Is this vapour lock?

[Legolas894]

My truck (283 with Q-jet carb) starts like a dream every time when cool. If I drive for about 30 minutes or so, stop at a store for 5 minutes then get back in, it takes quite a few trys to get it to start. If I hold the pedal to the floor it will start so I guess somehow it's flooded.

Any suggestions for warm-starts?

Thanks

[westofb]

try adjusting the mixture on your choke, should be 3 screws to loosen, then the entire assembly turns to richen or lean out the choke...usually marked with a + for rich and a -sign for leaning it...you will want to lean it some...adjust small amounts at a time, drive it and see how it starts warm. You may have to do this a few times.
Vapor lock is when the fuel vaporizes in the fuel line, leaving a air gap so to speak, not allowing the engine to suck fuel. An old time fix for this is to clip a wooden clothes pin (like grandma used to hang out the laundry) on the fuel line...I don't know exactly how it works, but the old timers swear it does. But your problem I would guess is your choke is too rich, causing the flooding problem on warm start ups. Hope this helps!

[Longhorn Man]

the clothes pun helps like cooling fins on electrical components by increasing the surface area.
It allso acts as a heat soak. When your steering wheel is hot from the sun, you put your hand on one part of it and bear with it for a moment. Then when you move your hand to anotherr section, you realize it is still hot where you didn't have your hand, your body soaked the heat out of it.

[dwcsr]

Get a 1 inch or 1-1/2 phenolic space under the carb and your problems will go away. Mine did. Whats happening is the gas boils out of the bowl into the manifold and you have a hard start problem. The real problem is the passage under the manifold heats up the mainfold and the carb to the point it boils out.

The vapor lock was from old time gas when it boiled in the line. They reformulated the gas so that doesn't happen anymore. If you think you have vapor lock wrap some tin foil around the gas line from pump to carb, if the problem persists after its cooled down and then driven for awhile you don't have vapor lock.

[68gmsee]

Personally, I've never had vopor lock problems on my trucks. When I've had similar problems it's always turned out to be flooding issues.

First thing I'd do is look into the carb throat with a flashlight and check to see if fuel is dripping into it after you stop. You should also be able to smell it. Then I'd have someone crank it and try to start it like you are doing. Look at the exhaust for a dark gray or blackish smoke when it does start.

If you know for a fact that it's not flooding on you, then do the other checks for vapor lock. Make sure all of the fule lines are away from any extremely hot parts of the engine.

[cdowns]

vapor lock is mostly an old wives tale myth// rare cases are caused by fuel lines resting directly on very hot surfaces// more common thing is lazy guys using long lengths of cheap rubber hose that either kink or collapses// i too believe in using the phenolic spacers under the carbs that's why most carb manufacturers reccomend they b used

[Longhorn Man]

vapor lock is not a myth or anything. It is a non issue in cars made since the mid 80's when everything went injected with a high pressure electric fuel pump that pushes the fuel instead of draws the fuel.
Any time you reduce the pressure, the boiling point goes down. We all learned that in grade school. When climbing big mounains, the boiling point of water drops from 212 degrees to a lower number, due to lack of atmospheric pressure. Increasing the pressure obviously has the oposite effect. This is why grandma used to cook her roast in a pressure cooker, this is why you have a pressurized rad cap, and this is why the fuel pumps are now in the tank pushing fuel at unreal PSI... to raise the boiling point.
Vapor lock has also gone away considerably in older cars and trucks becouse fuel quality if better than back in the day, and most old cars are ownerd by enthusiasts who (most of them) know to kwwp the fuel lines away from heat and some of them know not to put fuel filters before the pump (a filter is a restriction which causes more of a drop in pressure which makes vapor lock more likely)
Anyone who has ever fan a glass fuel filter has probably seen vapor lock in its begining stages where it is not actually a problem yet. Where it looks like there is no fuel in the filter and it just 'bursts' fuel in every couple moments.

[mclairmo]

Sounds like choke is not coming off when warm. Choke plate stays closed and flooring it, allows a little more air into the carb. Verify choke plate is open when warm. If it is, then maybe the needle and seat are stuck open or float level is not adjusted correctly causing some flooding?

[Legolas894]

Thanks for all the great tips. The fuel line is close to the engine so it could be boiling off 9and it is a few pieces of rubber there too). Maybe a new fuel line is the first fix. I think the carb spacer is a good try too.
Engine starts great otherwise.

