Super Chevy
Click here to find out more!

please help me vapor out of carb

  
Super Chevy
Item Posts    Sort Order

please help me vapor out of carb

 
gallegosr2005 gallegosr2005
I love my Chevy Chevette! | Posts: 1 | Joined: 09/11
Posted: 09/05/11
10:15 AM

I have a 70 nova with a 350 chevy it has vortec heads 268 comp cam fordge

flat top pistons
My problem is vapor coming out of front vent tube on all carburetors. Things I have tried
2 demon carburetors 01 holly
3 different distributer 1 h e I
number 1 cylinder is 130 compression took head off had it cleans and inspected
New timing chain and gear had can and lifters inspected
Pulled gas cap off gas tank
2 new fuel pumps
And fuel pressure regulator  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/05/11
10:43 PM

Why do you think this is a problem? There is something making the vent tube do that? Now to find out what it is? That is really what the vent tube is for. To get rid of any undo pressure in the carbs, and vent as it comes out as a vapor. You may also see a vapor comming from the throttle bore of the carbs. Thats a normal thing that is going to happen when you shut the engine off.

Unless you have fuel dripping from the carbs, from too high a fuel float level. (You should be able to see the fuel dripping), and if it's dripping that much it will be a vapor until the fuel evaporates.  Then you will have a hard time starting the engine.When you shut the engine off you will get a little vapor from the vent tube or the throttle bore itself. Unless I'm missing something in the translation of the write up? Maybe give us a little more info. There are smart guys in this forum and we will get you running. Unless you can't start the engine when this is happening I would say it's alright.

Why did you take the head off? Confused  If you did that to do a compression test, you have done all eight cylinders and compared them all. Give us a little more info...130 psi cranking is good, you need to compare it to the other seven cylinders. The longer you crank the engine without charging the battery. The compression may drop from the engine cranking slowly. You may need to keep a charger on the battery to get a good cranking speed from the engine........... Thanks.......... Cool  

gallegos2005 gallegos2005
I love my Chevy Chevette! | Posts: 12 | Joined: 09/11
Posted: 09/08/11
07:27 PM

Sorry i couldn't get back to you the it wouldnt let me back on my user so i had to create a new one.
The problem is the car sounds great when you rev it up but when you drive it, it back fires and dies. The vapor out of the carb spits little balls of gas and i think its choking the car. This vapor happens as soon as you start the car. When you put your figure over the front vent tube the car dies. With all three carbs; we put on my dads vette and none of them die nor do they vapor thats why i think this is a problem. Every cylinder is 140 compression except that one 130 that is why i took the head off and had it checked. then i thought it was a bad ignition so thats why i changed so many distributors. Right now i have a brand new msd with the 6al box.Am i missing something everything keeps pointing to timing i feel but cant seem to get it anything to change i dont understand why the carbs would vapor out on one car but not on the other. if i lower the float down to the bottom and pull the sight glass out it looks like a hippie rolling down his windows jk vapor (smoke) rolls out and doesnt quit. The car starts great and sounds great but if you drive it its a dog unless i really advance the timming but back fires more and you can hear the ping of the rods.
Thanks for your time.
Ryan  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/09/11
05:01 PM

The head checked out OK? Lets forget  about all the carbs the distributors and the vapor for the  time being. That cylinder you had 130 PSI is low compared to the other seven. It's ok as far as cylinder pressures go. Here is what you need to check.

It sounds like you wiped out a camshaft. Check that cylinder lift on the intake and exhaust with the ones on either side and compare them. I would guess that is what is starting to go away.............Good Luck. REMEMBER SPEED NEVER KILLED ANYONE, IT'S SUDDENLY BECOMING STATIONARY THAT KILLS YOU...... Confused  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/09/11
05:09 PM

I forgot one thing, if you have the head back on, you can always put a dial indicator on the rocker arm and check it.  You may see it just by cranking the engine, that the valves aren't going up as far as the others..  

gallegos2005 gallegos2005
I love my Chevy Chevette! | Posts: 12 | Joined: 09/11
Posted: 09/10/11
08:16 AM

I will get a dial indicator and put it on my rocker arms and get back to you thanks alot  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/10/11
11:07 AM

Just take your time and as long as you have the intake off pull some of the lifters up and compare them to each other. Put a straight edge over the bottom of them. If any of them are con-caved theres a problem in the cam area.

I didn't say anything about the valve springs because the machine shop should have checked the valve springs for the correct rate. If you have a broken or weak valve  spring you can get the same condition, that back-fire and popping through the carb, that's what makes the vapor you see. Did you up-grade the valve springs when you changed the cam? If not you could be getting into valve float.

Let us know thanks........  

gallegos2005 gallegos2005
I love my Chevy Chevette! | Posts: 12 | Joined: 09/11
Posted: 11/06/12
09:31 AM

This is for anybody with the same problem searching the Internet has found any  Answers it turned out to be a hole in my fuel line acting like the gas is boiling.