Holley carb 4779-9 problem all of a sudden. - Team Camaro Tech
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post #1 of 7 (permalink) Old Aug 1st, 13, 05:26 AM Thread Starter
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Holley carb 4779-9 problem all of a sudden.

So I have a mechanical secondary Holley carb that has been working FLAWLESSLY on my car. It tended to leak fuel ever so slightly but nothing major. It would always start right up and idle right away happily at around 1000rpm. Blip the throttle and it would have no hesitation at all and very very responsive.

I noticed the other day a very strong gas smell in the garage. Pulled the car out and started it up. It ran very very rough and when I tried to get it to idle it would idle then chug down slowly until it would finally die (not right away but about 15 seconds later) When I shut the car off I could see fuel on top of the intake. So I cleaned all of it off removed the air cleaner and started the car.. NO LEAKS but it still would run rough and I had to hit the throttle to keep it running. When I hit the throttle it would be very very responsive with NO HESITATION at all. I tried adjusting the idle but all that did was make the engine idle HIGHER once I hit the throttle and then over 30 seconds later it would go from 1500 rpms to 1000 rpms and chug at 500 rpms.

Couple of notes.. the car runs an electric fuel pump and it reads steady at 8 lbs. It is deadheaded at the carb dual feed with a return line. Again this car ran flawlessly for about two months and 5000 miles with this setup. It just seems like all of a sudden this happened. I also checked all the vaccuum lines and plugs to be sure none came off. Also, I notice that when the car is off about a teaspoon of gas continues to trickle into the carb itself....Any help would be greatly appreciated. Could it be the idle circuit? What should I check first? Not very carb savvy so any help is appreciated.

Thanks in advance

Mark
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post #2 of 7 (permalink) Old Aug 1st, 13, 05:57 AM
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Scott
 
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Re: Holley carb 4779-9 problem all of a sudden.

Sounds to me like your needle & seats in the float bowl(s) are not sealing and/or the float levels are set too high allowing flooding of extra fuel from the bowl(s) into the intake manifold. Also your fuel pressure is just a bit on the high side so that doesn't help your situation. 6lbs of fuel pressure is ideal plus or minus .5lbs.

Try checking/adjusting your float levels and if that doesn't cure it, remove the float bowls and check the needle & seats to see why they are not sealing. Regulating your fuel pressure from the 8lbs you have now down to 6lbs will help the needle & seat setups to do their jobs more effectively.

69 Camaro Z/28 RS, original Azure Turquoise, M21 & 3.73 12-bolt posi. NOM 406ci, AFR 210 heads, Straub hyd. roller cam & Dynatech 1-3/4" > 1-7/8" headers, QuickFuel 750 Annular. Photos at:
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post #3 of 7 (permalink) Old Aug 1st, 13, 07:38 AM Thread Starter
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Re: Holley carb 4779-9 problem all of a sudden.

Quote:
Originally Posted by NH69Z28RS View Post
Sounds to me like your needle & seats in the float bowl(s) are not sealing and/or the float levels are set too high allowing flooding of extra fuel from the bowl(s) into the intake manifold. Also your fuel pressure is just a bit on the high side so that doesn't help your situation. 6lbs of fuel pressure is ideal plus or minus .5lbs.

Try checking/adjusting your float levels and if that doesn't cure it, remove the float bowls and check the needle & seats to see why they are not sealing. Regulating your fuel pressure from the 8lbs you have now down to 6lbs will help the needle & seat setups to do their jobs more effectively.
Thanks for the advice. I did notice one more thing... after the car is shut off I can hear fuel going into the carb. I would say about a teaspoon is trickling into the carb..... and after further reading on the net I found a great article that explains the problem I am having with the carb. Especially the part that says that fuel is leaking past the needle and float and dripping onto the throttle plates after shutdown... I am going to pull the bowls, needle and seats and take a good look at everything as well as adjust the pressure on the regulator to 6 psi from the 8 I am running. Anyways I will report back once I take a look... Here is the link that shows a great description as well as pics of how to remove it step by step as well as setting it back up for baseline adjustments... I am hoping this works. I missed a major car show that I have been dying to go to yesteday because of this problem. Hopefully I can get it on track and to the next one!!! (fingers crossed)

http://www.vintagemusclecarparts.com...eandseat1.html

Mark
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post #4 of 7 (permalink) Old Aug 1st, 13, 11:19 AM
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Re: Holley carb 4779-9 problem all of a sudden.

Good article you found and if you follow it I'm pretty sure you'll solve you problem. I'll be interested to hear back how you made out?

69 Camaro Z/28 RS, original Azure Turquoise, M21 & 3.73 12-bolt posi. NOM 406ci, AFR 210 heads, Straub hyd. roller cam & Dynatech 1-3/4" > 1-7/8" headers, QuickFuel 750 Annular. Photos at:
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post #5 of 7 (permalink) Old Aug 1st, 13, 01:23 PM
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Re: Holley carb 4779-9 problem all of a sudden.

no need to take the bowel off to change the needle and seat, just take it out and replace it with a new set, it is cheaper to buy a rebuild kit that includes the needle and seat for say $35, the N&S alone will cost you 20 bucks. I agree with everything above, the first thing I would do is tap on the N&S with a hammer to see if you have dirt stuck in it

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post #6 of 7 (permalink) Old Aug 1st, 13, 04:04 PM Thread Starter
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Re: Holley carb 4779-9 problem all of a sudden.

Well I checked the float level and yup it was too high. Pulled the needle and seat which looked really good and moved freely with the o ring looking like new and the tip also looked new and undamaged, but gave it all a real good shot of carb cleaner, readjusted the float and BAM! Started right up and sat at a perfect 850 idle with super response. Only thing is the needle and seat are at the very end of their adjustment. I just barely got the nut back on to retighten everything back up. But it runs PERFECT like it did before. If it happens again I can only assume that maybe the float may have a hole in it and it is not comeing all the way up??? Is that why there is not any adjustment left on the needle and seat to the low end? I also lowered the fuel pressure to 5.5 lbs of pressure as well. KEEPING MY FINGERS CROSSED BUT ALL IS GOOD! Took it for a test drive and it ran like a beast!!

Now I will change out the oil and filter just for a good bit of insurance just in case some fuel got mixed in... THANK YOU TO EVERYONE for all your advise. That article worked out awesome!!

Mark
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post #7 of 7 (permalink) Old Aug 1st, 13, 09:13 PM
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Scott
 
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Re: Holley carb 4779-9 problem all of a sudden.

If it has a hollow brass float with a hole it won't work at all, more likely is the arm or tab of the float that positions the needle in the seat is bent out of position and needs to be "adjusted" so the float adjustment hardware won't be so far to the end of it's adjustment range.

69 Camaro Z/28 RS, original Azure Turquoise, M21 & 3.73 12-bolt posi. NOM 406ci, AFR 210 heads, Straub hyd. roller cam & Dynatech 1-3/4" > 1-7/8" headers, QuickFuel 750 Annular. Photos at:
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