Best guess milage for gasser

[m139h2otruck]

Drove the water truck to a truck show in Barrington (about 50 miles one way) on Sunday, and accounting for the level of the tank when I started and the amount of fuel bought ($117 @ $2.66/gal) I think that the mileage is between 3 to 4 miles per gallon or between $0.70 and $0.90 per mile just for the gas!! Per the manual, the Army stated that the gassers were rated @ 4 mpg and the diesel @ 5 mpg. Had about 500 gallons of water on going up but dumped this for the ride back. Just this amount made a difference in the hills.

The truck will easily run 2600+ rpm on the highway for an extended period (about 50-55 mph) with no problems. Oil, water and all gear cases seem to be within limits, although the transmission was the warmest out of all the gear boxes. Even with the Zenith carb, the exhaust still smells like a two-stroke bike, but there is little to no black smoke. Oil use is little to none.

 

[acetomatoco]

Aren't those 6602s just wonderful engines... I now have three...again...taking the winch and body off one of the M139s to make a sportster out of it... ha.

 

[ARMYMAN30YearsPlus]

My 6602 is begging me to come home and drive it just to suck down my pay. I know my truck coming up from Virginia was choking my Son and his fiancee in the chase car so they fell back and the fuel I used was somewhere near what you did per mile. Just not use to this and would like to find a way to lean it out without harming it when I get back from Korea next year.

 

[Monty]

Are the Holley carbs better than the zeniths? I 've tweaked and tuned on the Holley I have but I just won't run great. It starts good when it's cold but once it the engines warms it seems to loose power and If I shut it off when its warm it's a bear to start if it does at all.
I thought that carb might be getting to hot and vapor locking or maybe I'm chasing a warped carb base that's alowing air in?
Soory to hijack the post If the Zenith carbs are better I might look at trying to find one and put it on.
Chad

 

[m139h2otruck]

We tried the Holley for a very short period after I got the truck home, and we were not happy with the performance, especially the tendency to be over rich after warm-up. The Zeniths are on E-bay sometimes, and Saturn sells them for a fair price. Regardless of the carb make, check for leaks using some sort of spray (WD40) around all gaskets and joints as vacuum leaks kill drivability. Also, make sure the PCV valves and lines are installed correctly and that the PCV valve itself is clear.

 

[acetomatoco]

Float level in the Holley and good needle and seat are very important. The zenith carb, newer replacment as the gummint couldn't get Holleys anymore...is a masterful simple design from the 1930s and comes with all the line extensions for the tubing so it is just a bolt on...The Holleys run rich as a matter of design and I remember them choking us on Mogas in the 60s in convoy in Germany....Blue Crown spark plugs would last about a week.. You cannot let the truck idle at low rpm or it will load up badly... always bring it up to 900 or so if you are going to be setting for a while.. The anti Diesel valve is important because of the richness and its tendency to run backwards if shut off hot... The Zenith has no anti Diesel valve...so don't try to hook that cable up!!! The little Jeep sized fuel filter under the Driver's fender has to be tended to very often because of the volume of fuel and water and trash than travels thru it...when it gets dirty it passes little fuel and the pump tries to suck a vacuum...thru it...take heed...

 

[m139h2otruck]

We fabed a replacement filter using a spin-on from WIX with the water drain in the bottom. Was able to connect to the same fittings and lines with no changes. Just drain fuel every so often and the filter element should go a long time. The original was all rusty and gaskets NG.

 

[DDoyle]

RAM - er, ACE - has hit this dead on. If you tweak your carb so that it "smells" clean, then it is NOT set right, and you'll know it when you try to go down the road. I keep a spare set of plugs in the tool box ALL the time. In a M62 you can figure 2 or a LITTLE more MPG, regardless of Zenith or Holley. NOT designed for fuel economy, or enviromental issues - but you can pull a house down - IF you've kept the fuel filter clean.

DD

 

[ARMYMAN30YearsPlus]

I was even thinking of machining an adapter so I could mount a very nice 4 barrel Eldebrock I have left over from my old Suburban V-8. Do you think the engine would tollerate this or would this hurt the 50 year old monster?

 

[m139h2otruck]

A gas engine does not care how it gets its fuel mixture, as long as it is in the right proportion. We use a 500 cfm Carter/Eb on a hypo slant six which turns 6000 rpm and it runs great. Be aware that a 6602 will draw between 400-475 cfm max at 2800 rpm so a 600 carb may never or rarely open the secondary barrels. Also, if the fuel distribution is messed up, you may get starved cylinders and rich ones which will make the engine run rough.

 

[No.2Diesel]

With an inline engine, one carb feeding 6 cylinders that are each a different distance from the carb creates uneven Air/Fuel ratios, etc. To maximize operating efficiency, small multiple carbs would be the answer and it wouldn't be that expensive.

I'd like to see how it would run with six very small one barrel carbs (strombergs) all hooked to the same linkage mounted on a fabricated manifold. That would be pretty cool. I'd like to do the something similar to my Slant Six.

 

[JasonS]

Keeping the intake hot will alleviate distribution problems. I think that it would be worthwhile to examine better carbs. Lots has changed since then. A 500 cfm holley would be easy to adapt; a four barrel would take some modification to the intake. Not impossible but more difficult.

 

[Monty]

I was even thinking of machining an adapter so I could mount a very nice 4 barrel Eldebrock I have left over from my old Suburban V-8. Do you think the engine would tollerate this or would this hurt the 50 year old monster?

I was thinking the same thing, I have numous carbs sitting around that I could use. Something in the 500-600 cfm range would work, I think smaller than that might evan be better since these engine don't turn alot of RPM. I'd like to keep it orignial so I may spend the money on a Zeinth and see how it works.

Chad

 

[Monty]

Float level in the Holley and good needle and seat are very important. The zenith carb, newer replacment as the gummint couldn't get Holleys anymore...is a masterful simple design from the 1930s and comes with all the line extensions for the tubing so it is just a bolt on...The Holleys run rich as a matter of design and I remember them choking us on Mogas in the 60s in convoy in Germany....Blue Crown spark plugs would last about a week.. You cannot let the truck idle at low rpm or it will load up badly... always bring it up to 900 or so if you are going to be setting for a while.. The anti Diesel valve is important because of the richness and its tendency to run backwards if shut off hot... The Zenith has no anti Diesel valve...so don't try to hook that cable up!!! The little Jeep sized fuel filter under the Driver's fender has to be tended to very often because of the volume of fuel and water and trash than travels thru it...when it gets dirty it passes little fuel and the pump tries to suck a vacuum...thru it...take heed...

Part of my problem was letting the engine idle while I was tweaking on the carb, I'd get it to sound good and give it a little gas and it would just bog, sputter and spew black exhaust.
Thanks for the advice.
Chad

 

[m139h2otruck]

I always thought that a port fuel injection system on the 6602 would be a great step up, as the '40s tech for the old carb system leaves a lot of room for improvement. Ford's 300 straight six after it got injection was an unbeatable motor, we had a company truck that went over 200,000 on the original engine with no problems. With enough time and money, one of the aftermarket systems should be easy to install on the big six, maybe even a modified 300 Ford. Would need to change to 12 volt for ease of installation, and a controller that will also run the spark would be great too. Only thing with this monster, I would not turn it over 2900-3000 rpm or I think the stress on the rod bearings would be it's undoing.