TIming Advance - How much is too much? (1 Viewer)

[dtm]

I have a late (December) 1978 FJ40, I've had it since May. PO had desmogged and installed a Weber 38 carb with an electric choke and no cut-off solenoid. It always started and ran reliably - but it also ran rich. The manifold would get extremely hot and there was a smell of gas when it got hot. It dieseled when shutting down.

Some additional pertinent info:

* Stock US 1978 distributor, vacuum advance is working.
* Measured vacuum steady at 15
* Poor compression numbers (low teens, more than 10% variance between cylinders)

The weber install was pretty sketchy- adapters fashioned from PVC pipe etc, but I tried to make it work. I adjusted the timing with the bb right on the needle (it was retarded a few degrees to start) and tuned the carb as best I could. Made little difference. It did idle better, but all the other issues remained.

My plan is to get one of the Japanese carbs from CityRacer, but while I'm waiting I ordered a cheap carb from Amazon and an adapter from CityRacer to plumb it to the original air filter. I bolted it on, re-adjusted the timing, and adjusted the carb. The initial result was not good: no power, super hot manifold (600 degrees after some city driving), vacuum down to 14 steady. It stuttered when it came off idle: I had to be careful to accelerate slow and smooth to keep it from dying. It did fix the dieseling at least.

After scratching my head a while I decided I would adjust the timing by ear and vacuum instead of by the mark on the flywheel. I just kept cranking it CCW, and eventually was stopped by the diaphragm hitting the oil filter. It must be 20 degrees advanced at this point but the truck seems happy. Acceleration is responsive, the manifold is cooler, and idle is maybe a bit less smooth. The gas smell is diminished - I still smell exhaust but that is a different issue.

Questions:

How much advance is too much?
My 14yo son, who has been helping with all of this, suggested that maybe the distributor is off by a click. That seems plausible if a click is something like ~7 degrees - how would I know if this were the case?

Thanks

 

[Green Bean]

I think you have a smart son. With the cap off of the distributor, and the engine set at TDC, where is your rotor pointing? Someone posted this illustration the other day which I believe is from the FSM.

 

[Pighead]

Advance your timing to the point where you can make it "ping" on an uphill climb, then back it off a bit. Or, advance to your best vacuum, then back itoff a bit. Or both.
You can "clock" you dizzy body to anywhere you like to avoid interfering with oil filters, you have to pull the dizzy, rotate the shaft to the next gear over and re-seat the dizzy (important) then move your plug wires the same way so that your #1 plugwire is near the rotor at TDC.
I'm at 15 BTDC right now but still working on it.

 

[dtm]

I think you have a smart son. With the cap off of the distributor, and the engine set at TDC, where is your rotor pointing? Someone posted this illustration the other day which I believe is from the FSM.

View attachment 3117393

Thanks for this, I think I'd come across it and forgotten about it already! We are learning as we go and taking in a lot of information. We'll check the position this afternoon and go from there.

 

[Skreddy]

Are you adjusting the timing with the vacuum advance disconnected and plugged off?

 

[dtm]

Are you adjusting the timing with the vacuum advance disconnected and plugged off?

I am not. I was doing that at first, but I didn't notice any advance at idle - only when revving the engine up - so I stopped. Sounds like that is bad form, I'll go back to plugging it while I'm tinkering today.

 

[Green Bean]

 

[Skreddy]

I am not. I was doing that at first, but I didn't notice any advance at idle - only when revving the engine up - so I stopped. Sounds like that is bad form, I'll go back to plugging it while I'm tinkering today.

Yes disconnect and plug the vacuum advance. Set the timing so the silver bib is right at the pointer or even counter clockwise of the pointer to the edge of the viewing window.

