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Old 03-24-2004, 06:20 AM
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Confusing Carb Problems

Chevy Corvette 454 w/ 795cfm carb in a 68 Camaro.

Had some problems with fouled plugs/bad wires/bad dist so I replaced the dist, wires and plugs. Started running great.

Strange problem. Using a dialback timing light at idle I am showing 36degrees advance. Engine idles smooth, temp is good, not running rich. But it's 36 degrees.

Strange problem 2:
With air cleaner off and 36 degrees advance engine is lean, if I put my hand on the primaries (edelbrock q-jet) the engine idle increases significantly.

If I put the air cleaner on w/ 36 degrees advance engine is rich. Nothing changed except putting on the air cleaner. Once the air cleaner is on it is the same as "choking" the carb with my hand and idle picks up. So, my lean problem is fixed, now I have a rich problem.

I adjusted the idle screw, mixture scres all the way closed, timing, still running rich and now running hot.

So, questions are:

How do I fix the rich problem
How do I fix the 36 degrees, Do I need to fix it, or am I just screwwing up the timing somehow?

Thanks
Rick

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Old 03-24-2004, 06:33 AM
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I see that you have the K+N (or similar) air filter, if this unit is over oiled, it can become restrictive causing the rich condition that you describe!! You may need to wash it out and start over! Timing is 36* at idle? If it starts and runs smooth, I would guess a slipped balancer ring or the wrong timing tab are giving incorrect readings!
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Old 03-24-2004, 12:52 PM
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You have a couple problems it sounds like and you need to address them individually. I would start with the timing, as suggested you may have mismatched timing parts or a slipped damper ring, but maybe you're timing off the wrong cylinder. Just a thought. The air filter suggestion also addresses the rich condition when on, but you say it is lean without it. Try spraying a flammable contact/brake cleaner around the manifold ports and carb base to determine if there is an air leak. If you don't have one, I would guess the carb needs jetted up. The reason you need to address on issue at a time is fuel and ignition problems can give the same problems, and you need to determine which it is before flogging yourself too long.
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Old 03-24-2004, 01:24 PM
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I agree on checking the balancer and timing tabs for compatibility and slippage. However, on a 90degree v8, the cylinders fire 90 degrees apart so timing off of the wrong wire would not show a timing mark unless the balancer had slipped as well.

Chris
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Old 03-24-2004, 03:09 PM
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Well, I am sure I am timing off the correct cylinder. 1 so that is not the issue.

For some reason when I unhook the vacuum advance from my dist the engine dies immediately. Before replacing the dist she would still run, rather poorly but running none the less.

I will check for vac leaks like suggested.

I don't think the damper/mark has slipped. When installing the dist we cranked the engine over to TDC. Checked by removing plug 1 and waiting for compression stroke while kicking it over with the starter, then manually cranked it to TDC and felt w/ a screwdriver to be sure piston was up. Mark was at 0. So I don't think tha tis the problem.

Carb needs to be jetted up? Does that mean bigger jets? If I am already running rich wouldn't that make things worse? I would think I need smaller jets. Maybe I just have the terminology wrong. I don't know jack about carb tweaking and mod'ing.

About the K&N filter. I haven't oiled it since it took it out of the box. Car has never been on the road so I didn't think I needed to worry about it. I don't have any oil anyhow, unless there is some sort of regular stuff we can find around the shop that is OK to use. Should I just wash it with water, soap and water, hot water?

