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Old 06-13-2006, 01:12 PM
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I got the fouled plug blues.

I need some suggestions from all you folks I know are smarter than me.

I have a 1974 400CID Chevy engine with stock cam, Holly 500 CFM carb, stock electronic ignition and manual choke that I built a couple years ago. The project is posted in my album. I have always had an issue with plug fouling due to carbon resulting from what I assume is too rich a mixture. I am running Auto-lite 26 plugs. I can clean the plugs and run for a while but I know it is still running too rich just by the smell. My mixture screws are all but closed, maybe 1/8 open. I tried spaying starting fluid around the intake gaskets to detect a leak through RPM increase. I am not sure how much vacuum I should be pulling. If I start it up in the garage more than a couple times, the plugs are dry black.

I would swear when I built the engine that I had the timing marks lined up mark to mark (Cam 6:00 and crank 12:00) but I guess it is possible I screwed that up. Is there any way of confirming the alignment without pulling the water pump and timing cover off? Is this a possible cause of my fouling?

I would appreciate any advice I can get. My next step is to suck-it-up and pull the cover just to confirm everything is lined up right.

Take it easy on me. I am just a shade tree mechanic. Thanks.

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Old 06-13-2006, 01:37 PM
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Quote:
Originally Posted by rfowler
I need some suggestions from all you folks I know are smarter than me.

I have a 1974 400CID Chevy engine with stock cam, Holly 500 CFM carb, stock electronic ignition and manual choke that I built a couple years ago. The project is posted in my album. I have always had an issue with plug fouling due to carbon resulting from what I assume is too rich a mixture. I am running Auto-lite 26 plugs. I can clean the plugs and run for a while but I know it is still running too rich just by the smell. My mixture screws are all but closed, maybe 1/8 open. I tried spaying starting fluid around the intake gaskets to detect a leak through RPM increase. I am not sure how much vacuum I should be pulling. If I start it up in the garage more than a couple times, the plugs are dry black.

I would swear when I built the engine that I had the timing marks lined up mark to mark (Cam 6:00 and crank 12:00) but I guess it is possible I screwed that up. Is there any way of confirming the alignment without pulling the water pump and timing cover off? Is this a possible cause of my fouling?

I would appreciate any advice I can get. My next step is to suck-it-up and pull the cover just to confirm everything is lined up right.

Take it easy on me. I am just a shade tree mechanic. Thanks.
If it is dry black , the carb needs to be jetted down on main jet size , or your floats may be too high , letting gas seep into the venturi's ( can check this by shutting off warm motor and seeing if there is a vapor coming up out of carb, like fog rising)
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Old 06-13-2006, 01:45 PM
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Thanks. Based on this Engine size, do you have a recommendation on the size jets I should try?
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Old 06-13-2006, 01:52 PM
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Plugs

Changine the jets is going to do nothing for a rich idle.... The jets control the fuel to the power circut of the carb and are not connected to the idle circut.

What is you initial and total timing??? if you are cleaning the plugs and not replacing them that could also be a part of the problem..

Have you tried a step hotter plug???

Also are you sure you have a true 12 volts to the hei???

Keith
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Old 06-13-2006, 02:03 PM
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Any recommendations on a hotter plug? I thought I was running the hottest available (Autolite 26). When I clean the plugs I glass bead blast them.

The engine runs really bad at the prescribed timing mark so I have had to set it by what seems to start and idle well. This may be more reason to bite the bullet and pull the timing cover?
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Old 06-14-2006, 05:37 AM
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plugs

25 should be the middle heat range for that plug, so 26 would be one step hotter.. the next hotter plug should be a 27 but i cannot tell you if they are available...

You really need to get the correct TDC marks and then set the timing at around 12 degrees initial with the vaccum un-hooked.then make sure there is not more then 38/40 degrees total. then hook the vaccum back up. I am sure this wwill clean the idle... Also after you do that install a new set of plugs...

Check to make sure there is 12 volts at your HEI power input.

