update on to-30 random misfire

[steve-in-ga]

Thanks for all the things to check. I've performed all the checks to determine if the miss is in the ignition side and haven't found a culprit yet. No fire bouncing around at night. I jumped around the ignition switch and ammeter. I connected a timing light to each plug wire and don't see a miss. The spark is not weak at any plug.

I do have a very slight amount of play in the distributer bushing.

I was telling my friend about the issue and he was telling me about a test to see if an issue is in the valves. He said to hold the corner of a piece of paper up to the tail pipe and see if there is any sucking at the tail pipe. When I performed this test, before the miss, the paper is sucked into the tail pipe instead of blowing away. I checked the valve clearance with the engine off and cold and each valve (intake and exhaust) was set to roughly .015. What could be causing this? Sticking valve, weak or loose spring?

thanks
-steve

 

[olddavid]

Does a compression check show any irregularities?

If it is sticking valves an oil (or gas?) additive or change to a different brand of oil might help. Had that problem with a 2007(oops! 1997) Plymouth Breeze.

If a compression test looks good and you don't see any irregularities while doing it, it may be that even though the spark looks good maybe they aren't occurring at the right time.

This post was edited by olddavid on 11/26/2023 at 04:31 am.

 

[Ericp351]

Frustrating, ain't it? Did you watch each valve closely with cover off? Running best.1 weak or bent spring or a bit of grit can ruin your wits.
Anyway- Light oil- marvel mystery- never a bad idea to fuel and oil in case like yours. Also- if not already done, check dist cap for burs and carbon
track- even if new. Borrow some young eyes and good light if needed and good luck! Post script- plug wires. I still use steal core, as designed.
Modern stlye, even new, do not play well with old-low energy point systems.

 

[Tom H.]

Get ready to pull the head off. Then either do, or have a valve job done. You have a valve not seating.

 

[6 SLY PLACE]

what spark plugs are you using?

 

[steve-in-ga]

(quoted from post at 23:59:31 11/25/23) Does a compression check show any irregularities?

If it is sticking valves an oil (or gas?) additive or change to a different brand of oil might help. Had that problem with a 2007(oops! 1997) Plymouth Breeze.

If a compression test looks good and you don't see any irregularities while doing it, it may be that even though the spark looks good maybe they aren't occurring at the right time.

This post was edited by olddavid on 11/26/2023 at 04:31 am.

Here are the compression numbers (psi) with the engine warmed up.

Cyl 1 - 112
Cyl 2 - 116
Cyl 3 - 118
Cyl 4 - 116

I think my friend has a cylinder leak down tool. I'm going to see if he will let me borrow it for a day and check each cylinder.

 

[steve-in-ga]

(quoted from post at 18:22:19 11/26/23) what spark plugs are you using?

Autolite 386 gapped at .025"

 

[6 SLY PLACE]

Leaked down test is the way to go

 

[olddavid]

"Here are the compression numbers (psi) with the engine warmed up.

Cyl 1 - 112
Cyl 2 - 116
Cyl 3 - 118
Cyl 4 - 116

I think my friend has a cylinder leak down tool. I'm going to see if he will let me borrow it for a day and check each cylinder."

Those numbers look pretty good to me. I guess the valves might not be sticking at cranking speed. Someone suggested Marvel Mystery Oil in both the gas and the oil. It might be worth a try. I still wonder about the electronic ignition but I don't know how you would test it unless you converted it back to points just to see if the miss still occurred. Did you do the install of the electronic ignition?

 

[Ericp351]

Comp #'s look like seating A Ok to me..... Sticking- possible (Marvel Mystery oil can't hurt) . Weak spring- Could be. Bad-cap/ plug wire: With or without wee bit lean- Maybe (+ Cheap!) Leak down test= why not AFTER ya check basics! Best O Luck- think horses, not zebras!

 

[olddavid]

You have compression and spark. About the only thing left is fuel. Have you checked fuel flow? Break the line at the carburetor. It won't be high pressure but should be a full line flow. Could your sediment bowl be FULL of water? You almost need to remove it to be sure. I just got my TE-20 running this summer and a problem I had was as simple as the tank shut off valve. Opening it wide open was actually closing it a good part of the way so I now open it only around 2 and 1/2 turns. I had never seen that before. It could be a problem in the carburetor as well, but it misses at both idle and at wider throttle openings. I guess it's possible, though.

 

[jhwis]

Could it be a bent push rod?

 

[Steve@Advance]

Do you still have the rocker cover off?

If so check the valve springs. Visually inspect for breakage and push down on each spring by hand. They should all be about the same. If one is notably easy, it is bad.

Also have you checked centrifugal advance in the distributor? It should turn a few degrees CCW and spring back when released. If stuck, slow to return, or springs missing, the distributor will need to come out, disassembled, lubed and reassembled. Not a difficult job. You can try adjusting the timing by ear to get the best idle and performance. It is not critical, as long as it is not kicking back against the starter or clattering under load it will be OK.

There could also be a carburetor problem. The engine needs to idle down to around 400-500 RPM, any faster it will be trying to idle off the intermediate circuit instead of the idle circuit. That will cause rough idle. The idle mixture screw is an air bleed. Turning it in richens the mix, out leans it. If it has no effect, it is clogged and the carb needs to come apart and be carefully cleaned. Rod each passage and jet with a stiff wire. Spraying and blowing will not get all the residue out! Usually it can be eased apart without buying a kit.

 

[Bruce(OR)]

Fatten up the carb mix before you play with much else. Then go play the paper exhaust game again.
A loose valve at .015 is not a problem. A tight valve at .012 is a problem that it never seats and burns which will give you a steady noise. NOT intermittent. Lean mix can cause your erratic miss.
If it still flutters after a fat mix, possible sticking valve(s). Cheap fix? Oil additive/soak the cylinders, then drain/fill fresh oil after 24 hours. 1 can of Seafoam each cylinder.

 

[J.Wondergem]

Get a vacuum testing gauge and put it on there. I 'll bet it'll tell you what's wrong with it. Any auto store should have them.

This post was edited by J.Wondergem on 11/28/2023 at 05:18 pm.

 

[Dave murray]

What do you think is better for a old tractor? Marvel
mystery oil,sea foam,or lucas fuel treatment. I just
purchased an old tea20 and it has a slight miss.

 

[Jim L WA]

(quoted from post at 15:37:42 12/03/23) What do you think is better for a old tractor? Marvel
mystery oil,sea foam,or lucas fuel treatment. I just
purchased an old tea20 and it has a slight miss.

Hi Dave, I see you are a new user, so all is forgiven. It will be best to start a new post for your question. What you have done here is hijacked someone else's thread. The problem, then is that it may not be clear who future responders are referring to.

 

[Dave murray]

ok I understand,sorry about that.

 

[rustred]

Have u pulled the plugs and actually checked the spark at them when cranking it. Just because u have spark to the plugs dont mean the spark is good coming out of the plug. Seen that many times. I suggested that before but I see nowhere that u confirmed that. Or do this. that engine should run on one cylinder at 1/2 throttle. So remove 3 wires From each cylinder as u go through all 4 cylinders. If it dont run on one cylinder u have the culprit. Plus u can remove the plugs and read them to see how they are firing. All should be the same color. If one is black and sooty thats another indication of poor firing or miss firing. Do these checks.