Hunting Idle JD 450B

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labbe001
40C crawler
40C crawler
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Hunting Idle JD 450B

Post by labbe001 » Thu Jun 16, 2022 7:44 pm

Hi Guys
I was out running my JD 450B the other day and decided to replace the fuel filter. Directly after replacing with new, the machine started hunting for a steady idle. The RPMs fluctuated up and down and up and down. Any thoughts on what could have caused this? Is there a fuel prime out something I was supposed to do after replacing filter? Kind of lost at what to do….thanks

B Town
350 crawler
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Re: Hunting Idle JD 450B

Post by B Town » Thu Jun 16, 2022 9:00 pm

How long did you run the engine after the filter change.

It sounds like air in the fuel system (kinda fits with the filter change). The is a priming lever to pump up the fuel. This lever is attached to the mechanical fuel pump on the right side of the engine, towards the front.

My experience is that it can take quite a few minutes for this behavior to calm down.

Bruce

labbe001
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Re: Hunting Idle JD 450B

Post by labbe001 » Fri Jun 17, 2022 7:28 am

B Town wrote:
Thu Jun 16, 2022 9:00 pm
How long did you run the engine after the filter change.

It sounds like air in the fuel system (kinda fits with the filter change). The is a priming lever to pump up the fuel. This lever is attached to the mechanical fuel pump on the right side of the engine, towards the front.

My experience is that it can take quite a few minutes for this behavior to calm down.

Bruce
I ran the engine maybe 4-5 minutes after I swapped the filter....and mostly at a lower RPM range because I didn't want to risk the RPMs surging very high. Looking online and in my service manual, I've noticed most 450B machines have dual canister type filters. Mine is a single square glass type filer. Was there a change at some point or a conversion kit that was sold? My machine doesn't have and serial numbers on the engine nor on the body but it is a pre 142199 serial and is a straight 450B with the HLR controls located down b/t your feet as your sitting in the seat.

Jim B
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Re: Hunting Idle JD 450B

Post by Jim B » Fri Jun 17, 2022 7:49 am

Sounds like someone converted it to the rectangular glass one.

There is a bleeding procedure for fuel filters, did you bleed the filter itself after changing it? If you didn't it, may have pushed air towards the injection pump. You say it runs now, so I would just keep it running for a while at half throttle or a bit better to let it clear the air out.

labbe001
40C crawler
40C crawler
Posts: 13
Joined: Fri May 13, 2022 5:58 pm
Location: Alabaster, Alabama

Re: Hunting Idle JD 450B

Post by labbe001 » Fri Jun 17, 2022 8:24 am

Jim B wrote:
Fri Jun 17, 2022 7:49 am
Sounds like someone converted it to the rectangular glass one.

There is a bleeding procedure for fuel filters, did you bleed the filter itself after changing it? If you didn't it, may have pushed air towards the injection pump. You say it runs now, so I would just keep it running for a while at half throttle or a bit better to let it clear the air out.
I did not do the bleeding procedure to the filter itself. I should have known to take a look at my service manual but I was so distracted by how dirty the fuel was coming out of the old filter. No doubt it's the air as you described. I will try to get the air out of the fuel lines as best I can at this point and run it for a while. Thanks guys.

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