IH 345 Running Rough Intake Backfire

Discussion in 'General IH Tech' started by Bpenz14, Sep 10, 2019 at 5:05 PM.


  1. Bpenz14

    Bpenz14 Farmall Cub

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    Hi all,
    I have a 72 1210 which I have been fighting to get running well for a while now. Parts I have replaced are.
    Carb - 2300 list 6391 (same as what was on it)
    Fuel lines
    Tank was recoated and cleaned
    Fuel sending unit
    Fuel filter
    Plugs, wires, cap, rotor
    Checked timing and firing order
    Checked that rocker arms were moving

    I am able to fire the engine up but it seems to be running on only a few cylinders. When I have the choke on it will rev up (very slowly) but with the choke off if throttle is applied it fires up through the intake and dies.

    Thanks in advance for all the help!

    -Brad
     
  2. Bill Bennett

    Bill Bennett High Wheeler

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    Are you timing the engine from the #8 cyl? Rear on passenger side? Verify fireing order using cyl# as cast on the intake manifold runner, about 1 inch from where the manifold meets the heads.
     
  3. 1975IH200

    1975IH200 High Wheeler

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    "Checked timing and firing order"
    How were they?
     
  4. Bpenz14

    Bpenz14 Farmall Cub

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    Timing and firing order looked good. Timed off of #8. I just went out to check points gap and that looked good also.
     
  5. Bpenz14

    Bpenz14 Farmall Cub

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    Also not sure if this could be somehow related to how the distributor is turning or in some other way. But from what I can tell there is no eccentric on the cam for the fuel pump.
     
  6. Jeff Jamison

    Jeff Jamison Lives in an IH Dealership

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    Did you look at the points contacts,are they clean,when where they changed last along with condenser
     
  7. Bpenz14

    Bpenz14 Farmall Cub

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    I haven’t changed the condenser yet I’ll get one ordered up and see what that does but every cylinder seemed to have good spark.
     
  8. Bill Bennett

    Bill Bennett High Wheeler

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    When you changed and adjusted the points, did you use the little capsule of lube on the distributor points cam and rubbing block of the points? Doesn't need much.
     
  9. mallen

    mallen High Wheeler

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    Check compression.

    Change the condenser
    Change the points if you have not

    Check firing order (again) Draw a picture of the engine showing the front (a fan) end and back (tranny) end , and a picture of the distributor cap,and draw where the wires go. Then snap a pic with your phone and upload it. (Its easy to misunderstand where the wires go) Also upload a picture of the engines bay so we can see how the wires are routed correctly. There are some wires that have a tendency to crossfire and are thus routed a certain way to avoid that.

    Check the dwell with a dwell meter. It's a lot more accurate than measuring with a feeler gauge. Is the dwell steady or does it vary wildly.

    Check the firing order yet AGAIN. That's what it sounds like. Don't just eyeball it. Run your fingers along each wire, going back from the cap , to the plug boot, one at a time. Eyeballing it is prone to error, no matter how carefully you try. Also check that each wire is properly attacked at each end. You should be able to feel it when it clips onto the spark plug.

    I'm thinking you will find one (or both) of two things. Either , to spite thinking it's correct, the firing order is off. Or there is a bad intake valve. Even if you didn't swap some wires mistake the firing order COULD be exactly what you INTEND it to be, but somehow, you have the wrong order. That's why I want you to draw what you have. A typical reason that it backfires through the carb is that the mixture ignites in the cylinder, but the intake valve is not closed or is not sealing and thus the flame propagates into the intake. If your ignition timing is WAY off, that can do it. If you have a bad intake valve, it can also do it. Or if you have a crossfire (two wires running close together, where on plug fires , and a spark is inductively coupled to another) A common cause is having two wires reversed. This probably blew your power valve on the new carb as well, so that will need to be fixed. I use Carter carburetors mostly, so someone else will have to provide you more details on that particular issue.
     
    Last edited: Sep 11, 2019 at 2:27 AM
  10. Bpenz14

    Bpenz14 Farmall Cub

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    Okay I will check the firing order again. And yeah I have a couple extra power valves laying around I can check to see if mine blew out from the backfires. What kind of wires are usually associated with crossfire?
     
  11. winchested

    winchested High Wheeler

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    #5 and #7 cyl wires.
     
  12. wjajr

    wjajr Binder Driver

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    You may have a big vacuum leak. Is the carburetor's float level correct? If it's too low will that will cause lean condition mimicking a vacuum leak. Like the other have suggested, check firing order, condition of plug wires, and coil. A weak coil will cause poor idle and throttle response due to weak spark.
     
  13. Bpenz14

    Bpenz14 Farmall Cub

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    I will double check the float level again but last time I checked it was good plug wires and coil are brand new but maybe I got a faulty coil. I thought a vacuum leak could be my issue since when I tested it was making only a few in of merc but I thought that could also be because of how it was running a few cylinders short. I replaced the intake manifold gasket and carb base gaskets and I only have vacuum lines running to the advance and to the PCV and there was no obvious leaks there.
     

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