No power?

[Ciciro]

My '84 has ran great for months with no problems, but last night it lost all it's power over an hour. It was completely undrivable. I eventually got it home by using a stick to keep the top flap on the carb shut. I don't know anything about carbs but this made it drivable, even if it really hesitates.

 

Anyone had this happen to them? What problems could cause this?

[captain720]

Your timing chain jumping 2 teeth blowing a head gasket pretty much anything bad. You need to check your compression (wet and dry) check for solid spark on all cylinders.

[datzenmike]

Blown head gasket. They don't blow instantly and the slow progression of the problem is indicative of the leak getting worse. A compression check may show two adjacent cylinders lower than the others because the gasket is open between them. You can fix this yourself for the cost of a head gasket.

 

There are other possible causes but eliminating the head gasket is first.

[Ciciro]

I am curious why holding th flap shut made the truck run alot better, almost normal. I'll check the compression today

[captain720]

I am curious why holding th flap shut made the truck run alot better, almost normal. I'll check the compression today

I have had this happen before, if closing the choke makes it run normal something is wrong. I have had it where if you closed the choke it would run normal, but the carb was just hanging on and had the worst vacuum leak ever.

[datzenmike]

I am curious why holding th flap shut made the truck run alot better, almost normal. I'll check the compression today

 

A blockage of the jet(s) would force a lean condition. A severe vacuum leak would do the same. The choke reverses this by forcing a rich mixture.

 

A compression test is cheap and easy.

[distributorguy]

Might also be a fuel supply issue.  Adding choke enrichens the mixture.  

[banzai510(hainz)]

I had a tiny rock in my main jet. I had to put the choke on and it would cause the 2ndary to run enough(more vacuum) to get home. It was a weber 32/36

 

 

see if it runs when pouring gas in the carb. this bypasses most of the car so helps you trouble shoot.

 

 

also as above mention a crack causing a massive vacuum leak

[bottomwatcher]

Try a new fuel filter first if you have not changed it recently. Disconnect the fuel line and put it in a jar and check the flow. Actually do this before and after the filter change and see if it makes a difference.

[banzai510(hainz)]

bttom that's a good one forgot about that but since it runs with flap down(choke on) so its getting gas but I could be WRONG 

Im not a 720 expert

[datzenmike]

Might also be a fuel supply issue.  Adding choke enrichens the mixture.  

 

If a shortage of fuel supplied, the choke can't make more. It can only use what's there, or not there.

 

Unless you mean a blockage in the jets, mentioned earlier...

[distributorguy]

Mike, the choke blocks air so that the mixture richens for cold starts.  It CHOKES air.  That means the air fuel ratio goes richer than before, even if the same amount of fuel is being supplied.    

[datzenmike]

I thought you meant a supply problem to the carb. Like filter plugged or pump dribbling fuel in.

[distributorguy]

I mean there isn't enough fuel getting past the throttle plates into the engine - for whatever reason.  Debris in carb, limiting filter, kinked fuel line, could be anything.  Choking air can make a small problem appear to go away.  A manual choke is a great way to check fuel mixture at any speed, at any time.  Of course this doesn't necessarily pinpoint a fuel problem.  It could be a vacuum leak.  

[banzai510(hainz)]

if you pump the gas and see gas shooting in it means the bowl has gas in it. unless it running out as it runs. But usually at idle takes aehile before it empties the bowl

[datzenmike]

I mean there isn't enough fuel getting past the throttle plates into the engine - for whatever reason.  Debris in carb, limiting filter, kinked fuel line, could be anything.  Choking air can make a small problem appear to go away.  A manual choke is a great way to check fuel mixture at any speed, at any time.  Of course this doesn't necessarily pinpoint a fuel problem.  It could be a vacuum leak.  

 

My point was if there is lack of fuel in the carb the choke can't fix this. If you run it till it's empty or near empty a choke has nothing to work with. If fuel bowl is full but a jet part blocked or maybe too small and the mixture lean this would work.