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Low compression on 1/2 side
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My52MGTD
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PostPosted: Sat Aug 08, 2020 11:26 am    Post subject: Low compression on 1/2 side Reply with quote

I have a question about my stock dual port 1600. Struggling to get it running correctly. I have rebuilt the carb(34 pict 3). Adjusted the valves, and timing but starts and when warm dies out unless I feather it. I checked the compression warm and have 50 on cylinders one and 2. 3/4 have 115 and 120. What reasons would there be for such low compression on a whole side? I checked the lower head studs and they were at the right torque. Looking for help
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Dauz
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PostPosted: Sat Aug 08, 2020 11:41 am    Post subject: Re: Low compression on 1/2 side Reply with quote

bad rings, non concentric valve seats, valves too tight, etc? What color are your plugs? Do you have blowby?
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PostPosted: Sat Aug 08, 2020 11:54 am    Post subject: Re: Low compression on 1/2 side Reply with quote

Cracked head?

Try running a leak down test.
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My52MGTD
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PostPosted: Sat Aug 08, 2020 12:08 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

Th aks for the response. I have never done one. How do I do that?
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Xevin Premium Member
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PostPosted: Sat Aug 08, 2020 12:57 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

My52MGTD wrote:
Th aks for the response. I have never done one. How do I do that?


Do you have an air compressor? You will need one. Some FLAPS have a tester to
borrow. Good videos on the internet to visually understand what’s going on and how to perform said test. But like most things on internet lots of misinformation. Read the instructions they come with the kit. It is pretty straight forward though.
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Chickensoup
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PostPosted: Sat Aug 08, 2020 1:03 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

YouTube will tell you how
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GARRICK.CLARK
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PostPosted: Sat Aug 08, 2020 1:11 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

All of above and a Loose head
Do tappet clearances 1st
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My52MGTD
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PostPosted: Mon Aug 10, 2020 12:23 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

I have adjusted and rechecked the valves. I don’t have a leak down tester, but will soon. I performed a compression test again using adding oil in the 1/2 side and compression came up to 120 on 1 and 125 on 2. I am guessing rings or loose head. Is it common for this to happen on just one side with two cylinders? I will remove tin and re-torque head to be sure. At least till I get a leak down tester.
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GARRICK.CLARK
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PostPosted: Mon Aug 10, 2020 2:08 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

1 head out of 2 can come loose yes... But there are many reasons your motor is playing up.
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My52MGTD
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PostPosted: Sun Aug 30, 2020 12:38 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

Ok, the head on 1/2 side had exhaust valves not seating so I replaced the head. All good with compression now 120 120 120 125(1234). I still have idle issues after the choke warms up. This is what I have done so far. Adjusted and rechecked the valves. Replaced and Set the points, retimed it. Replaced the condenser. I replaced the intake boots and made sure no leaks at the head or boots. Cleaned and rebuilt the card and made sure all ports are clear with air. Adjusted the carb best I could do being that the idle is rough. Checked the plugs and put in new plug wires, replaced coil. I am at a loss of what to do next. I have ordered a new fuel pump. Any help would be appreciated. PICT 34-3 with single vacuum advance dizzy.
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Luff
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PostPosted: Wed Sep 02, 2020 8:33 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

I hope this helps, I was doing this same back and forth trying to get it right. A dwell meter did the trick. It even has an RPM setting so it helped me there also.
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frenchroast
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PostPosted: Thu Sep 03, 2020 2:49 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

My52MGTD wrote:
PICT 34-3 with single vacuum advance dizzy.

Did it idle and drive ok before the new head? I dont use it but I have an SVDA distributor and measured the vacuum required to advance with a mityvac; it takes ~2x the vacuum to advance than my SVA. The SVA advances with the same vacuum produced by the vacuum port on the 30PICT2 and H30/31. Could be wrong here but wouldn’t a PICT 34 fully advance an SVA at idle?
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My52MGTD
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PostPosted: Thu Sep 03, 2020 3:22 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

No did not idle before after warming up. Just sputtered and died. The distributor was checked by sucking on the vacuum hose and advanced good. Did find a tremendous amount of slop in the distributor that could have been part of the issue. I put an old 009 with points in and seems better at least no sputtering. Not out of the woods yet, but feel I am making progress.
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frenchroast
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PostPosted: Thu Sep 03, 2020 4:41 pm    Post subject: Re: Low compression on 1/2 side Reply with quote

My52MGTD wrote:
I put an old 009 with points in and seems better at least no sputtering. Not out of the woods yet, but feel I am making progress.

That’s good on the 009. Pretty sure the SVA doesn’t work with that carburetor.
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