free... I forget the rest...

Fj.itis

If pilot screw isn't making a change then wouldn't that indicate an air leak somewhere on number one? This is exactly what happened when my vacuum  advance unit crapped it self, except on number two carb.