[mclairmo]

How close is close? The oem put fuel lines close to the engine. Try using hard line from the pump to the carb and maybe very short pieces of rubber to make it from the hard line to the carb. I use 3/8" hard brake line from Kragen and cut one end off to connect my filter and then to the carb. I think the hard line would be safer and maybe more resistant to heat, especially if wrapped with a heat resistant thermal wrap. A spcaer is good, but a carb heat shield is even better, it will actually have peices of sheet metal that extend under the float bowls to deflect heat away from the bowls. GM used these in some HIPO cars.

[dwcsr]

Originally Posted by mclairmo

A spcaer is good, but a carb heat shield is even better, it will actually have peices of sheet metal that extend under the float bowls to deflect heat away from the bowls. GM used these in some HIPO cars.

He has a qjet, a shield won't help because the bowl is directly on the manifold.

[mclairmo]

Sorry, I was thinking Holleys.

[bigred1957]

Hey fellas, thought I'd chime in as I had a very similar problem with my 72. it ended up being a tiny leak in the bottom of the carb. Every time it would warm up (but not vapor lock) it would leak into the intake when parked and make for a hard start. But it ran great otherwise. There are several lead looking plugs on the bottom of the carb (mine looked all koked up with fuel due to the leak) Only the two I think below the metering jets had leaked but I worked on all of them. I peened the slugs with a punch to seal it up a bit then JB welded over the top of that. Worked like a charm! That may not be the problem in question but it's a thought. Saw on Trucks (spike tv) last summer they showed the same repair but they drilled them out, tapped and instaled threaded plugs......with JB weld.

My 2 cents

[Shyguy]

Originally Posted by bigred1957

Hey fellas, thought I'd chime in as I had a very similar problem with my 72. it ended up being a tiny leak in the bottom of the carb. Every time it would warm up (but not vapor lock) it would leak into the intake when parked and make for a hard start. But it ran great otherwise. There are several lead looking plugs on the bottom of the carb (mine looked all koked up with fuel due to the leak) Only the two I think below the metering jets had leaked but I worked on all of them. I peened the slugs with a punch to seal it up a bit then JB welded over the top of that. Worked like a charm! That may not be the problem in question but it's a thought. Saw on Trucks (spike tv) last summer they showed the same repair but they drilled them out, tapped and instaled threaded plugs......with JB weld.

My 2 cents

What you are describing is what I have to do with mine. If it sets more than about 4 hours without running the only way to start it is to use starting fluid or carb cleaner. Once it starts it runs real good. The carb was rebuilt by a garage just before I bought the truck and it ran ok for a year or so before the problem started.

[Legolas894]

This is an old thread but still a problem. I switched out the carb to an identical quadrajet (4MV) with divorced choke that was in much better condition.

Changed plugs, wires, distributor cap, rotor, points, adjusted timing (bought a timing light), adjusted dwell (bought a dwell meter). I think you get the picture. Runs better on the road than it ever did but the warm-start problem is still there.

When I took the old carb out, the gasket had a metal face on it. The other "new" Qjet had a thick fibre gasket. I bought a new "Mr. Gasket" gasket but it was really thin. Should I switch to the thicker gasket?

Like I said, it always starts great when cold but I have to floor it to restart if warm. Could it be the choke thinks the engine is cold? Mine had a manual choke from the factory (with a 2G carb).

[coloradosean2009]

Originally Posted by Longhorn Man

vapor lock is not a myth or anything....

Any time you reduce the pressure, the boiling point goes down. ...

Increasing the pressure obviously has the oposite effect. This is why grandma used to cook her roast in a pressure cooker, this is why you have a pressurized rad cap, and this is why the fuel pumps are now in the tank pushing fuel at unreal PSI... to raise the boiling point.

Longhorn Man at his finest. This classic reminds me of the burned breakfast analogy for the reoccurring PCV post.

Taking the advice from Longhorn Man and applying the recommendations I have seen in similar posts, I have added a 2" spacer to insulate the carb and reduce the heat sink that delivers all the heat to base of my carb. Now, I am good for most short drives in the summer. However, if it is around 100 and I go for a long drive, the carb will heat up.

For $20 try the spacer.

[bigred1957]

Originally Posted by Shyguy

What you are describing is what I have to do with mine. If it sets more than about 4 hours without running the only way to start it is to use starting fluid or carb cleaner. Once it starts it runs real good. The carb was rebuilt by a garage just before I bought the truck and it ran ok for a year or so before the problem started.

I only wish I would have learned that a little sooner, I can't remember how many quads I had rebuilt for friends that either had the problem and it got worse or had the proble new after the rebuild (possibly as in your case. Now I realized the carb soak cleaned out the fuel varnish and made the leak worse. Oh well we live and learn right?

Dan.......also