Need ignition upgrade help/advice.

[5Tractorguy]

Originally Posted by massey478

'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.
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.

I can give that a whirl. The jets that were in the original carburetor I messed with some and opened up last year. Probably to around .057+/-, and it made a noticeable difference when I did that. Compared to those modified jets, with the new 57's I have to keep my foot into it a lot more and as you said, I'm cooking through gas. For the few flat stretches of road here in NE just touching the throttle keeps it at 45, but most of the time I'm laying into it keeping it at speed or climbing hills.

Power piston I'm not sure if it's working. I'm matted it a few times and there is no noticeable difference that the plunger has hit the valve. Might not be coming down... or heck, who knows... might not be moving up. But I know my vacuum is good since the truck is hydro-vac brakes.

Thought about the ignition upgrade just wasn't sure what to get. I'll take a look into the MSD's!

Originally Posted by 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

I still have the factory setup on this one (seems like factory up until the Y). 2-1/2" pipe out of the manifolds, Y's under the drivers side and then runs 3" pipe about 6ft back into a muffler. So it might not be a bad idea to put dual exhausts on it with pipes straight back. Seems like it breaths pretty well with what it has but it might not be enough.


Thanks guys, I'll start with modifying the old pair of jets in the next week or so and I'll report back.

[massey478]

For the timing, I rotate the distributor both ways, retard and advance with the motor idling. I rotate it retard until the motor sounds like it is starting to labor, then rotate it advance until the motor starts to 'flutter'. I back it away from the flutter setting until it just starts to run smooth and does not kick back at the starter when cranking which is a good place to start finer tuning as you drive it. Listen for pinging and do not set it so that persists more than a bit off the idle on acceleration if you hear it at all. Gasoline nowadays with the added alcohol will tolerate more advance without pinging. I bet you will find the motor freeing up a good bit from the cookie cutter factory timing light setting. When you are happy with it you can then put a light on it if you wish so you know where the setting is you like the best.
The 478 in my Massey 1100 seems happiest when the jet sizes cause just a bit of black smoke when under light load. Under really heavy load at night I get a 4" cone of blue fire out the exhaust stacks with a circular shock ring showing just at the top of the pipes. You will never see that on a truck because the tractor has vertical headers and short collector pipes; the longer truck exhaust system will burn it up before it gets to the end of the system. Because it is happy this way, the MSD system keeps the plugs cleaned up much better than the stock system. With the MSD you also can open up plug gap to around .050" or a bit more to create even better ignition of the fuel charge. For a truck you probably will not want to set it that rich because the truck motor is not running at 50 to 60% + of the rated HP or more all of the time.

[AZKen]

Be absolutely 100% sure there are no vacuum leaks. At carb, manifold, fittings, tubing, hoses, gaskets and etc. That would cause BIG power loss.
It will seem like carburetor or ignition problems. It's a sneaking symptom.

I repeat, these hot coils and trick ignitions do not do anything for a normal everyday motor. I just sounds cool to say "I have a super blaster, lightning carbonite spark, lightsaber, deathstar coil."....but a guy with a Napa stock coil still blows your doors off.

[massey478]

I am sorry AZKen, but I totally but respectfully disagree with your comment that 'trick' ignitions do not make a difference on stock motors. I have had the experience of the difference too many times on stock as well as race motors to agree with what you are saying. I am 72 now so I have worked on and owned many, many motors in my time, and have tried many things. Engineering facts come into play. The wider plug gap these ignitions allow one to use gives better lighting of the fuel charge. Multiple sparks like the MSD uses keep lighting more charge as the swirl in the cylinder passes the mix past the plug. Yes, we are talking milliseconds here, but it adds up. As compression comes up with the piston approaching TDC it takes more voltage to get the spark to jump the plug gap, so systems with stronger spark will keep working dependably with the beneficial wider plug gap. Have you ever tried a system like the MSD and drawn a truly objective conclusion based on facts and observations? I do not think you would say what you are if you had given them a really good, objective try. A stock system consistently blowing my doors off does not hold well for me with well over a thousand passes down the drag strip, setting and still holding the record number of class wins at Osceola drag strip and hours upon hours behind the Massey 478 and other motors in the field. The enhanced systems give much better long-term dependability at a higher level of performance than the stock system. On the strip, track, or hours in the field it is long term dependability one needs. The MSD system gives reliable spark even if system voltage drops a bit or goes higher due to some system malfunction you may not be immediately aware of, or may happen for only a short time. A tenth of a second, even a few thousandths of a second lost due to that on the strip and you go home. I have won and lost races by .001 second. Again I want to say I am not trying to put you down, just that I cannot agree from experience. This is an example of the freedom of speech we have in the good old USA that grants us both the freedom to have an opinion and express it respectfully even if we walk away still disagreeing. Many times both people learn something!

[AZKen]

As most do, you are mixing drag strip/race motors with everyday motors. Spark is one factor on high compression, high RPM motors. You are in love with an idea that has no basis on a GMC truck motor. He is not looking for .001 second, he is trying to get up a hill. With a 3400-4000 max RPM motor. With all due respect to your experience, MSD style, multi spark, hot coil suggestions, for this fellow, are bad advice and a waste of money.
HEI is a good upgrade as well as a good coil. All of these will probably last longer and start better in cold weather. They may help with fouling, but fouling has a root cause. They won't get a big truck up a hill faster.
Just to let you know, you are not talking to a young kid, I'm 71 3/4. I do respect your opinion and will leave it to the poster and the other members to help decide the best troubleshoot approach. I think some are thinking the motor, with whatever mileage it has, is giving all it has. The weight, grade of hill, gearing= maxed out.
The "extra" spark issue is not supported by others on the internet.

