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  #136 (permalink)  
Old 11-09-2010, 02:25 AM
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Quote:
Originally Posted by akorcovelos
Is there a problem with having 220psi?
Possibly- if this engine is going to be using pump gasoline, and given the cam you are using, AND the reading is accurate- I believe it is.

The first thing I would do is compare the readings from your gauge to another gauge.

You should run the numbers to see what the dynamic compression ratio looks like, just for S&G. The DCR is not a hard rule IMO, buy it can be helpful in cases like this- where there's conflicting data.

A simple calculator is HERE. You need to know the static CR, stroke, rod length, and Intake Closing Point in degrees ABDC @ 0.050 lift. This can be found on the cam card or online.

In any event, the 220 psi- if accurate- means either a high static CR and/or an early closing intake (cam advanced), given what I see w/the cam you have. Or an incorrectly manufactured cam.

But to have a low vacuum reading, you would expect there to be an error that RETARDED the cam (i.e. late closing intake).

That would seem to be somewhat of a paradox. I suspect you may well find something when you check the cam phasing when you degree it. Be aware that an error (if present) could be anywhere on the cam- this means checking ALL the lobes...

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  #137 (permalink)  
Old 11-09-2010, 09:03 AM
Technical Support Barry Grant
 
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Something else to throw out there based on what we saw with the carburetor and only a speculation but between it having 100% idle fuel [too much] and rougly 40-60 thou showing on the transfer slots those 2 things alone could give a lower vacuum reading imo.

Would def bring #1 up and make sure it is timed properly but before taking the engine apart would reinstall the carb and recheck the vacuum and see if it will idle without having to crank the butterflies back open like they were.

It may still be a cam and/or timing issue. Could be electrical as well but lets see how it runs with the changes we made in the carburetor for you.
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  #138 (permalink)  
Old 11-09-2010, 10:27 AM
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That is the info I was looking for Cobalt, thank you. I would love to know the DCR as well, but I'm not sure what the static CR is. AFAIK the bottom end is stock stroke and I know it's a standard 4" bore. I can look at the cam card online, but I don't know how to figure out the static CR without pulling the heads again.

BG_Tech, I'll wait and see what if any changes to vacuum I get with the carb properly setup then move on to checking cam timing.
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  #139 (permalink)  
Old 11-09-2010, 03:16 PM
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Quote:
Originally Posted by akorcovelos
I can look at the cam card online, but I don't know how to figure out the static CR without pulling the heads again.
If you know what the engine came from (the casting number, casting date and suffix code can help here), and the pistons are stock, and the decks weren't cut, you can make a good educated guess what the SCR is. Then use that to see what pops up for DCR.

It might not (and likely will not) be 100% accurate- but it'll at least be something you can judge the cranking pressures by.

My thinking at this juncture, is that the gauge may be off off.

But also after hearing Tech @ BG's rundown of the carb, I believe the engine couldn't help but to have better idle vacuum after closing down the butterflies and tweaking the air/fuel mixture at idle.

I do also believe a distributor w/a functional vacuum advance hooked to manifold vacuum will bring up the vacuum. In fact, I will almost guarantee it.
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  #140 (permalink)  
Old 11-09-2010, 05:08 PM
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The bottom end is from a '91 Vette, and the heads are from a '96 C1500 pickup. I was told the rods where upgraded (pink rods?), as was the fuel pump. The intake is the Edelbrock Vortec dual plane manifold. The pistons look stock but I don't know for sure.




All I know for sure is the engine took a standard ring and gasket kit for a '96 c/k1500 with the Vortec engine, and all the old gaskets/rings/bearings looked the same as the new ones from the kit.
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  #141 (permalink)  
Old 11-13-2010, 03:09 PM
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Big update: I got the carb back from BG and WOW, I can't say enough good about them! I'm not even certain I got the same carb back because it looks brand new!

how it looked when I sent it to them;


How it looks now;






The good: I bolted the carb on and fired the engine and the vacuum gauge jumped to 16"! I'm so glad that it seems the vacuum loss is taken care of.

The bad: I don't think this is related to the carb, but it's backfiring through both the carb and exhaust now. It backfires through the exhaust constantly, and through the carb when I crack the throttle.

I heard a terrible whining noise when I fired it up, and found after a little investigation it was coming from the distributor. After pulling the distributor I found that the cap was not completely seated and was cocked a bit, causing the rotor to contact one side of the cap too much, and likely the other side not enough. Could this cause the backfiring through the exhaust? I don't think it would cause the backfiring through the carb, so not sure where the problem is there.

At least it seems I'm making progress, and it seems to just be down to tuning now. I'm ordering a new cap and rotor so that should be here some time next week.
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  #142 (permalink)  
Old 11-13-2010, 06:49 PM
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Quote:
Originally Posted by akorcovelos
Big update: I got the carb back from BG and WOW, I can't say enough good about them! I'm not even certain I got the same carb back because it looks brand new!

how it looked when I sent it to them;


How it looks now;






The good: I bolted the carb on and fired the engine and the vacuum gauge jumped to 16"! I'm so glad that it seems the vacuum loss is taken care of.

The bad: I don't think this is related to the carb, but it's backfiring through both the carb and exhaust now. It backfires through the exhaust constantly, and through the carb when I crack the throttle.

