Hi - I have a 81 FJ-40 and when I start accelerating at any gear the engine start hesitating/bucking until it die. After a couples of seconds I can restart the truck without problem but as soon I accelerate in gear the problem repeat. In neutral I can accelerate as much I want with not problem. I already change the fuel pump, filter and most of the fuel lines. Also I tried driving it without the fuel tank cap and the problem persist...Do you guys think it is the carburetor ? I'm not a "mechanic" but I can do basic stuff. Please help me.. photos for reference.
81 FJ-40 - Hesitating / bucking under acceleration
- Thread starter YOTA40
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Copying and pasting this list of homework I sent to a customer this morning who was interested in a replacement carburetor.
1. Verify current base ignition timing
1.5. Check your point gap (I'm assuming you have points and that this is a non-US vehicle based on the shiny chassis, small distributor cap, non-smog carb, etc)
2. check / adjust hot valve lash.
3. compression test all cylinders.
4. current manifold vacuum (I see an uncapped fitting on your intake manifold aready, that would be a good place to hook a vacauum gauge to)
Check these things and post your results here before you purchase any more parts.
1. Verify current base ignition timing
1.5. Check your point gap (I'm assuming you have points and that this is a non-US vehicle based on the shiny chassis, small distributor cap, non-smog carb, etc)
2. check / adjust hot valve lash.
3. compression test all cylinders.
4. current manifold vacuum (I see an uncapped fitting on your intake manifold aready, that would be a good place to hook a vacauum gauge to)
Check these things and post your results here before you purchase any more parts.
Drain the tank and put in some fresh gas, maybe see if it runs better on premium.
You are missing a vac cap on that barb, closest to the firewall. I've never had luck with rubber caps, aside from OEM, but, the silicone seem to be better, I think. A bit of a vac leak will go away if I'm reading the photo correct.
Pull the battery negative cable. Open the distributor cap. Inspect rotor for off-axis play, and inspect / clean cap-electrodes.
The carb needs love. It is possible that corrosion is collecting in the bowl, or inlet screen. Rebuilding one isn't that hard. Get a Vessel or Toyota JIS screwdriver. I can see the burrs on this carburetor from someone using a Phillips. I don't see a choke cable or idle cut solenoid wire hooked-up? Both of those items might be a cause for a lean-condition.
I'd inspect, photograph (forced flash option), and clean your spark plugs. A bit of wet-dry 220-grit sand paper between the electrodes, and remove as much deposit as you can with a steel brush without bending the grounding strap, and reinstall them.
Pull the battery negative cable. Open the distributor cap. Inspect rotor for off-axis play, and inspect / clean cap-electrodes.
The carb needs love. It is possible that corrosion is collecting in the bowl, or inlet screen. Rebuilding one isn't that hard. Get a Vessel or Toyota JIS screwdriver. I can see the burrs on this carburetor from someone using a Phillips. I don't see a choke cable or idle cut solenoid wire hooked-up? Both of those items might be a cause for a lean-condition.
I'd inspect, photograph (forced flash option), and clean your spark plugs. A bit of wet-dry 220-grit sand paper between the electrodes, and remove as much deposit as you can with a steel brush without bending the grounding strap, and reinstall them.
John McVicker
SILVER Star
Your picture #2…unless I’m disoriented and I may very well be, can’t really tell just from that one picture, but to me it appears as if your fuel filter is facing backwards.??
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- #6
Thanks to everyone, definitely I need to learn more because I don’t really understand most of the items you guys are suggesting. I will Google the items mentioned and trying to figure out. The only thing I know is correct is the fuel filter. Because the carb is in back shape I’m wondering if it’s better to buy a new one ?
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No - first you check your vitals before you buy more parts. You don’t actually know that your carburetor has a problem yet. It might, it might not.
You need to get a timing light, a vacuum gauge, a set of feeler gauges, and a Toyota FSM. Without these tools you are shooting blind.
Got any car people friends. The tractor is really easy to work on, a good tune up is a couple hours if you know your way around under the hood , they could show you how. Youtube has good vids on everything, there is also a lot of trash too.
Don’t underestimate what a clogged up fuel filter can do. Been there a couple times
If the paper element in a fuel filter gets wet with water, fuel cannot pass easily. If you leave the filter out in the sun for a few days it will dry out and be as good as new. Warm days cold nights - the breathing of the gas tank will condense water right out of the air. Full tanks less so than nearly empty ones. A yellow bottle of methanol fuel dryer every few weeks will take care of that issue.
