Rochester M Vacuum Attachment - The 1947 - Present Chevrolet & GMC Truck Message Board Network

notahybrid · 06-30-2008, 02:37 PM

I have a 68 c10 250 w/ a Rochester M monojet. Where is the vac advance hose supposed to attach? If facing the engine there is a tube on the right front corner at the base of the carb and on the left side of the carb there are 2 holes one on top of the other. I think this is where it was attached when I got the truck but the tube on the right has vacuum when you hold your finger on it.
Thanks

telly · 06-30-2008, 03:40 PM

I have a 70 C10 with a Monojet "M". My vacuum advance goes into the front right of the carb (where you are saying you feel suction). One of the spots on the left side on mine goes to the PCV.

I'm no expert, just bought my truck a little over a week ago - first one.

68gmsee · 06-30-2008, 05:07 PM

On my Rochester the vacuum advance goes to a port on the bottom left side of the carb as you're looking at it. The front one on the bottom right is also a vacuum port but is plugged with a rubber cap.

The PCV goes on a tube at the top of the carb that the breather attaches to.

The vacuum on the front is a constant vacuum.

notahybrid · 06-30-2008, 05:07 PM

Thanks Telly, I'll give it a try there.

notahybrid · 06-30-2008, 05:10 PM

68gmsee thanks for the post. There is a constant vacuum on the front right tube and I currently have it capped. I seem to remember that when I got the truck it was connected on the left side like yours. I guess I'll try both and see which works best.

68gmsee · 06-30-2008, 05:25 PM

I've tried it both ways in the past. For some reason that I don't recall, I put it back in the original position.

The manual says that the one on the left is the "Distributor Vacuum Tube." The one on the front bottom is for "Thermac Tube." I believe that's for trucks from California and other states that required emission controls.

notahybrid · 06-30-2008, 05:33 PM

Left it is... thanks again.

telly · 07-01-2008, 01:18 AM

Maybe that's why mine doesn't run so well right now. I'll try putting the advance on the left side of the carb and plugging the front right port in the morning.

Just went out an took a picture of my current carb setup.

You can see where the vacuum advance is currently attached under the fuel line on the right-front side. The line coming out of the left side of the carb is currently running to the charcoal cannister. Do I need to cap the port where my vacuum advance currently is and reroute it to the port on the left side?

The right-front port was plugged when I bought it a week ago and the vacuum advance was not attached anywhere. So I plugged it in where it looked like it would go (as well as that is where the vacuum advance attaches on my '80 Camaro with a Q-Jet).

Any help would be appreciated.

**El Jay** · 07-01-2008, 01:55 AM

I'm not trying to steal the thread.
Telly, get rid of that fuel filter before it breaks and burns your truck to the ground.

telly · 07-01-2008, 02:01 AM

It came with the truck and I plan to take it off asap. Thanks for the concern.

notahybrid · 07-01-2008, 07:07 AM

Thanks for the reminder. Funny you have that fuel filter, mine came with the same one. I have been meaning to pick up some new line but keep forgetting. Telly, not sure if you know, but the normal filter sits in the bowel of the carb where the fuel line goes in. There is also usually a spring in there with the filter.

telly · 07-01-2008, 04:02 PM

Thanks all!

It appears that the PO had the vacuum advance (from the carb) hooked up to the charcoal cannister. Due to this conversation and making the proper attachments to the carb (and then resetting the timing) my 70 C10 is now accelerating like it should.

Shoot, I even burned rubber today!

06-30-2008, 02:37 PM	#1
notahybrid Registered User Join Date: Mar 2007 Location: Chesapeake, Virginia Posts: 39	Rochester M Vacuum Attachment I have a 68 c10 250 w/ a Rochester M monojet. Where is the vac advance hose supposed to attach? If facing the engine there is a tube on the right front corner at the base of the carb and on the left side of the carb there are 2 holes one on top of the other. I think this is where it was attached when I got the truck but the tube on the right has vacuum when you hold your finger on it. Thanks

06-30-2008, 03:40 PM	#2
telly Registered User Join Date: Jun 2008 Location: Stanwood, WA, 98292 Posts: 151	Re: Rochester M Vacuum Attachment I have a 70 C10 with a Monojet "M". My vacuum advance goes into the front right of the carb (where you are saying you feel suction). One of the spots on the left side on mine goes to the PCV. I'm no expert, just bought my truck a little over a week ago - first one.

