73 power lost
Thread Starter
6th Gear
Joined: Feb 2009
Posts: 6
Likes: 0
From: Manahawkin NJ
73 power lost
Hi,
Have a low miles 73 vette,just got it.It ran rough,so I did points and plugs R44t AC per specs.plugs had lots of carbon.New points set at 30 degrees.Timing set at 12 degrees before TDC.Car starts good,but still runs rough,and has no power,and getting worse. It has only 15 inchs of vaccume stady.New plugs are very light gray,and exust tips are the same.I verified all settings,and dwell,and timing still good.I was told late timming,but it is 12 degrees and in spec.Also maybe lean fuel burn.How do I check lean fuel,or late timming.Could I have a timming chain,and how to check that.This car has 16k miles,and is all original.Hope someone has ideas.
Have a low miles 73 vette,just got it.It ran rough,so I did points and plugs R44t AC per specs.plugs had lots of carbon.New points set at 30 degrees.Timing set at 12 degrees before TDC.Car starts good,but still runs rough,and has no power,and getting worse. It has only 15 inchs of vaccume stady.New plugs are very light gray,and exust tips are the same.I verified all settings,and dwell,and timing still good.I was told late timming,but it is 12 degrees and in spec.Also maybe lean fuel burn.How do I check lean fuel,or late timming.Could I have a timming chain,and how to check that.This car has 16k miles,and is all original.Hope someone has ideas.
Racer
Joined: May 2007
Posts: 370
Likes: 0
From: Cherry Hill N.J.
rough idle
How old are your spark plug wires.......?
33 year old wires (broken,burned, rotted,chewed on)
might be the cause of the rough idle..
Good Luck
33 year old wires (broken,burned, rotted,chewed on)
might be the cause of the rough idle..
Good Luck
Last edited by BHRIG; May 10, 2010 at 03:24 PM. Reason: omission
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Agree,..also check the distributor cap for cracks and double check the plug wire / firing order.
In addition:
1) How old is the fuel?
2) There are dozens of places vacuum can leak on a Vette. Start at the carb and work out. 15 inches is good, but you should see 17-18 at idle with a stock engine.
3) Setting the timing: With the vaccum advance disconnected and plugged, set the mechanical to 34-36 degrees BTDC, all in at 3000 RPM. Then let the initial fall where it falls.
4) Is your choke behaving as it should?
If the above doesn't help, get back to us for more diagnostics.
In addition:
1) How old is the fuel?
2) There are dozens of places vacuum can leak on a Vette. Start at the carb and work out. 15 inches is good, but you should see 17-18 at idle with a stock engine.
3) Setting the timing: With the vaccum advance disconnected and plugged, set the mechanical to 34-36 degrees BTDC, all in at 3000 RPM. Then let the initial fall where it falls.
4) Is your choke behaving as it should?
If the above doesn't help, get back to us for more diagnostics.
Thread Starter
6th Gear
Joined: Feb 2009
Posts: 6
Likes: 0
From: Manahawkin NJ
73 power lose
Hi,
Thanks so much for HELP.Chock works great.New fuel in tank,The car actually ran better before tune up,and new fuel.I think you are on to somthing with the vac advance,how do I check vac advance,are you suggesting I set inital timming at 36-38 degrees BTC? Also plug wires appear originals,and have date code,but this problem is all cyclinders.I would like to check vac advance.
Thanks
Jim
Thanks so much for HELP.Chock works great.New fuel in tank,The car actually ran better before tune up,and new fuel.I think you are on to somthing with the vac advance,how do I check vac advance,are you suggesting I set inital timming at 36-38 degrees BTC? Also plug wires appear originals,and have date code,but this problem is all cyclinders.I would like to check vac advance.
Thanks
Jim
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
The total timing is set to 34 to 36 total and should be all in by 3000 rpm. This is a better way to set the timing than the initial timing. You have to make sure the weights in the dist. are advancing the timing and you are getting full advance. I also check the vacuum advance with a mighty vac vacuum tool. This will pull the vacuum advace cam in with the engine at an idle so you can see how much timing you have. A dial back timing light is a huge help when setting this all up.
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Hi,
Thanks so much for HELP.Chock works great.New fuel in tank,The car actually ran better before tune up,and new fuel.I think you are on to somthing with the vac advance,how do I check vac advance,are you suggesting I set inital timming at 36-38 degrees BTC? Also plug wires appear originals,and have date code,but this problem is all cyclinders.I would like to check vac advance.
