Help troubleshooting miss at all rpms
 

Hi all, new guy here back again. I have a 52 customline 8ba three on the tree. Before I explain further, I may follow everyone's advice soon and "send the carb to charlie in ny." :)

I pulled this car out of a barn, but it had run at least 10 years ago. The car had (has) a pertronix ingnitor I in it, the one that is recommended to use with a stock points coil.

I just recently got it running:

- rebuilt 94 carb. i don't recall what kit I used.
- new coil (.6 ohm 6 volt)
- new plug wires and plugs (7mm supression wires)
- new cap/rotor
- new stock style fuel pump
- new gas tank and sending unit

The engine has a bit of a miss and slightly shakes at idle, and all rpms. As rpms increase, the shake gets worse. As if one cylider maybe isn't hitting.

I have spark at all plugs. Could the carb be the culprit? What should I do to continue troubleshooting? I've driven it about 45 miles total and it doesn't seem like it would be down on power, but it's my first time behind the wheel of a flathead. I don't know, but I imagine that it's never been apart and looks to have 122,000 miles on it so its a bit tired.

As you can tell I'm not knowledgeable about flatheads but am here to learn.

Thanks for any help!

UPDATES:

- all valves in engine are moving (doesn't mean they're sealling of course). I verified this with a snake cam.

I did a cold, dry compression test with carb removed and all plugs out. It's not good:

1- 80
2 - 70
3- 75
4- 90 (this is actually the cylinder I thought was the problem because I didn't hear any difference when disconnecting the spark plug wire when it was running)

5 -100
6- 60 :(
7- 70
8 - 85

Afterwards, on #6 I did a wet test and it really didn't change - I saw about 65psi. Maybe a valve isn't sealing?

A wet test on the other low cylinders saw about a 10-15psi change.

I don't have the money to put into this thing. I'm thinking about pulling the intake and head, and trying to look at the #6 valves closer.

Re: Help troubleshooting miss at all rpms
 

Last time it ran is 10 years ago?

Could be as simple as one of the valves hanging up from sitting. Did you isolate which cylinder that has the miss? If not, pull the plug wires off one by one and note any changes in the engine idle, rpm, etc. The one wire when pulled that does not change the way the motor is running, that cylinder has the issue.

Report back what you find out and we can give you some better recommendations.

Re: Help troubleshooting miss at all rpms
 

I don't remember; have you taken a compression test yet? After 122,000 miles, I would guess that at least a couple of cylinders have problems. There could be some burnt valves and/or a broken ring or three. While wear tends to effect all cylinders equally, things like these don't.

I you don't have a compression gauge, beg, borrow, or steal one and find out for sure.

Re: Help troubleshooting miss at all rpms
 

There’s a wire underneath the breaker plate in the distributor that gets old and brittle and will short out. Check that.

Re: Help troubleshooting miss at all rpms
 

without vacume gauge and compression test your chasing ghosts [remember to remove all plugs and lock the throttle wide open when doing comp test ] if possible do wet +dry +cold and hot tests for a really good look

Re: Help troubleshooting miss at all rpms
 

I have a vaccuum gauge I used to use on motorcycle carbs to balance them 20 years ago. Where should I connect it, and what should the reading be?

Thanks for the helpful tips! Much appreciated.

Re: Help troubleshooting miss at all rpms
 

Thank you, that is a good idea to verify compression. I'll grab a kit. Is it OK to disconnect the fuel line and run my mechanical fuel pump dry while doing this check? It's a new pump. Thank you for the help.

Re: Help troubleshooting miss at all rpms
 

Thanks. I did do this previously, but I didn't really hear a difference. I'll try again and report back. It may be a couple weeks before I can get back to troubleshooting so please bear with me and thanks again everyone for the suggestions.

Re: Help troubleshooting miss at all rpms
 

why was it parked—- usually perfectly good cars are not parked,usually they are parked because of a problem that wasn’t a easy fix.

Re: Help troubleshooting miss at all rpms
 

Previous owner passed unfortunately. I was told he drove it often.

Re: Help troubleshooting miss at all rpms
 

Sure thing. I'm really hoping for your sake it's a stuck valve or valves. If so, there a couple of ways you can fix that. Compression tests are also a wise recommendation. I like to go with the easiest first. LOL!

