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High idle after riding

Started by FcWilson, June 14, 2017, 08:40:37 PM

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FcWilson

June 14, 2017, 08:40:37 PM
Hi guys. I recently got a 92 fj1200 running I've had after a full carb rebuild, including new  diaphragms.  I have a high idle problem now. It can sit on the center stand and idle at 1100 rpm all day. But go ride it and get on it and it'll want to idle at about 2400rpm. It idles smooth no matter what, I can't find a vacuum leak anywhere. It's like it's computer controlled. I attached a YouTube video of how it acts after a ride.   Thanks for any input

https://youtu.be/zbcfK7LUvfU

I should add that I got the bike needing a rebuild so I have no previous experience with how it ran.

FJ_Hooligan

#1
June 14, 2017, 09:24:36 PM
Either a vacuum leak or a sticking throttle cable
DavidR.

ribbert

#2
June 14, 2017, 09:38:36 PM
If you've had the carbies off, the symptom you describe, and is most commonly the cause, is not enough free play in the cables. The idle will rise as the bike warms up. Give it a bit more slack and see what happens.

Noel
"Tell a wise man something he doesn't know and he'll thank you, tell a fool something he doesn't know and he'll abuse you"

FcWilson

#3
June 14, 2017, 09:49:27 PM
I'll give it more. It's got about 3/16th of play and I pulled the tank off yo make sure it's closing while it was running. 

Anything is worth a shot at this point.

ribbert

#4
June 14, 2017, 10:17:12 PM
Is the cable routing such that it's not affected when the tank is fitted?
You should be able to hear them "snap" shut when you let go the twist grip.

Noel
"Tell a wise man something he doesn't know and he'll thank you, tell a fool something he doesn't know and he'll abuse you"

FcWilson

#5
June 14, 2017, 10:34:12 PM
Yeah, you can hear a good slap when the tank is on.  I'm done with her tonight, need a break to regroup. I'm gonna check all the  diaphragms even though they are new. And check the valve clearance

Pat Conlon

#6
June 18, 2017, 05:08:50 PM
Setting the idle is the last step. Before that, make sure your valves are adjusted and your carbs are balanced.

A normal idle on a cold engine turning into a high idle on a heat soaked engine, can mean several things.... One of the many things it could be is that your idle mixture screws are set too rich.
When the engine is cold or warming up, the rich idle mixture does not affect the idle, however when the engine is thoroughly warm, the rich mixture can and will affect the idle.

So....try this, turn your idle mixture screws in 1/2 turn, (leaner) see if that does not help the symptom.
If it does, you're going in the right direction, from there, Fine tune in 1/4 turn increments.

Hope this helps.  Pat
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

FJmonkey

#7
June 18, 2017, 05:13:37 PM
Quote from: Pat Conlon on June 18, 2017, 05:08:50 PM
A normal idle on a cold engine turning into a high idle on a heat soaked engine, can mean several things.... One of the many things it could be is that your idle mixture screws are set too rich.
When the engine is cold or warming up, the rich idle mixture does not affect the idle, however when the engine is thoroughly warm, the rich mixture can and will affect the idle.

So....try this, turn your idle mixture screws in (clockwise) 1/2 turn, (leaner) see if that does not help the symptom.
If it does, you're going in the right direction, from there, Fine tune in 1/4 turn increments.

Hope this helps.  Pat

Edit in bold...
The glass is not half full, it was engineered with a 2X safety factor.

'86 Ambulance - Bent frame, cracked case, due for an overhaul
'89 Stormy Blue - Suits my Dark Side

Pat Conlon

#8
June 18, 2017, 05:15:30 PM
Yep, thanks Mark.... :good2:
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

FJ_Hooligan

#9
June 18, 2017, 07:56:39 PM
Or, you've got an air leak somewhere. 

Dump extra fuel into a an intake without adding air and the engine will flood out and probably die.

Add extra air to an intake and the engine RPM will increase (just like when adding throttle).

Have you ever replaced the intake O-rings? 
DavidR.

Pat Conlon

#10
June 18, 2017, 08:48:48 PM
Yep :good2:
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

lazercobra

#11
November 13, 2017, 10:08:29 PM
Found this post and i too am having the same issue. I can add that during the increase  idle (of up to 2000 rpms) , if I so much as click open the choke so slightly, the engime immediately dies. So it cant be a vacuum leak. Im thinking a rich mixture like the previous member mentioned. I'm going nto hijack this post and try the mixture screws and get back to post my results. Thanks

Alf

#12
November 14, 2017, 01:44:24 AM
If you have dismantled the carbs at any point, it could be that 1 needle is out of its position due to that the hard plastic part where fit the needle is out of its position, the little nub out on the little hole, so the needle is not completely vertical and slightly askew

When the throttle is closed, this carb diaphragm is slightly open

It has happened to me

ZOA NOM

#13
November 14, 2017, 09:05:33 AM
Same symptoms here... I'll proceed with mixture screws...
Rick

Current:
2010 Honda VFR1200 DCT (Full Auto!)
1993 FJ/GSXR 1200 (-ABS)
1987 Porsche 911 Carrera (Race)
1988 Porsche Carrera (Street)
Previous:
1993 FJ1200 (FIREBALL)
1993 FJ1200ABS (RIP my collar bone)
1986 FZ750
1984 FJ600
1982 Seca

FJ_Hooligan

#14
November 14, 2017, 04:02:56 PM
Quote from: lazercobra on November 13, 2017, 10:08:29 PM
Found this post and i too am having the same issue. I can add that during the increase  idle (of up to 2000 rpms) , if I so much as click open the choke so slightly, the engime immediately dies. So it cant be a vacuum leak. Im thinking a rich mixture like the previous member mentioned. I'm going nto hijack this post and try the mixture screws and get back to post my results. Thanks

For an engine running at idle, add a small amount of raw fuel into the intake and it will die.  For an engine to rev up, it needs additional air.  Otherwise, we wouldn't need a throttle plate, just something to properly meter fuel to make it accelerate.

When you crack open the choke, initially all you're going to get is a rush of air (which will really lean out the mixture and the engine will die).  It takes some finite amount of time for the vacuum that the choke circuit sees to draw fuel up from the float bowl.  If you have an engine that's up to temperature with the choke off and try to open the choke, it will die.

Have you replaced the intake O-rings?
DavidR.
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