06-30-2008, 05:07 PM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rochester M Vacuum Attachment On my Rochester the vacuum advance goes to a port on the bottom left side of the carb as you're looking at it. The front one on the bottom right is also a vacuum port but is plugged with a rubber cap. The PCV goes on a tube at the top of the carb that the breather attaches to. The vacuum on the front is a constant vacuum.

06-30-2008, 05:07 PM	#4
notahybrid Registered User Join Date: Mar 2007 Location: Chesapeake, Virginia Posts: 39	Re: Rochester M Vacuum Attachment Thanks Telly, I'll give it a try there.

06-30-2008, 05:10 PM	#5
notahybrid Registered User Join Date: Mar 2007 Location: Chesapeake, Virginia Posts: 39	Re: Rochester M Vacuum Attachment 68gmsee thanks for the post. There is a constant vacuum on the front right tube and I currently have it capped. I seem to remember that when I got the truck it was connected on the left side like yours. I guess I'll try both and see which works best.

06-30-2008, 05:25 PM	#6
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rochester M Vacuum Attachment I've tried it both ways in the past. For some reason that I don't recall, I put it back in the original position. The manual says that the one on the left is the "Distributor Vacuum Tube." The one on the front bottom is for "Thermac Tube." I believe that's for trucks from California and other states that required emission controls.

06-30-2008, 05:33 PM	#7
notahybrid Registered User Join Date: Mar 2007 Location: Chesapeake, Virginia Posts: 39	Re: Rochester M Vacuum Attachment Left it is... thanks again.

07-01-2008, 01:18 AM	#8
telly Registered User Join Date: Jun 2008 Location: Stanwood, WA, 98292 Posts: 151	Re: Rochester M Vacuum Attachment Maybe that's why mine doesn't run so well right now. I'll try putting the advance on the left side of the carb and plugging the front right port in the morning. Just went out an took a picture of my current carb setup. You can see where the vacuum advance is currently attached under the fuel line on the right-front side. The line coming out of the left side of the carb is currently running to the charcoal cannister. Do I need to cap the port where my vacuum advance currently is and reroute it to the port on the left side? The right-front port was plugged when I bought it a week ago and the vacuum advance was not attached anywhere. So I plugged it in where it looked like it would go (as well as that is where the vacuum advance attaches on my '80 Camaro with a Q-Jet). Any help would be appreciated. Attached Images Last edited by telly; 07-01-2008 at 01:50 AM.

07-01-2008, 01:55 AM	#9
El Jay Gone to greener pastures Join Date: May 2007 Location: Gateway to the Delta Posts: 7,354	Re: Rochester M Vacuum Attachment I'm not trying to steal the thread. Telly, get rid of that fuel filter before it breaks and burns your truck to the ground. __________________ '69 Chevy 1/2 T LWB Stepper: Daily Beater '72 GMC 3/4 T Fleet: Another Daily Beater '72 Plymouth Gran Coupe: ? "Ah women. They make the highs higher and the lows more frequent." Friedrich Nietzsche "Never kick a fresh turd on a hot day." Harry S. Truman GUN CONTROL: Never having to say, "I missed you." Always fire two warning shots into your attacker's chest area before putting a bullet between his eyes. Paraphrased from Louis Awerbuck

07-01-2008, 02:01 AM	#10
telly Registered User Join Date: Jun 2008 Location: Stanwood, WA, 98292 Posts: 151	Re: Rochester M Vacuum Attachment It came with the truck and I plan to take it off asap. Thanks for the concern.

07-01-2008, 07:07 AM	#11
notahybrid Registered User Join Date: Mar 2007 Location: Chesapeake, Virginia Posts: 39	Re: Rochester M Vacuum Attachment Thanks for the reminder. Funny you have that fuel filter, mine came with the same one. I have been meaning to pick up some new line but keep forgetting. Telly, not sure if you know, but the normal filter sits in the bowel of the carb where the fuel line goes in. There is also usually a spring in there with the filter. Last edited by notahybrid; 07-01-2008 at 07:10 AM. Reason: additional comment

07-01-2008, 04:02 PM	#12
telly Registered User Join Date: Jun 2008 Location: Stanwood, WA, 98292 Posts: 151	Re: Rochester M Vacuum Attachment Thanks all! It appears that the PO had the vacuum advance (from the carb) hooked up to the charcoal cannister. Due to this conversation and making the proper attachments to the carb (and then resetting the timing) my 70 C10 is now accelerating like it should. Shoot, I even burned rubber today!



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