FJ40 Carb issue--rich at idle

[Shes Mad]

I am having a challenging issue with my 70 FJ40. This is a rebuilt carb. It is running rich at idle, and I can't get it adjusted out. When I disconnect the idle solenoid, the engine will die if i do not hit the throttle. The idle mixture screw has no effect.

so it is too rich with the idle circuit open, but must be too lean if it is disconnected.

HELP!--here is the carb

http://www.sor.com/shared/image/042B2.gif

 

[Trollhole]

Post a pic of your carb installed.

What is your timing set at?

Smogged or desmogged.

 

[Pin_Head]

Chances are that you have a manifold vacuum leak and that the idle speed screw has been increased to compensate. Check for vacuum leaks.

 

[Shes Mad]

Here are pics. The timing was set above factory, but I can't recall--but I thing it was 9-10. I also included a pic of the dizzy I got from Marks.

It runs great down the road, but backfires a little bit out the exhaust when you let off and coast in gear. Not really backfire, but noticable puff sounds.

 

[Pin_Head]

Really can't tell anything from just looking at it. Check the manifold vacuum at idle with a gauge and check for manifold leaks.

 

[Shes Mad]

Trollhole asked for pics.

What should the vacuum be at idle--or slightly above, since it won't idle

 

[edwjmcgrath]

When you check for manifold leaks, don't forget checking for a crack in the bottom of the manifold right under the carb from exhaust manifold heat. Impossible to see with the carb on. Check it out with carb cleaner.

 

[Pin_Head]

Trollhole asked for pics.

What should the vacuum be at idle--or slightly above, since it won't idle

I know; I'm just saying that I don't see anything obvious in the pictures that would account for your problem.

Vacuum at idle should be above 18 inches of water.

 

[kurtnkegger]

Wouldn't a vacuum leak lean out the mixture? If it's too rich, I would suspect a bad rebuild, and the primary and secondary jets perhaps were swapped. It's not mentioned when the rebuild was done...so this might not be a valid idea. What about a weak coil? Bad spark not effeciently burning fuel?

 

[Pin_Head]

It really isn't running rich. The idle screw has no effect because the idle speed has been bumped up so that it runs off the transition slot or main jet.

 

[Pighead]

Vacuum at idle should be above 18 inches of water.

18 inches of mercury.

 

[edwjmcgrath]

245 inches of water.

 

[Trollhole]

Hey sorry for not posting sooner. It looks as though you have everything installed correctly. That is always a concern.

As stated above. What's your vac reading?
Does it bounce much?
It sounds like the idle solenoid is working considering the motor dies with it disconnected.


Also I'm not exactly certain but your port for vac advance isn't right. I'm not familiar with that year carb. I thought all vac advance ports were on the cast iron base. Mark or Jim would know this answer.

 

[subzali]

18 inches of mercury.

Except if you're at altitude, which can drop that number down to the 12-13 range (in Denver for instance).

 

[Shes Mad]

Hey sorry for not posting sooner. It looks as though you have everything installed correctly. That is always a concern.

As stated above. What's your vac reading?
Does it bounce much?
It sounds like the idle solenoid is working considering the motor dies with it disconnected.


Also I'm not exactly certain but your port for vac advance isn't right. I'm not familiar with that year carb. I thought all vac advance ports were on the cast iron base. Mark or Jim would know this answer.

I'll get some vac readings tonight if I can get it to idle at all. The only vac port on the cast iron base is on the drivers side, and it is hooked up to the vac module on the choke linkage. You can see it in the third pic under the master cylinder cap

 

[Pin_Head]

Hook the vacuum gauge to the PCV fitting on the spacer below the carb.

 

[Shes Mad]

Hook the vacuum gauge to the PCV fitting on the spacer below the carb.

I hooked the vacuum gauge up to the PCV line as Pin_Head suggested. When I pulled the pcv line, the engine killed. I hooked up the gauge to the line, and started it up. Got the idle down to about 500, and the vacuum gauge read 14-15. Really wasn't bouncing around beyond that range. but it wasn't a solid steady needle either. I adjusted the idle mixture out about 7 turns, then in till the vacuum and idle dropped, then out 1 turn. Ended up at 5 turns out. Vacuum at 14-15. Readjusted the idle to about 700, and the vacuum was at 16. Idled fine. Put the air cleaner back on, and the idle and vacuum stayed he same. Shut it down, and hooked the PCV line back up. Would no longer idle. The Pass side of the carb is quite wet when running, even at 500 RPM.

So I am assuming the PCV has a malfunction, stuck open or something??? This isn't a new engine-its got 90K on it. or 190K.

I will check the timing and advance tomorrow. I believe the factory mark is 7. Should that be what I time it at? What should the advance be, and at what RPM's. Sorry, I dont have a FSM yet.

Thanks for all your help so far

 

[Pin_Head]

It may be a bad pcv, but you may also have a manifold vacuum leak. Check for leaks by spraying carb cleaner around all the possible leak points. What do you mean the passenger side of the carb is wet? with what, gas? That doesn't sound right.

 

[Shes Mad]

It may be a bad pcv, but you may also have a manifold vacuum leak. Check for leaks by spraying carb cleaner around all the possible leak points. What do you mean the passenger side of the carb is wet? with what, gas? That doesn't sound right.

I just meant a lot of gas flowing in the Venturi. I ran out of daylight, so i didn't get to checking for vac leaks

 

[Pin_Head]

If gas is dripping out of the primary nozzle at idle, then there probably is a manifold vacuum problem. This is consistent with the lack of response to turning the idle mixture screw. The key is to find out where the vacuum leak is.