Need Help 70 250 vaccum hose route? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

RR67gto · 11-07-2008, 10:40 AM

Hello friends I have a real problem trying to under stand where my 70 250 vaccumn hoses go? It's a manual transmission truck and a 1 Bbl carb. Same one I had a problem with the auto choke for. Anyway, I know the PVC from the valve cover goes to the manifold. I also hooked the distributor advance up to a small silinoid mounted on the manifold like it was when I got the truck. But, in a 70 VAN with this engine it shows advance going to the carb? I also have a PVC valve the parts store sold me with a normal top for the hoes. BUt it looks like th old one I found in the truck had a smaller fitting on it's side for a second line? I have a real 1970 issue factory manual, and some other books on the truck. Yet, nothing I have or anything I get on the web shows any of the hose diagrams. What a silly thing to not make avalabile. You can see how to rebuild the engine, transmissions, rear ends, carbs, but nothing aboue where the hoses go. I'm not the first person I've heard of having a problem with this. But, no any of my Pontiac cars I own back to 1962m, I can get the information for all the cars.

Anyone has ay idea about a diagram or information about the hose locations pleaselet me know, and I'll say something special for you when I talk to the big guy again. Thanks friends, and what a wonderful place this is. So much information, and so helpful. I didn't miss something posted about the vaccum hoses did I?

Mike

68gmsee · 11-07-2008, 11:46 AM

It seems like you have some sort of smog/emissions control stuff on your truck that is not installed on other trucks like mine. I believe it"s called a "Thermac" system. It's also possible someone changed things around on you. Maybe somenone from the west coast has more info.

I have a plain vanilla six on my 68 and as you mentioned, the pvc valve goes to a fitting on the intake manifold next to the carburetor. The vacuum advance goes to a fitting on the carb that's on the passenger side of the carb next to the pvc fitting. This is ported vacuum. There should be another vacuum on your carb lower than that one that's engine vacuum. I've used both but prefer the ported vacuum on this truck. Any other open vacuum ports should be capped off.

If you need it, I can take a picture of mine later on today to give you an idea.

11-07-2008, 10:40 AM	#1
RR67gto Registered User Join Date: Apr 2004 Location: Oregon Posts: 5	Need Help 70 250 vaccum hose route? Hello friends I have a real problem trying to under stand where my 70 250 vaccumn hoses go? It's a manual transmission truck and a 1 Bbl carb. Same one I had a problem with the auto choke for. Anyway, I know the PVC from the valve cover goes to the manifold. I also hooked the distributor advance up to a small silinoid mounted on the manifold like it was when I got the truck. But, in a 70 VAN with this engine it shows advance going to the carb? I also have a PVC valve the parts store sold me with a normal top for the hoes. BUt it looks like th old one I found in the truck had a smaller fitting on it's side for a second line? I have a real 1970 issue factory manual, and some other books on the truck. Yet, nothing I have or anything I get on the web shows any of the hose diagrams. What a silly thing to not make avalabile. You can see how to rebuild the engine, transmissions, rear ends, carbs, but nothing aboue where the hoses go. I'm not the first person I've heard of having a problem with this. But, no any of my Pontiac cars I own back to 1962m, I can get the information for all the cars. Anyone has ay idea about a diagram or information about the hose locations pleaselet me know, and I'll say something special for you when I talk to the big guy again. Thanks friends, and what a wonderful place this is. So much information, and so helpful. I didn't miss something posted about the vaccum hoses did I? Mike __________________ Build It Fast Build It Right Hold On Tight !!

11-07-2008, 11:46 AM	#2
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Need Help 70 250 vaccum hose route? It seems like you have some sort of smog/emissions control stuff on your truck that is not installed on other trucks like mine. I believe it"s called a "Thermac" system. It's also possible someone changed things around on you. Maybe somenone from the west coast has more info. I have a plain vanilla six on my 68 and as you mentioned, the pvc valve goes to a fitting on the intake manifold next to the carburetor. The vacuum advance goes to a fitting on the carb that's on the passenger side of the carb next to the pvc fitting. This is ported vacuum. There should be another vacuum on your carb lower than that one that's engine vacuum. I've used both but prefer the ported vacuum on this truck. Any other open vacuum ports should be capped off. If you need it, I can take a picture of mine later on today to give you an idea.



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