What makes a WD pop when throttle is closed?
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=210398
Printed Date: 16 Mar 2026 at 4:07pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: What makes a WD pop when throttle is closed?
Posted By: kevin LA-CA
Subject: What makes a WD pop when throttle is closed?
Date Posted: 14 Mar 2026 at 8:39pm
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I know that the WDs always pop when you close the throttle quickly. Mine really pops. Loud - 2 or 3 bangs. Magneto ignition. I have timed by ear - don't have a timing light. Also aftermarket marvel carb with adjustable main jet. If I got found a light, where is the timing mark? |
Replies:
Posted By: steve(ill)
Date Posted: 14 Mar 2026 at 9:01pm
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you dont need a light.. You can static time it at TDC on #1 cylinder.... When started, the MAG impulse will change that to the FIRE mark.. i think your timing mark is the set screw on the front pulley, pointed straight down... but others will confirm. ------------- Like them all, but love the "B"s. |
Posted By: SteveM C/IL
Date Posted: 14 Mar 2026 at 10:45pm
| Mostly the idle jet setting I think. POP BOOM POP! Yep they are great! |
Posted By: sparky
Date Posted: 15 Mar 2026 at 1:20pm
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To me sounds like it’s tuned correctly. ------------- It's the color tractor my grandpa had! |
Posted By: Ed (Ont)
Date Posted: 15 Mar 2026 at 6:44pm
| My WD45 does the same. Means it is running properly but I have no idea why! I think maybe because the exhaust is so short and straight thru. No back pressure. Automotive engine with just headers on it has same tendency. |
Posted By: HudCo
Date Posted: 15 Mar 2026 at 7:41pm
| remember when cars had carburators ? what they sounded like when they was going down the hiway and they let all the way of the gas |
Posted By: Gary Burnett
Date Posted: 16 Mar 2026 at 12:18am
And turning the key off going down a hill with a big truck and then turning it back on.Big bang
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HudCo wrote:Posted By: rw
Date Posted: 16 Mar 2026 at 5:35am
| It is a lot of things changing all at once. Throttle closing quickly lowers volume and temp and the raises the percentage of unburned fuel in exhaust flow through muffler. Fresh air with oxygen gets drawn in and causes the pop (explosion and flame). If you slowly close the throttle you control the rate of these changes and it stops the sudden rush of cool air full of oxygen so no sudden explosion. My WD has some exhaust leaks at the manifold. At level throttle mid RPMs with not much load it puts out a lot of blue flares with not much pop only visible after sundown. |
Posted By: Les Kerf
Date Posted: 16 Mar 2026 at 12:30pm
Yup. Followed by a continuous loud roar from the split muffler!
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Posted By: DanielW
Date Posted: 16 Mar 2026 at 12:46pm
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Although I'm not an expert and I agree with all others about them (and a lot of other old carbureted equipment with primitive ignition advance) often popping, it doesn't hurt to check the exhaust valve lash and (most significantly) the seals around the throttle & choke plate shafts going into the carb. Those are two aspects that can cause a heck of a lot of popping when idling down or when the engine is being pushed/over-sped by a heavy load. At our Northern farm, one of the hills between on the road between our hayfields and the farm is very steep (almost dangerously steep). Back in the day when we did more square bales and were running the roads several times with a heavy load of square behind and old tractor, they'd often popping as you idled down towards that hill, and even more so as the load was pushing against the engine going down that hill. You never noticed it much in normal operation. If you kept the carbs shaft seals tight and exhaust valves set with a couple thou extra clearance, it would significantly reduce the amount of popping. The Massey 44 and Super W6 were always the worst offenders. Eventually the W6 got a valve job and it pretty much elminated popping.
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