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Back fire when cold? Edelbrock carb

2K views 19 replies 10 participants last post by  Tom Mobley 
#1 ·
It don't get cold much in the south but when it does my engine will back fire through the carb at anything more than half throttle and start to stall, and when I say cold I mean about 10 minutes of idling and 180 temp out of the thermostat. The problem goes away after heating the engine more. The choke is working properly, went though many guides and videos. I'm thinking I need to go more rich but looking at the plugs and intake it looks like im running to rich, if that makes sense? Thinking of getting rid of the eddy carb, I cut my teeth on quads so maybe I'm expecting to much out of it? Any suggestions or advice?
 
#2 ·
I have ran the edelbrock carbs for many years and ran Carter AFB's before that and Q jets and Holleys.

The absolute worst has been some of the newer ones like sold in the last 6 years.
The issue I have found is Float issue.

Seems an off road needle and seat will allow the float in some carbs to not seat the needle and run rich.
The float will move up as the fuel level rises. Just like normal.
BUT the float arm on some floats will rest against the steel baffle that is above the float before the needl shuts off.

Other times the floats are bent wrong.
Could have happened in shipping as I have seen Fedex and others toss packages like a football.

I have ran the old style Edelbrock RPM intake and single plane Strip dominator and Iron and aluminum Q jet intakes and have ran many spacers and some intakes were ported.
Now with that said all of them ran fine .. no lean popping etc.

The Edelbrock RPM air gap gave me fith with 2 different carbs an Edelbrock and my 750 Double pumper.
Took a long time to get heat into the runners before it would act right.
15 minutes of driving usually.

I pulled it off and stuck the old style RPM back on and no issues and I was able to pull a lot of fuel out of it.

It might make more on a dyno at full throttle but driving around on my SBC it was not a good experience.

I have ran the 12" tall tunnel-ram with 2 edelbrock 600's and it ran great also.

I have no idea what intake you have or what timing curve you have either.

Could be the timing.
I run 18 minimum timing at idle and sometimes 22 at idle.

In the winter time I can screw my idle mix screws out 3/4 more and it makes it happy.. usually have them 2.5 turns out on my Edelbrocks for warm weather .

Clean the plugs and you may need hotter plugs or hotter coil etc.
I have seen weak coils blacken the plugs and make the engine run like poop.
 
#3 ·
likely the cold incoming air is freezing the gasoline in the carb air horn, venturi effect,high pressure to low pressure, one of the reasons heated air from the exhaust was directed into the air cleaner in later years.
 
#11 ·
Yes, what are the timing parameters?

I NEVER completely block off the heat cross over passages on street engines. I do restrict them by adding one each, 1/4 inch hole in the block off plate for one side, and 1/8 hole in the other one.

Completely blocking off heat passages makes for serious problems, especially in things like the stupidity of trying to run an "Air Gap" disaster on the street. Instead of the exhaust heat, even in the small transfer volumes of it I use, water heating under the carb and plenum is the best way to do it, can be shut off for drag racing, used for street use.
 
#12 ·
I need to check it again but the timing is 35 all in at 2500 if I recall right. It has vac advance, hei distributor, CS XE262H-10 cam, eddy 1406 carb with rpm intake, hedman full length headers. Other than that it's fairly stock idle in park is 1000 rpm, always had problems getting it to run on cold days.
 
#14 ·
Please outline these parameters for timing, if you would:

INITIAL timing, with vacuum advance hose disconnected and plugged
Mechanical advance degrees, this specification, added to the INITIAL, will give the total advance (INITIAL and mechanical degrees)
VACUUM ADVANCE degrees of timing the unit will add
What source is the vacuum advance working on, ported, or full manifold vacuum?

What we are attempting to do is form a set of specifications the tmiing is working from

NO OFFENSE INTENDED, but, "36" really doesn't tell us anything.
 
#16 ·
No offence taken, HEI will only give about 20 mechanical advance, so that should put me in at about 15 initial, I don't recall what the vac advance was at but it starts and runs well when it's more than 80 degrees outside, I plan on checking it tomorrow to give some solid numbers, thanks for the help.
 
#15 ·
What octane fuel you running? Higher octane fuel burns slower by nature and can cause problems during cooler operating conditions.If the car runs good when warmed up, try changing your fuel grade to a lower octane. Easy and cheap thing to try. If you live up in my part of the country, there are specific warm and cold weather blend fuels. Generally speaking, octane level requirements drop in colder conditions. Cooler intake charge helps to deter detonation.
 
#18 ·
X3 on the timing question. Idle numbers. Dave Ray and 4 Speed are thinking you have the timing too retarded at idle. Thus, the "36 degrees doesn't tell us" comment. Retarded timing, sooty plugs, rich idle.

I'm in Houston with an Eddy on an AirGap disaster. Like any disaster, it's cool to look at. No heat spacer, but it would hot start better if I had one. With the mechanical choke adjustment dialed in per the book, mine has started great, comes onto the highest high idle step and warms up fine for the first minute or two. Then when it drops down to second idle step it would die unless I was vigilant and on the pedal. And it was REALLY hard to start because it was lean. Never backfire. Always problem below about 60 degrees. Restart it and let it warm up to a coolant temp of about 160 (vs your 180) and then I could drive it even though the choke wasn't fully open. This is about a 6 minute window, versus your 10 minutes.

I just gave it 3 ticks on the choke dial richer last weekend. Temps were in the 50's so I could play with it. Cold start up high idle was the same, dropping to the second high idle step was better because the choke dial was holding the choke on more. No dying now. More drivable before fully warmed up.

FYI I'm airflow limited on my cooling system and running a 180 stat, so in cool temps I'm never above 180.
 
#20 ·
Zeke, sounds like you're getting there. don't be concerned about tightening it up a few notches. You can always back it off when the weather warms up.
 
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