"bum bum bum POP" - Introduction to Tanimal & a rookie's cry for help. (1 Viewer)

[Mechranic]

Hi all! I recently acquired a 1971 FJ40 (currently nicknamed "Tanimal") I've been over the moon in ownership so far, though I bought it running and I fear I've already ruined it... I could use some guidance.

The drivetrain is stock; it's been lifted & given both power steering and disk brakes. It has a weber carb now, but i've got a Holley Sniper ready to install... The plan is to have it reliable as a daily, while maintaining as much stock as possible. I'm hoping to lower it back down once the rest of it's stable.

However, when I drove it home over the Rockies I stalled out after a popping noise developed around 11k elevation. (it had been living closer to 8k, and I have it at 5k.)

I got towed over the pass, and let gravity assist me the next 20 miles. Once I was back down near 8k I could get it to start again but the popping stayed. I drove it attmiddatly much too long like this, another 20 mi or so before the engine cut again.

I have it home now at 5k elevation, and have been running diagnostics to the best of my (limited but growing!) ability.

I can get is started, but it pings/backfires? consistently every 4 "beats". I have a video I could share if helpful. The engine will consistently shoot compression back up through the carb every 4th thrum of the engine. You could write a song to it, the beat is: bum bum bum POP, bum bum bum POP. With the air cleaner off, if I accelerate you can see a plume of the fuel air mixture shoot about 2 feet out of the carb.

I replaced the spark plugs, they were beyond fouled. Next I'm working on timing but I have limited tools and haven't figured out a good way to turn the engine without using the starter. Currently, the bb is right on the indicator pin & the dizzy is right on plug 6's terminal. I figure this means I'm TDC for cyl 6, and I'll need to find a way to spin it 360 deg to get it to TDC on 1 and verify timing.

All that being said, do these symptoms sound familiar to anyone? I've dug around mud & other forums to little success. Really it sounds like it could be a whole host of issues. My current plan is to read up on each one and tackle it to the best of my ability, if nothing else I'm learning a ton!

Cheers yall, I've enjoyed getting my feet wet in the cruiser world, and am looking forward to getting to know yall.

 

[CRZR45]

Replace cap rotor and wires with oem ones. And new points and condenser if equipped with them. That’s where I would start .

 

[B y r o n]

Is it worth it to you to get it running with the Weber or does it make more sense to just start the Sniper install and go form there?

 

[45Dougal]

I had very similar symptoms on my Honda Super Magna just a few weeks ago..
It turned out to be crap in the fuel line causing fuel starvation. Some debris had found its way through to the carburetor too.
I replaced the fuel filter and drained the carb float bowl a few times and it cleared right up.

 

[Pighead]

I set the timing with engine running, no need to find TDC#1 unless you're pulling the dizzy.
Oftentimes, timing at the BB is not enough advance, especially at altitude.
You can also use your timing light to test your sparkplug wires, cap & rotor.

 

[franklin40]

is it popping out the tail pipe or the carb?

 

[South Texas 97]

At least clean the points and rotor cap and take a good look the cap is not cracked.
I agree with the above of setting the timing with the engine running. Just slightly loosen the distributor enough so you can reach under the cap and turn the body of the distributor. If you have a simple timing light like I do, zip tie the trigger to hold it on, and with the engine running, as you slowly turn the distributor you will see the bb move back and forth. Hint: dab a bit of white paint or marker on the bb mark. Makes it easier to see.
I had a similar setup with a Holley carb, and got it running somewhat smoothly before installing the sniper. Which one did you get? Mine is an in tank pump with return. Take a look at my thread for what I did to get it running properly. Super happy with it now, sea level to 12000 ft without an issue

 

[franklin40]

popping out the tail pipe is often an ignition issue. popping out of the carb is a valve adjustment/problem issue.

 

[samatulich]

Backfire out the carb= lean; backfire out the tail pipe= rich
The plugs were fouled? How so?
I'd make sure the carb it jetted correctly for your elevation.

 

[franklin40]

true. early ignition (often lean) will also cause carb backfire

 

[Mechranic]

Thank you all for the responses! A quick update:

It's popping out the carb. It sounds like a coin hitting the bottom of an empty can. A bit of a metalic "plink".

I just tried adjusting the dizzy, as expected the revs adjusted greatly but the noise is still there. I don't think it's strictly a timing issue.



One thing I don't understand is the consistency of the popping, it's 95% on beat, if it were just a mixture issue would it show itself this frequently? I adjusted the idle screws a little and it didn't make an impact to the noise, just the idle, I can try that again.

