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302 + Edelbrock 1406 tuning... (warning LONG)

akforsyth

Contributor
Sr. Member
Joined
Jun 17, 2004
Messages
359
Ok a bit of a disclaimer, this one is running in my 65 Mustang, but I am hoping that someone on here may have the knowledge to help me diagnose a new issue. I have a 302 roller motor that I built last year and I topped it off with an Edelbrock 1406 car that I had on an old 289. It is running with 1" aluminum spacers on the stock intake manifold. I jetted it down (knowing that a 1406 comes jetted from the factory for a Ch##y 350) to the primary being .095 and secondary being .092, rods remained stock .075 x .047, and until recently it has run pretty damn good (but still rich and smelled a bit like gas on occasion)

So we recently have a heat wave for this time of the year hitting us here, temperatures going up to about 32 degrees C (which is normal here in the summer). I was out cruising down the highway and had to brake pretty quick as there was a stall ahead and traffic backing up. As I did, it died as quick as if I turned the key off an would not restart. I pulled over and checked the ignition thinking it was something electrical but everything checked out as best I could roadside, and then popped the air filter off. Gas was boiling in the bowls even though the temp gauge showed 195. So my first inclination is a phenolic spacer to keep the heat transfer down, but that's not all. I was able to restart the engine by keeping my foot to the floor on the throttle and cranking it over. It then began running like shit, stumbling and sputtering, but it got me home.

Today I took it out for some running around. Again its a hot day at 32 and for the first couple of hours it ran like a top. A little rich as usual as I could smell some has occasionally, but no issues, Until I stopped for a half hour. I hopped into the car, fired it up and went to drive away and it stalled. And again it would not start, fuel bubbling in the bowls and eventually using the full throttle method it fired up, but this time it was way worse. Stalled multiple times on the way home, smelled of gas and carbon something fierce and really made it look like I was learning to drive stick as it jerked and jumped.

Once I got home and into the garage, I began pulling plugs and found each one of them carbon fouled. Black soot on all plugs, a slight gas smell but not much, wet threads, but not wet electrode. I figure it is severely over fueling itself, but only once it gets hot. This is confusing me some and the manual for this carb is just short of rocket science....

So does anyone have any insights into the tuning? I'm thinking a phenolic spacer to keep the heat transfer down, but am wondering if I am still jetted too high? Could timing be an issue? Do I need to change the metering rods out?

I tuned it last spring using a vacuum gauge as per the manual and it ran really nice all last summer, but this year its running like a heep.

I was contemplating putting this same setup into my Bronco, but now I am leaning again toward fuel injection.

Thanks if you've read my ramble this far....
 
Last edited:

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,345
Well, it sure sounds like the typical float issue that is associated with them when going off-road. All the bouncing around, putting it on it's nose and tail, and just generally jiggling it into submission.
When you braked hard, the fuel sloshed forward and perhaps did something to jam up the floats a bit? Maybe even bent a tab or something?
I don't know, and just throwing it out there.

I've used that carb (or the carter version of it) extensively, and like you it ran very well. I never had any trouble with it on the street like this, and when I did have the off-road blues, it cleared up and never stayed running bad. So I'm not coming from a position of experience here. Just trying to think through what might be going on.

Since the engine is not running overly hot, I would not normally suggest the insulator. But in your case, since we know it happens, or at least is worse when it's fully warmed up and even hot, it might not be out of line to try it.
You might try an IR thermometer too, to see if the area surrounding the intake manifold plenum and the carb body itself are seeing any temps warmer than what the engine is running. There shouldn't be of course, but we all know now that goes with Broncos (and Mustangs too apparently!
Besides, an insulating spacer can't hurt.

Since it's not a lack of fuel, but an over abundance, perhaps lower the float level by 1/8" or so? You a metric kind of person? Maybe 1 or 2 mm at the most? A little goes a long way with float levels, but you can either start slow, or go for broke and lower it a 1/4" or so maybe.
Worth a shot at any rate.

While you at it, you can certainly re-jet it leaner. Obviously that's not what's causing fuel to boil into the venturi, but if it's overly rich, it's not helping either.

That's about all I've got for now. Words of encouragement and support, rather than any concrete advice.
Good luck!

