Curious 79 FJ40 Project Runs Very Rough - Ideas?

[CruiserInProgress]

I picked up a 79 FJ40 2F desmogged project (on right in attached pic) a while ago that had been sitting for years. It's very rough and pretty rusty but still has much of the original running gear. So, I'm trying to get it running and driving to verify components before I pull it apart and re-do it. Looking forward to that first drive!

Due to sitting for years and cobbled repairs before that, I have done quite a few things so far, including: compression check (around 130 on all cylinders), rewiring the ignition circuit, reconditioning the stock distributor, replacing its bad pickup, setting timing, replaced plugs, reconditioning the rocker assembly, rebuilding the aftermarket clone carb, adding new fuel, and verifying I have fuel in my bowl.

The clone carb allowed it to start, roughly, backfiring in the exhaust, but would eventually idle, fairly smoothly. However, it bogged when adding any throttle (no load), making impossible to get past idle. It did a bit better without the distributor vacuum line connected and vacuum port plugged, which seemed weird. So I contacted an expert on IH8MUD who thought the distributor wasn't the problem. There doesn't seem to be any vacuum leaks that I could find.

Armed with that datapoint, I picked up a City Racer Fuji carb thinking that's the next obvious possibility.

Unfortunately, the very nice and shiny new carb presents the exact same symptoms.

So, running out of ideas, my next step is to swap out my stock electronic distributor for an aftermarket electronic distributor on the shelf and see if that changes things.

Any other suggestions would be appreciated to help solve this problem.

Thanks!

1979 FJ40 project on right
1969 SBC FJ40 FrankenCruiser on left

 

[Pighead]

What did you set your timing at?

 

[bhsdriller]

second the timing question

Does it run better with the choke on

 

[60 40]

First thought I have is fuel pump or other fuel delivery issues. Sometimes the diaphragm in the fuel pump is on its way out and the vehicle will idle or even drive but when you try and accelerate the pump can't keep up and it bogs down.

 

[mattressking]

Where in Idaho are ya? If you can get the truck to Boise area I can help you sort it out.

 

[Pighead]

First thought I have is fuel pump or other fuel delivery issues. Sometimes the diaphragm in the fuel pump is on its way out and the vehicle will idle or even drive but when you try and accelerate the pump can't keep up and it bogs down.

Easy enough to check. He should have half a porthole window of gas at idle (if not, fix that) if it still bogs down with any throttle, it's not a fuel delivery problem yet.
I have always had fuel delivery problems occur when climbing long hills with the pedal down and the engine sucking gas as quick as it can.

 

[CruiserInProgress]

Thanks for your input.

I set timing on the BB, at idle with the vacuum port plugged. When I could get it to rev, the centrifugal advance seems to work.

About fuel flow, I have fuel mid-way in the carb sight glass at idle, so the pump seems to work. I did have to blow out the lines between the pump and tank to get there.

It only starts with the choke when cold, and backfires in the exhaust, but after running for a minute or two, I open the choke and the engine smooths out.

It doesn't smell of unburned fuel and it doesn't smoke.

I just checked the plugs and they all seem a bit sooty but not oily, except #1 which is clean this time around only. That may be a secondary issue due to putting a the original rotor (slightly longer reach) in an aftermarket cap. I then put the aftermarket rotor back in and cleaned up the terminals. I may have messed it up. Distributor caps are hard to find for the 79 2F so I'll attempt to clean things up more until I can source a new one.

Fyi, even before the new #1 issue, the symptoms above were there. So, I don't think that explains my inability to go past idle.

Oh, and I'm in far Northern Idaho, near Priest Lake, so Boise may be a challenge, but thanks very much for the offer to assist.

 

[Pighead]

Maybe try advancing your timing a bit and see if that helps.

 

[CruiserInProgress]

I'll sort out that spark issue on #1 and try advancing the timing a bit. Fingers crossed. Thanks!

 

[CruiserInProgress]

Progress made, questions remain -

Thanks Pighead, for your suggestion to advance the timing. It helped!

I repaired (carbon trace) and cleaned up the oem distributor to get all cylinders firing again. And went back to my factory static timing mark, advancing the distributor about 10 degrees from my dynamic timing setting.

The result: Although still pretty rough, it started with choke without backfiring, and after it warmed up a bit, it is now able to take the throttle and rev. The plugs aren't sooty after running for a few minutes.

