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Chevelle454 · 08-25-2003, 07:02 PM

I am having trouble getting this 350 in my '72 running right. It will fire right up and idle normally, but only with the vacuum hose from the carb to the advance on the distributer disconnected. If it is connected, it will run horrible and backfire and pop while idling. It runs like crap with no power at any RPM above an idle with the hose either connected or disconnected.

I get about 20 inches when I check it with a vacuum guage while idling, but when I hit the gas it drops way down to almost zero then slowly works its way back up again. Someone said that I have it connected to a manifold vacuum or something, but this is the only connection on the carb that I can see that it would hook up to. Any help would be much appreciated, I would like to be able to get the truck moving around under it's own power...

Thanks,
Scott

**COBALT** · 08-25-2003, 07:14 PM

How's your timing? Take that vacuum line off the vacuum advance and check your timing. The mark should be somewhere in the 10-14 degree range. If it's not (I bet the mark is WAY counter-clockwise) you need to time your engine.

The vacuum diaphram on your distributor shoudn't have full manifold vacuum. From the picture it's hard to tell, but if I were to guess it's not full manifold vacuum at all. That's GOOD.

If you're getting good vacuum from the carb then make sure that distributor is in good shape. The diaphram may be busted.

Class of 69 · 08-25-2003, 08:22 PM

I agree with Cobalt on the timing being way off, but you didn't say if it was worked on. Did you do anything in the distrib?? The mechanical advance could be rusty, and stuck in full advance. The point gap could be incorrect, or the points burned.

Chevelle454 · 08-25-2003, 09:07 PM

I have replaced the points, but they are not gapped correctly because I could not fit a feeler guage in there. Do you think that could really be the problem?

Class of 69 · 08-25-2003, 09:13 PM

Very definately!! The proper gap is very important. I don't suppose you know someone with a dwell meter?? If not, to set the dwell turn the adjusting screw ( behind the metal window ) in with a hex head wrench until the engines begins to miss. Then turn the screw back out 1/2 turn. This should get the dwell very close to 30 degrees. Then check, and set the timing with the vacuum advance hose OFF the distrib, and PLUGGED. Hope this gets you going!!

fast71 · 08-25-2003, 09:24 PM

well for the first thing where your vac hose is connected is straight vac. that isnt correct because you are advancing the timming as soon as it fires. you need to find a port that doesnt have vac. at a idle and has vac. when moving the throttle. disconnect the vac. hose and check timming ,make sure you block off the vac. line from the carb to the dist. and set at 8 degrees before top dead . after timing is set find the port that i spoke about and hook the dist . up to it.
hope this helps, Brian

fast71 · 08-25-2003, 09:26 PM

I forgot you have points also . set them to .018 and the dwell should be around 28 to 30 degrees. the truck should run like a champ.

**Classic Heartbeat** · 08-25-2003, 09:39 PM

Fast71 is correct. That vacuum port is the wrong one to hook up to. The correct port will either be this one under the vacuum choke:

**Classic Heartbeat** · 08-25-2003, 09:41 PM

or this one upper, left, front. Neither one of those ports are full vac. WES www.ClassicHeartbeat.com

**COBALT** · 08-25-2003, 09:50 PM

If you can't put a feeler guage (.018-.019) in there MAKE ONE. Buy a cheap set at the parts store, and bend the appropriate one over about 1/4" from the end.

If this bothers you then use a match book. This is all approximate anyway until you can get a dwell meter on your distributor. You can buy a cheap dwell/tach meter at any parts store.

You also have to lube the cam on the distributor, and place lube behind the cam lobe on the points. Did you do that?

Once the points are set up correctly make sure your plugs are clean and gapped. Make sure your plug wires are good and firmly connected. Make sure your coil is getting the right voltage from the starter and from the front wiring harness.

...then time your engine. Set it to 10 degrees from TDC on the first go-around. Check your response, and advance it until you have good off-idle response. Mine is set to 14 degrees from TDC.

Chevelle454 · 08-25-2003, 10:44 PM

I am pretty sure I have found the right vacuum port. It increases as I give it gas. Where do I hook an electric dwell meter up to?

08-25-2003, 07:02 PM	#1
Chevelle454 Registered User Join Date: Aug 2003 Location: MN Posts: 380	Does this look correct? I am having trouble getting this 350 in my '72 running right. It will fire right up and idle normally, but only with the vacuum hose from the carb to the advance on the distributer disconnected. If it is connected, it will run horrible and backfire and pop while idling. It runs like crap with no power at any RPM above an idle with the hose either connected or disconnected. I get about 20 inches when I check it with a vacuum guage while idling, but when I hit the gas it drops way down to almost zero then slowly works its way back up again. Someone said that I have it connected to a manifold vacuum or something, but this is the only connection on the carb that I can see that it would hook up to. Any help would be much appreciated, I would like to be able to get the truck moving around under it's own power... Thanks, Scott Attached Images __________________ 1972 C10 1972 C20

08-25-2003, 07:14 PM	#2
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	How's your timing? Take that vacuum line off the vacuum advance and check your timing. The mark should be somewhere in the 10-14 degree range. If it's not (I bet the mark is WAY counter-clockwise) you need to time your engine. The vacuum diaphram on your distributor shoudn't have full manifold vacuum. From the picture it's hard to tell, but if I were to guess it's not full manifold vacuum at all. That's GOOD. If you're getting good vacuum from the carb then make sure that distributor is in good shape. The diaphram may be busted. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

08-25-2003, 08:22 PM	#3
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	I agree with Cobalt on the timing being way off, but you didn't say if it was worked on. Did you do anything in the distrib?? The mechanical advance could be rusty, and stuck in full advance. The point gap could be incorrect, or the points burned. __________________ 69 GMC K10 ..some restoration required....still..