I heard a terrible whining noise when I fired it up, and found after a little investigation it was coming from the distributor. After pulling the distributor I found that the cap was not completely seated and was cocked a bit, causing the rotor to contact one side of the cap too much, and likely the other side not enough. Could this cause the backfiring through the exhaust? I don't think it would cause the backfiring through the carb, so not sure where the problem is there.

At least it seems I'm making progress, and it seems to just be down to tuning now. I'm ordering a new cap and rotor so that should be here some time next week.
I hate to say it but looks like someone in our building did mess up and that is a completely different carburetor both size and type. I'll have to figure it out on Monday but the carb you got back is a marine carburetor hence the J style vent tubes. It also is a bigger carb as I see it has 1 3/4 butterflies in it.

I'll get one of my guys to contact you Monday with our shipper number so we can get that one headed back and find out where yours got swapped to as well.
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  #143 (permalink)  
Old 11-13-2010, 06:59 PM
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um, oops! Guess that explains why it looks so much better than mine did. Well the good thing is the vacuum loss is obviously in my carb, hope that is fixed when I do get mine back.

I assume the backfiring could be related to it being the wrong carb then?
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  #144 (permalink)  
Old 11-13-2010, 09:15 PM
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I would expect your backfire to be from the miss-installed cap. Spark scatter would be terrible from the way you described it was sitting and hitting the rotor, feeding the wrong wire on the side that was away from the contact point. Bet it goes away with the cap and rotor fixed.

I knew the carb wasn't the same at the first clance, glad BG is looking into it.
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  #145 (permalink)  
Old 11-13-2010, 11:48 PM
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Quote:
Originally Posted by ericnova72
I would expect your backfire to be from the miss-installed cap. Spark scatter would be terrible from the way you described it was sitting and hitting the rotor, feeding the wrong wire on the side that was away from the contact point. Bet it goes away with the cap and rotor fixed.

I knew the carb wasn't the same at the first clance, glad BG is looking into it.

yeah it was a mess under the cap, shavings from the contacts everywhere, hoping the new parts fix this.

I should have known it was not the same carb, I just didn't give it too much thought. I hope my vacuum is still good when I get my carb back.
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  #146 (permalink)  
Old 12-01-2010, 07:07 PM
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another day another update. I got my carb back from BG, and they where nice enough to go through and do a complete rebuild on it free of charge to make up for the mix up.

I bolted and hooked up the carb, and installed the new cap and rotor, and fired the car up to see that I have my vacuum back. It's not a steady vacuum reading, bouncing from wildly from around 5" to 16" at idle. When I bring idle up a bit with the butterfly adjustment it stabilizes at 15-16". I am also getting some backfire when I pop the throttle quickly.

I have initial timing set at 18*, and from what I've found online about my distributor the mechanical advance is 24* total crankshaft. When I was installing the new rotor I saw there is an adjustment in the distributor (see pic), I assume for when full advance comes in? Is this something I should adjust now or just leave it?



So I'm guessing the problems mentioned above involve the tuning of the carb, which I know nothing about. Any insight or helpful links is greatly appreciated, I'm looking forward to learning how to get this thing dialed in.

On a side note, I'm holding out on installing the pro-jection kit until next winter because I have some major work to do on my autox car.
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  #147 (permalink)  
Old 12-01-2010, 09:09 PM
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The distributor flange might be bottoming out before fully seating on the intake manifold back. Check to see if you need to shim it up.

Demons are a pain. Get a Percy adjustable primary metering block. turn the jet screws and adjust the mixture till it is right on. Refer to the chart and convert the turns to the jet size. replace the stock metering block and correct jets thern it is set. Easy as cake. better than 10 jet changes.
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  #148 (permalink)  
Old 12-01-2010, 09:40 PM
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Distributor is seated properly, and it functioned fine before the rebuild so I don't think thats the problem. BG just did a complete rebuild so i don't want to go tearing into a fresh carb.. I really just need to know how to dial it in as it is. I'm doing some research now on basic carb tuning, but I appreciate any additional wisdom!

Quote:
Originally Posted by spinn
The distributor flange might be bottoming out before fully seating on the intake manifold back. Check to see if you need to shim it up.

Demons are a pain. Get a Percy adjustable primary metering block. turn the jet screws and adjust the mixture till it is right on. Refer to the chart and convert the turns to the jet size. replace the stock metering block and correct jets thern it is set. Easy as cake. better than 10 jet changes.
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  #149 (permalink)  
Old 12-15-2010, 01:17 PM
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well, it's time to end this chapter of my build. Despite all the great support from BG and everyone here I am ditching the carb and installing my fuel injection kit.

I have been tying to get the carb dialed in, but this is just not my area of knowledge, and no matter what I do it still runs pig rich. I really don't want to do any damage to the fresh rebuilt engine so I'm going with fuel injection because I actually know how to tune that.

I'll start a new thread for the install so everyone can see what I'm doing.

Thanks to everyone who chimed in to help in this thread, it was immensely helpful, especially Tech@BG, they went above and beyond to help get my carb in proper working order. I'm sure the carb is perfectly fine, and would work well in hands of someone who knows what they are doing with a carburetor.
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