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Discussion Starter #1
we just finished overhauling a 420u and we messed with timeing and valves but it still back fires through the carb. any help appreciated!
 

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Discussion Starter #3
Yes we are pretty sure we did. Any other possibilities?
 

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Yes we are pretty sure we did. Any other possibilities?
There are only a limited number of possibilities.

Intake valves open at the wrong time:
1. Cam and crank out of sync
2. Valve(s) stuck open (bent valve, missing shims)

Ignition timing:
1. Distributor installed incorrectly
2. Ignition timing too far advanced
3. Plugs wired incorrectly

Al
 

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Does it run. Or does it backfire trying to start it?

I am guessing it runs because you said you messed with the timing.
 

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Discussion Starter #6 (Edited)
No it does not run. we are trying to start it for the first time since the over haul....... timing seems to be exactly right compared to the manual. We have good compression and good plugs,wires,new points,new valves and springs. We had it over bored and the timing on the crank shaft is right so we are stumped..... Yes it backfires out the carb when choked.
 

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Is the condenser new as well? This can cause weird issues and they’re dirt cheap and easy to replace.
 

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Discussion Starter #8
No it is not new but we are getting consistent spark.
 

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There are only a limited number of possibilities
Ignition timing:
1. Distributor installed incorrectly
2. Ignition timing too far advanced
3. Plugs wired incorrectly

Al
I would lean towards these and retard the timing to get it to run.

Sounds dumb, are you sure your have the plug wires correct for the direction the distributor turns. Trust me this happens. Firing order correct but backwards,
 

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Discussion Starter #10
Yes we have been through timing and we switched wires to see what happened but it backfired worse. changed wires took the dist. off and inspected it. i can give it another try but......
 

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i can give it another try but......
Sometimes it’s the simplest thing. Don’t be afraid to try something or repeat what you’ve done before. We all see and learn new things everyday. :drinks:

Condensers are cheap..... :laugh:
 

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If your compression is good as measured against specification then mechanically you should be OK. Good compression generally eliminates cylinder, piston, rings, valves and camshaft timing problems.

I'd double-check the distributor timing. Make sure that the rotor is pointing towards the appropriate ignition terminal in the distributor cap when the reference cylinder is at TDC on the compression stroke.

I'm assuming you've got a decent spark? If it can jump 1/8" gap to ground and is bright your ignition components should also be OK.
 

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Discussion Starter #13
Sometimes it’s the simplest thing. Don’t be afraid to try something or repeat what you’ve done before. We all see and learn new things everyday. :drinks:

Condensers are cheap..... :laugh:
well i have to admit switching plug wires again makes it run on one cylinder... :bigthumb: we know timing still needs adjustment.

but it is not getting oil to the top of the head any ideas here? You guys are great help to me..
 

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but it is not getting oil to the top of the head any ideas here? You guys are great help to me..
Does it have any oil pressure?

If not, stuck pressure relief valve or plugged/disconnected sump pickup (not familiar with this engine).

If yes, maybe head gasket since you've had the engine completely apart. It's blocking the oil passage. Installed wrong or wrong gasket.

Al
 

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Discussion Starter #15 (Edited)
We are getting oil to the filter with good pressure. Here is the line oil is supposed to go through. we took it of the block but still no pressure. this metal line bypasses the head hqdefault.jpg this is NOT our tractor!!!:flag_of_truce:
 

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Discussion Starter #17
We did not put a working gauge on it but it should have enough to make that line squirt oil. I think we will try to run it a bit. some guys think we might just have air in the system because we had every thing empty.
 
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