Motor missing at higher RPM Maybe even just above an idle

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Post  digger460 on September 8th 2012, 10:21 pm

Seems like #3 and #7 are not firing. When we were at the track today someone had a temp guage and 3 and 7 were always cooler by 100+ degrees... New wires ,changed spark plugs, swaped spark plug wires, ckd valve adjustment, removed carb spacer,. Changed cap and rotor. I have all MSD ign. I pulled #3 spark plug and ckd for spark and was good. Anyone have any other idea what I could ck for.
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Post  Larry Williams on September 8th 2012, 10:57 pm

compression. I would do a leak down test
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Post  dfree383 on September 8th 2012, 11:47 pm

Lean condition?

When did you notice the change? What did you change?


Last edited by dfree383 on September 8th 2012, 11:49 pm; edited 1 time in total
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Post  cool40 on September 8th 2012, 11:48 pm

vacuum leak.
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Post  Dave De on September 8th 2012, 11:59 pm

Larry Williams wrote:compression. I would do a leak down test
X2
Do the leak down test. I had 2 cold holes and the leak down showed ring leakage that led to finding burned pistons. If I continued to run it #5 piston would have failed completely and ventilated the block.

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Post  crittersf1 on September 9th 2012, 9:34 am

Leak-down test will identify the problem.
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Post  digger460 on September 9th 2012, 8:16 pm

I did try a couple tank fulls of the Q16. And since than it hasn't run right. When I went to the Q16 I installed bigger jets.
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Post  IDT-572 on September 9th 2012, 9:17 pm

If you didn't step it up 8-10 you may have leaned it out and hurt something............
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Post  digger460 on September 10th 2012, 12:48 pm

I went up from 84 to 96. Oh well, I'll get it taken apart in the next couple days and find out.
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Post  IDT-572 on September 10th 2012, 12:51 pm

digger460 wrote:I went up from 84 to 96. Oh well, I'll get it taken apart in the next couple days and find out.

Let me know what you find...............
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Post  digger460 on September 12th 2012, 1:09 pm

I removed the heads and found nothing wrong. Valves look OK.. Pistons don't have any holes in them... I ckd the cam lobes and lifters on 5 and 7 and they looked Ok.



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Post  dfree383 on September 12th 2012, 1:24 pm

Check the pressures on the valve springs.

And check all the valves while they are out.
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Post  HorsinAround on September 13th 2012, 10:36 am

Dave De wrote:
Larry Williams wrote:compression. I would do a leak down test
X2
Do the leak down test.

X3
And if you still have the heads off, check the spring pressures as it's a good time to do it. Also, check all the push rods and rockers.
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