272 rebuild issues/problems
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5th Wheeling
Joined: Jun 2013
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272 rebuild issues/problems
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
Thanks, Rmc292
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5th Wheeling
Joined: Jun 2013
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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!
Cargo Master
Joined: Apr 2003
Posts: 2,389
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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.
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.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
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?
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?
Fleet Mechanic
Joined: Oct 2007
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Make sure #1 wire is on #1 terminal on the cap. Its right next to #2 terminal and its easy to be one off.
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Post Fiend
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From: Waterloo, Iowa
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5th Wheeling
Joined: Jun 2013
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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.
Cargo Master
Joined: Apr 2003
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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.
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.
Cargo Master
Joined: Apr 2003
Posts: 2,389
Likes: 58
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.
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.
Believe Nothing
Joined: Jun 2004
Posts: 7,513
Likes: 394
From: W. Central FL.
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.
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.