Re: Help troubleshooting miss at all rpms
 

Hook vac gauge to the port for the wipers. Maybe look at youtube for vacuum reading video. There is a lot out there on the subject and much can be learned from the reading. Really need to do a compression check too. Hung up valve so very common from sitting. If your solenoid has the button on the bottom, put car in neutral and depress button, Engine should spin. Pull all plugs and spin with thumb tight on the hole. Hung valve will be obvious. Can tap stuck valve Lightly with allen wrench down the hole. Drizzle marvel mystery oil down the carb at idle. Others will have more. Have patience, we all have been there.

Re: Help troubleshooting miss at all rpms
 

A remote possibility is a that a nest was made in the exhaust. Not the exact symptoms but anything is possible. Compression check ,then vacuum check . One will tell the directions you need to go .

Re: Help troubleshooting miss at all rpms
 

Just to make sure you know what's available, there are compression gauge sets on Amazon as low as $12.95. Every car owner should have one at that price.

Re: Help troubleshooting miss at all rpms
 

Quick update. I believe I found that cylinder #4 does NOT make any difference in sound when I disconnect the spark plug wire. i didn't notice it before because I had the idle set way too high. The plug is firing for sure. I think that cylinder has an issue, either stuck intake valve (probably unlikely) or worn rings. There is a decent amount of blow by that comes out of the top breather when I shut the engine off. I can see the exhaust valve moving through the spark plug hole.

when cranking, the engine has a pronounced gallop which I assume is that cylinder being dead.

Next step will be a cold compression check. I have a friend coming over this weekend hopefully to help since I can't really bend over with this herniated disc in my back.

thanks all for your input.

Re: Help troubleshooting miss at all rpms
 

At this point, you have nothing to lose. I would squirt some Marvel Mystery oil into the spark plug hole and let it sit for a day or two. While running, pour some Seafoam down the carb. If it is a stuck intake valve, this may help free it up.

Another option is to do the compression check. If the #4 hole is dead, pull the head so you can visually inspect what's going on. If you are careful, you may be able to reuse the head gasket as well.

Re: Help troubleshooting miss at all rpms
 

Another quick update - I put a snake cam into the spark plug hole - both valves are moving up and down. that doesn't mean they're sealing, but they are moving. next step, compression check this weekend. thanks!

Re: Help troubleshooting miss at all rpms
 

I admit to not reading all posts but here goes . Non vented gas cap , not enough volume of fuel ( not pressure but volume) blocked exhaust , plus your typical electrical and mechanical issues. Coil , condenser , valve springs, sticking valve .

Re: Help troubleshooting miss at all rpms
 

My dad's '32 roadster set for years. It ran fine when it was parked (15 years ago?) and now it runs with a terrible misfire. I did a compression check and it definably has a stuck open valve. I don't know what it is about flatheads, but they don't like to sit for years. I have not gotten around to working on it because of a stroke. I've had a little misfire of my own to deal with and I just don't feel like working on cars right. Now if it ran fine when it was parked and now misfires, I'd be looking at the valves. If #4 has no compression, it's no big deal to remove the intake and knock the valve loose. The reason I have not dealt with mine is I had a full race Clay Smith cam ground for it, so I figure I might as well change the cam lifters and springs if I have to pull the intake to unstick a stuck valve. so, for now the poor car just sits.

Re: Help troubleshooting miss at all rpms
 

UPDATES:

- all valves in engine are moving (doesn't mean they're sealing of course). I verified this with a snake cam.

I did a cold, dry compression test with carb removed and all plugs out. It's not good:

1- 80
2 - 70
3- 75
4- 90 (this is actually the cylinder I thought was the problem because I didn't hear any difference when disconnecting the spark plug wire when it was running)

5 -100
6- 60
7- 70
8 - 85

Afterwards, on #6 I did a wet test and it really didn't change - I saw about 65psi. Maybe a valve isn't sealing?

A wet test on the other low cylinders saw about a 10-15psi change.

I don't have the money to put into this thing. I'm thinking about pulling the intake and head, and trying to look at the #6 valves closer.