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Discussion Starter #1
Earlier this week a local Outlaw Promod racer was doing some testing with his new torque-arm P/M car (new to him anyway). I noticed between rounds they spun/rotated the motor through a few cycles with a long ratchet or torque wrench on the blower pulley. When they did this a large amount of raw fuel gloshed out of the zoomies.

I have seen the nitro guys do this before but didn't know it was needed with alcohol as well. Is this procedure of rotating the engine between rounds done only to remove raw fuel from the cylinders, or is it also done for other reasons as well? Is this only a "426 hemi" thing or is it done with Ford wedge & hemi headed engines too? Is this only done with drag cars, or do other blown applications (monster trucks, boats) do this as well?


On a side note, I finally get to see a P/M with a genuine/real "torque-arm" rear suspension setup, watch the car launch/work, & talk to the owner about the differences/quirks vs a 4-link,....and I still walk away with more questions than answers (LOL).
 

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I wonder if they are not cutting the fuel out before killing the spark & its dumping a lot of fuel in there at idle,
I would assume they are spinning the engine over backwards since they are using a braker bar, I had an old roundy rounder tell me one time that when there car would flood or hydrolock, they would through it in gear & roll it backwards to pump the fuel out of the cylinders,

I usually cut the fuel & listen for it to lean out a bit, (usually a couple seconds) then kill the ignition, (not letting it run compltetely out of fuel) by doing this restarting for the next round is a breeze, (crank it over til I see oil pressure & flip the ignition on & it lights right up)
 

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agree, suspect they are using an ignition kill, and letting near WOT fuel flow fill the engine. NOT a great idea, some volumes of feed and higher compression engines... you can push the damn crank out the bottom of the engine with all that raw fuel.

Emergency proceedures on even my little POS< close fuel feed valve first, then kill ignition. No need adding the crank and all the oil to an emergency situation......

Mechanical injection, barrel valve may be slow to return to idle, and or it might just be siphoning fuel (not closeing off fuel delivery valve) between rounds, so they have to clean out the engine before they try and fire it up.
 

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It's been SOP for at least 40 years, that I know of personally, to "back off" race motors with MECHANICAL fuel injection. If you look at the bottom of the lowest point on each header tube (Zoomies) you will find a small hole for fuel to drain from. Turning the motor BACKWARDS ("backing it off") pushes any residual fuel out of the cylinder and the small hole lets it drain out instead of pooling in the header. If you don't do it you run the risk of hydraulicing the motor when you go to start it. BT, DT.
 

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Discussion Starter #5
"backing it off and/or roll it backwards", I knew it had a name but I couldn't remember what it was called, thanks.

I though maybe they might have been loading up the cylinders with fuel because they were shaking the tires bad at the hit. Some times they lifted after the shake and drove/coasted through. And some times after the shake they got back in the throttle which kinda lugged the engine down, (I guess because the clutch had locked up some at that point). I guess both could wash the cylinders down some with raw fuel, but not using the fuel cutoff soon enough before killing the engine does makes sense too.
 

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While watching the top fuelers at vegas, I noticed that almost all of them would just shut the fuel off and let it run til the engine died, kind of scary to me but they did not seem concerned,

I see wnat Chuck is saying about backing the motor off, unfortunatly my application makes that kind of hard ( everything but the hat is under the front clip)

The thing that really makes me wonder is, why is there so much fuel in the engine? I have to crank mine over quite a while with the fuel on & no spark to get any to come out the pipes,
 

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It depends, A LOT, on where the nozels are with respect to the lines, barrel valve and distribution block. IF the nozels are the high point in the system there is not much problem. However, if the barrel valve, distribution block, and lines are higher...any fuel left in there will drain down while the motor is shut off. Even if you "lean'r out" by pulling the shut off valve, there is still fuel in the system after the motor quits.
 
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