Carb burping/popping <<<and timing jumping all around>>> (timing issue fixed)

Have a real issue ... '66 Jeep CJ5 with 225 v6, Delco points distributor, Rochester 2G carb.

First - I have a very loud valve tick ... put some MMO in and decided to just live with it for a while, but that's (maybe?) another story. THEN ...

Jeep was running great and then gradually started popping back through the carb ... barely noticeable at first then got worse and worse over about 15 min and I felt like I barely made it home. Made a video of it (link below) ... and then checked the timing ... timing is jumping around all over the place! Thoughts? My first thought is a bad distributor, so I am about to pull it and check it. Any other thoughts?

Video: http://youtu.be/8wYnCsfVltY

 

Re: Carb popping and timing jumping all around

Jumped time? There may be a new timing chain and gears in your future.

 

Re: Carb popping and timing jumping all around

Maybe the tick is a collapsed exhaust lifter so it's puking fire back through the intake on the overlap and the timing is just a side effect of vacuum feedback. I'm probably wrong.


Sent from my iPhone using Tapatalk

 

Re: Carb popping and timing jumping all around

Wouldn't jumped time (unless it is continuing to jump) be steady on the timing line but way off? It seems to move around the zero mark (more and less than TDC), not walking around in one direction. Double checked plug wires are in the right place and order (besides, it was running great before). Pulled the distr and, while dirty, it seems ok and does not have any appreciable play in the shaft. Weights seem to move relatively easy. There was a black ground wire in there that is connected to the vacuum advance can arm and wasn't connected to anything on the other end ... see pic below - it's the black wire sticking out not connected to anything ... but it looks like an old points/condenser ground wire that wasn't being used? Take a look below ...

I should be able to tell if timing has jumped if I pull the valve covers and observe valve movement while hand turning the engine with a soda straw in #1 cylinder plug hole, no?


photo 1 (1) by Troy Davis, on Flickr


photo 2 (2) by Troy Davis, on Flickr

 

Re: Carb popping and timing jumping all around

Actually, now I see in the Service Manual that the loose back wire should be connect to the breaker plate ... that loose connection wouldn't be the cause would it?

[/URL] photo (2) by Troy Davis, on Flickr[/IMG]

 

Re: Carb popping and timing jumping all around

The breaker plate moves per vacuum advance control so it does not have a good continuous ground so that is the purpose for that wire. Any mis-fire at any RPM can be blamed on loss of ground in the ignition system. Yes this could be causing that burp up through the carb. Put a socket and breaker bar on the crank pulley and rock it back and fourth. You will feel the bar move real easy to and fro for some distance. This distance is what's important. Roll the crank around clock-wise to match the damper mark to the 0 deg mark.Then rotate backwards taking out the slack in the timing chain. It shouldn't be over 20 deg for an average used timing set.

 

Re: Carb popping and timing jumping all around

OK, I think the timing moving around was potentially user error - new fancy timing light. I fixed the ground wire like the manual picture, installed a pertronix that I've had sitting on the shelf (while I had the distributor out) + the pertronix flamethrower coil. Timing rock solid now at 5 deg BTDC with the vacuum disconnected.

Still burping/popping back through the carb, though. Sounds very regular now, rhythmic. Popping/burping maybe once a sec at around 750 RPM (Check my math, but 720 RPM equals 12 Rev/Sec ... so each cylinder would be firing once per second?) Now thinking it's in the valvetrain. Worn cam lobe, really stuck lifter, bent pushrod ... what else could it be? Can I see the cam enough if I remove the intake to evaluate it? I have the valve covers off and the rockers look good from what I can tell.

Burping back through the carb would have to be an Exhaust valve sticking closed or an Intake valve sticking open?

 

Burnt valve? But that's more likely on the exhaust side.

Intake sticking open may explain the click, too.

 

Is there any way to test intake valve sticking without taking the head off? Or should I say what's the best way? Leak down test?

 

I'd run it with the valve covers off and just look at them. You should be able to see and hear a collapsed lifter or stuck valve.


Sent from my iPhone using Tapatalk

 

So, if you read my other thread on worn rocker arm shafts, you know I took them off, cleaned them out, and replaced all of the pushrods and lifters. Also blew out the oil galleries to the head/rockers. I think the the drivers side head wax not getting near enough oil and a valve was sticking open allowing ignition in the intake. In any case, when I put it all back together, the burping and the valve tick went away and it runs much smoother! Just wanted to close this one out.

 

It just needed some TLC. Their like a woman...If you neglect them they won't purrrrrr.