New Theory! Carb issue?

[fropleyquark]

5.0/Alpha 1 Gen II

So I was originally thinking that Im leaking oil into the cylinders. I thought this because when I pulled the old plugs they were oily. To add to it, with the new plugs, when I start her up cold, I get a big choke/cough/cough/cough of smoke.

But I started thinking. The puff is black not blue which indicates fuel not oil. Im also having an issue where the throttle doesnt return entirely to idle without actually pulling the linkage. (Im going to fix this tonight).

Do you think that maybe because the throttle is still out a little, when I shut down, fuel accumulates in the carb then when I start her up, POOF!

Am I thinking right here? What do you guys think?

 

[fc3]

Excess fuel does not leave the plugs oily. Oil fouling looks very different from excess fuel fouling. Show us your plugs!

 

[JediJD]

+1 Completely different animals. Check to see which animal you have. Leaking oil stem seals pretty flippin' common in automotive applications...not completely sure about your model.

Certainly possible, if the plugs are fuel fouled, for it to be a carb problem. The most common reason would be a bad seat in the fuel intake float, allowing fuel to leak into the main chamber. I assume you have a manual fuel pump? Sometimes people will put hi pressure electric fuel pumps on carbureated engines. Most carbs are not designed for the same levels of pressure needed by injected engines, and the excess pressure blows the seat completely out of the float bowl.

 

[fropleyquark]

+1 Completely different animals. Check to see which animal you have. Leaking oil stem seals pretty flippin' common in automotive applications...not completely sure about your model.

Certainly possible, if the plugs are fuel fouled, for it to be a carb problem. The most common reason would be a bad seat in the fuel intake float, allowing fuel to leak into the main chamber. I assume you have a manual fuel pump? Sometimes people will put hi pressure electric fuel pumps on carbureated engines. Most carbs are not designed for the same levels of pressure needed by injected engines, and the excess pressure blows the seat completely out of the float bowl.

I think maybe I explained that wrong. The original plugs I pulled out were oily. I have no idea what the new ones look like. What I do know is that I get a big puff of black smoke with the new plugs, I also did carb work at the same time (it wouldnt even run with the old plugs). Ill pull a new plug tomorrow to see what it looks like. Im really thinking I have excess fuel not oil.

-It doesnt smoke at all after the 1st 15 seconds of a cold start (sitting all night). I can start her up without a problem all day long with no smoke after that. Only time theres smoke is after about 8 hours or more of sitting.

-Yes manual fuel pump

-I just put a sping on the carb throttle to help it return to normal idle. So far so good.

I figure rather than all of this guessing, pulling one of the new plugs will give me a difinitive answer... :grin:

You guys think Im on the right track? Thanks

 

[SCORPIO]

Could you have a stickey or missadjusted choke? I'd sooner think the choke is causing a rich mixture before I'd condem needles or seats. Start simple and work to the complex. I posted a reply in your other post about adding a auxillary return spring to pull your throttle closed, its cheap and it works.
As others have said, oil on plugs will look different than fuel loading. Are you sure you wern't seeing left over fogging oil residue on the old plugs?

 

[fropleyquark]

Could you have a stickey or missadjusted choke? I'd sooner think the choke is causing a rich mixture before I'd condem needles or seats. Start simple and work to the complex. I posted a reply in your other post about adding a auxillary return spring to pull your throttle closed, its cheap and it works.
As others have said, oil on plugs will look different than fuel loading. Are you sure you wern't seeing left over fogging oil residue on the old plugs?

Positive, she wasnt winterized last year.

I want to agree with your choke theory but I cant see the choke causing that much hesitation and smoke. Its really like 15 seconds of hesitation and DARK smoke. Then, presto! Like someone flipped a light switch, its all gone and she purrs like a kitten.

 

[Southpaw II]

Worn valve seal........after you shut down, accumulated oil on top of the cylinder head seeps down the valve into the cylinder. When you start up, you get the puff of (black) smoke, and it's gone. while running, the valve stem seals off the clearance between the seal and the valve stem, or the seepage is so small you don't notice it while running. Typically, no problem now, but it will gradually worsen till oil usage goes up and smoke worsens. That's when you get the valve job.

 

[fropleyquark]

Yeah thats what I thought originally. I replaced the valve seals on one of my Jeeps for the same reason. Not a fun task.

 

[fc3]

Sounds like Scorpio might be right. You have a mis-adjusted choke. It's easy to tell if the smoke is from oil or fuel. What does it smell like? If it's too rich it'll smell like gasoline. If it's oil it'll smell oily.

BTW, I always found changing stem seal to be rather trivial. Why was it so hard on the jeep?

Best regards,
Frank

 

[sprink56]

If you have a Quadra Jet I might have the answer. QJ's are notorious for the fuel bowls leaking out of 2 plugs in the base of the carb. There is a fix. Do a complete re-build on the carb and while you have it down and clean, put epoxy over the 2 plugs at the bottom on the out side of the bowl, let it dry 24 hrs and re-assemble with all of the new parts in the kit and you are good to go.

Here is a link to an article that explains this in detail.

http://www.cadvision.com/blanchas/54pontiac/qjet.html

I have repaired Q-Jets on several occasions for over 35 years and as these carburetors age this is what happens.

The 10% ethanol in today's fuels probably hasn't helped much as either.

My money is on this condition as well as your needle valve , seat and the float are probably due for replacement. If it hasn't happened already your engine will be hard to start after it sits for a while because there is no fuel in the bowl. Once the fuel pump builds up the fuel level you are good to go. This will get worse untill you correct it.

I don't know how confident you are in your ability to re-work a carburetor but it sounds like you know what you are doing and can handle it. If you do it yourself you will save hundreds$$$.:thumbsup:

Good luck and if I can provide any more info I will. Hope this helps.

 

[fropleyquark]

Sounds like Scorpio might be right. You have a mis-adjusted choke. It's easy to tell if the smoke is from oil or fuel. What does it smell like? If it's too rich it'll smell like gasoline. If it's oil it'll smell oily.

BTW, I always found changing stem seal to be rather trivial. Why was it so hard on the jeep?

Best regards,
Frank

Wow, no one was posting in this thread anymore. Didnt notice new comments. :grin:

I really couldnt tell you. The tool I had to compress the springs really sucked. Last 2 valves up against the firewall were inaccessable. The Jeep was lifted too. I dont really know, it was just a difficult job. Nothing went easy. :huh: