What causes this?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ric83 · 04-14-2004, 03:59 PM

My dad asked me to chech the timing on his truck yest. ('83 Scotsdale w/ stock 305)
When I took a look at it, it sounded like it was idleing a little too fast. When I pulled the vac. hose off of the advance to check the timing, it made very little diff. as to how it idled. Well, while shining the light, I noticed that every few seconds, the timing mark would jump quite a bit to the advance side. What would cause it to do that?? I know his truck needs a tune up pretty bad so we will do that, but is there something in specific I need to look into?? After setting the timing at 10, I took it for a drive and it drives like a dog. It has not kind of power, you have to let it build up speed and forget about passing anyone. I ended up setting the timing at 8 instead. It seemed to like it a little better but had all the mentioned problems still. Anyone have any suggestions?

Russell · 04-14-2004, 04:18 PM

If it is idling too quickly, the mech advance may be kicking in occasionally. Another possiblity is that the harmonic balancer has slipped, causing you to not be able to time it properly...

chevyjr73 · 04-14-2004, 05:25 PM

the vacuum advance may not have changed idle when you pulled it because it might be connected to ported vacuum. if the timing is jumping around either your springs in your distributor is worn or the distributor itself is bad. also you may have some slack in your timing chain. it may feel too sluggish because your timing is noy set high enough. i have mine set at 14 degrees btdc. anything less and its a dog. you could also have a vacuum leak causing it too idle so high.

79BIG10 · 04-14-2004, 06:32 PM

Sounds like a worn timing chain like chevyjr73 mentioned. If it has alot of miles on it then I would spend the time and money and get a new set. Plus you can check your balancer while you're there.

Ric83 · 04-15-2004, 10:42 AM

I am not too sure on the distributor. We thought it might be it, but not sure if it was something in it which could be changed or if it might be the whole thing.
As far as the timing chain, I just replaced it a few months ago. Not sure on how long ago exactly, but I would definatly say no more than a year. When I installed it I reset the distributor as well and set the timing to 10* and it ran great. Beter than I think it has run the whole time he has had it.

chevyjr73 · 04-15-2004, 10:58 AM

if you already replaced the timing chain i would definately go with a new distributor. the mechanical advance in it is probably worn out.

04-14-2004, 03:59 PM	#1
Ric83 Registered User Join Date: Jan 2003 Location: Austin, TX Posts: 824	What causes this?? My dad asked me to chech the timing on his truck yest. ('83 Scotsdale w/ stock 305) When I took a look at it, it sounded like it was idleing a little too fast. When I pulled the vac. hose off of the advance to check the timing, it made very little diff. as to how it idled. Well, while shining the light, I noticed that every few seconds, the timing mark would jump quite a bit to the advance side. What would cause it to do that?? I know his truck needs a tune up pretty bad so we will do that, but is there something in specific I need to look into?? After setting the timing at 10, I took it for a drive and it drives like a dog. It has not kind of power, you have to let it build up speed and forget about passing anyone. I ended up setting the timing at 8 instead. It seemed to like it a little better but had all the mentioned problems still. Anyone have any suggestions? __________________ Ric '83 Silverado SWB Fleetside Here she is

04-14-2004, 04:18 PM	#2
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	If it is idling too quickly, the mech advance may be kicking in occasionally. Another possiblity is that the harmonic balancer has slipped, causing you to not be able to time it properly... __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

04-14-2004, 06:32 PM	#4
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	Sounds like a worn timing chain like chevyjr73 mentioned. If it has alot of miles on it then I would spend the time and money and get a new set. Plus you can check your balancer while you're there. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

04-15-2004, 10:42 AM	#5
Ric83 Registered User Join Date: Jan 2003 Location: Austin, TX Posts: 824	I am not too sure on the distributor. We thought it might be it, but not sure if it was something in it which could be changed or if it might be the whole thing. As far as the timing chain, I just replaced it a few months ago. Not sure on how long ago exactly, but I would definatly say no more than a year. When I installed it I reset the distributor as well and set the timing to 10* and it ran great. Beter than I think it has run the whole time he has had it. __________________ Ric '83 Silverado SWB Fleetside Here she is

04-14-2004, 05:25 PM	#3
chevyjr73 Registered User Join Date: Mar 2004 Location: chesapeake,virginia Posts: 117	the vacuum advance may not have changed idle when you pulled it because it might be connected to ported vacuum. if the timing is jumping around either your springs in your distributor is worn or the distributor itself is bad. also you may have some slack in your timing chain. it may feel too sluggish because your timing is noy set high enough. i have mine set at 14 degrees btdc. anything less and its a dog. you could also have a vacuum leak causing it too idle so high.

04-15-2004, 10:58 AM	#6
chevyjr73 Registered User Join Date: Mar 2004 Location: chesapeake,virginia Posts: 117	if you already replaced the timing chain i would definately go with a new distributor. the mechanical advance in it is probably worn out.



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