Small Block & Big Block Chevy Specific Mouse & Rat Motor Discussion & Conversions

355 SBC Misfire help

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Old 06-24-2014, 01:28 AM
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Angry 355 SBC Misfire help

Well, hello, this is my first post here.

Anyway, I recently built a mild 355 for my Camaro. Its had as strange misfire ever since it its first startup. The no.4 cylinder does not want to run right. Its a misfire that you can hear at idle and upto about 2500 RPM but then it picks back up. This seemed to me like bad rings, so i checked and the compression on no.4 was about 165 pounds, along with the other 7. Checked plugs, wires, distributor, all getting good spark. I already know its running rich, and i plan on swapping my 750 Cfm for a 650 this weekend, but i dont think that would cause only the no.4 cylinder to not run right. This leads me to believe it is the cam. Is there anything else to try before i pull the cam and get it checked out? Im at my wits end here.

Edit: Do you guys think filling it with 92 octane could help? Considering its 11.2 compression. Though i still cant imagine that would only miss only one cylinder

Last edited by Stormdrain; 06-24-2014 at 01:33 AM.
Old 06-24-2014, 12:46 PM
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is the cam solid or hydraulic, roller or flat tappet? have you checked the valve lash?

on another note 11.2:1 on junk pump gas is too much, you will have to back off on the timing to keep it from detonating. which in turn negates the power you would gain in higher compression. you will have to run a higher octane fuel once you get it running right.
Old 06-24-2014, 02:34 PM
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Flat tappet. And yes, all the rockers have been checked and none are too tight.
Old 06-24-2014, 02:50 PM
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Hyd or solid .............. were any too loose on the second adjustment? Particularly on cyl #4
Old 06-24-2014, 04:41 PM
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Hydraulic. No.4 was a touch loose but i dont believe i pushed the oil out of it. i may loosen it up tomorrow and check again but i dont believe the valves are staying open.

Edit: Yeah it couldnt be that because the compresion is good.

Last edited by Stormdrain; 06-24-2014 at 04:49 PM.
Old 06-24-2014, 07:16 PM
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How did you break in the cam and lifters?
Old 06-25-2014, 12:20 AM
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had already been broken together in with previous motor. Ill call up my pops and ask if needed. And yes i kept them matched to the cam lobes they were already worn to. Old motor had about 8k miles when i got the cam and lifters.
Old 06-25-2014, 07:24 AM
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look at the adjusting nut on the rocker stud. if its further down than the rest you could have a lobe going flat
Old 06-25-2014, 11:07 AM
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Just pulled all the plugs, wet wet wet. Im thinking im overloading the plugs with fuel causing it to misfire. it may not be just no.4 because that plug is dry. Im going to try downjetting the carb before i do anything else. And the rockers all look uniform.
Old 06-25-2014, 12:39 PM
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try this, take the handle of a screw driver, and tap the float adjustment on the fuel bowls. the needle and seat might be stuck letting fuel pour in
Old 06-25-2014, 01:30 PM
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first thing i tried. Swapped the jets from 72's to 64's and shes running muuuch better! Thanks for the help though!
Old 06-25-2014, 10:06 PM
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okie dokie



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