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What makes a WD pop when throttle is closed?
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kevin LA-CA View Drop Down
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Joined: 12 Sep 2009
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Points: 80 		Post Options Post Options   Thanks (0) Thanks(0)   Quote kevin LA-CA Quote  Post ReplyReply Direct Link To This Post Topic: What makes a WD pop when throttle is closed?
    Posted: 14 Mar 2026 at 8:39pm
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?
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steve(ill) View Drop Down
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Points: 90510 		Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 14 Mar 2026 at 9:01pm
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.
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SteveM C/IL View Drop Down
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Points: 8946 		Post Options Post Options   Thanks (0) Thanks(0)   Quote SteveM C/IL Quote  Post ReplyReply Direct Link To This Post Posted: 14 Mar 2026 at 10:45pm
Mostly the idle jet setting I think. POP BOOM POP! Yep they are great!
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sparky View Drop Down
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To me sounds like it’s tuned correctly.
It's the color tractor my grandpa had!
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Ed (Ont) View Drop Down
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Points: 1587 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Ed (Ont) Quote  Post ReplyReply Direct Link To This Post Posted: 12 hours 1 minutes ago 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. 
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HudCo View Drop Down
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Points: 4063 		Post Options Post Options   Thanks (0) Thanks(0)   Quote HudCo Quote  Post ReplyReply Direct Link To This Post Posted: 11 hours 4 minutes ago 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
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Gary Burnett View Drop Down
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Originally posted by HudCo HudCo wrote:

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
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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rw View Drop Down
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Points: 388 		Post Options Post Options   Thanks (0) Thanks(0)   Quote rw Quote  Post ReplyReply Direct Link To This Post Posted: 1 hour 10 minutes ago 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. 
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