Just inside the fuel inlet of the carb is a small filter and mine was getting clogged causing bucking under load like you are describing.
I was a dumb dumb and put PTFE tape too far on the threaded fuel line and it started to break down leaving chucks that inhibited the fuel flow. Live and learn. Another place to check though especially if the fuel filter hasn't been catching anything.
I was a dumb dumb and put PTFE tape too far on the threaded fuel line and it started to break down leaving chucks that inhibited the fuel flow. Live and learn. Another place to check though especially if the fuel filter hasn't been catching anything.
- Thread starter
- #12
Alright guys, I finally had some free time to follow up on some of your advice. I purchased a vacuum gauge and checked a few other things.
I opened the distributor. I saw a guy checking the vacuum advance by sucking the hose to create a vacuum and confirm that the vacuum advance is working properly. In my case, no matter how hard I tried, the distributor didn't rotate. I even tried to rotate it manually and could barely move it. I'm thinking the vacuum advance diaphragm is bad and needs to be replaced. Can you help me identify the model and replacement? How difficult is it to replace?
I connected the vacuum gauge to the connection on top of the intake manifold that was missing the cap. I started the engine from cold, and it took almost 2 minutes to get to 15-16. After that, the reading was stable during acceleration. According to the gauge, the engine has "late ignition timing." What do you guys think? I also bought a cap.
I connected the vacuum gauge to the carburetor connection that goes to the distributor. As I accelerated, the readings moved from zero to 10 and up to 17-18.
I took a few photos of the inside of the carburetor. What do you guys think? One more question, Can I replace the carburetor bolt that hold in placed the air filter box..somehow is stripped.
Thanks again for your help
A vulnerable part of the vacuum advance system are those tiny ball bearings in the sandwich that composes the breaker plate. I've seen them sooo rusted on my distributors, and the grease was caked with rust. If it is stuck the diaphragm can't perform vacuum advance. To rebuild it takes patience - you carefully move the bearing with a blob of grease to a greased bearing race. Mine is a '75, and your distributor is a different style. It might just need penetrating oil to regain function? I imagine that the other distributor parts need to stay clear of something like WD-40, but, if you can isolate the breaker plate from the rest of the distributor, it might be worth doing an inspection, at least.
pb4ugo
SILVER Star
^^^^^^^^^This^^^^^
If you can suck air from the vacuum advance diaphragm, then it's bad. If you can't suck air, then the diaphragm is good. If the advance plate doesn't move when vacuum is applied and the diaphragm is good, then the plate is stuck or frozen.
Does the fuel level in the carb stay constant between the two points on the sight glass at all times (idle and accelerating in neutral)? Does it idle steady with vacuum readings about 18” of vacuum when connected to intake vacuum?Does the vacuum gauge needle stay steady at idle?
Pls report findings from above.
Pls report findings from above.
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- #16
How can i confirm that the plate is stuck ? Should the plate move if I try to rotate it with my hands ?
I believe you should be able to move the plate at least a little by hand (so you know its not seized). Under vacuum it should move, release the vacuum it should go back.
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More importantly then the vacuum advance is the actual mechanical advance. If that is stuck then the truck will run like garbage.
pb4ugo
SILVER Star
^^^^^This^^^^^
Mechanical advance and initial timing are the most important. To check mechanical advance you can slightly twist the rotor easily and It should move slightly and snap back when released.
Mechanical advance and initial timing are the most important. To check mechanical advance you can slightly twist the rotor easily and It should move slightly and snap back when released.
Following/ Watching...
I've got the same problem, but have not started the process of investigating it. My problems started after a mechanic "fixed" / changed the breaker in my distributor. Its never been the same...
My thought process :
I've got the same problem, but have not started the process of investigating it. My problems started after a mechanic "fixed" / changed the breaker in my distributor. Its never been the same...
My thought process :
- Change the vacuum piping from the Carburetor. Just noticed it is fairly loose, dont think its doing anything. I will try to put a gauge on it.
- Check the distributor cap / electrodes and the "coil" inside.
- I also have some concerns on the fuel pump; might change it. Same mechanic put that doubt in my head, but I dont trust him. I will change the fuel filter first; that's a easy fix.
- Check / adjust spark plugs, valve spacing; then do a compression test.
