Turning up the pump....are we wrong??

[Diezel_Cowboy]

I had a friend tell me today that the screw behind the triangle shaped cover has to do with timing and not volume of fuel. He believes turning up the pump consists of turning the screw located in the input line of the pump. From what i gather from the pump manual the screw he is talking about does increase fuel pressure. The screw many here are familiar with (the one behind the triangle inspection cover) actually adjusts the stroke of the pump pistons which would also result in an increase of fuel volume. Someone who knows a lot about these pumps please set the record straight. Are both screws increasing fuel? If so is one better to adjust than the other? I have a hard time believing that turning the screw behind the triangle plate is only adjusting internal timing of the pump. I have the service manual for the DB2 fuel pump published april 1984 that my friend let me borrow but i have never heard of anyone adjusting the screw in the inlet port of the pump. Comments or clarification is much appreciated!

 

[Cheaper Jeeper]

I had a friend tell me today that the screw behind the triangle shaped cover has to do with timing and not volume of fuel. He believes turning up the pump consists of turning the screw located in the input line of the pump. From what i gather from the pump manual the screw he is talking about does increase fuel pressure. The screw many here are familiar with (the one behind the triangle inspection cover) actually adjusts the stroke of the pump pistons which would also result in an increase of fuel volume. Someone who knows a lot about these pumps please set the record straight. Are both screws increasing fuel? If so is one better to adjust than the other? I have a hard time believing that turning the screw behind the triangle plate is only adjusting internal timing of the pump. I have the service manual for the DB2 fuel pump published april 1984 that my friend let me borrow but i have never heard of anyone adjusting the screw in the inlet port of the pump. Comments or clarification is much appreciated!

You've got it right. The one behind the cover increases stroke length - which means more fuel per stroke of the pump piston.

I'm not familiar with the purpose of the one on the inlet line you are talking about, but if it increases pressure I don't believe that alone will increase the amount of fuel delivered. It would cause the injector to "pop" sooner, spray a shorter burst, and maybe spray (atomize) a little better, all of which will mess with your timing, but unless there is more fuel flow there won't be any increase in fuel delivery.

 

[mike3dpro]

Someone said that the inlet screw is a high elevation screw, and that if you want smoke, thats your ticket. You only need to turn it no more than 1/4 turn in. I do want more smoke, but I have not messed with this one yet. Other two screws are maxed, and smoke is still see-thru. (unless bogging it uphill GV on) The EGT still stay well within limits. I think minimal smoke is due to turbo.

 

[Mr_Roboto]

I believe the screw in the inlet adjusts transfer pressure (the first stage of the pump).

Injection pressure is controlled by the injectors, not the pump.

 

[Diezel_Cowboy]

Thanks for the response.......I still find it unusual that my friend was convinced that the screw in the inlet port was the one to be adjusting rather than the one behind the cover. More unusual than that is that I have heard the opposite every where else and there has been no metion of the inlet screw on the forums here that I was aware of. I would still like to hear from the rest of the pump gurus on here as well

 

[Mr_Roboto]

The GM 6.2L uses the same pump (basically set up as a mirror image to have the linkage etc on opposite sides) so there should be plenty of info on the net.

 

[zigg]

Changing the inlet fuel pressure changes the timing of the pump. When I put on my electric pump, I had to move the timing back a couple degrees to compensate for it.

The internal screw definately increases the fuel. I have done this on a couple trucks, and you can see the difference in smoke, you can feel the difference in power, and you can certainly see the difference on the pyrometer...

Oh, and if you don't have a pyrometer, I would highly recommend not messing with this screw. I know this the hard way(read "burned up a 6.9 from overfuelling...")

Zigg

 

[IDIeselman]

The screw behind the triangle is the one to increase fuel! I have done it to many many pumps to increase fuel and in the instructions of every turbo manufacturer for these engines is the instructions of how to do it.

 

[Diezel_Cowboy]

http://files.asme.org/asmeorg/Communities/History/Landmarks/10001.pdf

I found this pdf file online......It is very interesting but it also has on pages 4 and 5 the same information that my friends Stanadyne manual has. Good reading! Still from what i gather it sounds as if the inlet screw could also be a candidate for adjusting the fuel. With the comments in this thread so far and the pictures in that pdf file i think it is safe to say that the screw behind the cover definitely increases piston stroke and therefore fuel delivery. Information about what the inlet screw does is still cloudy to me though.

 

[Mr_Roboto]

The timing advance works off the the transfer pressure. So changing that pressure will change your timing.....

 

[Agnem]

The screw behind the triangular cover is holding a steel leaf spring, the ends of which are pressing on the shoes which hold the rollers which follow the timing advance cam, which contains the lobes which push the pistons in to inject the fuel. By screwing in the screw, you make the leaf spring longer end to end (because if you take a semi circle and squish it flat, it becomes longer) which allows the pistons in the injection bores to move farther away from each other, allowing more fuel to enter the injection bore. It IS the definitive way to cause more fuel to leave the pump.

 

[Diezel_Cowboy]

The screw behind the triangular cover is holding a steel leaf spring, the ends of which are pressing on the shoes which hold the rollers which follow the timing advance cam, which contains the lobes which push the pistons in to inject the fuel. By screwing in the screw, you make the leaf spring longer end to end (because if you take a semi circle and squish it flat, it becomes longer) which allows the pistons in the injection bores to move farther away from each other, allowing more fuel to enter the injection bore. It IS the definitive way to cause more fuel to leave the pump.

Thanks Mel........we are on the same page. That is exactally the way i understand it especially with the help of the pictures from the link i posted earlier. Do you have an explanation for the "inlet screw"?

 

[85hauler]

The inlet screw adjusts transfer pump pressure. Adjusting that screw will not increase the fuel volume. However since transfer pressure has an effect on timing messing with that screw could throw your timing completely out of wack. For the average guy just trying to get a little more power and/or smoke there is no reason to change transfer pressure.

 

[Agnem]

I second that. Nothing messes up a pump faster than making a mistake in that transfer pump area. I did that at last year's rally while dealing with my leaking nose cone and boy was I sorry.

 

[Diesel JD]

What happened?