Is this vapor lock or something else??

B

BlackRat

Well-known member
Joined
Mar 27, 2008
Messages
196
Took the Vette out on one of these rare occasions and as always it runs great for a while and inevitably something happens!!!! Rodae around for about 15 minutes in light traffic and about 85 degree weather. Stopped at a buddies house and stayed there for about 20 minutes. Headed for home about 10 milles away. Halfway home the engine starts to symble and chug. Pushing on the pedal seemed to kill it faster. dropping it down in 2nd and putting it under a load would let the engine come back a little. This went on for about a mile with a max speed of 10mph. It then got so bad that it finally cut off. It would fire right back up but when I gave it throttle it was like there as no gas. Now I am moving about 100ft and dying, 100 more and dying just trying to limp it home. Finally dies and I get out and go under the hood. Pump the throttle linkage and the squirter spits a little then nothing. I am getting a full squirt from the secondaries. I crank the car up and it runs rough. Watchung the squirters in the front I am seeing no fuel. manually opening the throttle I am getting spits again. Now I am thinking maybe stuck float. Having no tools I pull the rear veiw mirror out of the floorboard where it fell off earlier:hissyfit: and tap all over the front bowl. At this point the car has been sitting for a coupe opf minutes with the fans running. I get back in the car and it cranks so I take off. It stumbles a little but then cleans out. I am thinking ok it was a stuck float. Make it about 1 miles and 200 yards from home and it starts doing it again!!!!!!

This is an 850 Mighty Demon on a solid cam 454. I pulled theEarl's filter and it was clean. Pulled the float bowl and the float appeared to be fine. So is it vapor lock???? If so what can I do to help this? I am running a heat sheild under the carb and a full K&N extreme air filter and lid settup. Some one had suggested that I might have the fuel going through to much metal with the braided line going to a AN elbow to coupler to earl's filter to coupler to dual feed line.

Help please!!!!
 
I bought my Holley fuel pump from a guy who had nothing but trouble with it, he did not run a return line.
I use a pressure regulator and the return line comes off that. I installed a 3/8NPT plug and drilled a .125" hole in that to limit flow to the return. Works great....
 
MYBAD79 said:
I bought my Holley fuel pump from a guy who had nothing but trouble with it, he did not run a return line.
I use a pressure regulator and the return line comes off that. I installed a 3/8NPT plug and drilled a .125" hole in that to limit flow to the return. Works great....
Click to expand...

Hmmm. I am running a Holley mechanical pump. It has the outlet for the return line I just have it plugged.
 
Do you have a heat riser going from head to head for exhaust gasses passing under the carb??? unless you are in Minnesota type climate, you maybe want to pull that intake and fill that passage with plaster of paris, nothing else, plaster of paris, tape one end, set on edge pour it in slowly, let set over night....plug any EGR crap also....

I have had to do that to keep carbs cold over the years, works like a charm....

oh...need eliminate any heat riser valves too, maybe check they are not stuck closed if you have one....

:twitch::smash:
 
BlackRat said:
SmokinBBC said:
Mechanical fuel pump with vapor return line?
Click to expand...

Yes mechanical fuel pump but not running a return line. Should I? How would this help?

Thanks
Wade
Click to expand...

If I recall correctly, all the 454's had return lines...but I'm not certain about that.

The return line returns excess fuel back to the tank keeping fuel circulating through the main fuel line. Helps reduce vapor lock.
 
My car was origionally a SB car. When I changed it to the BB I did not run a return. It sounds more and more like I need to do this even if it is not the root cause. But If fuel is just sitting in the feed line waiting to be used I can see where it would boil. The intake is an RPM air gap it doesn't have a heat riser that I recall. I know that the intake gaskets I used had the HR block off plates that I installed.

Wade
 
BlackRat said:
Hmmm. I am running a Holley mechanical pump. It has the outlet for the return line I just have it plugged.
Click to expand...

Didn't know there are Holley pumps with return line, most only have supply and discharge.

Circulating the fuel is going to help reduce or eliminate vapor lock.
 
BlackRat said:
Hmmm. I am running a Holley mechanical pump. It has the outlet for the return line I just have it plugged.
Click to expand...
Can't do that, get a 2 line pump or better yet run a return. You may have other problems but sort out your fuel pump first
 
Sounds a lot like the problem I just had!

