3F Carb intermittent high idle (1 Viewer)

[Cruisunder]

Hi guys, did some searching on the forum but it seems almost every problem is unique. The carb on my 1989 FJ62 3F engine (330k) has a high idle problem, but not always. It usually idles at 700-800rpm when just started, but after driving for a while and getting the rpms up, it wants to idle around 1500 rpm. Aircon on/off doesn't seem to have an influence. It didn't do this at all when i bought the truck about 2 years ago. it seems to be getting worse. Could use some help here - where do i start troubleshooting? I'm not a mechanic, but happy to learn.

 

[LAMBCRUSHER]

you have a vacuum line or sink unconnected/misconnected. start at the BVSVs at the thermostat and chase the vac lines out from there. make sure they are hooked up right and not all old and cracked. sounds like your leak is in a line downstream of one of the Bimetal Vacuum Switching Valves(BVSV) mounted to the tstat- engine gets warm and open vacuum passage in these switches, allowing vacuum to pull from things that are needed once an engine warms up...there should be a plate in the engine compartment that outlines the vacuum routing...HTH

 

[Landpimp]

I had the AC idle up switching valve(vsv) go bad, so that it had vacuum always pulling(or maybe other way around) on the AC diaphragm, making the idle go up. But it was not random, it went up and stayed up

 

[Output Shaft]

Does it have a manual choke? Do you use it at start up?

 

[Michael Hanson]

I have a 1987 fj60 that does the same thing. I usually can stop it with 2 cans of carb cleaner . Mike

 

[Cruisunder]

Thanks guys.
Lambcrusher, i'll go have a look at the lines this weekend.
Output Shaft, yes it has a manual choke, when it's cold (it does happen in sunny QLD), or when it hasn't been started for a while, i might use the choke a bit.

 

[Output Shaft]

I ask about the choke because the choke also is a throttle positioner.

On a cool engine (doesn't have to be frigid) when the carb idle speeds (fast and slow) are set correctly and the choke is pulled out all the way on a cold engine, and the engine is started, the idle will be at about 1000 rpm or so at first start then slowly rise as the oil circulates and the engine warns up. Eventually, the idle speed will rise to about 1800 rpm if the choke isn't pushed in.

If a cold engine is started without the choke, if it starts at all, the initial idle will be way low. Much lower than 700-800 RPM.

If you're starting the engine in the morning without the choke and the engine is idling at 700-800 rpm after the starter is disengaged.... The idle speed is set too high.

 

[Cruisunder]

you have a vacuum line or sink unconnected/misconnected. start at the BVSVs at the thermostat and chase the vac lines out from there. make sure they are hooked up right and not all old and cracked. sounds like your leak is in a line downstream of one of the Bimetal Vacuum Switching Valves(BVSV) mounted to the tstat- engine gets warm and open vacuum passage in these switches, allowing vacuum to pull from things that are needed once an engine warms up...there should be a plate in the engine compartment that outlines the vacuum routing...HTH

Ran some tests this weekend. Vaccuum tested all lines using LPG but could not detect any change in idle speed. Today it also seemed pretty steady, purring around 600 rpms. Then thought i'd try to do a smoke test. Blocked the carb air inlet with a household cleaning glove (so i could see the system being pressurised), and blew in air with smoke (can still taste the incense!) through what the manual calls the vent pipe, which sits above the secondary diapraghm (also visible in the photo). Then i saw some fuel weeping out through both valve spindles, which may be normal cause normally the system operates under vacuum so never leaks fuel, just sucks in a bit of extra air. Is this normal though? If it is, then i still haven't found anything. I'm reluctant to change the fuel mixtrue and idle speed screws as this doesn't address a root cause. Any comments or ideas?

 

[LAMBCRUSHER]

how hot was the engine during this test? If the engine wasn't hot enough for the BVSVs to open, then you may need to rerun the test...yes, the carb shafts are known to leak a bit of air...

 

[LAMBCRUSHER]

my theory revolves around the BVSV opening and allowing vacuum to be pulled thru a leak AFTER the engine is good and hot...of course, I could be wrong, but that could explain why it only does so after driving for a while...I should ask, when the idle goes high, does it ever settle back down before the rig has cooled all the way off?

 

[Cruisunder]

my theory revolves around the BVSV opening and allowing vacuum to be pulled thru a leak AFTER the engine is good and hot...of course, I could be wrong, but that could explain why it only does so after driving for a while...I should ask, when the idle goes high, does it ever settle back down before the rig has cooled all the way off?

Thanks Lambcrsuher. It idled for 15 mins at a time, then some short runs after that. It was hot alright. I don't think she has "resolved" the high idle before cooling down. Looked at the thermostat but can't see a valve. Where is it and what does it look like? Is it further away from the thermostat?

 

[Cruisunder]

I also saw the post by Dxfr Carb/ accelerator linkage mystery which points to linkages being influenced by temperature. There doesn't seem to be a lot of info on the correct setup of the linkages? Your thoughts?

 

[Output Shaft]

I believe that carb issue was a sticky pump plunger pivot and maybe a slightly short accelerator linkage. Something easy to check.

 

[Cruisunder]

I believe that carb issue was a sticky pump plunger pivot and maybe a slightly short accelerator linkage. Something easy to check.

View attachment 1179130

So many things to check ...
You won't believe what I just discovered when i opened the carby and peeked inside with a flash light. On both the primary and secondary throttles there appears to be some dirt - about 6 or 7 1mm grains in one, and something more thready in the other! I checked and cleaned the air filter yesterday. How did that get there? Must have been sitting there for a while? Made a mini vacuum cleaner to get it out this afternoon. The more you look, the more you find ...

