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Topic: timing issue

in Forum: C3 Engines


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timing issue (1/8)
 9/18/10 10:36am
scrappy78
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enterprise, AL - USA

Vette(s):
1978 silver anniversary vette l-48


Joined: 6/27/2010
Posts: 63

Okay I need some help.

 What’s the timing on a mostly stock 78 L-48. No emissions stickers under hood to check by.

 Okay now what little info I have on motor passed on from previous owner. Rebuilt 20,000 miles ago with mild cam. He said 350 horse feels like 200. New parts include newly remand Quadra jet one month old.New stock fuel pump and new rapid-fire ac-Delco’s as of yesterday. 

Now engine pops/misfires under part throttle but only on one cylinder (not sure which one can’t replicate at idle) and seems to surge about 50 to 75 rpm at idle. I accidently  moved the distributor and I believe it’s now out of timing


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timing issue (2/8)
 9/18/10 12:55pm
aceintheholeLifetime Member
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Manteca, CA - USA

Vette(s):
1978,two tone,Metalic Rootbeer & gold 1975 L48 4 speed


Joined: 11/20/2005
Posts: 3623

Hi J, Unless you have a pro timing light that switches to full advance you can really only get a ballpark reading. Turning the dist. counterclockwise will advance the spark and clockwise will retard it. It shouldn't be popping at all unless the wires are crossed. You can double check the firing order from the sequence on the manifold in front of the carb. If your not using a timing light and just want to get it close again, mark the position of the vacuum diaphram before you start turning the dist. so you can always come back without worry. Factory specs say 8 degrees before top dead center with the vacuum hose to the diaphram removed and plugged but most seem to run better closer to 12. Over advance will cause excessive heat to the motor and cause it to jerk at start, too far retarded will cause it to idle down and die. let us know how things turn out.

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Jimmy B.
Just can't wait to get on the road again.

 
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timing issue (3/8)
 9/18/10 9:17pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

From what I read in your post, you just installed new plugs "yesterday", and the problem started after that, correct?
Moving the distributor will certainly effect the timing, but you'd have to move it quite a bit to make it start running that bad, and popping. Perhaps what you have is a combination of a bad/mis-gapped plug, and retarded timing.
Was there any issues with the engine before you did the plug change?


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Joel Adams
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timing issue (4/8)
 9/18/10 9:56pm
lukesvetteLifetime Member
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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.


Joined: 5/18/2004
Posts: 6812

Just a safety question. All wires went back on the correct plugs?
timing issue (5/8)
 9/18/10 10:40pm
yostusota
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top


Joined: 5/18/2010
Posts: 1518

Nailed that one on the head Paul..do need a little more info..when did it start back firing out the carb..BTW this is very dangerous, the only thing that has kept your car from going up in smoke is that your engine hasn't stalled or shut off when it did the back fire..the flame that comes out of there can go several feet in the air..check your air filter and the top of the filter cover..I am sure you will find a nice burn mark..you probably have several things going on..from a wire on the wrong plug to a lean misfire from a carb not set up right..I know you just had it rebuilt but it still needs tuned to the car..if you have a Sears near by they do sell a basic advance timing light..it has a little knob on the back that allows you to check the total timing as well as base timing.If you want to go nuts buy a digital one..it shows tach speed as well as advance and retard..if 8 is where it is supposed to be then start there and move it around untill it doesn't ping..then move it back 2 degrees..that's on the edge unless your carb is tuned..be carefull with this..if you can't figure it out ask for more info on how to do this tune stuff..it can make or break rings and pistons!!
Rich
 


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timing issue (6/8)
 9/19/10 10:34am
scrappy78
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enterprise, AL - USA

Vette(s):
1978 silver anniversary vette l-48


Joined: 6/27/2010
Posts: 63

Thanks guys went "back in" yesterday and found a plug wire boot had broken off exposing the wire electrode! I believe the spark was jumping to block causing the misfire. So I bit the bullet and bought a new 8.5 mm set of MSD wires and installed them too. Then got my trusty NEW timing light and set the timing to the 8 btdc that was recommended by you guys. Took her out last night for a 60 mile road trip and she ran great.

 on a side note I joined this site  because the members have always helped each other out and with me not being a mechanic I’m sure gonna need all the help I can get.

THANX NOW AND IN ADVANCE 

YOU GUYS ARE GREAT

JB

timing issue (7/8)
 9/19/10 11:38am
yostusota
Former Member

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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top


Joined: 5/18/2010
Posts: 1518

That's what we do! I joined thinking it was just an online forum and found a club instead..glad it all worked out.
Rich

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My first parade at Carlisle 2010
timing issue (8/8)
 9/19/10 11:51am
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

Clap
Good Job!!! Glad it was something relatively simple!!(As if running new wires on a Shark could be simple!)

btw...if you're interested, Paragon(and others, also) has repro emissions decals for under the hood...
Might give Larry and crew at a call, first.
Adams' Apple2010-09-19 09:03:05

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Joel Adams
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(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

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