Carburetor perculation problem?

[ClydesdaleKevin]

 Hey guys.  I have a theory as to why my Edlebrock carburetor starts to perculate fuel on hot days...meaning sunny days over 85 degrees...and I want your opinions on this to see if I'm on the right track.

As those of you who have followed my posts in the past know, this past winter I replaced our Quadrejet carburetor with an Edlebrock, and then went ahead and simplified our vacuum system and even blocked off the EGR valve with a blockoff plate.

I then went one step further, and this is where I think I goofed up:  I replaced the stock air cleaner housing with an Edlebrock open element air cleaner.

Let me explain why I think this is the culprit:

We had really cool temperatures this winter, nothing over 80 degrees, and usually considerable cooler, all the way from Louisiana, to Arizona (all over AZ, from Tombstone to Phoenix, Sedona to Flagstaff) and from Arizona to Oklahoma.  Cool weather all through the winter months and absolutely no carburetor problems, perculation or otherwise.  We arrived in Oklahoma at the end of April.

Leaving Oklahoma, when the outside temps started to really heat up, is when we started having the problem.  But never until the outside ambient temperatures got over 80+ degrees on sunny days.

So my theory is that without a snorkeled air cleaner, the very hot engine compartment air going right into the carburetor on a hot day is combining with the heat already coming off the manifold, and raising the carb temp just high enough to start boiling the gas.  Sound logical guys?

We never had this problem when using the snorkelled stock air cleaner...which is long gone by the way...but that was also when we still had the QJ.

It just seems to make sense to me.  It can be 85 degrees and cloudy out, and it doesn't happen.  So I'm guessing the road heat reflecting into the engine compartment also plays a part in the high engine compartment air temps.

By the way, the engine is running nice a cool relatively speaking, as is the transmission...average water temp is around 190 and never exceeds 210, and the average trans temp is right around 150 on hot days, never exceeding 170. 

What do you guys think?  Should I go back to a cold air intake system...ie snorkel?  And do you think this should eliminate the perculation problem by dropping the temp of the carb?

Kev

[DaveVA78Chieftain]

It is worth a try Kevin.  You should be able to pick up a air cleaner assembly at a junk yard fairly cheap.   I may change mine also as I have the same issue.

Dave

[cncsparky]

You may need a carburetor heat shield.  I believe they were factory installed on some cars for the same problem.  You can also install phenolic carburetor spacers that should help. 

http://www.summitracing.com/parts/mrg-3710/overview/

[Oz]

I followed the posts before about using an open air cleaner and the "consesus" was that the 454 "likes" warm air   Well, you know the air going over the engine isn't warm... it's hot.  I don't recall if I replied on that topic since the responses (and you already had your own mind pretty much set on it from the get go) was to go ahead and use an open air filter.

But, if I did or didn't say at the time, I'm saying now that running with an open air cleaner is a no-go when the air cleaner is sitting on top of a Heavy-Duty motor putting off high temps, inside a packed engine compartment with little room for air circulation over it to begin with, and with the cooling fan helping to blow all that hot air into the open air filter with a big carb just sucking it in.

I believe the whole idea behind snorkels is to draw in cooler air from the front of the motor, closer to the fan.

Whether or not this would cause percolation of fuel in the carb, I do not know.

[cncsparky]

Another thing to think about, your original Qjet had a thick base gasket that helped shield manifold heat from the carb.  What does your Edelbrock have for a base gasket?  Usually its just a thin paper gasket. 

[ClydesdaleKevin]

Hmmmmm...the Edlebrock actually uses 2 gaskets.  There is the gasket from the manifold to the thick aluminum spread bore to square bore adapter, and the gasket between the adapter and the carburetor.  So I don't think its gasket thickness causing the problem, and I don't think a spacer is going to do much to solve the problem, since the adapter essentially acts as a spacer.

I'm definitely thinking its the hot hot hot air in the engine compartment on 80+ degree sunny days bringing the fuel temp up just enough to start boiling the gas.

Before we leave the NY faire, I'll have installed a cold air intake system of one kind or another...of course by then the weather will be cool for the rest of our travelling season...lol!  So I might not be able to tell you if the problem is completely solved until next summer...unless we get hot weather on the way to Charlotte, NC at the end of September, which can happen.

I'm going to keep and stow the Edlebrock open element setup when I do, in case I notice a big drop in gas mileage when its cold out.  I can then put it back in for cold weather, but we'll see.

Thanks for the replies so far, guys!  Keep 'em coming!

Kev

[HandyDan]

Kevin, would your old snorkle air cleaner off the Quadrajet fit on the Edlebrock carb?
Dan

[pvoth1111]

Usually the further away you can get the carb from the intake the better...they make spacers from wood and composite materials of various thickness designed to insulate the carb from the heat. If the spacer is make from aluminum or steel it is in direct contact with the manifold.....and heat is easier transferred. On a steel intake I would always like to see a composite spacer to reduce possibility of electrolysis....

