M715 bogs going up hills?

[Wintermute]

I had a question for the M715 owners on here. I've talked to a number of people now with M715 trucks (two with different engines than the original Tornado straight 6's). Four of the people I talked with said that their trucks would run fine up to 50mph on flat ground but would bog down and slow to 30-35mph maximum going up hill (with or without the front axles engaged).

What I was wondering is:

Is this something that is normal due to the design of the truck, or is it something that has to do with a particular component on the truck being damaged?

One of the trucks that was bogging had a carburetor problem (heavily overfueling) so I thought that one was just due to the carb, one had a blown #1 piston (or headgasket, didn't pull the engine apart to check). The others were all good engines and the two with replacement engines had the same problem.

Any insight here would be greatly appreciated.

Thanks in advance,

--Wintermute

 

[NDT]

That's about right for 715's, M37's, gas deuces, 5 tons, etc. Lots of drag, not a lot of hp.

 

[jfnemt1ff1]

I dont know about that. When I had my M725 all stock after cleaning out the fuel tank and lines and rebuilding the carb. All because of not running for years. The truck would bottom tout the spedo and keep the speed on most hills .
John

 

[gimpyrobb]

Yeah, I have a 725 also. When it was stock, it would slow a little, but for the most part - it did pretty good. I don't think It would lose more than 5mph on a good hill. I DO know that keeping the plugs clean and the timing right makes a difference.

 

[m16ty]

A good tuned tornado will pull pretty well as far as MVs go. When I first got my M715 it had no power at all. Turns out the timing was way off. Seems the tornado will run well with the timing way off but will not have any power.

 

[Barrman]

It really depends on the hill and as mentioned above your total state of tune. My stock engine had trouble when empty on certian hills around here. Yet, I could hit the same hill while towing a 2000 pound trailer with a 7000 pound vehicle on the trailer and not really slow down more than maybe 5 mph more. My Gasser M35 does about the same thing empty or loaded.

Something else to think about is how much has the truck been used? My Gasser M35 gets driven to town at least once a week just to keep the batteries up and the oil flying. I don't get to a place with the speed limit over 40 mph during such a drive. After 3 or 4 trips to town, I can't hit 35 with it held to the floor. Then it is time for a minimum 10 mile WOT run. I go through the gears and run down a hill outside of town to build the speed up to 45-50. Then I just hold it to the floor for the next 8 miles. It will hold 50 at the bottom of the hill and after a mile or so, start climbing up to 60 or beyond. Once that happens, it will hit 60 on its own with ease. Until I let it idle around or lug around again. I know I am writting about two very different engines, but they have the same basic spark plugs and ignition systems as well as the hard to get all 6 the same temp engine design.

Finally, remember what all of these vehicles were designed to do. Move men and material on dirt paths at speeds up to 30-45 mph. They still do that in a manner that is about second to none. Anything above and beyond that is pure gravy or mis use depending on your view.

 

[bcowanwheels]

IT doesnt take much engine with 5.87 axle ratios

 

[91W350]

Are they not equipped with a Holley designed carburetor, ie... fuel bowl forward. Setting the fuel level too high results in spilling fuel over and causing a flooding situation. My original Tornado had all kinds of power. It would hold 45 up about any hill, even loaded. It also loved to drain oil out the rear seal.

 

[rboltz]

Not much power

Mine is loaded with a 1 ton comm shelter and is really sluggish. Even before, a hill will require a downshift. In the winter, with all that gear lube being stiff, it takes ALOT of power to just get going!!

Mine has the 2 barrel carb and civy ignition which helps but not enough. I want to keep it stock so will live with the 230 as long as it runs.

 

[glcaines]

I drove a 1968 M-715 while stationed in Germany in 1970 for about a 4 month period of time. I was lucky in that I drove it all over Germany to many different bases, much of it through the Alps. Much of it was also pulling a trailer, sometimes heavily loaded. I loved to drive that truck. It slowed down a little on hills and in the mountains, but not exceptionally so. However, during one trip, I couldn't get it to go over about 30 at full throttle all the way back to base. If I remember correctly, the problem was timing and specifically a faulty centrifugal advance in the distributor. The engine was running with a retarded spark. Maybe you have the same problem. Check the timing at higher RPMs.

 

[coreystinson]

One thing worth checking according to some other reading I have done is to make sure that the vacuum advance is connected / working on your distributor. I guess this would fall under the general rubric of "checking timing" that another poster mentioned?

As it happens, mine is disabled at the moment and was that way when I got it. Doing some other work on the vehicle right now, so I haven't had a chance yet to see if there is a power loss at higher speeds or up hills. I suspect there will be.

FYI, I am not a professional or even skilled mechanic, so take this for what it is worth.

 

[rboltz]

One thing worth checking according to some other reading I have done is to make sure that the vacuum advance is connected / working on your distributor. I guess this would fall under the general rubric of "checking timing" that another poster mentioned?

As it happens, mine is disabled at the moment and was that way when I got it. Doing some other work on the vehicle right now, so I haven't had a chance yet to see if there is a power loss at higher speeds or up hills. I suspect there will be.

FYI, I am not a professional or even skilled mechanic, so take this for what it is worth.

There is no vacuum advance on the M-715

 

[KsM715]

Seeing how this thread is from 2009 I would hope the OP has it figured out by now.