1946 gmc

[05snopro440]

Originally Posted by zzrodder

Still lookin good Colin, happy cruisin'

Thanks Charlie!

[05snopro440]

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.

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.

[smallfoot]

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.

[05snopro440]

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.

[gene49]

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.

[earthman]

I will be interested to learn what this.

[05snopro440]

Originally Posted by gene49

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.

[smallfoot]

"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!

[05snopro440]

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.

[dutch]

nice... you can drink a cold one on that progress