Need ignition upgrade help/advice.

[5Tractorguy]

My reply should be coming guys (replyed last night), when I quote a post it says it has to go to the moderator first for some reason....

George, I haven't checked it with a gauge, but I think my vacuum is okay. I have the Hydro-vac booster for the brakes and the large vacuum reserve tank. Booster was rebuilt and brakes work nice. When my foot is on the brake and I first start the truck from sitting, the pedal goes up about 1/2"-1" so it must be pulling a good vac.

[5Tractorguy]

Quick update on the truck...

Adjusted the timing back to 5deg. Cleaned and set points to .020 according to shop manual.

Hauled everything to and from the show this weekend. Truck ran a bit better but is still lacking power.

Once I start reaching an incline and put my foot into it, the first 1/3 or so of pedal travel makes a difference. After that if I stomp it to the boards there is no RPM change, no power change, doesn't seem to fire much harder.

Any ideas? I'm going to change my fuel filter again. Is there secondaries in these WW carburetors? If so maybe they aren't kicking in? Maybe the vacuum piston in the carb isn't working?

[TJ's GMC]

Sounds like fuel starvation somewhere.....I would pull the sending unit out of the tank and see if there's a bunch of crap built up on it....then check the tank. After that I would disconnect and blow out all fuel lines. There could be some blockage in the main jet of the carb still. I had a pesky arctic cat quad with a rather odd carb design do that to me....first 3rd of the throttle was fine....floor it and no change except you could hear it bog. Turns out there was a bit of crap stuck in the main jet "tube" where the fuel flows after the jet. Issue is different issues can cause the same symptoms. If you are sure you have a clean fuel system and good carb...then there's still something else lacking.

Edit: Check fuel filter or filters for any signs....excess crap built up...or really any crap at all.

[1972RedNeck]

Originally Posted by 5Tractorguy

Once I start reaching an incline and put my foot into it, the first 1/3 or so of pedal travel makes a difference. After that if I stomp it to the boards there is no RPM change, no power change, doesn't seem to fire much harder.

Any ideas? I'm going to change my fuel filter again. Is there secondaries in these WW carburetors? If so maybe they aren't kicking in? Maybe the vacuum piston in the carb isn't working?

I have been hauling 1500 gal of water every 4 days with my '65 5000 6X6 (also ex fire, has about 40K miles).

Going up a slight incline I make about 20 MPH. Decent incline (4% to 6%) 15 mph is tops. It seems to pull hardest at about 1600 RPM where, as you say, after the first 1/3 or 1/2 of the pedal travel, there is no more power to be had. If you wind it up to 2500 or 3K RPM, then it is more "responsive", for lack of better term.

My truck scales in just shy of 14K empty for a total GVW of 26K loaded. No matter what you do to the little 351, it's not going to light the world on fire. It will get you there no problem, but it might take awhile.

JFYI, on the 30% grade that I have to pull, I have to drop to 2nd gear in low range. At 2500 RPM, the speedo needle doesn't even come off the stop...

[5Tractorguy]

Will do TJ. I won't get to the truck for another week or so due to work here, but when I do, updates to follow.

'72, I know this thing won't be a rocket sled on rails I just thought that it should have a bit more pep than what it has now. Maybe the 351's is running good and it's all in my head...

Anyways, here's a street view of a road in town. I'm not up to par on % grades so I don't know what it would be... Pics kinda small but it's a pretty fair hill.

Pulling a load of 4 garden tractors, about 2600 lbs, I dropped the brownie back into direct and the main down to 4th pulling the hill at about 20-25mph. So it sounds like that would be about average for what my truck is.


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[1972RedNeck]

Any idea what your empty weight is?

[5Tractorguy]

I'm guessing 7500-8000.

When the guy hauled it up here from NC, he went over the scales and it was about 6500 just cab and chassis.

GVW is same as yours 26,000.

[5Tractorguy]

Reviving this thread since I've done some more work to the '61 and had some questions.