When I rev it up a just a tad it seems to run very smooth except for the consistent ping. I'll try attaching when I figure out how.

 

[Mechranic]

Backfire out the carb= lean; backfire out the tail pipe= rich
The plugs were fouled? How so?
I'd make sure the carb it jetted correctly for your elevation.

Good to know, by that logic it's "lean" which is funny with all the residual gas that's getting blasted out the carb. I'd increase richness by backing out the idle screws, correct? Am I right in thinking I should be able to adjust idle to "altitude" without touching the main jets?) Obviously to correctly tune the whole range i'd need to make changes to the jets.

I ask because I'm just trying to get it running smooth enough before I switch to the Holley EFI setup.

 

[franklin40]

i had a persistent constant carb backfire and it was a lifter that went bad and wouldn’t open an exhaust valve. you might want to check your valves as that will cause a consistent backfire. it releases the pressure back through the carb when the next intake valve opens

 

[Mechranic]

At least clean the points and rotor cap and take a good look the cap is not cracked.
I agree with the above of setting the timing with the engine running. Just slightly loosen the distributor enough so you can reach under the cap and turn the body of the distributor. If you have a simple timing light like I do, zip tie the trigger to hold it on, and with the engine running, as you slowly turn the distributor you will see the bb move back and forth. Hint: dab a bit of white paint or marker on the bb mark. Makes it easier to see.
I had a similar setup with a Holley carb, and got it running somewhat smoothly before installing the sniper. Which one did you get? Mine is an in tank pump with return. Take a look at my thread for what I did to get it running properly. Super happy with it now, sea level to 12000 ft without an issue

I can't wait to move on to the Holley install, I got the 2300 2bbl. I saw at least one of your threads, great call on being cautious of the fuel line routing!

 

[65swb45]

Your symptoms are consistent enough with an intake valve issue that I wouldn’t want to run it anymore without pulling the valve cover and having a look-see. You could have a deteriorating situation that could turn catastrophic if you bend/break a valve.

So being able to spin the motor over and see consistent rhythmic cycling through the valvetrain is an important thing to check off of the diagnostic checklist.

 

[Its me shaneus]

Listen to the above from 65swb45.

Pull the valve cover and check top end is all as it should be. If so, then a compression test. Good thing is, all this is easy in a 40 with F/2F.

I recently switched to FITech efi. Big bold print “Have running well before starting to convert to efi”. Good advice.

 

[knuckle47]

Well I found that in order to locate my BB , I had all of the plugs out, jacked up one on the rear wheels and dropped the transmission into 4th gear(3rd in your case). By rotating the lifted wheel, the flywheel spins slowly until it pops up in the window on the housing.

I work alone so I rigged up a Wyze cam and watched it all play out on the phone while turning the rear wheel. As said…definately add a dot of paint on the BB or the line

For what it’s worth, my ‘75 was Weber equipped and I did convert to the Sniper EFI, it was running so well, I opted for the Hyperspark ignition system…wanna talk? Happy to do so. My FJ40 is running as good as my Silverado

 

[Mechranic]

Good news!! There's quite a problem. I got the valve cover off and there's a lot not to like. The valve on the non-springy side of the cyl #2 exhaust rocker has been 'self-modified'. (see the photos). Also, I think there's an issue with oil getting up here because it seems much to dry.

When the engine runs, the cyl2 exhaust rocker doesn't rock (the rest still do!). Not hard to see why! This must be the root cause of the popping. Perhaps the oil is the root of why it broke in the first place.

The good news here is that I found something to fix! The bad news is that I have no idea how... yet! Has anyone modified the interaction between the rocker and the valve head before? I'd bet that's iffy territory, but I'd like to avoid opening the engine up if I can.

As for the oil, I'm going to do a change or two to see if that helps free things up.

(Do you need all 6 cylinders?)

Thank you again for all the replies, you all treat newbies well!

 

[65swb45]

Bad news: you’re going to have to “open up the engine” even if that only means replacing the rocker assemblies.
Good news: there are tons of people here to coach you through it. After 20 years on the forum, I am no longer a regular in tech, so it may not be me.

It does seem you are lacking oil. So you should plan on having to replace the entire rocker arm assembly. Just because the other parts aren’t frozen, doesn’t mean they’re not damaged from lack of lubrication.

Based on my experience, I’d say there is also a fair chance that the lack of oil is from a breach in the copper tube that feeds the rockers. You are going to have to take the side cover off the engine to inspect/ replace that.

P.S. I have all of the required parts available for sale.

www.marksoffroad.net

 

[South Texas 97]

It should look more like this