FJ40 2F Running on Five Cylinders?

[HoundDog]

New to me 1980 FJ40 is running rough. South American spec with no emissions equipment. Has lack of power, is backfiring occasionally either through carb or in header (towards front of truck). Less than 500mi on freshly rebuilt 2F, brand new Trollhole carb.

Sprayed carb/starting fluid around base of carb and around intake manifold while running and didn't notice any change in idle. Oil looks clean, no smoke out tailpipe.

Pulled all the plugs and the plug in the number one cylinder (closest to radiator) looks oily/dirty. The rest look clean/normal. There may be a hose missing off the distributor but don't know if I have a vacuum or electronic distributor. Attached pics of bad plug next to a good one and also one of the distributor.

Any idea what to do next?

 

[91 4runner]

How long ago was it rebuilt?? Motor in pics looks abit dirty to have been rebuilt "Fully"

Figure out what's missing,

She only needs
-fuel
-spark
-timing( compression)

If u have a dead cylinder then something more then a hose is wrong,

And get some new plugs, or at least clean and gap them,


...

 

[Tezmac]

I'd think with an 1980, that's a vac advance dizzy. There's a small hose that should run from it to the TH carb to advance the timing under throttle. I can't speak to what you're seeing on your plugs...

 

[vszUnclear]

I just went through something similar on a 60. If you rule out something obvious like a bad plug, wire, then...

Idle the rig and then pull spark plug wires one at a time and listen for changes to idle, especially your suspect. If nothing changes when you pull the wire you have more evidence of a cylinder that isn't firing.

Also do a compression test to confirm your findings.

 

[sometlc]

It may also be possible that you have a sticky valve on either the intake or exhaust. I would pull off the valve cover as it may be a broken valve spring.

 

[marketShark]

I'm leaning towards an advance issue if its misfiring like you say. This thread might help: https://forum.ih8mud.com/threads/request-for-info-2f-timing-big-cap-by-the-numbers.701215/

I understand that to help with troubleshooting, these engines were designed to run without a valve cover (in the garage). Like sometlc suggested, Id look at your lifters and springs in case its bent or stuck valve

 

[gherndo]

1st, your vacuum advance is not hooked up. Yes it has one. It is in the photo. It is a .125" ID vacuum hose. Buy it at orielly and get vacuum hose or it will collapse.
2nd, one cylinder not hitting wasn't caused by the vac advance, so you have multiple problems. Unplug the spark plug wire from that dead cylinder. Plug it into a loose spark plug and ground it against the block. Crank the engine. Use gloves. Look for a spark. Needs to (a) have a spark (b) be a strong spark. Do this again on another cylinder and compare the "strength" of the spark. This is a rough test to verify spark, not rocket surgery.
3rd, if the spark checks out, it most likely a valve issue, like someone else mentioned. I just like to test the easy things first. Let us know how the spark checks out.


...via IH8MUD app

 

[sggoat]

Compression check is in order here, I think -esp with the gunky plug in #1.(as VszUnclear says) The backfiring could be a carb issue, but with the other symptoms, it may be valve/timing related.

 

[FJcovet]

2x on the vac line. Not only will the distributor not advance properly, it looks like the vac port on your carb is open to atmosphere causing a vac leak. Mt trollhole carb has a cap on the port at the base towards the valve cover.