1946 gmc

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So now I'm chasing 2 issues. Now I have a whistle under load at about half throttle and the full-throttle stumble I was chasing.

Last night I took the street avenger off my 62, put it on the truck, and both issues persisted. So it seems I'm not chasing carb issues after all. I was ready to buy a new carb but glad I didn't.

For the stumble, I'm going to use a temporary fuel tank (Jerry can) with fuel line direct to the pump. If that solves it then I'm betting my issue is the rubber line in the tank collapsing.

If it doesn't... Maybe distributor? (everything except coil was replaced last year)

For the whistle, I'm thinking it's either a bad vacuum hose connection to something OR the aluminum manifold has a very tiny crack.

When I find whatever the issues are I'll be a hero in my own mind. I the meantime, it's slowly killing me. :p

Oh yeah, my fancy valve cover gaskets from TA performance are leaking for the second time, so they're about to be replaced too. It's a good thing I'm not paying someone else to troubleshoot this crap.
 
Not being able to hear that whistle until under a load would be hard to find unless you have somebody that could help. Do you get spark knock under load too? Depending on where that whistle is coming from, your problem may be a leak causing a lean condition and maybe also causing the stumble.
 
Yeah, definitely not an easy thing to solve. Very trial and error.

The whistle appeared a few weeks ago after I did some work on it including tightening the intake (I had a coolant leak at the time). I assumed a vacuum leak or intake leak. I resealed the intake and it was the same. I'm thinking of taking it back off and checking it for cracks with liquid penetrant or under my microscope at work even.

No detonation/spark knock.

From running and driving I can now get the intake off in 20 minutes with all hand tools. Something you don't want to be efficient at.
 
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I'm betting your whistle and your stumble are related, and probably a vacuum leak someplace.

Can you produce the whistle without moving the truck? It will be easier to find if you can stand right next to it and look while its whistling.
 
I'm betting your whistle and your stumble are related, and probably a vacuum leak someplace.

Can you produce the whistle without moving the truck? It will be easier to find if you can stand right next to it and look while its whistling.

The stumble has been around for a long time, the whistle only just started. I added a ton of squirter which made it perform better, but the stumble persisted. I don't think it's something as simple as a vacuum leak, as everything has been touched with no change.
 
"I added a ton of squirter which made it perform better, but the stumble persisted. I don't think it's something as simple as a vacuum leak"

Think about that a minute... Probably the first thing anybody does when finding a lean condition is add more fuel. Keep at it, you'll find it!
 
Alright, so I learned some things over the weekend.

I bypassed my fuel tank and lines by routing a fuel line straight to the pump from a jerry can. The stumble was gone and the thing seemed to have all the torque it should from idle. I have some squirrely black marks on the road in front of my house that agree that I'm on the right track. I'm fairly certain that the hose in the tank is collapsing. So this week I'll pull the bed floor and investigate further. I think I have a good solution for a better pickup, but need to have a look in the tank first. The collapsing hose makes sense of why it's so hard to diagnose as it's not predictable.

I have never liked the wood stain colour I used for the bed floor and it's peeling, so I got something in a better colour that should be more UV resistant that I'll refinish it with while I have it apart.

Regarding the whistle, I was driving my 62 to the Model T races and I know it has a slight oil leak from the intake manifold that I haven't got to yet. It just started making the exact same whistle. So I'm pretty sure I've got an intake manifold crack or gasket leak on the 46. I'll be investigating that too, but it finally seems like I'm on the right track with my mysterious issues.
 
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Finally I can say I solved my stumble.

The pickup in the fuel tank had rubber hose that was collapsing under various loads. I put in a new tank with a steel pickup and a sock on the pickup. I refinished the bed floor, twice because the first stain I tried was patchy. Built a new fuel filler neck and resolved a fuel filling problem when it was over half a tank. Crack checked the intake manifold (none), but in the process it stained my intake pink so I had to blast it and re-clearcoat it. New gaskets on the intake, put the carb back to old tune settings with some tweaks, filled it with coolant and fired it up.

I sliced my palm open in the yard a few weeks ago so I only have one good hand right now. My father-in-law helped me button up everything on it yesterday and after several years of fighting with this thing and it sitting half apart since last summer, it finally came out yesterday for a test drive.

On cold and damp asphalt it wouldn't keep traction with my foot down in second gear at 80 km/h (50 mph), and it pulls hard with no stumble. I'll try it out on dry roads this week but those issues I was chasing seem to be solved. The whistle was most likely my rubber end seals on my intake not being tall enough, so I went with the seals and RTV, at the recommendation of TA Performance.

I've got a couple little bugs to still work out of it, but at least I can drive it again. Just in time for snow.
PXL_20241020_230507957.jpg
 
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I've got a 1" rear sway bar on it but I think I'm going to try to disconnect it again. Now that I've got the engine sorted, the torque reaction of the rear end is a bit much and it snaps back a bit too much when it breaks traction.
 
Congrats on fixing the gremlins on the 46! It's looking fine! And yessir those quick release front attachment rigs are quite the deal on the newer tractors..saves a lot of cussing!
 
You achieved a goal I'm still chasing. Making it roadworthy and trouble free so you can drive without worry.
It's definitely getting there.

I forgot that I had to replace my brand new steel core valve cover gaskets from TA Performance because they leaked (outside rubber is too hard) with a set of cork-rubber gaskets from Edelbrock which seem to be great.

I could throw it in the shed and bring something else in now, but in my mind I have a couple things to do still. I have a slight driveline vibration, so I'm going to check my angles with the truck on the 4-post lift here soon and see if I need any shims. I have a Lokar kickdown switch to install, and I will probably get a new driveshaft made as mine is a little bit shorter than I would like.

Then I'm going to finally get the seat upholstered.
 

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