 

[Cruisunder]

Resolved! Sucked out the grains of dirt from one throat, and a spider corpse (!) from the other. Can't believe they haven't fallen through. When i checked out the complete air pipe between the filter and the carb, a bit more dirt dislodged from the corrugated rubber sleeves. Probably someone allowed dirt to get in a long time ago. Took it for a spin, cold iidles around 500 rpm, hot just under 700 rpm. Beautiful!
Anorher mystery solved and recorded for future. Thanks guys.

 

[Cruisunder]

Hi all, I'm updating this thread with a couple more observations. First off, the issue wasn't resolved as I thought when I wrote the previous post in 2015. Phew doesn't time fly! Some 20,000 kms later the cruiser still runs strong. The carby idles fine I'd say 90% of the time, but it keeps idling high occasionally. Still haven't found a physical defect, or been able to identify a condition (hot/cold, dry/humid weather, petrol quality) that seems to be of particular influence.
A new observation is that quite often, I'm able to stop the high idle by depressing the gas pedal for a second: say it is idling at 1200 rpm, when i hit the gas and increase the revs to 1500 rpm for a second and then let go of the gas, it goes back to a more normal idle speed of 700 rpm. Occasionally it idles faster say 1500-2000 rpm and it becomes harder to use this "trick". Funny thing is when i then stop the engine and immediately start it again, it may have a perfect 600- 700 rpm idle speed!
Maybe it is all just wear & tear causing things to go off without a real pattern or explanation, but short from rebuilding or rightout replacing the carburetor does anyone have a clue what these new observations might be telling me?

 

[Thamunkii]

Hi, my mate was having similar idle issues. Linkages worn on the carby and sticking a little. Half a can of WD 40 on the outside over a week helped a little bit. New carbys are cheap enough though so that got done and solved the issue completely.
If you get it idling high and then put a little bit of pressure on the accelerator linkage under the vacuum lines the revs should drop off to normal with minimal movement. Then you know they are worn.

 

[Cruisunder]

Reviving this thread, again. Late 2018 I had found the solution for the high idle, posted here:

Have had a similar high idle issue since three years. Read threads, tried many things. Recently bit the bullet and took the Aisan carb (Aussie 3F petrol model) out and apart for a clean and rebuild. Had the reassurance thta the carb was ok but the high idle issue was still. The last test i did was to try a different throttle return spring and oh boy wjat a difference that made!!! Drives like a different car, the revs actually drop down to around 700rpm every time i change gear - i have to learn to drive it again!
I may have cracked this nut, and hope someone else may too after reading this. Here is some pics of the original spring and the heavier one i replaced it with:

OEM primary throttle return spring

• Cruisunder
• Dec 30, 2018

C-83 replacement spring

• Cruisunder
• Dec 30, 2018

C-83 spring details

• Cruisunder
• Dec 30, 2018

Happy New Year!

Now the issue has come back and is testing my sanity.

What has changed/happened since 2018:
- 3.5 years passed by so more wear & tear
- recent work: new spark plugs, leads tested ok, new dizzy breaker points, rotor and cap, timing reset to specs, valve clearances checked & adjusted

Investigated since return oer issue:
- replaced the spring that solved the issue for the last 3.5 years, with no result
- discover fuel acc pump boot has cracked ( aftermarket, only lasted 3.5 years), replaced with old but not cracked oem
- linkages checked an wd40 applied
- vacuum lines checked including VSV
- a/c and idle kick up working fine
- re-set fuel mix screw, idle and high idle screws
- checked play in prim and sec throttle shafts, no excessive play, doesn’t seem to stick
- reduced some slack in choke cable
- no play in throttle cable or pedal

The odd thing (for me) is the problem has come back for no apparent reason. Rather suddenly. After 3.5 years. I may drive to work for an hour, no problem. If the idle goes up, it generally increases gradually and by the time i get home in the afternoon it may have crept up to 1,500 rpms. A push on the pedal generally restores idle speed to 600-700. Drive and it’s up again.

Love applying logic to work through issues on the cruiser, but can’t get my head around this one. Is it wear & year after all, defying logic? Or is there something left to be tested?

Help! Is @FJ40Jim in the room?

 

[g-man]

You may get the award for sticking with trying to problem solve an issue for the longest time!

Sounds like it gets worse.. more sticking throttle as it gets hot. Weird, seems like things would loosen as it warms up.

At first I was thinking throttle linkage and return springs....but they don't get weaker when they get hot.

Just a wild guess but the secondary throttle operates on vacuum and the diaphragm returns that throttle valve back once vacuum is removed. so what if the diaphragm was weak or the gasket/o-ring between the carb body and the diaphragm were leaking? Then maybe the secondary plate doesn't return all the way?

 

[Cruisunder]

You may get the award for sticking with trying to problem solve an issue for the longest time!

Sounds like it gets worse.. more sticking throttle as it gets hot. Weird, seems like things would loosen as it warms up.

At first I was thinking throttle linkage and return springs....but they don't get weaker when they get hot.

Just a wild guess but the secondary throttle operates on vacuum and the diaphragm returns that throttle valve back once vacuum is removed. so what if the diaphragm was weak or the gasket/o-ring between the carb body and the diaphragm were leaking? Then maybe the secondary plate doesn't return all the way?

Hahaha, thank you, not a very good problem solver then!

Yes, it doesn't seem to happen straight after startup with the engine cold.

It does happen way before WOT though, so the secondary throttle wouldn't be open.

Some of the linkages are pretty loose where they attach with the little C-clip, is that normal or okay? I think the one attaching to the choke breaker is the loosest. Can't see how that relates to the issue though.