vaporlock?? how do i fix it?

[cap14]

How do i Fix it? I have noticed that sometimes my engine feels considerably more powerful than others. When i turn the key to the off postion the engine putters a few extra times. the days it feels more powerful i notice it does not putter after i shut it off. I have been told this may be do to vapor lock. Any thoughts??

Its newly rebuilt 340.

thanks--
mark

[dave571]

Carb heat shields help.

Blocking the heat crossover(in the intake) is another good method.

It is also felt that mechanical fuel pumps serve as a fuel "heater". Electric ones do not transfer engine heat to the fuel.

There's a few things you can try anyway.

[timty2]

Consider changing the fuel line routing as well. Move fuel lines away from sources of heat, such as headers/manifolds. If not practical to move the lines, consider heat shields in high heat areas.

Vapor-lock is typically used to describe "No Start" conditions, where the fuel actually starts to boil and vaporize, if I'm not mistaken, and prevent the car from re-starting.

At any rate, you are describing more of a performance reduction issue here it seems to me.

My advice is to get a notebook, and when you notice a drop-off in performance, note the time of day, the engine/coolant temp, oil PSI, air temp, how long the engine has been running and under what conditions (FWY? City?) and where you last filled up, etc... and anything else that is "Note-Worthy"

You may stumble across a "Trend" that will help you to reproduce the problem and take steps to correct.

If I were to take a guess, (Not knowing how many miles are on the engine) you may be dealing with carbon buildup on the cyl heads/pistons when accounting for your run-on or dieseling problem. Usually pinging accompanies this issue, but you may not always hear it when it is happening.

You can try a decorbonization kit, where distilled water or specific chemical is ingested though a vacuum line and "Steam cleans" the combustion chambers. This makes for a great deal of smoke out the exhaust... (Your neighbors may call the fire department on you!) but this would be a great way to see if this is what you are dealing with! I would make some notes first over a few days, then try this trick and see if anything gets better.

Hope this helps! Good Luck...

[451Mopar]

It sounds more like the intake manifold and carb is getting too hot. I would install the manifold gaskets that have the heat crossover blocked so the exhaust gas does not run through the intake manifold. This will cool both the carb and the air entering the engine. The run-on could be form the engine chamber or spark plugs being too hot also.

Also if you have the stock exhaust manifolds make sure the exhaust heat valve on the passenger manifold is not sticking closed. It should move very easely.

You can also use a thicker insulating carb to manifold gasket. The gaskets are about 5/16" (0.320" for the Edelbrock ones) thick. There are also plastic, phenolic, and wood carb spacers that are about 1/2" to 1" thick. Some have heat shields, but they are pretty much for Holley carbs, not Carter type carbs.

If that dosen't fix the run-on problem, check your engine tempature and make sure the engine is not running overly hot.
Also check the spark plugs to make sure the air/fuel mixture is in the ball part and the spark plugs are the correct heat range.

If you had a "true" vapor lock problem the engine would just lay down, be down on power and maybe sputer durring acceleration.

[6pakman]

yea do what timty2 says about the notebook, and when you find out that is not going to work, you have a dieseling problem. and dont let it go on to long otherwise your going to blow a hole right thru a piston!! your engine is to far advanced, or retarded. what ever the case have it looked at soon.good luck.oh by the way, its not vapor lock you have.

[Buddy Branon]

If you suspect vapor lock I would check the fuel pressure. If you are low on fuel pressure it can get hot enough under the hood to boil the fuel in the line, and of course the engine can't run on vapor. Increasing the fuel pressure in theory will raise the boiling point in the fuel line to help counteract the problem. Keep in mind your problem can be some of the other things mentioned even a combination of them. Some testing is in order.
I think the fuel pressure should be around 7 psi with stock pump less under WOT.

You should pick up some good info on this one. Oh, BTW the old farmers use to clip clothes pins on the lines to help with vapor lock. Helped cool the line I suppose.

[cap14]

hey thanks for all your suggestions. You ve certainly given me a place to start. Currently there is no spacer between my intake and carb which i suspected was a problem and i will definitely check out where my fuel lines are and maybe reroute them furthest away as possible. I also am suspicious of the flaps on the exhaust manifolds since there are some snotty looking welds on the nuts to em. The exhaust minifolds are stock from a 318. i have Also notice the temp rides a notch lower when it feels like its running better so maybe those flaps are stickin as some one suggested. The temp rides a hair past the second line on the left in my gauge. Does that sound right to any one? Its a challenger dash, sorry i have no numbers in degrees.

[mtrv8n]

Hey, cap, I work in Brooklyn, have a lot o time in on the 340. ring me at 768-1498,
SCott

[kdoghouse]

Vaporlock will cause a lack of power which is the same as too lean an a/f mixture but i never seen it cause dieseling. There are only two things that cause the engine to diesel, those are too high of an idle and/or too much initial timing, or both.