Acceleration and Deceleration Issues (2 Viewers)

[CTrain224]

Hey there, new to the fj40 club. Just bought a 71 fj40 FULLY STOCK over a month ago. Heres the condition of it when i got it:
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Well, this was it after a few modifications..
First, the front rear and back left drums and the master cylinder were locked up tighter than Alcatraz. I went ahead and converted it over to JT Outfitters 4 wheel disc brake conversion. Worked out great, has awesome stopping power, very pleased.

Second, i was having some serious engine problems. After checking the points, I rebuilt the carburetor myself and was not able to pull the bearings out of it (small little steel balls) so i skipped them, drank a beer, and reinstalled the carburetor... wouldnt start without dumping fuel into the carb, so i said f&%k it, sent it in to be rebuilt by a professional. Got the carburetor back, which might i add still has a sticking choke, meaning the manifold gets stuck open/closed, i found a loop hole by backing of the choke after i pull it and it snaps back into place. In the mean time i replaced the radiator, for good measure.

Got the carburetor reinstalled and got it running pretty rough. I decided to do some troubleshooting, I checked the points again, adjusted the timing, i took the fuel line off and turned over the engine, got plenty of fuel. I replaced the plugs and showed some signs of improvement. I sprayed starting fluid around the base of the carb and didnt get any change in idle. I plugged all the vacuum lines with golf tees while it was running.. no change. I checked the plug wires to make sure they were in the right order, all good. Still runs like the ridge line of the rocky mountains...rough.

At this point i did my best to adjust the mixture/idle screws and i had it running decent. I mean decent as, would die if i eased on the throttle, would accelerate if i pumped the throttle hard and got the RPM's high. Started driving it(for the first time, and after i get it into second gear i could lug the engine by going slow and accelerate out which had good performance, im talking acceleration from below idle in second. When i decelerate i get a popping and unhealthy sounds.

Long story short i winged it from Fallon Nevada to Las Vegas Nevada (450 miles at 55 mph) she performed excellent after i learned how to man handle the throttle. I was decelerating though Hawthorne (army base) and they pulled me over because they thought i was firing weapons as i decelerated into town...
As i neared the end of the trip i noticed, at high RPM's in, started to get an abrupt jerking, as if i was pumping the throttle... so i resorted to accelerating and decelerating back and fourth for an hour...Stumped!!!

Here i am in vegas (my home) and im real motivated to get it running smoothly, im so close!
SO
1. I changed the plug wires, no difference.
2. I did a pressure test where i plugged a pressure gauge into each plug hole at once and turned the engine over for about 8 seconds until the gauge reached anywhere between 70-80psi. Singled out no burnt valves...(i think)
3. Decided to upgrade the dizzy to protroniox(electric) from SOR, threw a flamethrower coil in, new dizzy cap, new dizzy rotor. I started getting some backfiring out of the carb when applying throttle so i knew i needed to check the timing again.
4. Adjusted the timing and got a much better idle and no more backfiring.
5. leaned out the mixture all the way and screwed it in 5 turns

The idle is really good - i dont hear any missing or backfiring. Guess what?? apply slight throttle and it fights to stay running if it keeps running at all. But i give it heavy pumps and it jumps up to high RPM's i cant keep it at a constant high RPM, wants to die, i just have to keep pumping it to keep the RPM's high.

So i drive it again and it accelerates great, through all 3 gears. I let off the throttle and it starts missing worse than a blind kid pitching a baseball. (which it has always done)

I am so f&%&ing mad at this point, ive changed almost everything..

Burnt valve? needs valve adjustments? new vacuum hoses? Thats all that i got left.

I feel like Tom Hanks on a raft with a volleyball... Stranded with a useless toy.

SEND HELP

 

[Solace in Solitude]

Welcome... and welcome home to Vegas!!

