78 FJ40 idles too fast

[BDPC]

Hello. I am new to this forum, so thanks in advance.

My 17 year old son scored a rough FJ40 for $500. It runs and stops, and is complete, though rusty. The guy who sold it told us the Holley 2 barrel carb that was on it was dumping gas (his words - not sure what that means) and so we bought a new, aftermarket carb. When we put it on, the engine revs up really fast and it backfires out the tail pipe. It wont slow down to a normal idle speed unless I push on the linkage, and as soon as I let go, it revs way up again. We set the timing to be on the button at a low idle - not sure if its 650 rpm, but its close. I confirmed the position of the rotor button, etc. Afterwards, we dismantled the rotor to find the governor weights thing was dirty and sticking. That was cleaned and rotates freely within its range now.

Other relevant data - the car evidently, being a 1978 model, once had a bunch of emissions stuff on it. All that stuff is gone. Also, new rotor button, distributor cap, wires, coil.

So that is my story. Can anyone offer tips we can try to make the engine idle? Thanks -BDPC

 

[78fj40mg]

Check the ignition timing if it's too advanced it will keep the engine from idling normally. Also check the choke settings and fast idle rpm and stuck linkage.

 

[BDPC]

Mike,

Thanks for your reply. When you say check the ignition timing, I think we have done that. Is there more to it than setting the BB on the needle with a timing light on cylinder 1? We also set the gap on the 6 pointed signal rotor thing that triggers the ignition. This is not a model with points, as you may know.

One other relevant piece of data, maybe: When it idles without the air cleaner on top, I can mostly cover the carb air intake with my hand. When I do, the engine will rev up with more vacuum, presumably.

Regarding stuck linkage, I am not sure which linkage you mean - all the linkages on the side of the carb move against their springs with finger pressure. Is there another linkage you mean?

And as for choke settings, I guess you mean the set screws on the side of the carb? None of those even comes into play - the carb linkages never touch them. When I push the linkages to the set screw stops, the engine revs WAY too high or it stalls.

I appreciate your suggestions.

 

[handcannon]

My first thought when I read the title was that you may have a vacuum leak. Do you have a vacuum gauge available? A vacuum leak can make it difficult to get the motor to idle. Use WD40, or something like that, and while the motor is running spray around the base of the carb, around the intake where it joins the head, etc. As the spray goes across any vacuum leak the idle speed will lower.

It is also entirely possible that you have more than one problem to correct.

Don

 

[78fj40mg]

Mike,

Thanks for your reply. When you say check the ignition timing, I think we have done that. Is there more to it than setting the BB on the needle with a timing light on cylinder 1? We also set the gap on the 6 pointed signal rotor thing that triggers the ignition. This is not a model with points, as you may know.

One other relevant piece of data, maybe: When it idles without the air cleaner on top, I can mostly cover the carb air intake with my hand. When I do, the engine will rev up with more vacuum, presumably.

Regarding stuck linkage, I am not sure which linkage you mean - all the linkages on the side of the carb move against their springs with finger pressure. Is there another linkage you mean?

And as for choke settings, I guess you mean the set screws on the side of the carb? None of those even comes into play - the carb linkages never touch them. When I push the linkages to the set screw stops, the engine revs WAY too high or it stalls.

I appreciate your suggestions.

Set the ignition timing at 7* BTDC so the engine is running according to specs as per the FSM. Then set the idle speed to the desired RPM, then adjust mixture screw so RPM and vac peaks. If RPM has gone up, readjust RPM and then fine tune mixture, repeat steps as needed. Back firing is directly related to improper timing and carb tuning.

You might want to also check the accelerator pedal linkage to see if its sticking and lubricate all joints also clean and lub all linkage joints on the carb.

As far as vacuum leaks typically when there's a vacuum leak the engine will not idle properly, however, in your case check all vacuum hoses for cracks, also check the PCV and make sure it is connected to the proper port on the intake manifold and not the carb.

Please post some pics of your engine so we could see all the hose connections, etc.

Which aftermarket carb did you install?

 

[edwjmcgrath]

Start by disconnecting the throttle linkage where it attaches to the carb. Start it up and operate the throttle by hand.
If it works normally, the problem is in the linkage. Often people modify the linkage to get it to work with aftermarket carbs like the holley. When you say that you have to push the linkage to get it to idle, this sounds like it may be the problem.
Also repeating the previous question about which aftermarket carb did you get? An OEM copy? or new Holley or ?

 

[BDPC]

Guys (and gals?)

