1970 292 engine issue

[awc7772000]

well when i get past 2500 rpm it sputters and like bucks really bad and i changed the plugs wire cap rotor condenser fixed a vacuum leak and it still does it its a granny 4 speed and it only seems to do it in 4th any ideas and i heard about vacuum on the tank and idk if mine is but its going PSHHHHHHHH when i take it off to fill up?

['68OrangeSunshine]

Timing?
Manifold vacuum leak?
Do you have a 4 barrel Holley w/ old style power valve?

So you're saying you get a sucking sound when you pull off the gas cap? On a pre-emissions truck that's good. It means your gas cap is airtight. No fuel leaks is good.

[292farmer]

mine does same thing, it used to only do it in 4th gear but now in 2nd-4th. i don't know what it is i've done fuel lines and fuel pump, rebuilt dizzy,and i'm thinking its my carb is tuned too lean, mines a 1bbl, my carbs off a 77 250/292.
68orangesunshine if its timing which way do i go? advance or retard it? or just play around with it?

[awc7772000]

well its supposed to be vented right ? so it shouldnt have a vacuum on it and its a 292 inline six 1 barrell manual everything

[68gmsee]

Usually caused by a lean condition. Too much air not enough fuel.

Start by checking to make sure your fuel delivery is sufficient.

Disconnect the fuel line going to the carb, insert it into a plastic container and remove the coil wire from distributor. Have someone crank the engine and check to make sure you are getting a sufficient quantity of gas into the container. A pint of gas should take just a few seconds don't remember exactly how many but 7-10 seconds come to mind.

Clogged filters, defective or weak fuel pump and/or restricted fuel lines may be the cause of insufficient fuel flow.

If all that checks out, then the carb float adjustment and air/idle settings need to checked.

[cdowns]

gas cap should not make noise when removing//you've probally got the wrong cap

have you changed your fuel and air filters recently? you should


could also b caused by crap in the tank clogging the in tank strainer

if you still have points have they been cleaned and gap/dwell set?? that should b done on a regular basis every 5000miles or less

[jayman68]

When you remove the gas cap the air is probably rushing in. Maybe a vacuum is being created that is overcomming the suction of the fuel pump, at higher rpm. Try running for a time with your gas cap not completely tight. Just a thought.

[Richard H.]

Originally Posted by awc7772000

well its supposed to be vented right ? so it shouldnt have a vacuum on it and its a 292 inline six 1 barrell manual everything

I think you're on it , there are two ways to check a fuel pump,pressure or the vacuum side. After you ride for a while you are drawing to much vacuum on the tank. Try a vented cap.

[69GMCLonghorn]

Originally Posted by Richard H.

I think you're on it , there are two ways to check a fuel pump,pressure or the vacuum side. After you ride for a while you are drawing to much vacuum on the tank. Try a vented cap.

That was my thought, too. it has to be starving for fuel because of the vacuum being created in the tank. To verify this, run it down to maybe 1/2 a tank or less and pull the gas cap off. Go for a drive and just don't turn hard to the right. See if it still does it. If it doesn't, then get a vented cap and be done with it.

[awc7772000]

yea i was thinking it might be the wrong cap cause when its topped off it doesn't do it NEARLY as much and i appreciate all the feed back guys i really do appreciate it and yea i did gap the points and all a few times just incase i made a mistake and nothing but im gonna try it with the cap partially off and see

[PanelDeland]

Another cause can be the vacuum advance.If the digaphram in it is leaking and stopping the dist from advancing it may do the same thing.Just something else to check.Just take the cap off and suck on the line.You should see the advance plate in the dist move.If not you may hear it leaking.I suggest you do this with the engine off.

[292farmer]

how much should it move? just a fraction of an inch or a decent amount? i'm not sure how much suction i create compared to the motor.

[awc7772000]

yea i fiddled with the timing and it appeared that it was working

[awc7772000]

well i took the cap off today and drove it and nothing maybe ill look into the vacuum advance

['68OrangeSunshine]

Originally Posted by 292farmer

mine does same thing, it used to only do it in 4th gear but now in 2nd-4th. i don't know what it is i've done fuel lines and fuel pump, rebuilt dizzy,and i'm thinking its my carb is tuned too lean, mines a 1bbl, my carbs off a 77 250/292.
68orangesunshine if its timing which way do i go? advance or retard it? or just play around with it?

Try the factory settings for a baseline. [1968 specs]
Mechanical Advance
[292 w/automatic]
0 @ 900 rpm
19*@ 2000
28* @ 4200
Vacuum Advance
0 @ 7" Hg
23* @ 16" Hg
Point Dwell 31*-34*
Timing 4* BTDC
500 rpm

[292 w/ manual] Mech Adv:
0 @ 900
9* @ 1200
23* @ 2000
32* @ 4200
Vac Adv:
0 @ 7" Hg
23* @ 16" Hg
Dwell 31*-34*
Timing TDC
700 rpm

[292farmer]

thank you!

[awc7772000]

well theres a fuel filter in the carb and that was it lol i spent like 200 bucks looking for the solution tto a 3 dollar problem ohwell lol lesson learned