Detroit 6v91 smoking

[goatijoe]

I have a buddy that is trying to straighten out a wheeled apc that has theDetroit 6v91. the yahoo's at another shop that somehow changed the transmission in it and had the heads off the motor and who knows what else has been tinked with for some reason. so the the police department took it to my buddy and he was telling me it produces lots of black smoke and no power it runs smoth at idling and smooth when you race the motor it will only get up to 25mph and it will not go any faster with the lack of power and cannot for the life of him figure it our or have anyone that can remember those motors to help him . has any of yall ran across any thing like this? thanks for any help

 

[brianrbull]

Turbocharged? If so check that the turbo is not stuck, found that on my Stewart and Stevenson Seismic Vibrators with the 6v

 

[goatijoe]

no the turbo is the first thing he checked. is there a port to find out how much boost the supercharger is producing?

 

[militarytrucks.com]

Is the emergency shutdown flap closed? The fuel rack may need to be adjusted.

 

[Coffey1]

That would be my thought these engines have to have lots of air
Check that supercharger

 

[battlecr]

I would say rack adjustment, also check the quill shaft that runs the blower, those were a problem if it was reved up and shut down it can break. Sounds like the blower is not working. We had that issue on the 113's.

 

[goatijoe]

he said the blower was turning in it when he check it

 

[battlecr]

It might be turning when you look at it but that shaft may still be broke and not letting it turn up to speed. Really should check the blower drive!

Don G.

 

[WillWagner]

^^ this and a 6v91? Maybe either a 71 or 92 series, 53 if older. Other issues are a plugged return line or a sucked shut/obstructed clean air inlet. There is also a screen between the blower and the engine. I have seen that plugged with paper and tape.

 

[m16ty]

Is the emergency shutdown flap closed? The fuel rack may need to be adjusted.

This is what I would check first if you haven't already. They can sometimes hang and not be open all the way.

 

[Two Stroke Madness]

If the heads have been off then you need to run the rack. That refers to injector timing and height adjustment. You need a 92 series service manual, and a few special tools. You also need to find out what number and color code the injectors have, and to make sure they all match. Unfortunately it's a big pain if you've never done it, and impossible without the right tools. Your best bet is to ask around and find an old 2-stroke Detroit mechanic to do it for you.