[DaveVA78Chieftain]

Kevin, would your old snorkle air cleaner off the Quadrajet fit on the Edlebrock carb?
Dan

He got rid of it so has to do a junkyard find

[GONMAD]

Hey guy's about that heat shield Try A GM part that was used on the Hi Performance engines. The # is 3969835 & you can get it from Summitracing for a good price. Here's the link

http://www.summitracing.com/parts/oer-3969835

I trimmed off anything in the way & folded the front up at a 45 degree angle to divert the HOT air around the carb. I believe everyone is right to use a fresh air system to the carb. I did a CHEAPO fresh air intake using an old clamp on light bell & clothes drier aluminum flex hose from the hardware store & connected it by making alternating tabs & silver GOOD duct tape leading over the radiator I straight to the stock snorkel air cleaner. Using insulating tape insures the air stays moderately cool It looks a little funky but it's been on for 5 or 6 years now & no worries. Besides has anyone priced a Gale Banks fresh air system? I'd LOVE to have one but applying the K I S principle I'm happy. I hope this helps you out. Also look at your fuel pressure if it's low could could get vapor lock easily.
I'll send pics shortly of the cheap & easy fresh air induction
Thanks GONMAD

[ClydesdaleKevin]

Thanks everyone for your replies!  I think I'm going to start out with a new snorkeled air cleaner housing and hook it up to the fresh air hose I left in place in the engine compartment...it draws cold air in from in front of the radiator in the grill.  Or I might just go for a K&N style fresh air intake hose with the filter element in the grill area up high and out of the rain.

If that doesn't correct the problem...and I'm thinking it probably will...I'll try the composite spacer.

And if that doesn't work, I'll try a heat shield.

And thank Gonmad.  Fuel pressure is staying fine and no vapor lock...what I'm getting is vapor SMELL from boiling gasoline, and a serious drop in idle once its starts perculating.  Runs fine on the highway on hot days, even usually runs fine if I have to stop for gas or stop at a rest stop, provided I have recently opened the secondaries and nothing is running too hot...but the second I go to restart it, the gas has already boiled over into the manifold, and its a HARD start, pedal to the floor, then feather the pedal to keep it running until the idle evens out.  Only happens on days hotter than 80+ outside, especially if its a very bright and sunny day.

Kev

[cncsparky]

Kevin, I'm going to do the same mods as you so I hope you find a solution.  What snorkeled air cleaner are you wanting to use?  Do you have a link?  I will probably install the heat shield anyways since its a cheap add-on and I think I have a composite spacer hanging around from my race car days. 

[DaveVA78Chieftain]

You might want to give Ethenhol free gas a try.  http://pure-gas.org/

[Froggy1936]

Ha Ha Ha Ha Ha !!!   this would cost me $450.00 for 1 tank full That is ridiculous !! Frank

[bluebird]

You might want to give Ethenhol free gas a try.  http://pure-gas.org/

Why?? Takes more heat to vaporize ethanol than gas.

[ClydesdaleKevin]

I've heard that pure gasoline has a higher boiling point than ethanol gas...read it somewhere but can't footnote it...lol!

I'll try to fix the issue in the following order: 

1.  Either a snorkelled air cleaner with a hose going to in front of the radiator behind the grill, or a K&N type cold air intake system, also going up behind the grill but up high out of the rain.  I like the second idea better since I can just move the intake hose off the carburetor and out of the way if I notice a decrease in MPG in the cold months, and install the open element air cleaner...without having to store 2 air boxes.  If that doesn't work:

2.  A composite spacer under the carb as a heat shield.  If that doesn't work:

3.  One of the ugly heat shields from Summit Racing, because I want to clutter up my engine compartment again...lol!

Kev

[Froggy1936]

Hi Kev The rain is a GOOD THING The added moisture makes for better running mixture (as long as its not 100% water) Frank

[EarlJr]

We were having a similar problem. I wrapped the entire supply line in aluminum heat shielding (this stuff in case you're curious http://www.jegs.com/i/Thermo-Tec/893/14010/10002/-1 )

I used a remote thermometer to follow the fuel lines and found they really started to pick up heat when they ran up into the dog house after getting fairly close to the exhaust. I figured the longer I could keep the fuel cool the better off I'd be. It hasn't 100% solved my issue, but it has to be over 100 degrees outside before I have issues. before we had problems when the temp would get up around 90 or so.

[Oz]

That's a very good point which has been overlooked so far.  It may not be THE cure but that's certainly a contributing factor in high-temp climates and it's not uncommon for older Dodge big blocks to suffer from vapor lock due to extreme heat but, that's a different issue.   

However, since Kev runs in the desert and all kinds of heat extremes full-time, it certainly would be something for him and anyone running in hot climates to add to take a look at.

Good observation 

[Stripe]

I think I just might do that myself..

[ClydesdaleKevin]

Not a bad idea.  The metal supply line coming to the engine comes up the front of the engine block and is only over the intake manifold a short distance...it doesn't come very close to the exhaust manifold.  But the metal Edlebrock fuel filter sits right on top of the valve cover bolts where it meets the intake manifold.  I think I'll heat shield the line and the filter when I install the cold air intake.  Thanks guys!

Kev

[gary19734]

Hey kev ready to talk about recurving the distributor and advancing the timing it will lower those manifold temps by at least 400 degrees .and no it will not burn the valves actually they will love you for this.Did this to my rig cosistantly get 7 to eight miles to the gallon and lowerd temp at exhaust manifolds by 600 degrees at a full pull  Gary 

[cncsparky]

Gary, what timing specs are you using?  I just sent off a distributor to Dave Ray to have it recurved.  He said about 22 degrees advance by 3K, that and 10 degrees vacuum advance hooked up to full manifold (not timed) vacuum.  Initial to be set at 10 degrees.  I agree, retarded timing will spit the exhaust flame/unburned gas out the manifold, heating it up and worsening any vapor lock issues, let alone cracking the manifolds also.  Is your EGR removed?