7040 air in fuel system
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=209318
Printed Date: 12 Dec 2025 at 1:43am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: 7040 air in fuel system
Posted By: INAllis
Subject: 7040 air in fuel system
Date Posted: 11 Dec 2025 at 3:01pm
| 7040 used about once a week or so to load round bales, today lost power lots of smoke, could see air bubbles in fuel filter. Turned off hand primed bled air cracked injector ran great 10-15 minutes and repeat. Pulled this 3 times but got hay loaded, shut down repeat everything fine for short time. Final time hand primer didn't seem to wanna prime, could this be bad and allowing air into system?? If not the cause, im at a loss. Any help? TIA |
Replies:
Posted By: im4racin
Date Posted: 11 Dec 2025 at 6:13pm
| That’s where I would stert |
Posted By: injpumpEd
Date Posted: 11 Dec 2025 at 6:14pm
|
sounds to me like a fuel flow restriction from the tank. ------------- 210 "too hot to farm" puller, part of the "insane pumpkin posse". Owner of Guenther Heritage Diesel, specializing in fuel injection systems on heritage era tractors. stock rebuilds to all out pullers! |
Posted By: DrAllis
Date Posted: 11 Dec 2025 at 6:24pm
| Early 7040's had a plastic fuel supply line from the fuel filter base rearwards to under the cab floor to on top of the main fuel tank. The engineers made the injection pump draw fuel up thru a standpipe. It was a bad idea and oftentimes caused problems like this. Their fix was to go with a larger (than the plastic line) diameter rubber hose from the fuel filter base down and under the tractors belly and tap into the main fuel tank via the cross over hose between the tanks. This bottom draw system was what was needed and all the way thru the mighty 8000 series, that is the way they were. So, if you have the standpipe system, now'd be a good time to just eliminate it and convert to a home made bottom draw design. If you currently have a bottom draw system, disconnect the rubber supply hose at the filter base and hold it down below the fuel tank bottom and see if it GUSHES fuel out the end. It should. If it doesn't, you have a blockage at the outlet of the tank. By the way, if the hand primer squirts fuel all over when you pump it, it's junk. |
Posted By: Lynn Marshall
Date Posted: 11 Dec 2025 at 9:47pm
| If it does have the gravity flow system, then the hose from the tank should have an adapter and elbow at the filter base. They have been known to plug with debris at that area. May need nothing more than a fuel filter change. |
Posted By: INAllis
Date Posted: 11 Dec 2025 at 9:51pm
| New fuel filter about 6 weeks ago but haven't ruled it out. Tank about 3/4 fuel. Will continue to check lines thank you |
Posted By: INAllis
Date Posted: 11 Dec 2025 at 9:53pm
| Runs perfect for an amount of time, you can literally watch air bubbles form in the filter until it smokes horrendously |
Posted By: Les Kerf
Date Posted: 11 Dec 2025 at 10:15pm
I have a diesel tractor doing exactly that, I need to pull the tank and clean the gunk out; pulling the sediment bulb and poking a wire up through the wire was insufficient but it did make it able to drive it back to the shop.
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INAllis wrote:Posted By: DrAllis
Date Posted: 11 Dec 2025 at 11:12pm
| Check the flow from the disconnected hose FIRST. If OK, then move on to the filter base connections/base inlet being plugged. Then, the filter itself. |