Couple of questions/suggestions:

1. You don't mention a fuel filter anywhere... or, I missed it... have you changed the fuel filter? Is there crap in the filter? Fuel lines could need cleaning, tank could need cleaning.
2. Have you blown out the fuel lines? I'm not familiar with your year, but the hard fuel lines generally run in/next to the passenger frame rail and are lowest there... prone to holding water and crap at the low points. Take both ends loose and blow/clean them out.
3. You mentioned, "2. I did a pressure test where i plugged a pressure gauge into each plug hole at once and turned the engine over for about 8 seconds until the gauge reached anywhere between 70-80psi. Singled out no burnt valves...(i think)"... are you saying you performed compression tests and the results were 70-80psi, across the cylinders? , that's pretty low... I would redo the compression tests (operating temp, choke open (in), throttle plat wide open (pedal to the floor), all plugs pulled, coil disconnected... record the dry results, by cylinder. Then do them again, after squirting about 4-6 drops of oil in the cylinders... record the wet results.
4. You said, " i took the fuel line off and turned over the engine, got plenty of fuel."... are you getting about 1/2 cup of fuel, after cranking for 15 seconds?
5. Do you smell gas on the dipstick?
6. Is it still running a mechanical fuel pump?

Post your dry and wet compression test results back here, along with your other answers and we'll go from there.

HTH

 

[Pin_Head]

It sounds like a number of different things are going on:

1. intermittent fuel starvation. This leads to bucking, jerking and backfiring through the carb at high speed, especially full throttle conditions. Check for rust flakes or junk in your tank. Could be water too, although it would likely be out by now.

2. Popping and backfiring in the exhaust manifold during engine braking. Basically, the mixture is too lean to ignite by spark and then it explodes when it hits the hot exhaust manifold. There are several potential causes, like non functioning emissions control, leaky exhaust manifold, improperly adjusted carb, etc.

 

[micruz60]

Fuel pump.

 

[thebigredrocker]

If you haven't checked whether your exhaust valves and intake valves are out of whack, you might want to.

I'll add a link to a good thread below, "go/no-go" feeler gauges would be helpful to quickly check while your engine is running.

First valve adjustment on my 78 FJ40 ...

 

[CTrain224]

To answer questions: mechanical fuel pump, i drained the tank on day 1.. no i didnt wash it out, i bypassed the fuel filter once and didnt notice a difference so i think the fuel filter is still good but im going to replace it soon because its cheap.

In a recent update i replaced the vacuum advance on the dizzy and didnt notice any difference, luckily i had the advance from my dads FJ40.. no extra cost there.
I sealed my hand over the top of the carb and the engine died - that means no vacuum leak right??


I agree with most of you all here at this point that there is most likely a fuel problem. One thing that got me thinking that is this: i back the idle screw off ALL the way, to lower the RPM and it still runs.. Turn in the throttle adjustment to raise the idle halfway in or so... dies. Take a look at the fuel window,, completely full of fuel. Boom float adjustment i think. I took the top of the carb off and saw that the float actually had no setting on the center tab, meaning it was completely flat. WTF guy who rebuilt the carb??? i bent it up, to lower fuel delivery, and reinstalled the top of the carb and i got the fuel in the window to drain, also stepped on the gas and got it to die immediately... no fuel.

After tweaking that tab up and down in the slightest, and i mean the slightest, ive gotten it somewhat steady to fill up the window half way, not quite perfect yet im going to do some more adjustment tonight. Any idea of how i can adjust that tab without taking the carb out and flipping it upside down to get that measurement and what that degree is?

Secondly i looked at the timing with a buddy, John, and something i didnt know is i had the setting to 0 degrees, i was completely unaware that you are supposed to advance or retard the timing ahead of 0 degrees. We set it forward 7 degrees, not sure what the spec is but it sounded a little better right there. Also the @bigredrocker posted a link above and a guy said he had his at 7.5? Anyone know what degree thats supposed to be at??

Took it out for a drive and felt a world of difference in increased power, doesnt rev perfect but its getting closer/steadier, also still misses at constant high RPM but not as bad as it was.

As for the valves, im only waiting to look into them at this point because one i dont know crap about them to feel confident taking them apart/ the valve cover off and the idle is so frickin nice, she purrs. Thats a sure sign of no valve problems right?