[snazzypig]

Hey I'm 71 too. I guess we're not out to pasture yet! Lots of experience being shared by Ken and Massey478 and many others here on this forum. I just appreciate learning and gleaning what I can, and sifting it out to apply to my individual needs. I always appreciate others taking the time to share their knowledge and wisdom. Thanks to you both and many others who contribute to our knowledge of these great old trucks!!

[AZKen]

Sifting is a good word. That's what we all have to do when reading anything on the internet. This forum is on the internet.

[massey478]

AZKen, I am also referring to stock motors in my advice and not mixing the two. You do not have to spend the high dollars for the new MSD system. There are good used ones on Ebay. Read the Bosch fuel manual about the alcohol blend fuel. It states that the alcohol in the fuel attracts some water which, when present in the fuel charge, causes the mix to be harder for the ignition system to ignite, so enhanced ignition systems are a good idea. After sitting long enough I have had the blend fuel phase-separate. This is really ugly to the point you have to drain it and throw it away. Putting some of the drained fuel in a glass jar, one will actually see two layers of liquid! Also a factor in this is that many of the vintage trucks folks on here own are not driven regularly so the alcohol blend fuel draws even more moisture, too often to the point it rusts the bejeebers out of the fuel tank and corrodes the carburetors, giving even worse problems. Also, now we have computer control on all of the modern motors. It automatically controls spark advance and fuel rate to optimum conditions with knock sensors and exhaust mixture monitoring. For this reason we do not notice the difference caused by the alcohol blends. We do however have to make modifications to the older non-computerized systems on our V-6 and other older stock motors motors to give them the best performance we can in the absence of computer monitoring and control. This is one of the reasons why the enhanced multi-spark system helps. I have not put the MSD system on any stock motor that it did not immediately make a noticeable difference in idle quality, starting ease, and better performance. This is not bad advice and it definitely for me has not been a waste of money. Also you mention vacuum leaks causing power loss. They affect idle quality, not top end, foot on the floor performance. This is because intake manifold vacuum is at its maximum at idle when the carb throttle plates are closed, a condition when the vacuum leak would be most noticed by evidence of choppy idle. When you have the throttle plates fully open under full power, the vacuum in the intake drops to a very low reading. Because of this fact, the effect of a vacuum leak is minimized at full throttle because the manifold vacuum is not there to make it as much of a factor if at all as well as the air volume going into the motor makes the vacuum leak a very small percentage of the total flow. The vacuum leak would have to be large enough the motor probably would not idle at all to affect full throttle performance in a really noticeable way. I am not pointing this next comment following at you, AZKen, but as for things being supported or not supported on the internet, many times I do not get involved in the discussions and advice I see being given because it truly scares me to see what some post as solid advice. It makes me think "Wow, if some poor guy takes that advice as gospel and does it, bad things may happen!" Internet information is like all things in life, some good and some way off the mark. One has to carefully digest the information and try things on his own equipment in his own environment and way to see what works best for him. I have never seen one of these V-6 motors that bringing the timing forward as I advised and enriching the fuel and enhancing the spark system did not help in a noticeable way. I do agree the HEI system is a very good system but there are ones like MSD that surpass it, in my experience even on stock motors. Ignition point quality seems to be lower now than years ago. Stock systems charge/discharge the coil with the action of the points, putting a high voltage/amperage load through them, diminishing their life. All they do with the MSD system is trigger the system so the load is very low leading to longer point life. I had another brand of electronic ignition, single spark, on my Massey 478 before putting on the MSD. I immediately saw a difference, and still do. As with modern cars, and even back years ago, lessons learned in competition like the drag strips and oval track racing were applied to stock motors to enhance their performance. A lot of work was done at the strip by factory engineers like the Ramchargers for Dodge who used lessons they learned at the strip in testing to apply to their stock motor designs. I certainly bow to them and their likes for their engineering knowledge which I recognize is above and beyond my engineering training, which is in mechanical engineering. My training applies a good bit, but not to the level of factory engineers who work with it on motors as a life work. I take what people like them do and report and learn from it for my own enhancement, going forward to apply it in my way in my environment with more trust in them than what is found many times on internet. That is what I am dong here. All of this methodology I am recommending applied back in the 70's when I worked on these V-6 motors for a living, and now, even more so with the new alcohol fuels and worn motor components. Thanks, AZKen, for your comments and I always welcome good, open, respectful discussion.

[5Tractorguy]

Alright guys lets take it easy here!! I re-opened this thread for questions regarding my GMC 5000, not for a who's right contest...

I've put a lot of hard work into this rig and would like to just get it to run right.

As time allows in between work I'll pick though everyone's recent comments, do so some trials on the engine and see what happens. Fist things first will be the carburetor jets and vacuum leaks. Although the booster works well, I know some of the other vacuum hoses need to be replaced. Very good chance there might be a leak.

Once I get those squared away I'll let you-all know what happens!

[AZKen]

Chill Jr. Member. you got plenty of help. You are welcome.