Thanks
Jim
Thanks so much for HELP.Chock works great.New fuel in tank,The car actually ran better before tune up,and new fuel.I think you are on to somthing with the vac advance,how do I check vac advance,are you suggesting I set inital timming at 36-38 degrees BTC? Also plug wires appear originals,and have date code,but this problem is all cyclinders.I would like to check vac advance.
Thanks
Jim
36-38° TOTAL Timing, which means initial + centrifugal advance, with vacuum advance hose disconnected AND plugged.
I think you should read this post first, that could help a lot :
http://forums.corvetteforum.com/c3-t...long-post.html
Anyway, vacuum advance is probably not your problem, performance speaking, because you only have
vacuum advance at part throttle, NEVER at WOT, assuming your vacuum advance can works like it's supposed to...
Vacuum advance is only useful for economy and part throttle acceleration.
Last edited by 73StreetRace; May 6, 2010 at 07:47 AM.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Good advice above. To check your vacuum advance can, detach the hose at the carb. Suck on the end of the hose to see if the diaphragm is holding vacuum. If it's the original 37 year old VA can, the diaphragm could be cracked/broken which renders the VA useless and causes a mild vacuum leak at the carb.
When you changed your plugs, are you sure you properly attached the plug wires to the plugs? Just because the boot is attached over the insulator of the sparkplug, doesn't mean you have continuity. Might double-check.
When you changed your plugs, are you sure you properly attached the plug wires to the plugs? Just because the boot is attached over the insulator of the sparkplug, doesn't mean you have continuity. Might double-check.
Thread Starter
6th Gear
Joined: Feb 2009
Posts: 6
Likes: 0
From: Manahawkin NJ
73 power loes
Hi Again,
Thanks for all the great help.OK so I tested the distributor advance.I blow into hose on advance can,and get much resistance seems ok to me.With vac hose attached I got almost no advance on time light,and Vac check at intake of 15 inchs of vaccum and no vac increase wih rpms.If I bypass the TCS and AIR pump ,and run hose direct from carb to vac can I get timing light advance of about 4 inchs past top of time tab,and good vac reading of normal about 20 inchs at idle 900 rpms.This seems good. But with increased rpms the vac falls to red zone 15 inchs,engine is rough pops at carb.Now at this point the new plugs are not looking to good with this gray carbon,and they may not be firing.I still have a bad running car.The plug wires are on good.I will replace cap,and wires.But something is funny with timing.Un happy Jim, HELP
Thanks for all the great help.OK so I tested the distributor advance.I blow into hose on advance can,and get much resistance seems ok to me.With vac hose attached I got almost no advance on time light,and Vac check at intake of 15 inchs of vaccum and no vac increase wih rpms.If I bypass the TCS and AIR pump ,and run hose direct from carb to vac can I get timing light advance of about 4 inchs past top of time tab,and good vac reading of normal about 20 inchs at idle 900 rpms.This seems good. But with increased rpms the vac falls to red zone 15 inchs,engine is rough pops at carb.Now at this point the new plugs are not looking to good with this gray carbon,and they may not be firing.I still have a bad running car.The plug wires are on good.I will replace cap,and wires.But something is funny with timing.Un happy Jim, HELP
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Drifting
Joined: Nov 2003
Posts: 1,874
Likes: 7
From: l In
Hi Again,
Thanks for all the great help.OK so I tested the distributor advance.I blow into hose on advance can,and get much resistance seems ok to me.With vac hose attached I got almost no advance on time light,and Vac check at intake of 15 inchs of vaccum and no vac increase wih rpms.If I bypass the TCS and AIR pump ,and run hose direct from carb to vac can I get timing light advance of about 4 inchs past top of time tab,and good vac reading of normal about 20 inchs at idle 900 rpms.This seems good. But with increased rpms the vac falls to red zone 15 inchs,engine is rough pops at carb.Now at this point the new plugs are not looking to good with this gray carbon,and they may not be firing.I still have a bad running car.The plug wires are on good.I will replace cap,and wires.But something is funny with timing.Un happy Jim, HELP
Thanks for all the great help.OK so I tested the distributor advance.I blow into hose on advance can,and get much resistance seems ok to me.With vac hose attached I got almost no advance on time light,and Vac check at intake of 15 inchs of vaccum and no vac increase wih rpms.If I bypass the TCS and AIR pump ,and run hose direct from carb to vac can I get timing light advance of about 4 inchs past top of time tab,and good vac reading of normal about 20 inchs at idle 900 rpms.This seems good. But with increased rpms the vac falls to red zone 15 inchs,engine is rough pops at carb.Now at this point the new plugs are not looking to good with this gray carbon,and they may not be firing.I still have a bad running car.The plug wires are on good.I will replace cap,and wires.But something is funny with timing.Un happy Jim, HELP
