ran into something I haven't had happen before?

semocoachworks · 05-13-2009, 08:31 PM

My daily driver, 86 3/4 ton 4x4 suburban, developed a miss. I did a tune up, reset the timing, put new gas in. The timing was set at about 8 degrees btdc. It had a heck of a spark knock. I'm going to do a compression check this weekend when i have more time. I've worked on/rebuilt/built several motors and i've never had one spark knock this way??? The only way i can get the ping to let up a little is to set the timing at 4 degrees btdc. I have no sucking or blowing at the exhaust, no known vacuum leaks. Maybe a flat lobe on the cam? I'm really stumped on this one. Any ideas???

350 cid

hotrodpc · 05-13-2009, 09:16 PM

How about the possibility of some bad gas in the tank? Maybe some water in the tank? Is this a 350 cu in w/ HEI Ignition and Quadrajunk Carb???

leolkfrm · 05-14-2009, 02:43 AM

someone will correct me if i'm inacurate, but i think 86 still had advance weights under the rotor, make sure they are moving freely. does your 86 need the wire disconected on the firewall for setting base timing? it should show on the emmision label

bradrhale · 05-14-2009, 05:47 AM

i thought that they started that in 87 with the base timing??

semocoachworks · 05-14-2009, 06:01 AM

Yes, it's a 350 with a quadrajunk. This one is still old enough you don't have to have the wire unhooked(base timing). I ran it almost empty on gas and refilled. When I get in tonight, i'm gonna try another carb, I have several so hopefully one of them will work. I also am going to test my coil output. It has an accel super coil and i'm thinking maybe it is going bad. The spark knock is what's got me stumped??? I cannot get completely rid of it?? Thanks for the help!

hotrodpc · 05-14-2009, 09:15 AM

That would be a great suggestion leo. I am fairly certain 86 still has the centrifical weights for timing advance, and if its rusted or a spring popped off, that will sure throw the timing into a way advanced mode at lower rpm and make a ping for certain. Back in the day, that is how I would time my vehicle for best performance. Advance the timing as far as I could, then back it off just enough the ping was gone.

semocoachworks · 05-14-2009, 04:27 PM

Got time to tear into the burb today and number 7 has a burnt valve. Time to rebuild it anyway. I'll get into it more this weekend and see what other carnage is in there!!! Thanks for the replies!

05-13-2009, 08:31 PM	#1
semocoachworks Senior Member Join Date: May 2009 Location: rapid city, sd Posts: 817	ran into something I haven't had happen before? My daily driver, 86 3/4 ton 4x4 suburban, developed a miss. I did a tune up, reset the timing, put new gas in. The timing was set at about 8 degrees btdc. It had a heck of a spark knock. I'm going to do a compression check this weekend when i have more time. I've worked on/rebuilt/built several motors and i've never had one spark knock this way??? The only way i can get the ping to let up a little is to set the timing at 4 degrees btdc. I have no sucking or blowing at the exhaust, no known vacuum leaks. Maybe a flat lobe on the cam? I'm really stumped on this one. Any ideas??? 350 cid Last edited by semocoachworks; 05-13-2009 at 08:32 PM. Reason: forgot some info

05-13-2009, 09:16 PM	#2
hotrodpc Senior Member Join Date: Jul 2008 Location: OK Posts: 6,936	How about the possibility of some bad gas in the tank? Maybe some water in the tank? Is this a 350 cu in w/ HEI Ignition and Quadrajunk Carb??? __________________ *Winners NEVER Quit , Quitters NEVER Win !!!*

05-14-2009, 02:43 AM	#3
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,927	someone will correct me if i'm inacurate, but i think 86 still had advance weights under the rotor, make sure they are moving freely. does your 86 need the wire disconected on the firewall for setting base timing? it should show on the emmision label __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

05-14-2009, 09:15 AM	#6
hotrodpc Senior Member Join Date: Jul 2008 Location: OK Posts: 6,936	That would be a great suggestion leo. I am fairly certain 86 still has the centrifical weights for timing advance, and if its rusted or a spring popped off, that will sure throw the timing into a way advanced mode at lower rpm and make a ping for certain. Back in the day, that is how I would time my vehicle for best performance. Advance the timing as far as I could, then back it off just enough the ping was gone. __________________ *Winners NEVER Quit , Quitters NEVER Win !!!*

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05-14-2009, 05:47 AM	#4
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 9,528	i thought that they started that in 87 with the base timing??

05-14-2009, 06:01 AM	#5
semocoachworks Senior Member Join Date: May 2009 Location: rapid city, sd Posts: 817	Yes, it's a 350 with a quadrajunk. This one is still old enough you don't have to have the wire unhooked(base timing). I ran it almost empty on gas and refilled. When I get in tonight, i'm gonna try another carb, I have several so hopefully one of them will work. I also am going to test my coil output. It has an accel super coil and i'm thinking maybe it is going bad. The spark knock is what's got me stumped??? I cannot get completely rid of it?? Thanks for the help!

05-14-2009, 04:27 PM	#7
semocoachworks Senior Member Join Date: May 2009 Location: rapid city, sd Posts: 817	Got time to tear into the burb today and number 7 has a burnt valve. Time to rebuild it anyway. I'll get into it more this weekend and see what other carnage is in there!!! Thanks for the replies!

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