Just A Leak Or A Burned Valve? (1 Viewer)

[Iron_Pig]

Since the motor was first rebuilt I had a problem. On the first trip out it ran like a sewing machine for the first 15 dirt road miles. Once it was well warmed-up it stalled terribly every time I took my foot off the gas.I suspected the carb. When I got home I noticed the smell of gasoline.The tank was leaking. In the process of removing the interior, I saw the tub was shot. It was so rusty it was barely attached to the frame. So I had a buddy rebuild a tub by hand. It took nearly a year.
What all this means is there is no more warranty :whoops:

I have positively identified a leaking header/manifold gasket. I tried to torque it to 30 lbs,but it still leaks.
The air/gas adjustment screws on the front of the Motorcraft carb no longer affect the engines running as I turn them ??? That spells vacuum leak, doesn't it?
The black smoke pouring from the tailpipe has a very uneven stutter,I suspect a valve. I guess a compression check is due.
How else could I identify if it's a valve? I don't want to change the manifold/header gasket just to have to pull the head afterwards.
There was also something else I saw I didn't like. Evidently this aftermarket header didn't clear the intake manifold.So it appears "Bubba" took the ball pien hammer to one of the pipes until it cleared the corner of the intake. Of course, that restricted airflow to some extent.
Where would you start with this mess ??? I'm too far into it to quit now. I'm just a level 3 "wrench" running into level 4 jobs. But hey,I once was a level 2,then I kept learning. :-\

 

[dd113]

Does not really sound like a valve to me. Go ahead and adjust them and replace the manifold gasket. The stutter can be caused by bunchs of stuff. Take the MC carb off and throw it in a lake. Go back with Asain or better aftm. You need a vac test, compression test and possibly a leak down test.

 

[IDave]

Nothing you are experiencing is unfixable---yet. Start with a compression test. Do it dry and then wet: putting in a teaspoonful of oil into the tested cylinder and rechecking. Get a vacuum gauge and see what that tells you. But really, don't expect it to ever run right until you fix the vacuum leak at the manifold.

 

[IDave]

And since he wrote while I was writing, I didn't see Dave's note until I posted. I would personally agree with what he says, obviously, but you may not HAVE to throw the carb in the lake. (Mind you, I would, but there's no way you can tell anything about it realistically right now.)

 

[Poser]

You would be hard pressed to get ANY carb to run well with as massive of a vacuum leak that he has described. Before you start thinking that the sky is falling, verify and repair what you know is wrong, and focus on that, and stick with it, otherwise, you could likely talk yourself into doing something that you do not need to.

Good luck!

-Steve

 

[dd113]

I am sure there is a vac leak somwhere but nothing he posted leads me to see a "massive" vac leak. I bet the plugs are black and covered with soot, as is the exhaust. I have seen a lot of MC carbs suddenly give up and run rich as hell for no reason. A vac test will tell the truth.

Lake!Lake!Lake!Lake!Lake!Lake!

 

[toddslater]

If you opt not to put the carb in the lake for fish habitat...fix what you know first ..put a new ex/int gasket on there double it up and don't be shy with the permatex high temp. Now since you have the carb off...rebuild it. Take it apart and give it a dunking in some Berrymans Carb dip/cleaner. When refitting your new needles etc pay close attention to the operation of the float/needle/ seat arrangement. As I suspect based on your description of the black smoke, stutter and non effect of the mixture adjustment screw that your problem lies in the function or lack thereof of the float/needle/seat assembly. Basically, you could have crud in place, worn needle and seat, or a float that maybe sinking or rubbing on the sides....any and all of which will end up dumping fuel in there causing black smoke, stutter, etc...Since your motor was rebuilt I wouldn't run to the valves being burnt just yet. Especially since it ran like a sewing machine for the first 15 miles. Stock fuel pump or electric ?

 

[fsusteve]

Agree with all the above, first I would do the manifold gasket as that will probably solve much of your problem, then carb. Take the header and intake to a machine shop and have them planed, then double gasket them as posted. One step at a time, with a plan and it will run better guaranteed.

 

[Perfect Obsession]

Leak test ! Your opinion!

Bonjour,

I own a stock 2F '78 FJ-40 Landcruiser with 85,000 km (about 50,000 miles).

I am used to test for vacuum leak by spraying water where leaks could happen: carburator, intake, gasket, power brake booster and hose, ... (when cold and when hot)
- Is it a good practice?

By the way, at operating temperature, dry compressions on cylinder #3 and #4 are abnormaly low.
- Should I suspect head gasket, piston ring or valve seating?

I am familar with OHC, not pushrod.
- Is it normal that this sewing machine is ticaliklinging like that? This ticl...ing seams to come from only one pushrod.

 

[IDave]

Bon Jour, PO
Where've you been?

Most people I have read of use carb cleaner instead of water to test for leaks. Engine speed will change if it is sucked into the system. (Has worked for me.)

If you have low dry compression in two cylinders, try wet testing them with a few drops of oil. If compression comes up, then it is most likely worn rings. If it does not, worn valve seats are more likely, although with two contiguous cylinders poor, a gasket leak is also possible.

Ticaliklinging like a sewing machine is exactly how it should sound! If one is more than the others, then those valves are probably just a little looser than the rest. Not a problem, but you might want to check valve clearances.

 

[Nadeau71]

salut PO content de te revoir!! quelle belle snowstorm we had

 

[Perfect Obsession]

Merci Idave !

Yes, I was out. Today, we got about 12 inches of flaky snow. No storm here.