 

[dtm]

Thanks Skreddy & Green Been. I Checked the distributor this morning and the rotor is pointing in the right direction at TDC. Checked timing with the advance line plugged. With the BB on the needle, it sputters badly when transitioning from idle, and has no power at low RPM. Advanced it to the edge of the window (CCW) it does slightly better, but still struggles when coming off idle. Advanced it another ~7 degrees -best guess I don't have a programmable timing gun. At this point, it starts to drive well enough. I had it advanced a bit more yesterday, it felt like it drove better at speed but had a rough idle, so I'm just going to leave it at ~14 for now and see how it goes.

 

[Pighead]

Whenever I'm adjusting timing I'm also adjusting carb idle speed and idle air...

 

[dtm]

Whenever I'm adjusting timing I'm also adjusting carb idle speed and idle air...

Yes, we are doing this as we go too. Advance a bit, idle increases, go adjust the idle/mix on the carb again. I haven't done this for many many years and back then it was a chevy luv so 0 experience with this car - learning as we go along.

 

[Green Bean]

For what it is worth; ours is similar. It is a 1970 with factory carb and vacuum advance distributor. When I set the timing on the BB, the idle falls off by about 100 rpm. I can adjust the idle up but then on a drive it sputters on acceleration. Rotating the distributor counterclockwise makes a huge difference My timing light has a tach so I can find a sweet spot, but the BB is not in the window. I can get a steady idle and decent vacuum so the motor seems happy.

 

[dtm]

Came back to this over the weekend with fresh eyes. Son and I practiced adjusting the valves on the spare 2F, then gave it a go on the real one. There were three valves out of spec, but just barely. We reset those, checked, checked and re-checked our work before putting the cover back on. Checked the plugs. We then re-set the timing to 7 degrees on the nose, and re-adjusted the carb. It is running about the same, maybe slightly better but I'm happy the timing is now in spec. It is still sluggish and struggles on the local hills but I think we have it about as good as we can given our lousy compression numbers.

 

[Green Bean]

So, the way it was recently explained to me by a very experienced Land Cruiser guru, the 7 degrees BTDC was the factory spec when the engine was fresh. Since our engine is 50+ years old, its internal organs have worn considerably. The cam lobes are not what they should be, etc. When I set our timing on the BB, it ran like crap. So, I also used ear, idle and vacuum to get it purring. The BB was nowhere to be seen using the timing light. But using the advance function on the timing light, I determined that the advance was set at 35 degrees. The engine seemed happy with good vacuum and idle. But 35 degrees seemed excessive so I backed it to 21. The idle dropped a bit, but not too bad, so I'm going to give it a try.

 

[dtm]

Man I need a better timing light.

 

[Green Bean]

This timing light is way smarter than I am. But it is nice to use the advance function in order to see where you are at. Plus the TDC line on the flywheel becomes relevant again. I'm sure there are better ones but here is the one I got:
Amazon product ASIN B000EVU8J8

 

[Pighead]

So, the way it was recently explained to me by a very experienced Land Cruiser guru, the 7 degrees BTDC was the factory spec when the engine was fresh. Since our engine is 50+ years old, its internal organs have worn considerably. The cam lobes are not what they should be, etc. When I set our timing on the BB, it ran like crap. So, I also used ear, idle and vacuum to get it purring. The BB was nowhere to be seen using the timing light. But using the advance function on the timing light, I determined that the advance was set at 35 degrees. The engine seemed happy with good vacuum and idle. But 35 degrees seemed excessive so I backed it to 21. The idle dropped a bit, but not too bad, so I'm going to give it a try.

View attachment 3124509

View attachment 3124510

For years, I had only a dumb timing light. I timed by ear, vacuum and seat of pants. It ran fine (my engine is only 18 years old). A year ago i got a smart timing light, found out that i had been running at about 35 BTDC. Seemed excessive to me. Also found that the advance diaphragm on my 60 series dizzy was shot. Figured i had been running on the mechanical advance only. Got a new single diaphragm advance module, put it on and cleaned up the insides of the dizzy. Been fiddling with it ever since, haven't been able to get it just right. Thinking of disconnecting the vacuum and trying just the mechanical advance again.