 

[Fast Eddy]

"No valve problems" and valves adjusted properly is two different things. You should get yourself a FSM. There's a method to adjust the float once. It shouldn't be hunt-and-peck, but it sounds like that worked out ok. It's worth getting someone to boil out the tank and look inside. You can look into it from the top with a flashlight and get an idea of the condition.

There are enough things that can go wrong that you won't ever get it perfect unless you do it all at once.

 

[Tezmac]

Not that this addresses your issue, but since you asked, I wanted to add that my timing is set at 11 degrees advance. Although, I'm up at 5k feet, running 86 octane, w/a trollhole carb and vac advance dizzy. Your results will obviously vary depending on hardware and environment.

I was having issues that sounded somewhat similar to yours at one point. I had already popped the valve cover once the engine was nice and hot and adjusted the valves. A couple were off by just a little and the adjustment didn't really address my issue. But that said, you should probably still check, it's not difficult to do (I'm not much of a gear head). I also had gone through and done the lean drop method on the carb. It idled fine, but missed/surged under load from time to time. Then I went in and advanced the timing bit-by-bit and that's what made a world of difference.

My thread below in case you're interested:

Carb/Dizzy Blues...

 

[CTrain224]

Good thought. I'll give it a try after I get the fuel in my sight gauge to balance. Merely impossible, talk about touchy...

 

[Pin_Head]

Does your accelerator pump in the carb squirt fuel when you open the throttle? If you couldn't get the check balls out, there is a good chance it is plugged. That could explain why it falls flat when you try to accelerate.

 

[CTrain224]

Update:
Took the carb apart and adjusted the float because the sight window wasnt getting enough fuel. Adjusted the float and kept getting an inconsistent fuel reading. Took it for a drive after a few tweaks on the float and it ran really well, idled really well, accelerated and decelerated really well, no backfiring and sputtering, i thought i had it fixed.. Really excited, then at high RPM's the engine would die under throttle application, so i would turn off the engine and pump the pedal around 10 times, start it up and drive off just as great as right before. I figured the problem was either the fuel pump or the accelerator pump not providing enough gas..

After taking off the top of the carb and looking at the placement of the accelerator pump it looks like i put the accelerator pump needle in backwards. I swapped it around and flattened the adjustment back on the carb float (like i got it originally). Now im getting a consistent reading on the sight window right at half way.

Now, when it comes to driving it, its back to the original issues, good acceleration, backfiring on deceleration, really nice idle, no low RPMs (engine dies).

I bought a brand new fuel pump, new fuel filter, new fuel lines - no improvements.
I adjusted the timing, advanced 9 degrees (im at 35000 ft elevation and factory timing at sea level is 7 degrees) - no improvement
i unplugged all the hoses from the emissions control system. No change but could the emissions control be the problem?
I'm debating on buying a new carb.
@pngunme Do you think valves could still be the problem here?

Any ideas?

 

[handcannon]

Update:
After taking off the top of the carb and looking at the placement of the accelerator pump it looks like i put the accelerator pump needle in backwards. I swapped it around and flattened the adjustment back on the carb float (like i got it originally). Now im getting a consistent reading on the sight window right at half way.

Now, when it comes to driving it, its back to the original issues, good acceleration, backfiring on deceleration, really nice idle, no low RPMs (engine dies).
Any ideas?

Is it actually backfiring, or popping in the exhaust? Popping in the exhaust during deceleration can be caused by excessive gas building up in the exhaust system and then popping/firing, or "backfiring" within the exhaust pipe. Note that this is in the exhaust pipe, not actually backfiring up through the carb throat. An exhaust system can contribute to this from holes rotted in the pipes, as I've had this experience.

Don

 

[CTrain224]

Is it actually backfiring, or popping in the exhaust? Popping in the exhaust during deceleration can be caused by excessive gas building up in the exhaust system and then popping/firing, or "backfiring" within the exhaust pipe. Note that this is in the exhaust pipe, not actually backfiring up through the carb throat. An exhaust system can contribute to this from holes rotted in the pipes, as I've had this experience.

Don

It is actually backfiring through the carb.