However, two questions still have me puzzled -

(1) When connecting my OEM distributor vacuum line, none of the above is possible. When I add the ported vacuum line from my City Racer Fuji carb to my oem distributor's large diaphragm, it runs very rough with some backfiring. It's almost as if the vacuum line is retarding the timing?

(2) Also, why is there such a large delta (around 10 degrees) between static and dynamic timing settings?

It would seem those two odd symptoms would point to something wrong with the distributor. It was frozen (centrifugal and vacuum advance) when I acquired it, but it was working very smoothly, with both advance types functional after I finished cleaning it up. Fyi, I use the larger diaphragm for my ported vacuum.

I may not get to it today, but my next step is to swap out the oem electronic distributor for a cheap aftermarket electronic distributor that I have on the shelf. We'll see if that improves things. Sound reasonable?

 

[Pighead]

Progress made, questions remain -

Thanks Pighead, for your suggestion to advance the timing. It helped!

I repaired (carbon trace) and cleaned up the oem distributor to get all cylinders firing again. And went back to my factory static timing mark, advancing the distributor about 10 degrees from my dynamic timing setting.

The result: Although still pretty rough, it started with choke without backfiring, and after it warmed up a bit, it is now able to take the throttle and rev. The plugs aren't sooty after running for a few minutes.

However, two questions still have me puzzled -

(1) When connecting my OEM distributor vacuum line, none of the above is possible. When I add the ported vacuum line from my City Racer Fuji carb to my oem distributor's large diaphragm, it runs very rough with some backfiring. It's almost as if the vacuum line is retarding the timing?

(2) Also, why is there such a large delta (around 10 degrees) between static and dynamic timing settings?

It would seem those two odd symptoms would point to something wrong with the distributor. It was frozen (centrifugal and vacuum advance) when I acquired it, but it was working very smoothly, with both advance types functional after I finished cleaning it up. Fyi, I use the larger diaphragm for my ported vacuum.

I may not get to it today, but my next step is to swap out the oem electronic distributor for a cheap aftermarket electronic distributor that I have on the shelf. We'll see if that improves things. Sound reasonable?

View attachment 3689674

(1) I do not understand that at all. Are you getting ported vacuum from the same spot I am? (base of carb, valve cover side, next to the mixture screw) that port makes no vacuum at idle for me.
(2) By "static" you mean with the engine off? Dunno why. I understand very little of timing theory, just figuring out what works. Try giving your rig a little more advance. Give it all it'll take.
I would rather fix a Toyota dizzy than put in a cheap aftermarket, I don't trust an aftermarket to turn the oil pump forever.

 

[CruiserInProgress]

(1) I do not understand that at all. Are you getting ported vacuum from the same spot I am? (base of carb, valve cover side, next to the mixture screw) that port makes no vacuum at idle for me.
(2) By "static" you mean with the engine off? Dunno why. I understand very little of timing theory, just figuring out what works. Try giving your rig a little more advance. Give it all it'll take.
I would rather fix a Toyota dizzy than put in a cheap aftermarket, I don't trust an aftermarket to turn the oil pump forever.

View attachment 3689869

Yes, I use ported vacuum at that location on my Fuji carb.

Yes, when I say static timing I mean basic timing with engine off with #1 at TDC, lining up flywheel timing mark with rotor and pickup.

I need to check vacuum at that carb port at idle to see what it reads. All I know is when I use that port the timing must change making the engine backfire and run even more rough. Strange, as you would think, if anything, using that port would advance the timing as you suggest.

I'm still confused why static timing (engine off) is that far off (10 degrees) my dynamic timing (using inductive timing light with engine at idle and carb port plugged).

Maybe my very old Sears timing light is wonky somehow. I received it as a gift many years ago and had not used it until this project. Seems to work fine.

Or, maybe I'm wonky somehow. This "fun" project has thrown me a few more challenges than I was expecting. Harder to diagnose when multiple things are wrong. But, progress is being made.

About the distributor swap, I agree completely, and would prefer OEM, either refurbish this one or pick up a FJ60 distributor and dimpled push rod cover if I can find one. The aftermarket swap was intended just for diagnostic purposes.

