I just rebuilt my 272 y-block and now I'm having problems getting it to run. It starts but runs like crap #3,5,8 cylinders do not fire every time. I have check the timing about 5 times and it's spot on. I have set the valve lash at 0.19" hot. I have changed the intake gasket 3 times thinking it may not be sealing. I have checked the plugs, plug wire, cap and rotor and points. I have checked the compression it's 150+ in all 8. Any ideas?
Thanks, Rmc292

 

Is the distributor 1 or 2 teeth off?


Do you have good grounds? Block to frame and battery to frame?

 

I have check the timing and it is spot on. I thought the same thing about one tooth off but it's right on. Could this be a leek in the intake or could it be vacuum advance? I'm using headers and #3,5,8 exhaust ports just gets hot not like the rest very hot. I have noticed that if I increase the RPM's the engine smooth's out and then #3,5,8 seems to fire and #3,5,8 exhaust header ports get very hot (normal). Thanks for your replay!

 

3, 5, 8, ... and 2 use the same side of the carburetor. 1, 4, 6, and 7 use the other.
Since you have 3 of 4, my thought is a carb problem.

Ignition is pretty easy to rule out. Attach a timing light to the leads and watch for the flash. If it is erratic, then it is ignition. If it is consistent then it's very likely fuel.

 

I will check these out! I didn't think about the carb. I have checked timing with a timing light and it seem ok.
Thanks!

 

Stupid question but we're certain the firing order is correct with respect to wire routing? #1 cylinder is front, passenger side, 15486372 etc. just sayin'.

Vac advance not an issue here. Disconnect and plug to be sure, for now if you want. Will it idle at all? Is a new crank damper installed or, are we certain the timing marks are accurate?

Also new manufacture condensers are known to be junk, sub in a known good one to be sure. Is a new distributor installed? Make sure the ground strap from breaker plate to dizzy body is good, and the dizzy body is making good ground with block?

 

Make sure #1 wire is on #1 terminal on the cap. Its right next to #2 terminal and its easy to be one off.

 

Any updates?

 

Testing.. 1,2,3... check check

 

Sorry for the delay getting back to all of you. I have stated over with the timing. Now, does #1 need to be on a compression stroke to set the cam and crank sprocket timing? I' using Tim McMaster's cam timing tip. I think I know answer to this question but I just need to be sure.

 

When setting the cam timing, #1 will be at tdc on the exhaust stroke and #6 will be at tdc on compresison.

Cam timing is not your problem. The compression pressure and the fact that it smooths out with more rpm are evidence of that. The symptoms point to a fuel problem - likely the idle circuit is not providing fuel to the affected cylinders.

 

Could an intake leak do this as well? When you say "idle circuit" are you referring to the idle needle adjustment or the idle system in the carburetor it's self?

 

A vacuum leak can cause problems, too. It wouldn't hurt to rule that out.

The idle circuit includes anything involving the fuel supply at idle. It could be the adjustment screw. It could be a blocked passage within the carburetor.

 

I will check this out! I have a Holley Carburetor- C2TE9510-R (2300) 2bbl. Would you happen to have or know where I can find the manual for this carb?

 

Have you had a vacuum gauge on the engine and what does it say at idle, slightly off idle and at rpm? Is the needle steady at all three spots mentioned above?
How about spraying some starting fluid or WD40 around the intake and carb mount while the problem is occurring?
And, have you moved the plug wires at the cold cylinders to a hot cylinder?
I am betting carburetor or some kind of induction system leak.