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Fuel screw/droop balance?

moriboy

Member
124
22
18
Location
SW OR
Ok, I had to put a new IP on my truck. This was a depot rebuild, so all the settings were set by the "rack".

Although my truck runs great, it's pretty wimpy on power now. No problem, I will sneak up the fuel. However it is my understanding that the droop screw needs to be adjusted as well in order to maintain consistant fuel delivery across all rpm ranges.

Anyone here have any insight on this? I really hate to start turning stuff without having a little more knowledge. Thanks.
 

Motorcar

Member
271
3
18
Location
San Antonio, TX
I did a bunch of reading in the search function here before I messed with mine. You will find pictures and diagrams in the "bypass FDC" threads that are helpful to your question. I was bypassing my leaking FDC which brought me to the rest of the fuel metering and droop screw info.

The droop screw meters fuel for all practicle purposes from idle to around 1600 rpm, then the fuel rod that has two locknuts on it works above 1600. I adjusted mine measuring the boost at different rpm ranges and went with a modest 8 psi at 2400 rpm. I know the use of a pyrometer is the prefered method but I stayed on the conservative side. A little adjustment and a little test drive always keeping track of how much change in what direction.
 

Motorcar

Member
271
3
18
Location
San Antonio, TX
TM 9-2910-226-34 states code C and D pumps do not have a droop screw, depending on your rebuild...if you have one...clockwise decreases fuel flow, counter clockwise increases it.

The fuel rod on the other side, turn adjusting nuts clockwise to increase flow.
 

Squirt-Truck

Master Chief
Steel Soldiers Supporter
1,180
162
63
Location
Marietta, Georgia
Motorcar, I also appreciate the insight on the fuel screws. But, and please comment, I was told, by a very respected source, that the droop screw was where we should be making the adjustments because the main screw is part of the max RPM fuel issue. Yes it will increase fuel but will at over 1600 to 1800 the governor is already pulling the yoke off the stop. The droop screw is on the other side of the stop. Of course if no droop screw then no adjustment...duh.
Thoughts, and comments are desired, this is a learning opportunity, and a chance for the OP to get the performance desired without cooking an engine.
 

Floridianson

Well-known member
Steel Soldiers Supporter
7,390
2,434
113
Location
Interlachen Fl.
Most just leave the droop alone if you have that pump after bringing up the main fuel adj. The droop controls between idle and 2000 rpm and buy lowering it you might no be waisting so much fuel before the turbo kicks in and pistons get to speed.
Find the TM troubleshooting the 465 and you will see how easy it is to check boost at lower and upper rpm range. The order would be increase main till you get the boost you want then adj. the droop lowering it. Do believe on the pumps without droop screw then we adj. the smoke cam by increasing the angle.:D
 
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crazywelder72

New member
701
2
0
Location
Winchester Ma
I'm going to be getting my hands dirty with the IP and HH soon. i just heard about the droop screw jsut the other day. ugh.... so much to learn. there is nothing like skimming a 900 page TM to try to get information before you nod off from boredom.
 

skuhler

Member
32
0
6
Location
Columbia, MO
I've had good luck adjusting the rod for the high end range and the droop screw for the low end torque and performance. I adjust the droop screw with the engine idleing until the engine "barks" at a throttle tap. At a rapid throttle increase, there is about 2 seconds of blacker smoke as the engine passes unburnt fuel, then the exhaust clears as the fuel input matches the horsepower creation.
 

brianp454

Member
572
11
18
Location
Portland, OR
Hello from Portland moriboy!

I recently bypassed my FDC and love it! I posted the details in the "Sticky: how to turn up fuel...in pictures?" thread. I did not touch the droop screw or main adjustment after bypassing the FDC. Hope to hear from someone with the details of what they did and why after bypassing the FDC.


Ok, I had to put a new IP on my truck. This was a depot rebuild, so all the settings were set by the "rack".

Although my truck runs great, it's pretty wimpy on power now. No problem, I will sneak up the fuel. However it is my understanding that the droop screw needs to be adjusted as well in order to maintain consistant fuel delivery across all rpm ranges.

Anyone here have any insight on this? I really hate to start turning stuff without having a little more knowledge. Thanks.
 

Floridianson

Well-known member
Steel Soldiers Supporter
7,390
2,434
113
Location
Interlachen Fl.
OK to keep things straight if you FDC is bypassed ( this should be done if not already then do it ) then droop and or smoke cam is no longer in play. All fuel control is now the main fuel /twin nuts. This is because before when the FDC was working the FDC servo was moving. Bypass the FDC and it no longer mover and smoke cam and droop screw remain in the same place. So as said all we can do is adjust main fuel / twin nuts and have to deal with the extra smoke / unburnt fuel at the lower rpm range till the rpm come up and turbo starts to wind up. They run the best when they do roll a little coal on take off but exhaust clears when they get to much higher RPM. We can get the best fuel control by marking a flat on the inner nut and adjust slowly one flat at a time. Fear the reaper do not fear the governor.
 
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