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  #31 (permalink)  
Old 01-08-2012, 09:35 AM
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my KARMA ran over my DOGMA
 

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The backfire issue can be due to improper valve adjustment, has this engine been in use for a while or is this a fresh build? Cant hurt to double check the preload. What jets and what power valve in the holley? might be a good idea to service the carb and find out what you have. Go through and set the secondary throttle plate base setting as well since you have idle issues. Get yourself a good vacuum gage and use it to set the carb idle circuits & check on engine vacuum levels. Carb fuel pressure? check it out.

Do you have a constant full 12-14VDC going to the distributor for power when the engine is running? make sure you are getting full juice.

The vacuum advance on those HEI street fire can be limited using the MSD advance stop kit, do you have that part? you may need to install that or the crane limiter plate. Did you do any of this?

If you are going to set timing properly Check for proper TDC first off:

http://www.crankshaftcoalition.com/w...op_dead_center

Get a timing light with dial back or install a timing tape on the dampener

http://www.crankshaftcoalition.com/w..._a_timing_tape

Check and see how much vacuum advance the distributor is adding when the vacuum adv can is hooked to manifold vac, you want the timing to advance about 12 deg no more. Once limited you will not see such a big jump in the idle speed, chances are the thing is adding 20+ deg out of the box.

Base timing as mentioned needs to be higher 16-20 IMO, total at 38 + another 12 from vacuum advance = 50 total. Depending on the amount of vacuum the engine pulls you can use the vacuum advance can set screw to fine tune the amount of vac advance vs engine vac, that adjustment and adding the vacuum advance is the last step, get the base and mechanical advance figured out first, chances are that you need to limit the amount of mechanical advance as well once you raise up the base timing.

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  #32 (permalink)  
Old 01-08-2012, 12:45 PM
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most back fires (out the carb) are caused by retarded ignition timing and/or a lean mixture.

Yes, BBC's need lots of timing. I use 20 initial with 40 total.

Then I use an adjustable vacuum advance with 10 more degrees and I use the vacuum advance on a manifold source. That means the vacuum advance kicks in at idle, so my 454 idles at 30 degrees of timing (20 mechanical + 10 vaccum advance).

Adjust the idle mixture for highest idle but as lean as possible. Make adjustments when the engine is hot. And make sure each idle mixture screw is out the same amount. Also, these screws tend to move over time, so I set them and use a little rtv to hold them in place.
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  #33 (permalink)  
Old 01-08-2012, 01:19 PM
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Ok I will try that. Thanks guys. And is it difficult to put the timing tape on the balancer?
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  #34 (permalink)  
Old 01-08-2012, 01:22 PM
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The engine has been running since early march of last year. So it could use the lifters checked again, also the Holley is stock out of the box. It was put on about may of last year. I think I need to start with new intake gaskets because when the new aluminum intake was installed by my uncle he used the front and rear rubber gaskets and I can see that the front one is sticking out and causing a small oil leak.
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Old 01-08-2012, 09:00 PM
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Change the gaskets....dump the front and rear ones and use a nice thick line of RTV instead. Clean it with LAQUER THINNER...not paint thinner! BrakeKleen works well too. After all surfaces are squeaky clean do the RTV trick. Make it thick enough so when you set the intake the RTV sorta squeezes out a little. Don't be wiggling it around when you do the install! Torque it to specs and give the RTV a chance to set up. (I wait over night) Should be sealed up tight. MAY solve your initial problem. ZERO vacuum leaks or these engines won't work right!
6sally6
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  #36 (permalink)  
Old 01-09-2012, 07:49 PM
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Quote:
Originally Posted by jodylawrence66
Ok I will try that. Thanks guys. And is it difficult to put the timing tape on the balancer?
It's not hard at all. You want to align the tape to the line on the damper after verifying that it's accurately showing you TDC.

The tape is a temporary deal, but you can mark the damper w/permanent lines if you wanted. Adding marks every 90 degrees will make setting valves easier. The image below shows the correct orientation of the timing tape:
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  #37 (permalink)  
Old 01-10-2012, 11:45 AM
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Ok thanks I will see about changing the gaskets and see about the timing tape for the balancer. I really appreciate all the help.
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  #38 (permalink)  
Old 01-10-2012, 11:54 AM
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Would just regular felpro intake gaskets be good to use? I'm on a budget but I don't want to have to do this any more than i have to. Any input would be great.
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  #39 (permalink)  
Old 01-13-2012, 02:36 PM
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I have been told by one person locally that they think this vehicle isn't running right because this cam is for a low compression engine and that mine is a higher compression engine. With the info listed below does that sound like that could be the issue?


with a 454 bored .040 with flat top pistons, a summit racing Hydraulic flat tappet cam (Advertised Duration 276 int/286 exh, Duration at 050 inch Lift 218 int./228 exh, lift 0.500 int./0.500 exh, lobe separation 114)
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  #40 (permalink)  
Old 01-13-2012, 04:59 PM
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454 with flat tops and stock 1980 heads will be a low compression engine. Around 7.75:1 cr.
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  #41 (permalink)  
Old 01-14-2012, 07:09 AM
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Ok thank you I was just curious if that theory had any plausibility to it.
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  #42 (permalink)  
Old 01-14-2012, 09:04 AM
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do a compression test. It will be lucky to hit 125psi on the gage. Maybe closer to 110.
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  #43 (permalink)  
Old 01-14-2012, 12:27 PM
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You need to get a handle on the timing. What is the initial timing w/o vacuum advance hooked up (plug the hose to the engine), what RPM does the mechanical advance begin, what RPM is it ALL in by, and what is the total timing.

If the mechanical advance is dropping timing as you lower the idle speed, this alone can cause the symptoms you are having (dying as the idle speed is lowered). The cure is to use a stronger spring on the mechanical advance. Be sure the initial advance isn't affected by this, if the initial dropped, add it back- but be sure the total doesn't exceed about 40 degrees or so. You can get away w/quite a bit of timing if the compression ratio is as low as it will be w/open chamber heads and FT pistons.

You've been given advice on initial and total, and to use a vacuum advance. The rest is up to you.
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