Thanks
Rick
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Old 03-24-2004, 03:34 PM
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Only fools and morons waste money on K&N filters, Dam that is what they used in the 1900's
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Old 03-24-2004, 03:48 PM
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I know what you mean auto, those stupid guys are buying those high performace air filters when paper bags work just as well.
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Old 03-24-2004, 04:05 PM
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Well, if you really are in Japan, yes, you should change jets. One size down from standard. Most carb manufactures have a chart available for different parts of the world. I am not a good timing person. So, that is why I use dyno-shops. Yes, you do have them there, I just dont know where. If you ever spring for the money to dyno, you will be amazed. Good luck.

hr41pearl

Leave the paper bag at home.
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Old 03-24-2004, 06:18 PM
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if you have that high of timing at idle and when you take the vacuum advance line off it goes dead, sounds like you have it connected to a manifold vacuum source, vaccuum advance isn`t needed at idle, it`s needed off idle, disconnect it, reset the timing to about 12 degree`s BTDC as a starting point, reconnect the advance to a ported source or one that pulls vacuum off idle, then reset your idle speed, and readjust the carb.

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Old 03-24-2004, 07:35 PM
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First,

Bozo's making stupid comments, K&N makes a good filter and they are the ONLY one who makes a filter thin enough to fit my engine application. Because I have a 454 a standard filter sits up too high and I cant close my hood, K&N makes a 2.3" filter that fits perfectly. So, stick it up your tailpipe.

For those that aren't bozo's.

I have vacuum attached to the carb where I am kind of certain it goes but I will check if I can find an edelbrock qjet diagram.

Yup, I am in Japan for another couple of weeks. Been here for 10 years. Makes it a real pain in the rear to get parts. I will probably wait to change jets until I get back to the states.

How much does it cost to Dyno a car?

Thanks
Rick
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Old 03-25-2004, 08:29 AM
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Dyno

It runs 400-500. They put the car in a set of rollers that they can increase drag by adding water. Make the car think it is going up a very steep hill. They do the jetting, curve the distributor, plugs, vacuum checks, and much more. Takes about 3-4 hours per car. It really run it through the paces. I built a 383 for my el camino and was doing saturday night street races. Then I had it dynoed and man what a ride. In my case, they went as far as to recommend changing the converter to a higher stall rate. Very much worth the cost.

hr41pearl
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Old 03-25-2004, 11:58 AM
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I wasn't making fun of k&n's I have the extreme top with a 3 inch filter element
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Old 03-25-2004, 08:52 PM
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OK, I looked into getting new jets but I am confused

If I get "smaller" jets it appears that I may get MORE gas, So should I get "Larger" jets.

ie. My primary jets are currently .073. So to flow less fuel I would need .075 or .072? The way I see it .072 would be smaller in size allowing MORE fuel to get through making me even more rich. Of course I could be 180 off on this one.

Thanks
Rick
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Old 03-25-2004, 11:00 PM
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An .072 jet has a hole that is .072" in diameter. The .073 is 1/1000" larger, and will flow a greater amount of fuel.

The primary jets won't have much to do with your idle, the idle richness should be controlled by the idle mixture screws. Did you adjust the screws for maximum vacuum reading? If you don't have a vacuum gauge, just adjust for max idle RPM while adjusting the screws. In other words, if you can speed up the idle by placing your hand over the carb, then you haven't backed the screws out far enough. Although you should be able to kill the engine by seating both screws.
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Old 03-25-2004, 11:08 PM
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Quote:
Originally posted by rakundig
First,

Bozo's making stupid comments, K&N makes a good filter and they are the ONLY one who makes a filter thin enough to fit my engine application. Because I have a 454 a standard filter sits up too high and I cant close my hood, K&N makes a 2.3" filter that fits perfectly. So, stick it up your tailpipe.

For those that aren't bozo's.

I have vacuum attached to the carb where I am kind of certain it goes but I will check if I can find an edelbrock qjet diagram.

Yup, I am in Japan for another couple of weeks. Been here for 10 years. Makes it a real pain in the rear to get parts. I will probably wait to change jets until I get back to the states.

How much does it cost to Dyno a car?

Thanks
Rick


Funny you should mention the good ole 2.3 inch KandN, I have to use the same filter in my car with a 454 and air gap manifold. Works great.

That guy Auto part is a troll and I don't know why he hasn't been banned yet????
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