351c Won't RUN after Rebuild- carb backfire - Page 2 - Vintage Mustang Forums
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post #16 of 33 (permalink) Old 09-07-2019, 09:22 PM
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Water Outlet Restrictor

Does the engine have the water outlet/thermostat restrictor installed? It's a brass disc that is installed in the block below the thermostat. Clevelands need this to stay cool. It's easy to overlook.
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post #17 of 33 (permalink) Old 09-07-2019, 09:45 PM
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Does the engine have the water outlet/thermostat restrictor installed? It's a brass disc that is installed in the block below the thermostat. Clevelands need this to stay cool. It's easy to overlook.
^^^ Ditto. The 351C uses a Cleveland-specific thermostat and a metal disc that closes off the internal bypass when the thermostat opens. Without the disc in place coolant will recirculate back into the engine instead of going out to the radiator.


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post #18 of 33 (permalink) Old 09-09-2019, 10:39 AM Thread Starter
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Yes it does, to the best of my memory.

I think out overheating issue came from running so lean, but we shall see.

I've bought some new gaskets. We'll see what happens after we fix out vacuum leak.

P.s. Does anyone know where to buy a cheap shroud?

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post #19 of 33 (permalink) Old 09-09-2019, 05:04 PM
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A new shroud can be purchased from numerous vendors for a bit less than $100. I've driven a 70 Cougar 351C with A/C for many thousands of miles without a shroud and possibly not the correct thermostat. It wasn't until I fixed the sender that I realized it was running hotter than normal. As bad as it was, the coolant never overheated to the point of boil-over.
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post #20 of 33 (permalink) Old 09-10-2019, 09:03 AM
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Wow! Do these kids know how lucky they are to have such a cool project to learn on?
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It sucks to get old but at least the expectations are lower. 65 mustang coupe, 306, 10.4 compression, 180cc homeported Chinese heads, funnel web, t5z, 4.56 gears in a 9 inch locker
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post #21 of 33 (permalink) Old 09-12-2019, 10:33 AM Thread Starter
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Update-

Ok, so I'm not 100% sure we have a vacuum leak now, but I thought we did.

Our 351c is freshly rebuilt, by high schoolers mind you.



We have a Pertronix Flamethrower Ignitor 1 distributor(D134620) with matching coil.*

Crane cam H-278-2 with matching lifters.*

Stock pushrods, rockers, etc. Stock springs, all set to correct height by our machine shop.*

Currently running the stock intake.*

Right now she is hard to start, we get some backfires out of both ends. I retarded the timing some and it seemed to help. We set base timing at 10 degrees BTDC. We droped a new carb on it it it is getting good fuel now. She doesn't want to idle very well below 800 rpm.*

Once it is a little biy more stable I plan to try a power balance test to see if all the cylinders*are firing equally.*

We have not done a compression test as of yet.*

We did set the adjustable timing gear to 2 degrees BTDC as we were suggested after looking at our cam specs.*



On thing I am concerned about is the valvetrain geometry and pushrod lengths. I don't think they should be a problem, but maybe? If valves weren't seating, that would explain backfires.*

We can do a compression test today...*

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post #22 of 33 (permalink) Old 09-12-2019, 10:46 AM
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What carb spacer are you using?

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post #23 of 33 (permalink) Old 09-12-2019, 11:24 AM Thread Starter
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post #24 of 33 (permalink) Old 09-12-2019, 11:49 AM Thread Starter
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What carb spacer are you using?
We just installed a new Summit carb yesterday and that is the supplied spacer. (These problems existed before the new carb too...)

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post #25 of 33 (permalink) Old 09-12-2019, 11:59 AM
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a) Are you using the correct firing order?

b) If so, I believe you have a valve "issue".

I'd go next to a compression test followed by a leak down test.

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post #26 of 33 (permalink) Old 09-12-2019, 12:03 PM Thread Starter
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a) Are you using the correct firing order?

b) If so, I believe you have a valve "issue".

I'd go next to a compression test followed by a leak down test.
We're definitely good on the firing order. So I agree that compression test is next.

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post #27 of 33 (permalink) Old 09-12-2019, 12:47 PM
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Quote:
Originally Posted by Woodchuck View Post
a) Are you using the correct firing order?

b) If so, I believe you have a valve "issue".

I'd go next to a compression test followed by a leak down test.
Agreed, the rapidly swinging needle usually indicates a valve problem. I'd do a compression test, but I'd also check the lifter preload. IIRC, you put in an aftermarket cam with the factory bolt-down rockers. If you have too much preload, the valves might be hanging open. You can fix that temporarily with shims under the rocker stands. A permanent fix would be the Crane retrofit kit and some B351 rocker stands.

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post #28 of 33 (permalink) Old 09-12-2019, 03:39 PM Thread Starter
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So, we just did one rocker and what I've noticed is that once we hit zero lash, I can tighten the the bolt until it goes down another ~.033". But I also noticed that it is the valve that opens, not the push rod going down and the lifted compressing. So, I cannot tell how much the lifter is compressing, but the valve is definitely opening. I calculated by the amount I turned the bolt, but I may go grab a dial indicator now and measure more precisely.*

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post #29 of 33 (permalink) Old 09-12-2019, 03:52 PM Thread Starter
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OK, well with the dial indicator it pushed the valve open about .033, but then after tightening and loosening it a few times I think the lifter adjusted and it went to 0 lash.*

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post #30 of 33 (permalink) Old 09-12-2019, 04:46 PM Thread Starter
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A THEORY-
We are using an MSD 6A ignition box with the Pertronix distributor. They are supposed to be compatible. From what I read online, people have had issues with the MSD box arcing inside the cap and firing cylinders prematurely. Thoughts? Once the compression test is done we can bypass the msd box for a bit.

3 Cylinders down-
1=180
2=180
3=170.... so we may com back and investigate this one more. Check the lash/preload.

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