Not sure if you read this post but this is how I nailed it down.........

http://www.vettemod.com/forum/showthread.php?t=3626

"Turns out to be the sleeve or sock on the sender after all. Yesterday I rigged up a 2 1/2 gal gas can to a 10' piece of fuel line. I then connected it to the fuel pump inlet, car ran fine. I relocatd the rubber line to the rear on the metal line, car ran fine. Drained all the fuel from the tank removed the sender and inspected the sleeve. On the outside it looks like new, but on the inside hard as a rock, like cement almost covering the inlet tube. That just goes to show that a visual inspection through the filler neck is not a sufficiant way to check the sock! Now I have a very well tuned motor with perfectly functioning fuel pump and a brand new sender w/sleeve. "

Good luck,
RPO LS5
 
MYBAD79 said:
I bought my Holley fuel pump from a guy who had nothing but trouble with it, he did not run a return line.
I use a pressure regulator and the return line comes off that. I installed a 3/8NPT plug and drilled a .125" hole in that to limit flow to the return. Works great....
Click to expand...

00fxd said:
BlackRat said:
Hmmm. I am running a Holley mechanical pump. It has the outlet for the return line I just have it plugged.
Click to expand...
Can't do that, get a 2 line pump or better yet run a return. You may have other problems but sort out your fuel pump first
Click to expand...

Yeah I went out and looked last night and I don't have an outlet for a return line. What regulaor should I use and is there a parts store I can pick one up at like AutoZone. I was wanting to take the car to a local show tomorrow night and ordering from Summit will take a few days.

MyBAD79, do you have a pic of your setup? Also not sure I understand where you placed the plug at and then how you attached the hose to it after drilling the hole.


Thanks
Wade
 
Ol' Red has NO return line- or any provision for one. Never had any problem using a stock replacement GM pump.
 
I have had hot-run problems on every BG I've run without a return line. Use of a return line always fixes the problem, so I never run A BG or Holley without fuel return now. I run the fuel return right out the back end of the carb inlet line/fuel log through an oriface or through a return regulator. This keeps cool fuel circulating right past the carb and prevents the problem you're having. Photo below shows a BG installation I did with a return style regulator to return the fuel.

1-20-08TopView.jpg
 
lars said:
I have had hot-run problems on every BG I've run without a return line. Use of a return line always fixes the problem, so I never run A BG or Holley without fuel return now. I run the fuel return right out the back end of the carb inlet line/fuel log through an oriface or through a return regulator. This keeps cool fuel circulating right past the carb and prevents the problem you're having. Photo below shows a BG installation I did with a return style regulator to return the fuel.

1-20-08TopView.jpg
Click to expand...


Thanks Lars. Looking at the pic I see where the tube is coming from the back of the log I assume I can run brided line from there? Also where is that regulator mounted and which one did you use.

Thanks
Wade
 
If you install a restrictor oriface at the end of the fuel log to control the return fuel, the return line is not under pressure, so a braided line works just fine. I just happen to like the "clean" look of mandrel bent tubing. The return regulator in the photo is the Mallory Return-style reg and it's mounted to a bracket which attaches to an intake manifold bolt.

Lars
 
BlackRat said:
MyBAD79, do you have a pic of your setup? Also not sure I understand where you placed the plug at and then how you attached the hose to it after drilling the hole.


Thanks
Wade
Click to expand...


The regulator is pretty much a "T" - I connected the inlet from the pump at the bottom and the right side goes to the carb. The left side has a restrictive plug with a 1/8" (.125") hole, that can be anything that fits tightly in the hole.. I admit my previous description leaves a lot to be desired.... I tapped the inside diameter of the 3/8NPT connector, screwed in a bolt, cut the head off and drilled 1/8"... epoxy will work just as good....
 
MYBAD79 said:
BlackRat said:
MyBAD79, do you have a pic of your setup? Also not sure I understand where you placed the plug at and then how you attached the hose to it after drilling the hole.


Thanks
Wade
Click to expand...


The regulator is pretty much a "T" - I connected the inlet from the pump at the bottom and the right side goes to the carb. The left side has a restrictive plug with a 1/8" (.125") hole, that can be anything that fits tightly in the hole.. I admit my previous description leaves a lot to be desired.... I tapped the inside diameter of the 3/8NPT connector, screwed in a bolt, cut the head off and drilled 1/8"... epoxy will work just as good....
Click to expand...

Ok let me talk this out and make sure I understand. You took a "T" fitting (3 ports essentially)placed it inline of the feed line from pump to carb. Blocked off the 3rd port which should be the leg of the "T" and then drilled an 1\8 inch hole in the blocked port ("T leg") and ran the return line from there to the tank. Correct?

Lars, from your suggestion above can the same thing be done with your setup?

So in both instances there is not need for an actual regulator as long as you have the restriction correct?

Thanks for the info and patience guys!
 
Been using that setup for years and it works very well, not only for vapor lock but also to prevent over pressurizing the needle and seat in a Qjet.
Start with a smaller hole and go what you feel comfortable with, but make sure you have enough flow to the carb under all rpm's.

It is not as good a system as a quality regulator.
 
You must log in or register to reply here.

Latest posts

Back
Top