Secondary woes

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12-18-2005, 03:48 PM
79C10

Secondary woes

Okay heres the deal, I have a fairly new SBC 350 slightly modded with an Edelbrock performer intake, headers and a rebuilt quadrajet. The deal is that I'lll be cruising down the freeway around 65MPH and I'll open up the secondaries and the engine will start making a popping noise (backfiring/too rich?) at the same time the engine shutters slightly, It only seems to do this when im around 65-70MPH. On the other hand I can be cruising around 45MPH with it whining at 5000 RPM with the secondaries open and it performs top notch. So I don't think its related to engine speed.

EDIT:

It won't shutter/pop at anything slower than 60MPH

And if it matters Im running a 700R4 tranny.
12-18-2005, 04:03 PM
lt1s10

http://www.clubhotrod.com/forums/sho...784#post112784

read this and check those secondaries close 79C10.
12-18-2005, 07:23 PM
erik erikson

Re: Secondary woes

Quote:

Originally posted by 79C10
Okay heres the deal, I have a fairly new SBC 350 slightly modded with an Edelbrock performer intake, headers and a rebuilt quadrajet. The deal is that I'lll be cruising down the freeway around 65MPH and I'll open up the secondaries and the engine will start making a popping noise (backfiring/too rich?) at the same time the engine shutters slightly, It only seems to do this when im around 65-70MPH. On the other hand I can be cruising around 45MPH with it whining at 5000 RPM with the secondaries open and it performs top notch. So I don't think its related to engine speed.

EDIT:

It won't shutter/pop at anything slower than 60MPH

And if it matters Im running a 700R4 tranny.

What do the plugs look like?
12-18-2005, 07:35 PM
79C10

I don't know, I'll pull 'em tomorrow and snap pics.
12-18-2005, 09:17 PM
Oldf100fordman

Almost sounds like you are running out of fuel. What kind of fuel pump are you running?
12-19-2005, 03:11 AM
76GMC1500

Maybe your vacuum advance isn't pulling off quickly enough when you come up to WOT.
12-19-2005, 04:44 AM
R Pope

Too rich won't cause "popping", its too lean. Running out of fuel is a possibility, but I'd try new plugs. You can't tell a bad plug by looking at 'em, especially in a SBC, they're plug eaters. Also, don't use Champions, one or two of every batch will quit in a week or so. Plug wires will also cause it.
12-19-2005, 05:08 AM
79C10

Quote:

Originally posted by Oldf100fordman
Almost sounds like you are running out of fuel. What kind of fuel pump are you running?

As far as I know its the stock mechanical one. Also I have a fuel filter hooked up right before the carb and I can see into the filter & sometimes is not even half way full when the motor is at idle, and it won't rise if I hold the motor at a higher rpm.
12-19-2005, 05:29 AM
lt1s10

"I have a fuel filter hooked up right before the carb"
if its a Q-JET there should be a filter in the carb. also. i'd do away with one of them.
12-19-2005, 04:04 PM
79C10

Well I assumed since on the front of the carb it said "<------ Filter" that it meant attach a filter before the carb in the fuel line. Heres a pic of my setup, and the level of fuel that you see in the filter is about as high as it goes regardless of rpm.

http://www.xylicon.com/box/otherstuf...left_small.jpg
http://www.xylicon.com/box/otherstuf...ight_small.jpg

So I guess I'll pull the external filter off and see if that helps, or Ill get a new fuel pump.

Thanks for all the info.
12-19-2005, 05:51 PM
lt1s10

there should be a filter behind that big nut. take that one out and use the ext. one. if its made of brass they were bad about stopping up. take it out.
12-19-2005, 06:02 PM
lt1s10

http://www.carburetion.com/diags/4mv.jpg

here is what it looks like.
12-19-2005, 06:46 PM
erik erikson

Quote:

Originally posted by R Pope
Too rich won't cause "popping", its too lean. Running out of fuel is a possibility, but I'd try new plugs. You can't tell a bad plug by looking at 'em, especially in a SBC, they're plug eaters. Also, don't use Champions, one or two of every batch will quit in a week or so. Plug wires will also cause it.

