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  #1 (permalink)  
Old 04-09-2008, 09:14 AM
Terry Stapley's Avatar
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Cobra Make, Engine: Shell Valley, 418W, tremec 3550tko, 9" ford rear, 3.0 gear, silver/black
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Default Engine Misfire Saga - Update

Last evening after receiving all of the great suggestions from forum members I went to the garage and dove in!! I:

Checked that the plug wires were indeed in the correct firing order - check

Checked Dist. cap again for anything abnormal - raised the spring steel contact a bit just to make sure of contact - check

As per suggestion I removed the alternator belt - check

Used Carb Cleaner again on the air bleeds - the idle air bleeds(Toward the outside ?) were clear on both the primary and secondary sides - The high speed air bleeds (Center two ?) on the secondary side were clear but the primary air bleeds kept blowing back carb cleaner so I perservered and finally got those two clear

Checked the plugs on the two offending cylinders and they were a little dark but not wet - check

I did the MSD instructed spark check for the 6AL box - good spark - check

I then fired the engine and it ran fine but was idleing a lot faster then it used to so I lowered the idle with the idle adjust screw - I let it warm a bit and shut if off to put the alternator belt back on - Fired it again and again it ran fine - All header pipes were hot enough to flash water sprayed and the RICH exhaust smell was gone (Wife was happy with this)

I did all of this in about an hour and 15 minutes as I had another commitment
and I will fire it again this evening to see how it runs, but as for now it seems okay!

I really have no clue as to what the issue was as I changed more than one thing at a time because of the time constraint but the idle speed being different leads me to believe that the carb was the culprit.

Thanks for all of the suggestion!! You guys are the best!!
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Old 04-09-2008, 09:35 AM
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Great Terry,
Last thing to check might be your manifold vac reading. Idle rpm will increase with a small leak or it is just up because she is HAAPPY again. Check your baseline manifold vac just to be sure and only takes seconds to do. Good Job.... Enjoy
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Old 04-09-2008, 09:44 AM
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Great idea, I changed the intake gaskets last August because of a bad vacuum leak. I will check manifold vacuum this evening!!
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Old 04-09-2008, 05:44 PM
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First off, glad to hear it's running well again.

One word of advice. Only change one thing at a time. Now if it happens again, you do not that knowledge to fall back on to check first.

This is true of upgrades also. Change one item, get it running right, and then move on to the next.
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Old 04-21-2008, 09:55 AM
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After many trys at fixing the engine miss I put a different carburetor on it to see if that would make any difference and the engine ran fine with the new carb after some fine tuning. The Carb is a Quick Fuel Technologies 850 DP. So I rebuilt the Holley 750 DP that was on the engine using a Holley rebuild kit and put the 750 back on the engine and after some fine tuning it ran okay but was still a little rich at idle. But as I revved to 2000 - 2500 rpm it started missing again and black smoke was coming out of both sidepipes. Original engine missing problem was back.
Frustrated I turned it off and left it overnight and when I lifted the hood in the morning there was fuel in the intake manfold on both sides of the carb. About a tablespoon full in each of the indentations below the carb on both sides, so fuel is leaking from somewhere. The floats are new and the float levels were adjusted a bit low if anything!! Every moving part in the carb is new!!
I put the 850 carb back on and it needs some fine tuning but otherwise the engine runs fine.
What suggestions would you offer about the 750?? Is it toast??
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Old 04-21-2008, 11:46 AM
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Terry , you didn`t say how old the Holley is/was , but one thing I have found on older Holleys is that the butterfly shaft seals leak as they get old . If you check , you should find the fuel puddles/leaks very close to the ends of those shafts . When the engine is running , the vacuum doesn`t allow the fuel to run out .... only when the engine is shut off over a period of time . I can tell you from experience , that unless you work on these carbs regularly , it is a real bear to replace those seals . Don`t see where anyone else suggested you check your metering blocks and carb body to see if they are warped, but that is a possibility ... also check the gasket under the Power valve . If it is a fiber gasket type , typically , they are a two piece and can separate . The garbage that is called gas these days has some pretty nasty chemicals in it and they attack the gasket . I went to a nylon one from and problem solved . When I took the PV out of the metering block , half the gasket stayed on the metering block and the other half was on the valve . That is an internal leak . On my 427S/O Galaxie both of those items were a problem ... and I had the same fuel puddles on my manifold until I replaced those seals .... and a rich condition until the PV gasket was changed.
Sorry for the long post .

Good luck
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Old 04-21-2008, 11:48 AM
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If all of the gaskets, seals and floats new/replaced and you are still having the same problem, could it be a hairline crack in the carb housing itself leaking fuel? Whatever the problem, it seems to be the carb itself.
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Old 04-21-2008, 12:00 PM
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Bobcat,
The carb is 4 years old and 12000 miles!!
The fuel that leaked out was directly underneath the butterfly shafts on both sides so that may very well be an issue with the leaking but would that make the engine miss at 2000 rpm?
When I rebuilt the 750 everything was very clean with no gasket material anywhere before I put it back together. I also had blown out all of the passages numerous times so I am stumped.
If there is a hairline crack inside I do not know how I would ever find it!
The QFT 850 works very well but I do not know if I can pass emissions with that carb!!
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Old 04-21-2008, 12:37 PM
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I had carb problems for months, threw $$$$ at it and lots of time.

Finally sold it and bought a new one on ebay.

Should have done it sooner but it pissed me off.

Buy a new one on ebay and enjoy the drive.

Last edited by jhv48; 04-21-2008 at 12:43 PM..
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Old 04-21-2008, 09:00 PM
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Terry .... it`s possible that the shaft seals would cause the engine miss at 2000 rpm , but not probable . If the carb ran ok before , I would still look at the fiber gasket between the PV and the metering block . Even if it appears good , I would replace it with a nylon one .... or at the very least with a new one . That problem took several weeks for me to find . It is possible the PV itself has a leak... did you replace that also ? If the carb sat for several months with gas in it , you could have varnish/crud buildup in the internal passages due to the garbage they call gas today . It starts breaking down in a matter of weeks now . If that`s the case , soaking the carb and all internals in Lacquer thinner ( the carb cleaner you buy now isn`t strong enough ) for several days and then blowing it out should take care of that problem . The only times I have problems with Holleys is when I don`t use them on a regular basis .
Good luck ,
Bob
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