| Re: [GMCnet] losing power [message #220113] |
Tue, 27 August 2013 14:13  |
KB
Messages: 1262
Registered: September 2009
Karma: 0
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Senior Member |
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> I'm chiming in with John on this one. Recheck your timing, start at 12 deg
> initial.
Ok, naive question time: why 12 degrees instead of the 8 specified in the manual?
And would it matter whether it's 8 or 12 if you have EFI (since you
tell it what the base timing is and the computer compensates)?
I've got low vacuum on our new engine so I'm suspecting a problem
with the ignition or a vac leak. With the computer disabled
to set timing, it runs like crap at 8 degrees BTDC. It has an
RV cam if that matters, and the timing chain is set to 0 (ie
not advanced 4).
thanks
Karen
1973 23'
1975 26'
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Karen
1975 26'
San Jose, CA
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| Re: [GMCnet] losing power [message #220137 is a reply to message #220113] |
Tue, 27 August 2013 19:40  |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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Senior Member |
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Are the timing marks accurate?
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: [GMCnet] losing power [message #220145 is a reply to message #220113] |
Tue, 27 August 2013 20:21 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| KB wrote on Tue, 27 August 2013 12:13 |
>
I've got low vacuum on our new engine so I'm suspecting a problem
with the ignition or a vac leak. With the computer disabled
to set timing, it runs like crap at 8 degrees BTDC. It has an
RV cam if that matters, and the timing chain is set to 0 (ie
not advanced 4).
thanks
Karen
1973 23'
1975 26'
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Karen,
First, glad the engine is in. Good work. Second, not happy to hear you have low vacuum. Not happy at all. Your new engine should let you drive off into the sunset, unfettered by problems.
When you say low vacuum do you mean when you are trying to drive down the road? i.e. you need to give it lots of gas to keep going?
Or is it low vacuum at idle. If so, I am thinking about the intake. Did you put it on or was it done at the rebuilder's? I cannot remember which manifold you have but they can leak.
On Randy's stock 403 we were able to find it easily. Disconnected the PCV. Pulled the breather. Made sure the oil fill cap was tight. Took a baggie, held on to it TIGHT and put it over the breather. It really tried to suck it into the valve cover. On a newly rebuilt engine I would expect slight movement out due to blow by on new rings.
On the TBI, I am assuming you remembered the little wad of RTV that goes over the right rear bolt. (You rarely miss a step, but I have to ask.)
Keep us informed. I know you will get to the bottom of this. I hope it is soon so you can continue on the other GMC project you have in mind.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] losing power [message #220146 is a reply to message #220113] |
Tue, 27 August 2013 20:25 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I don't know much about aftermarket EFI. During the short period where some GM cars had a distributor and EFI I seem to remember it would run like crap when you put the distributor in test mode to set base timing. Does it run ok when you put it in normal mode? And the vac should improve if it does run better.
John Lebetski
Woodstock, IL
77 Eleganza II
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