fast idle engine speed

[30yearoldjunk]

I bought my well-used '77 Mack (tach shows 11,000 hours), and it only revs to 1750 rpm's, 50 mph. It may have been an old cement mixer truck, not too sure. I wonder if someone idiot-proofed it by stepping the governor down; will it hurt anything to have the injection shop guy speed it back up to 2100 (maybe 60 mph) like the tag in the truck says?

Thanks,

Zane

[turckster]

You need to make sure you are getting full throttle. Have someone push the throttle all the way to the floor, the throttle lever on the pump should hit the stop and slightly break over (spring loaded lever). If not, adjust linkage accordingly.You should not have to adjust the pump high idle setting, more times than not its usually the linkage due to wear.

[30yearoldjunk]

Thanks turkster, we've checked all of that out. I was kind of worried about speeding up an engine that has run a long time at a slower speed; I remember when the speed limit was raised from 55 to 70 there were a lot of car engines that thrashed, especially a few particular Fords. 300 rpms shouldn't make that much difference.

[turckster]

The engine should have a no load rpm of 2100 rpm, if not, it needs to be set there. You can set it yourself, should be an adjustable screw with a jam nut on it. The slightest movement can make a difference in rpm so you won't have to move it much.

BTW, it sounds like your mph is limited by gear ratios. You wont get much more speed from this truck without changing rear end ratios.

Edited December 15, 2012 by turckster