 

[fjwagon]

Usually when I see the engine backfire I usually suspect a timing issue, disti set incorrectly, a bad spark plug, a bad spark plug wire or wrong location, ( make sure they are seated correctly), run the engine in the dark and see if there is any arcing. Something that is not so obvious is having fuel in the crankcase. I have seen this issue a couple of times. Replace the oil and the backfire disappears. The idle issue may be an entirely different issue. Mark sure the EGR circuit is not leaking. If it still has an EGR, mark sure it's not stuck in the open position. The other most obvious thing to check if have not already checked is intake/ manifold leaks. Compounding problems can be confusing, using a oem maintenance manual has me help immensely when into these type of problems. You will eventually figure it....just keep working.

 

[CruiserInProgress]

Usually when I see the engine backfire I usually suspect a timing issue, disti set incorrectly, a bad spark plug, a bad spark plug wire or wrong location, ( make sure they are seated correctly), run the engine in the dark and see if there is any arcing. Something that is not so obvious is having fuel in the crankcase. I have seen this issue a couple of times. Replace the oil and the backfire disappears. The idle issue may be an entirely different issue. Mark sure the EGR circuit is not leaking. If it still has an EGR, mark sure it's not stuck in the open position. The other most obvious thing to check if have not already checked is intake/ manifold leaks. Compounding problems can be confusing, using a oem maintenance manual has me help immensely when into these type of problems. You will eventually figure it....just keep working.

Thanks for the check list. Most of those items I have tried to cover, with a couple of exceptions; No EGR because desmogged by PO, and I haven't tried the spark after dark test. I like the idea though. I'm chipping away!

 

[fjc-man]

You said desmogged? Does it still have the OEM catalytic converter in place?

 

[CruiserInProgress]

No, nothing from the original emissions system except the wiring harness remnants. No remaining emmissions vacuum lines or sensors. Aftermarket headers, stock electronic distributor with secondary vacuum port capped, non-us carb with only one vacuum port that should support that desmogged 2F engine. Should be simple, right?

 

[mrboatman]

No, nothing from the original emissions system except the wiring harness remnants. No remaining emmissions vacuum lines or sensors. Aftermarket headers, stock electronic distributor with secondary vacuum port capped, non-us carb with only one vacuum port that should support that desmogged 2F engine. Should be simple, right?

Does your vacuum advance module on the distributor hold vacuum?

 

[DeskJock]

I’d use the timing light and plug and unplug the vacuum to the distributor and see if 1 does nothing, 2 causes advance (it should) or 3 causes timing to retard.

 

[CruiserInProgress]

The vacuum diaphragm seems intact. When I suck on the vacuum hose attached to the large, inboard diaphragm it holds vacuum and moves the advance plate in the distributor. I'll have to rebook at that to see if it's moving in the advance direction.

In terms of symptoms, as mentioned previously, without the vacuum hose attached to to the carb port it is now able to rev without backfiring. With it attached it runs much more roughly, won't rev and backfires. I'll have to do more investigating to determine which direction the timing is moving with vacuum applied (advance or retard).

I'll report back. Thanks for the suggestions.

 

[CruiserInProgress]

The vacuum diaphragm seems intact. When I suck on the vacuum hose attached to the large, inboard diaphragm it holds vacuum and moves the advance plate in the distributor. I'll have to rebook at that to see if it's moving in the advance direction.

In terms of symptoms, as mentioned previously, without the vacuum hose attached to to the carb port it is now able to rev without backfiring. With it attached it runs much more roughly, won't rev and backfires. I'll have to do more investigating to determine which direction to the timing is moving with ivacuum applied (advance or retard)

The vacuum diaphragm seems intact. When I suck on the vacuum hose attached to the large, inboard diaphragm it holds vacuum and moves the advance plate in the distributor. I'll have to rebook at that to see if it's moving in the advance direction.

In terms of symptoms, as mentioned previously, without the vacuum hose attached to to the carb port it is now able to rev without backfiring. With it attached it runs much more roughly, won't rev and backfires. I'll have to do more investigating to determine which direction the timing is moving with vacuum applied (advance or retard).

I'll report back. Thanks for the suggestions.

Quick update -

The vacuum advance does advance when vacuum is applied (around 5 degrees full deflection), and the diaphragm holds vacuum. The centrifugal advance also seems to advance as it should (around 10 degrees full deflection).

I'll put the timing light on it again and see where that takes me.