Paul
 

Scott_T

New Member
Joined
Jan 19, 2018
Messages
26
Loc.
Boise, ID
Are you sure it is boiling the fuel over in the carb? Is it possible that your fuel pressure is too high and forcing it past the needle and seat? Depending upon your fuel pump setup, maybe the heat is boiling the fuel in the line between the pump and the carb which could increase the input pressure enough to push fuel past the needle/floats. Just guessing as I have not had the same issue with my Edlebrock setup (plenty of others though...)
 

PaveBronco

Sr. Member
Joined
Oct 30, 2012
Messages
912
You have what I used to call the 1406 Blues. IMO it is the worst carb ever..for off road...IMO..
Fought mine for years to make it work off road and gave up. Unlike most, carter included there is no fuel vent outlet tube, just an opening to the carb throat. Fuel can easily slosh straight into the engine. I did the usual, off road needle and seat, lowered the float level and put on a fuel pressure reducer. Helped but on heavy throttle applications I would run the carb out of gas.
Fuel boiling I couldn't fix, even made a large aluminum plate like a heat shield and made a hardwood space, wood being a pretty good insulator. it was a test. didn't help much.
so I got a used Holley and rebuilt it. problem fixed. although the secondary float would occasionally get stuck from sitting and would run like crap until a tapped the bowl with something, hammer, rock, wrench...
You might get it to work on your Stang, but with the Bronco under hood temps I couldn't.
 

77RHINO

Full Member
Joined
Feb 22, 2011
Messages
308
Do you have headers running near the fuel line? I added a heat shield on the frame rail to prevent some preheating prior to getting to the pump, I'd like to think it helped out as well. I run the 1826, and did have some issues when sitting in traffic or idling too long where it would act up prior to the heat shield and phenolic spacer. Also, could the carb have just enough gunk on it to function properly at cooler temps but start to stick once it heats up?
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
I am with Paul on this one make sure the float is set properly. Check everywhere for vacuum leak. The spacer you use is it divided keeping the left and right sides separated like they are on the intake? The carb likes to run divided like a stock manifold. Make sure you don't have a heat riser leak if your stock manifold has a heat riser. Your idle adjuster screws do they seem like a long way in or out? Before tearing into the carb I would pull the idle mixture screws and blow carb cleaner through the idle holes. Count the turns in before removing the screws so you can set them in the same place you took them out. Get the best gas you can with the least alcohol content if you can. Alcohol is the Devil.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
You have what I used to call the 1406 Blues. IMO it is the worst carb ever..for off road...IMO..
Fought mine for years to make it work off road and gave up. Unlike most, carter included there is no fuel vent outlet tube, just an opening to the carb throat. Fuel can easily slosh straight into the engine. I did the usual, off road needle and seat, lowered the float level and put on a fuel pressure reducer. Helped but on heavy throttle applications I would run the carb out of gas.
Fuel boiling I couldn't fix, even made a large aluminum plate like a heat shield and made a hardwood space, wood being a pretty good insulator. it was a test. didn't help much.
so I got a used Holley and rebuilt it. problem fixed. although the secondary float would occasionally get stuck from sitting and would run like crap until a tapped the bowl with something, hammer, rock, wrench...
You might get it to work on your Stang, but with the Bronco under hood temps I couldn't.

I agree that Edelbrock carbs are more affected by engine heat than other carbs. It's got a couple of issues that contribute to this.

Edelbrock floats have less leverage on the needle valves and don't hold as much pressure as well. When you shut off a heated engine, the fuel line between the fuel pump and carb continues to heat up and build pressure. That pressure is blocked by the check valve in the fuel pump and the needle valve in the carb. The needle valve is the point of least resistance, so that fuel goes into the carb overfilling it, and flooding the engine.

The other issue is Edelbrock's placement of its fuel bowl. It's right over the exhaust heat riser port in the intake manifold. This can cause the fuel to boil in the carb after the hot engine is shut down.

Both of these issues can be resolved by rerouting fuel lines, adding a pressure regulator, and installing a heat isolating spacer under the carb.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Install an AFR gauge. It eliminates most of the guess work.

^This is a good idea, but I see no need to leave the AFR gauge in the car after tuning.
My plan is to install the bung for the sensor, but keep the actual gauge portable and plug it into the cigar lighter for power. That way after I tune the car, I can remove the sensor, and plug the bung. I'll be able to use the same setup on all my cars.
 
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