Keith
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Old 06-14-2006, 08:52 AM
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Have you checked the fuel pressure? it should be around 5 to 6 psi. Make sure you have a fuel pressure gauge, if not it`s the same thing as being blind. With the car at idle, remove the air cleaner and shine a light in the carbs throat, see if you see any fuel dripping out of the boosters, if so it`s either fuel pressure, float too high, or sticking needle and seat assembly. Also check your spark, if you don`t have one you can get a spark tester from any auto parts store that plugs in and clamps to a ground, study the spark, if it`s blue it should be okay, if it`s yellow you have a weak ignition. The puzzling thing about a weak ignition is it often diagnosis the same as a carb problem. It didn`t appear by the pictures in your journal that you have any adapters or spacers, but if you do and it`s a open type it can cause this same condition. I know what many will say "it can`t be a fuel pressure issue it`s a stock pump" mine had 14psi fuel pressure with a stock pump, I was blowing the needles out of carbs as a result. I thought the same thing, stock pump, no problem, wrong. I was shocked when I installed the fuel pressure gauge, turns out I had a venting problem, there was no vent in the system, so it would build pressure and push it out the only way it could, via the fuel line to the carb.
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Old 06-14-2006, 11:55 AM
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your idle adjustment screws, your turn them in to "ritchen" the mixture, back them out to lean the mixture... Actualy a 600 cfm carb wouldnt be to big, and its possible that 500 cfm is just to small, and regurardless of what people tell you a carb to small is just as bad as one to big.. Like DV said a spacer might help, but first and foremost try backing the idle mixture screws out 2 or 3 turns and see if it responds..


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Old 06-14-2006, 12:55 PM
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Hey guys! You came up with a lot of good suggestions for my problem.

I neglected to say that I was unable to use a stock mechanical fuel pump due to the tight clearance between the engine and frame so I am running an aftermarket electric with about 3 foot of line before the carb. It is running continuous as long as the ignition is on. I suppose there are regulators out to control fuel pressure. I would guess I am running around 14 psi. Way too much? 4 to 6 is where I sould be at right? It may be possible I am over pressurizing the fuel to the carb. The carb is new out of the box so there should not be any concerns except adjustments.

With regard to checking the voltage to the hei, do I do this with the engine running or stopped with the key in the on position?

I made an aluminum plunger probe that works similar to a depth micrometer that screws into the #1 plug hole. It has a graduated stem that has an o-ring for a position marker. With this screwed in, I manually turn the harmonic balancer back and forth, I am able to peak the stem out at the highest position on the piston stroke. I marked the TDC on the timing scale using this method. You said it should be 12 degrees. Is the that 12 BTDC or 12ATDC? I really have no specifications for this engine readily available.

I am running an Edelbrock RPM Performer Aluminium Intake. Do I need a spacer between it and the Holly 500? I was running a 650 Holly and dropped down to a 500 thinking I was over carbed.

I may be mistaken but I thought turning the mixture screws in leans the mixture and out richens it. Am I confused on this?

Again, thanks for all the great tips. I have a lot of things to check now before I rip the front end off. I am sure I still can use your help along the way. Learn by doing is my theory. My wife will be glad if I can start the Buick up and not fill the garage with a thick black cloud. Until I get this figured out, I will have to keep all the windos open and wear a resperator.
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Old 06-14-2006, 01:00 PM
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Put a regulator on it, made a ton of differance on mine and my pump was only putting out 9 psi.
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Old 06-14-2006, 01:07 PM
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Turning idle screws in will lean out the fueling, out will richen the mix. Idle mix screws are fuel screws not air screws.

The first thing I would check is your float adjustment. Make sure the fuel level is right at the bottom of the sight plug with the engine running. It should take a shove against the fender to see fuel flowing out the bottom of the plug.
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Old 06-14-2006, 01:15 PM
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You may also have a busted power valve , due to backfire or the likes. I wouldn't recommend glass beading of plugs, may just insulate the firing tip, also if its an old Holley 500 2-barrel turn the screws in till you get a stumble and take it back out approx 1/2 turn , go to other one and do the same till you get the highest vacuum reading or till it sounds the best. You may have to go side to side more than once.
But you do have to much inlet pressure, so cure that first and reset floats, then adjust idle.
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Old 06-14-2006, 01:23 PM
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Quote:
Originally Posted by rfowler
I would guess I am running around 14 psi. Way too much? 4 to 6 is where I sould be at right? It may be possible I am over pressurizing the fuel to the carb.
I think you answered your own question right there!! If you're pushing fuel into a float valve at 14 psi you've basically eliminated the float valve as a member of the fuel management team!!! I'm surprised your motor runs at all!!!
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Old 06-14-2006, 01:29 PM
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14 psi ...nice.. there may be other set up issues

a 500 cfm? i would think you could get better mileage with a 600 4barrel
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Old 06-14-2006, 08:25 PM
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Quote:
Originally Posted by Rick WI
Turning idle screws in will lean out the fueling, out will richen the mix. Idle mix screws are fuel screws not air screws.

The first thing I would check is your float adjustment. Make sure the fuel level is right at the bottom of the sight plug with the engine running. It should take a shove against the fender to see fuel flowing out the bottom of the plug.

Better Check again...
http://www.holley.com/data/Products/...l/199R9881.pdf


2wld4u
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