Ron, I beg to differ.For the past 15 or more years I have been reading plugs.I make a pass, kill the engine pull the plugs and if they look black I keep (leaning it down) two jets sizes at a time.When I reach a (carmel color) I know I am very close.When it hits light tan I stop.To give you an idea of how close I was last time after I switched carbs we went back to the dyno and did a few pulls.EGT averaged 1310 not bad for a guy just reading plugs.I have used this method for many years only to burn just two pistons.The only plugs I really can't read are those on alcohol or when someone has added something to the gas.
12-20-2005, 03:01 AM
R Pope

erik...sure you can read a lot from a plug, like jetting, oil burning, etc., but you can't tell if its any good by looking at it. Some brand new ones won't fire.
12-20-2005, 03:14 AM
erik erikson

Quote:

Originally posted by R Pope
erik...sure you can read a lot from a plug, like jetting, oil burning, etc., but you can't tell if its any good by looking at it. Some brand new ones won't fire.

I mis-understood what you where saying.I do agree with the Chaampion statment.I switched from AC TO NGK 5 years back no problems.
12-21-2005, 11:05 PM
camaro_fever68

Re: Secondary woes

Quote:

Originally posted by 79C10
Okay heres the deal, I have a fairly new SBC 350 slightly modded with an Edelbrock performer intake, headers and a rebuilt quadrajet. The deal is that I'lll be cruising down the freeway around 65MPH and I'll open up the secondaries and the engine will start making a popping noise (backfiring/too rich?) at the same time the engine shutters slightly, It only seems to do this when im around 65-70MPH. On the other hand I can be cruising around 45MPH with it whining at 5000 RPM with the secondaries open and it performs top notch. So I don't think its related to engine speed.

EDIT:

It won't shutter/pop at anything slower than 60MPH

And if it matters Im running a 700R4 tranny.

Sounds like jets and/or secondary spring need tuning. Also, you need to check fuel level in the bowl. Sounds lean. Could be in the accelerator pump also.
12-22-2005, 05:13 AM
79C10

Yea, I ruled out the "lack of fuel" thoery, my fuel pump is fine and I've removed my external filter, as my internal one is brand new.
12-22-2005, 09:36 AM
camaro_fever68

Quote:

Originally posted by 79C10
Yea, I ruled out the "lack of fuel" thoery, my fuel pump is fine and I've removed my external filter, as my internal one is brand new.

Don't rule out 'lack of fuel' just yet. The carb jetting and squirter and accelerator pump needs to be checked out. Jeg's sells a hi-performance calibrating kit for your carb. You may need it and a good manual on Quadrujets. That's a lean pop and it may just be caused by the secondaries opening too fast or the jet's too lean in the secondary side.
12-22-2005, 10:01 AM
lt1s10

Quote:

Originally posted by 79C10
Yea, I ruled out the "lack of fuel" thoery, my fuel pump is fine and I've removed my external filter, as my internal one is brand new.

if you have the brass filter you can't look at it and tell whether its stopped up or not. they will stop up from sitting and look good. if you don't know how long it's been in the carb. put a new one in anyway. same thing with the paper one also.
12-22-2005, 03:08 PM
79C10

Quote:

Originally posted by lt1s10
if you have the brass filter you can't look at it and tell whether its stopped up or not. they will stop up from sitting and look good. if you don't know how long it's been in the carb. put a new one in anyway. same thing with the paper one also.

I just recently had the carb rebuilt and im pretty sure its brand new because I can look at it and see that its pretty clean, Its one of these http://store.summitracing.com/partde...=115+%2D128245
12-24-2005, 05:03 PM
79C10

I pulled the plugs and they look like...

http://www.xylicon.com/box/otherstuf...hand_small.jpg
http://www.xylicon.com/box/otherstuff/spark.jpg
http://www.xylicon.com/box/otherstuff/spark2.jpg
12-28-2005, 06:06 PM
lobster

Re: Secondary woes

Quote:

Originally posted by 79C10
It only seems to do this when im around 65-70MPH. On the other hand I can be cruising around 45MPH with it whining at 5000 RPM with the secondaries open and it performs top notch. So I don't think its related to engine speed.
It won't shutter/pop at anything slower than 60MPH

i have no real chevy-specific experience yet (just european engines), but ill put my 10 cents worth in as ive been taking advice with out giving any...

it seems very strange that it never happens below 60mph. as you say, it looks like its not related to engine speed. could there be something that happens to your ride only over 60mph? by this i mean some kind of wheel speed related vibration which then causes some other prob with the carb? prehaps wheel bearing or something? i know most fuel bowls really dont like been shaken around too much (even if its only a small high frequency vibration that aint that noticeable)

prehaps the increased air pressure/ram effect through the grill at speeds over 60mph (and prehaps therefore the airpressure into the airfilter/carb) can cause probs with the carb operation when the secondaries are opened?

i'll be quiet now and crawl back into my beginners box

lobster