08-25-2003, 09:07 PM	#4
Chevelle454 Registered User Join Date: Aug 2003 Location: MN Posts: 380	I have replaced the points, but they are not gapped correctly because I could not fit a feeler guage in there. Do you think that could really be the problem? __________________ 1972 C10 1972 C20

08-25-2003, 09:13 PM	#5
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	Very definately!! The proper gap is very important. I don't suppose you know someone with a dwell meter?? If not, to set the dwell turn the adjusting screw ( behind the metal window ) in with a hex head wrench until the engines begins to miss. Then turn the screw back out 1/2 turn. This should get the dwell very close to 30 degrees. Then check, and set the timing with the vacuum advance hose OFF the distrib, and PLUGGED. Hope this gets you going!! __________________ 69 GMC K10 ..some restoration required....still.. Last edited by Class of 69; 08-25-2003 at 09:26 PM.

08-25-2003, 09:24 PM	#6
fast71 Drive it like U stole it Join Date: Mar 2000 Location: tunnel hill ,GA /Chatt,TN Posts: 956	well for the first thing where your vac hose is connected is straight vac. that isnt correct because you are advancing the timming as soon as it fires. you need to find a port that doesnt have vac. at a idle and has vac. when moving the throttle. disconnect the vac. hose and check timming ,make sure you block off the vac. line from the carb to the dist. and set at 8 degrees before top dead . after timing is set find the port that i spoke about and hook the dist . up to it. hope this helps, Brian __________________ 71 custom 10 swb 72 nova ss 72 nova custom 87 s10 96 burb 94 camry 53 5 window 3100

08-25-2003, 09:26 PM	#7
fast71 Drive it like U stole it Join Date: Mar 2000 Location: tunnel hill ,GA /Chatt,TN Posts: 956	I forgot you have points also . set them to .018 and the dwell should be around 28 to 30 degrees. the truck should run like a champ. __________________ 71 custom 10 swb 72 nova ss 72 nova custom 87 s10 96 burb 94 camry 53 5 window 3100

08-25-2003, 09:39 PM	#8
Classic Heartbeat Project Junkie! Fishing Poor!! Join Date: Dec 1999 Location: Olympia,Wa. 98512 Posts: 10,770	Fast71 is correct. That vacuum port is the wrong one to hook up to. The correct port will either be this one under the vacuum choke: __________________ On-line catolog Classic Heartbeat Pickup Parts WEHEPP@comcast.net Call us Toll Free (888) 338-2502 Like Us on Facebook No appointment necessary. 72 BB Chevy Custom Deluxe / Custom Camper 67 I-6 (Soon to be 5.7 LS1) Panel 68 BB Chevy Short Bed 72 6.0 LQ9 Short Bed Chevy 4X4 Olympia's fastest growing truck parts supplier. Olympia's home for Wayward Chevys Last edited by Classic Heartbeat; 10-04-2007 at 07:02 PM.

08-25-2003, 09:41 PM	#9
Classic Heartbeat Project Junkie! Fishing Poor!! Join Date: Dec 1999 Location: Olympia,Wa. 98512 Posts: 10,770	or this one upper, left, front. Neither one of those ports are full vac. WES www.ClassicHeartbeat.com __________________ On-line catolog Classic Heartbeat Pickup Parts WEHEPP@comcast.net Call us Toll Free (888) 338-2502 Like Us on Facebook No appointment necessary. 72 BB Chevy Custom Deluxe / Custom Camper 67 I-6 (Soon to be 5.7 LS1) Panel 68 BB Chevy Short Bed 72 6.0 LQ9 Short Bed Chevy 4X4 Olympia's fastest growing truck parts supplier. Olympia's home for Wayward Chevys Last edited by Classic Heartbeat; 10-04-2007 at 07:02 PM.

08-25-2003, 09:50 PM	#10
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	If you can't put a feeler guage (.018-.019) in there MAKE ONE. Buy a cheap set at the parts store, and bend the appropriate one over about 1/4" from the end. If this bothers you then use a match book. This is all approximate anyway until you can get a dwell meter on your distributor. You can buy a cheap dwell/tach meter at any parts store. You also have to lube the cam on the distributor, and place lube behind the cam lobe on the points. Did you do that? Once the points are set up correctly make sure your plugs are clean and gapped. Make sure your plug wires are good and firmly connected. Make sure your coil is getting the right voltage from the starter and from the front wiring harness. ...then time your engine. Set it to 10 degrees from TDC on the first go-around. Check your response, and advance it until you have good off-idle response. Mine is set to 14 degrees from TDC. __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

08-25-2003, 10:44 PM	#11
Chevelle454 Registered User Join Date: Aug 2003 Location: MN Posts: 380	I am pretty sure I have found the right vacuum port. It increases as I give it gas. Where do I hook an electric dwell meter up to? __________________ 1972 C10 1972 C20



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