720
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=171081
Printed Date: 30 Sep 2025 at 5:24pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: 720
Posted By: Darrell G (MN)
Subject: 720
Date Posted: 13 May 2020 at 8:59am
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I recently bought a 720 and it runs rough and sometimes seems to backfire in the exhaust pipe, I replaced the gas, put in a new set of plugs and it's better but still seems to lack power. I am curious if anyone has had this problem and what did you do to fix it. Any ideas are welcome.
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Replies:
Posted By: Tracy Martin TN
Date Posted: 13 May 2020 at 9:05am
Points need adjusting or replacing. The Onans had a finicky setup. Once you get them set right, power will be awesome. BTDT, Tracy
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No greater gift than healthy grandkids!
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Posted By: Acdiesel
Date Posted: 13 May 2020 at 10:48am
second that.
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D19 Diesel,D17 Diesel SER.3
2-D14, 2-D15 SER.II WF/NF
D15 SER.2 DIESEL
D12 SER.I, D10 Ser.II
2-720'S D21 Ser. II
Gmc,caterpillar
I'm a pharmacist (farm assist) with a PHD (post hole digger)
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Posted By: AC720Man
Date Posted: 13 May 2020 at 12:03pm
Correct response, they generally need adjustment every 100 hours or when they begin to run like your saying. The timing could be off as well. Make sure the bolts holding the points box Have not come loose allowing the box to slide left or right.
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1968 B-208, 1976 720 (2 of them)Danco brush hog, single bottom plow,52" snow thrower, belly mower,rear tine tiller, rear blade, front blade, 57"sickle bar,1983 917 hydro, 1968 7hp sno-bee, 1968 190XTD
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Posted By: Steve in NJ
Date Posted: 14 May 2020 at 6:18am
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Big D, If you have Ethenol in the fuel in your area, could be the ethenol in the fuel is causing one of the exhaust valves to stick. I put some Seafoam in the tank of my Honda HT rider cause I was having the same problems. Running lousy on occasions and a backfire through the exhaust. I'm not a big "snake oil" believer, but that stuff works! All problems went away and the engine runs like a dream again. That was a few years ago. Everytime I fuel that machine, I toss a dash of Seafoam in with the fresh fuel.. HTH BTW, Hope everybody there is staying healthy there! Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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Posted By: Darrell G (MN)
Date Posted: 24 Jun 2020 at 7:22am
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Great news, the knowledge on this board and service providers is second to none. Called Sandy Lake Implement and ordered a set of points and a condenser and installed them and the 720 runs like a swiss watch. Great people at SLI and this board, Thanks
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