Off idle stumble...

[Ketzer]

My 79 FJ40 is new to me and my first FJ. I'm trying to troubleshoot an issue its had since I got it home...

In normal driving, when pulling off from a stop or during gear changes when the rpms drop, my FJ has a noticeable stumble. It is also hard starting even when warm, taking a dozen or more revolutions and some pedaling of the accelerator.

I've done some basic diagnostics. Timing is on the BB. No vacuum leaks. Fuel filter is new. Cap, rotor, wires, plugs, all look recent. (I did have to replace the cap, someone installed it heavy handed and it was cracked at all three bolts)

The only obvious issue I've found is the vacuum advance is not working. Tried pulling vacuum right at the distributor and it will not hold any vacuum. I assume the diaphragm is ruptured. Mine has the double port on the advance for retard also.

1- I wouldn't think the lack of advance would cause the stumble? Doesn't the advance come into play more on acceleration and load?

2- I will have to do something about the ruptured advance and it appears the only solution out there right now is to replace the whole dizzy. What is the best option on distributors?

Jeff-

 

[thebigredrocker]

On the hard starting: is your idle fuel solenoid clicking thus opening to allow fuel through the idle fuel circuit?

Here's a stumble thread: Vacuum Steady at 11.5 , idles/starts fine, stumble off idle

 

[Cruiser Corps]

79 would be dual advance, IIRC. 2nd stage being for high altitude. The stumbling and hard starting could be symptoms of a bad accelerator pump. It should squirt a healthy stream any time you press and release the accelerator. You'll also want to ensure the vacuum advance is functioning properly.

 

[Ketzer]

On the hard starting: is your idle fuel solenoid clicking thus opening to allow fuel through the idle fuel circuit?

Here's a stumble thread: Vacuum Steady at 11.5 , idles/starts fine, stumble off idle

Solenoid is definitely clicking when key is turned on. Has good vacuum 16-18. Has smooth steady idle.

79 would be dual advance, IIRC. 2nd stage being for high altitude. The stumbling and hard starting could be symptoms of a bad accelerator pump. It should squirt a healthy stream any time you press and release the accelerator. You'll also want to ensure the vacuum advance is functioning properly.

It is giving a strong healthy squirt through the whole range. I did not check it cold, but the stumble is present hot or cold.
My vacuum advance is not working at all.

I was hoping someone would have recommendations on a distributor replacement or someone who could rehab mine since parts are obsolete. A couple folks suggested I contact Mark's Offroad and I did but have not received a call back yet.

Jeff-

 

[Toyoland66]

The large cap distributor from a FJ60 will fit if you also get the dented side cover from the same engine (pushrod cover).

This may be easier to find than a small cap dist.

 

[Toyoland66]

Also @FJ40Jim should be able to help you with a rebuild, and he is closer to you than Mark's.

 

[Ketzer]

Also @FJ40Jim should be able to help you with a rebuild, and he is closer to you than Mark's.

It doesn't have to be period correct, in fact I'm more than willing to step up to something different/brand new if it performs as well and is readily available. Mine has an electronic module in the dizzy already (no points) which I'm assuming is aftermarket?

I'll give Jim a call tomorrow and see what he says.

More diagnostics tonight...
I was able to find a couple vac lines that were suspect and an air hose to the top of the carb body that was deteriorated. Swapping those did not net any improvements. Also, mine idles a bit high, 900-950. The idle adjustment screw is all the way out and not touching. This is confusing because I don't find any vacuum leaks, and it holds steady vacuum... and the timing is on the BB.

Jeff-

 

[Toyoland66]

If you have any pics I may be able to help with hose routing.

This may be helpful.

The Definitive 79-80 Desmog Guide

Not suggesting you should desmog but this does help explain how some of these systems work and how they are routed.

 

[Ketzer]

If you have any pics I may be able to help with hose routing.

This may be helpful.

The Definitive 79-80 Desmog Guide

Not suggesting you should desmog but this does help explain how some of these systems work and how they are routed.

Wow. I hope that is not in my immediate future. Even with your guide, that doesn't look fun. I will definitely keep the link, it helps me identify and understand the bazzilion hoses and ports.

I sorted out my fast idle (helps if you turn the correct screw) and re-adjusted the timing a little. Still have hard starting and stumble on accel.

 

[Pin_Head]

Off idle stumble is usually due to a lack of idle fuel, either because the idle fuel circuit is plugged or obstructed or because of a vacuum leak. It is hard to distinguish these two causes, but if you adjust the idle fuel mix and speed so that it barely idles and then disconnect the idle cut off solenoid, if it dies you know that it is getting some idle fuel. you can test for manifold gasket least using carb cleaner spray or propane gas around the sealing surfaces.

 

[Ketzer]

Off idle stumble is usually due to a lack of idle fuel, either because the idle fuel circuit is plugged or obstructed or because of a vacuum leak. It is hard to distinguish these two causes, but if you adjust the idle fuel mix and speed so that it barely idles and then disconnect the idle cut off solenoid, if it dies you know that it is getting some idle fuel. you can test for manifold gasket least using carb cleaner spray or propane gas around the sealing surfaces.

I did try the idle fuel circuit test. It dies if you unplug the idle circuit.
When I check the vacuum with a gauge, it shows 16-17 steady. I have looked, searched, sprayed several cans of carb spray everywhere that I can looking for a leak. If it is there, it eludes me still. I had a friend come by today to lend his .02, he thought it idles like it has a vacuum leak or possibly a sticky valve.

Had a good conversation with @FJ40Jim today, lots of newb questions answered along with some sound advice. I know for certain my vac advance is toast and my carb needs going through, best to start with those and see where it gets me. I will be removing my carb to send in to Jim for a freshen up.

Jeff-

 

[Nottajeep]

Off idle stumble is usually due to a lack of idle fuel, either because the idle fuel circuit is plugged or obstructed or because of a vacuum leak. It is hard to distinguish these two causes, but if you adjust the idle fuel mix and speed so that it barely idles and then disconnect the idle cut off solenoid, if it dies you know that it is getting some idle fuel. you can test for manifold gasket least using carb cleaner spray or propane gas around the sealing surfaces.

Please elaborate on the underlined. I have an idle noise when the engine is at hot idle and wonder if my manifold gasket is leaking. I realize now there is a bolt pattern order I did not follow correctly. Before tearing back into it, would like to use this test.

 

[Pin_Head]

As the post above your says, you spray carb cleaner around all the manifold gasket sealing surfaces and see if the idle speeds up. It is not so easy to spray the underside of the manifold, so maybe a little propane gas and a hose is easier to get in to the bottom.