I recently installed a like new take off Stromberg WW carburetor that was removed in the 60's. It was rebuilt with a new kit, correct size .057 main jets and #67 power by-pass jet for the 351.

It's a 23-133A. The only noticeable difference is the throttle plate has 2 small vacuum holes that run up into the vacuum port on the backside. The port on my truck is plugged so I'd assume those holes don't make a difference once I plugged the port.

The truck seems to hold a bit better on hills and accelerates up a hill a bit better.

My very rough estimated MPG is about 4.7+/-. Sound about right for a 351?

I was thinking of trying a set of .056 jets just for kicks since it almost seems like it might be running a bit rich.
For curiosity I swapped in the .055's that came out of the WW and it was struggling starting out so I think the 56's may starve it also.

Any thoughts appreciated. I should probably just run it, but I'm a bit finicky when it comes to this stuff.

[massey478]

My experience with these motors, especially the 478 in my Massey 1100 tractor, are that most of them are under-fueled. Now that we have the percentage of alcohol in fuels we have another problem different from the fuel these motors were designed to use. When pulling garden tractors on alcohol we had to increase jet sizes a lot to get the power from alcohol. The same is true here now; the alcohol in the fuel has a negative effect. More has to be put into the motor to get the power back. 'Back in the day', 1970's, when I worked at Meyer Motors GMC/Allis Chalmers dealership we would have complaints about these motors. We would drill out the main jets about .010" size increase and power would come up, run cooler, and mileage would actually increase because the driver did not have to have his 'foot in it' so much. When the weather conditions were right we would have motors 'backside' pistons, burning them. After repairing the damage we increased jet sizes and the problem never happened again. I suspect the industry's push for fuel mileage caused some of this leaning out from the factory to happen. For my Massey with the 478 (hence my name) I had several drilled jet sizes I tried until I got what I wanted. There is also an enrichment piston in the carb that drops dowm as engine vacuum decreases, opening an enrichment jet to give the motor more fuel. My 478 would drop more RPM than I wanted it to in a herd pull before the enrichment came in so I stretched the spring on the rod for the enrichment valve until I got it to come in at less RPM drop. When it let the RPM drop too far, when it came in the power boost would cause the tractor to spin out. I also throw away the timing light and 'power' time motors, moving the distributor and trying it until I get the proper performance. We also do that with out street/race motors then mark the distributor base so we know where to set it. I also find that the standard ignition system with a MSD 6 or MSD 6al and the associated MSD coil added will help tremendously. These units give five spark pulses per plug until they reach 3,000 RPM at which time they give one. Much better than Pertronix. The MSD 6al is different from the MSD 6 in that the 6al has chips that can be plugged into the side that limit the high end RPM the motor is allowed to reach. Made the motor run much better. I think the 5 sparks per plug help these motors light the fuel more efficiently in the large bore size they have. Believe me, you do not want to get shocked by one of these units! Big no-no! Just my experience here. Others may be different, but it has always worked for me on these motors.

[jimjaz]

I see Ken has mentioned exhaust.....
Back in the early 70's, I took my 63 GMC with 305 V6 to Midas Muffler and had a dual exhaust setup installed. Don't know if your big 5000 has the same single exhaust like all the 305's did coming from the factory that way.
That being said, I went from a steady 11 mpg to over 13 with dual exhaust and nothing else- nothing crazy- just two inch pipe through some low back-pressure type "turbo" mufflers that do not make a bunch of noise like some do today, and I noticed a BIG difference in how the engine performed, and it absolutely was better on the hills. The engine just breathes so much better. It was the best $80 I ever spent (back then). In my own situation, I had the mufflers installed outside the frame rail and dumped the exhaust out the sides at a 45 degree angle in front of the rear wheels/tires. Sounded great too! With a 20 percent jump in fuel "economy", I was impressed with this change.
Something ELSE to consider......FWIW,
JimJ AZ