Farm Equipment - 426 Hand Primer Question

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426 Hand Primer Question

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Category: Allis Chalmers
Forum Name: Farm Equipment
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=38165
Printed Date: 28 Aug 2025 at 3:10pm
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Topic: 426 Hand Primer Question

Posted By: tuckersnocat
Subject: 426 Hand Primer Question
Date Posted: 30 Sep 2011 at 12:56pm

I've been looking at an AC 426 Turbo that's in a Thiokol 3700 snowcat. It was running fine but the plunger got pulled all the way out of the hand primer. Even though it's back in place now the engine doesn't rev up (it will idle). Our thought is that it's sucking air in through the hand primer. The tractor guys in the area suggest replacing the hand primer with an electric priming pump, seems simpler to me to just replace the hand primer. Any thoughts? Thanks in advance. Russell

Replies:

Posted By: scott
Date Posted: 30 Sep 2011 at 1:55pm

Those hand primers are expensive if you shop at Agco! I put one in my old 220 and want to think it cost about $50 bucks. I'm running a 7040 now and have never touched the primer. Seems to me if the primer leaked air you would lose your prime when the machine was turned off and the primer would have to be used every time you go to start it. Does the 426 start right up? Does it need to be primed every time?

Posted By: injpumpEd
Date Posted: 30 Sep 2011 at 4:22pm

we have the whole primer assy for around $75.00, or just the plunger assembly for $24.00 plus the ride.

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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: tuckersnocat
Date Posted: 30 Sep 2011 at 4:28pm

It starts fairly well (about 20 seconds of cranking) but doesn't respond to the throttle. If you pump the hand primer it will sometimes pick up a bit.

Posted By: DougG
Date Posted: 30 Sep 2011 at 6:34pm

Get rid of the hand primer - they will suck air and the enginev will run poorly - the fuel will gravity feed to the pump

Posted By: DarrylinWA
Date Posted: 30 Sep 2011 at 6:50pm

I put electric fuel pumps on my 426 engines when the primer goes out. Always have fuel pressure when I turn the key on and not worry about it.

Just my 21 cents worth.

Darryl

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B 10 Custom. Serial # 1001 D21, First D21 built 69 #4498 and Last D 21 Built #4609. 1946 MM UTU. And 2000, 2005 Pete's. AC custom Hauling.

Posted By: MACK
Date Posted: 30 Sep 2011 at 8:30pm

Don't do away with hand primer unless you replace it with electric pump. Then if the pump has enough pressure it will advance pump timing at start up.

There are very few times the hand primer sucks air. MACK

Posted By: darrel in ND
Date Posted: 01 Oct 2011 at 2:22pm

Seems like every hand primer pump I've ever used has leaked like a bucket shot full of holes! Darrel

Posted By: tuckersnocat
Date Posted: 01 Oct 2011 at 3:58pm

Lots of different opinions out there!I think I'll replace the piston on the pump first since it's easy and cheap and I have to get it running better to move it, but plan on adding an electric pump later (just a standard 12 V fuel pump)?

I do appreciate the advice - I'll probably need more in the future. The other main project at the moment is replacing all the wiring that the marmots chewed up.

Posted By: tuckersnocat
Date Posted: 05 Dec 2011 at 6:27pm

A follow-up with the rest of the story. I replaced the hand primer but that didn't solve the problem. Pressurized the fuel system from the tank and found no leaks, then...took apart the air intake and found an old shop rag stuck in there right next to the turbo - runs like a champ now.

Probably a good deal for me overall, that was probably the problem all along, I doubt if the ski resort would've sold it if it had been running well and that was as cheap a fix as possible. The rag was intact so no evidence that anything was sucked in where it would cause problems, turbo seems to be fine.

Posted By: DougG
Date Posted: 06 Dec 2011 at 1:01am

Thats a good easy fix !!