John Deere 420 back firing through carb.
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    E.J.H's Avatar
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    John Deere 420 back firing through carb.

    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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    AlKozak's Avatar
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    Quote Originally Posted by E.J.H View Post
    we just finished overhauling a 420u and we messed with timeing and valves but it still back fires through the carb. any help appreciated!
    Are you sure you set the cam timing properly?

    Al

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    E.J.H's Avatar
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    Yes we are pretty sure we did. Any other possibilities?
    1988 John Deere 316 50" Deck SOLD
    1952 Ford 8n SOLD
    1987 John Deere 318 46" deck 54" 2-way blade ---- SOLD
    1958 John Deere 420U project
    1940 John Deere B SOLD
    Kubota B6200E 2WD
    Except a man be born again,he can not see the Kingdom of God....

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    AlKozak's Avatar
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    Quote Originally Posted by E.J.H View Post
    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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    Herminator's Avatar
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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.
    Welcome to Intermission.

    2017 2038R, 400, 3020 & HPX and thingies to hook to the them.
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    E.J.H's Avatar
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    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.
    Last edited by E.J.H; 08-13-2018 at 08:58 PM.
    1988 John Deere 316 50" Deck SOLD
    1952 Ford 8n SOLD
    1987 John Deere 318 46" deck 54" 2-way blade ---- SOLD
    1958 John Deere 420U project
    1940 John Deere B SOLD
    Kubota B6200E 2WD
    Except a man be born again,he can not see the Kingdom of God....

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    Keeper of the GTT Cookies dieselshadow's Avatar
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    E.J.H's Avatar
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    No it is not new but we are getting consistent spark.
    1988 John Deere 316 50" Deck SOLD
    1952 Ford 8n SOLD
    1987 John Deere 318 46" deck 54" 2-way blade ---- SOLD
    1958 John Deere 420U project
    1940 John Deere B SOLD
    Kubota B6200E 2WD
    Except a man be born again,he can not see the Kingdom of God....

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    Herminator's Avatar
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    Quote Originally Posted by AlKozak View Post
    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,
    Welcome to Intermission.

    2017 2038R, 400, 3020 & HPX and thingies to hook to the them.
    112 - Sold in July 2017 but took me until November to admit I just cast it out into this cruel world.
    #compactfarmer

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    E.J.H's Avatar
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    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......
    Herminator likes this.
    1988 John Deere 316 50" Deck SOLD
    1952 Ford 8n SOLD
    1987 John Deere 318 46" deck 54" 2-way blade ---- SOLD
    1958 John Deere 420U project
    1940 John Deere B SOLD
    Kubota B6200E 2WD
    Except a man be born again,he can not see the Kingdom of God....

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