Thanks for your replies. I am currently working on the theory that the problem is a vacuum leak and/or too much fuel. I am quite confident in the timing being awfully close to right on the cheese.

Now to respond specifically to the various previous posts:

DON - I do have a vac gauge in another location - I will get it and see what it reads. But I like the vac problem. I also agree that we probably have more than one problem.

MIKE - The PCV is missing, I think, and I get a little smoke out of the valve cover nozzle. We will go over the vacuum hoses and ports hopefully tonight if school and work permit. I will try to get some pictures posted - not sure when or how to do it...

ED - We bought an aftermarket Aisan looking thing. I dont know the brand. It was $100 on eBay new, and it looks like the one in the book. HOWEVER, I put the Holley 2 bbl that came with the car back on last night. I did not hook up all the vac lines on that (out of ignorance) so it ran worse than ever, and time ran out.

One other note/question. We are inclined to stay with the Holley Carb because we have the throttle linkage for it and the air intake/filter housing. I read last night that the Holley Carb does not handle excessive fuel pressure, and that an inline pressure regulator is recommended. Anyone have any experience or opinion on that? It would explain the dumping gas comment from the seller.

And thanks again to everyone for your continued help. My son (and his father) is learning a lot, and it continues to be a great father-son project.

 

[HoundDog]

Where are you in Virginia? Anywhere near northern VA?

 

[BDPC]

All,

It has been a while. I had to go to Europe for business, and were just getting back on this. The current status is:

We got the Holley carb installed, and it was still dumping gas. I say dumping gas because one of my employees noticed, as I had, a liquid sort of burping out of the Exhaust manifold. Also, insane fuel consumption, and you could look into the carb and see. So I bought a fuel pressure regulator and installed it - easy. I think it helped, but we decided today to rebuild the carburetor from scratch. That proved VERY fruitful: We found a torn paper gasket inside that was clearly passing fuel through some channel. Also, there is something called the power valve: it evidently opens under vacuum to inject more fuel. The power valve in the Holley we have was bent, so we are pretty sure it wan not closing correctly. Snaps to Advance Auto for having the rebuild kit on the shelf on Sunday, and double snaps to Holley for having 3 replacement power valves or 2 different settings in the basic rebuild kit. Amazing. Anyway, we replaced all the gaskets, O-rings, etc and the new power valve and acceleration pump diaphragm. All the jets and passageways are clean now, etc.

After all that, we STILL have over-revving. We can only slow it down by pulling the choke to over-rich it. Then we struggle with stalling. I plan to get a vacuum gauge to see where that leads me (I did not have one at work after all). In an effort to slow the RPM at idle, I twisted the distributor cap. That slows the RPM some, but before it gets reasonable it stalls.

My question today is: does anyone know about the clutch-looking thing under all the distributor cap? It looks like it should have something to do with slowing the spark advance if it revs, but maybe not? When we removed the rotor with one of my employees, the clutch parts were all sort of stiff and seized up with rust and dust. I got them completely freed up so the tiny springs work to pull in the counter-weights. My current theory may include this clutch/governor thing being faulty, allowing the RPM/spark advance to misbehave.

Also, I will be fixing the exhaust manifold gasket, but could that cause over-revving somehow?

I cannot see how to set the timing without getting the RPM under control.

Thanks for your help. Apologies for being incommunicado for so long.

 

[BDPC]

And we are near Roanoke, not Northern VA.

 

[BDPC]

Eureka! We got it idling very nicely. Turns out it was a combination of factors. The carb rebuild was key - it was missing the little cork sleeves around the two idle mixture adjustment screws, so they would creep a lot when the engine was running since they were so loose. Also, the messed up power valve didnt help. And we were evidently huffing bozone because neither we nor the mechanics we worked with thought to adjust the (ta-da!) IDLE SPEED ADJUSTMENT SCREW on the side of the carb. It occurred to me that I would not mention this part because it makes me look like an idiot. But I hope it helps the next guy avoid walking this path when he reads these posts.

Thanks to all of yall who helped so much with the diagnosis. I imagine we will be back with more questions as we get this thing on the road.

 

[Downey]

You evidently got your rig running right before I got around to responding. The number one problem with new Holley 350 installs is a blown power valve. You can't set the timing until the engine is running, engine won't start easily since timing is not set, so you pump the gas, get a backfire, which can blow out the power valve. A blown power valve does 1,000% what your problem was. Now that you've rebuilt the carb, you'll be tickled pink in off road terrain (steep hill climbing) if you install a "float bowl baffle" and "float bowl chimney", they eliminate 1,000% of any off road problem you might have. See ebay #252568209402 for this.