six pack surging back and forth at freeway speeds?

[70charginglizard]

So guys,

I finally got my brakes working to a point to where I could actually get the car out today to test drive the brakes and took it out on the freeway and I'm noticing a surging at freeway speeds (above 55mph) It's very suttle. wouldnt notice it unless your driving at highway speed but it's definately there.

Any one have any ideas?

Never did this with the edelbrock 4bbl

[mauve66]

put pressure guage on fuel line, raise rear axle on jack stands, go through gears CALMLY, have someone watch fuel pressure all the way through the rpm/gear changes
you may notice the pressure changing alot at idle but it might just not be keeping up at road speed
could also check float levels, maybe their full enough at idle but not storing enough for the pump to keep up at road speed

[b5blue]

What pump are you running six packs want 5lb pressure only?

[70charginglizard]

What pump are you running six packs want 5lb pressure only?

Yeah I was thinking perhaps fuel starvation. I only have one of those stock type big block fuel pumps. Not one of those carter hi flow ones. I was going ot upgrade to one of those later.

Whats odd is that even with the regular fuel pump I have on it I'm able to get on the gas and I'm not getting any hessitation at all when I do that.  This (very suttle....you can barely feel it) up and down surging issue only occurs when on the freeway doing a cruising speed of about 60 and above.

[charger Downunder]

what size jets do you have on the center carb stock are 62 by memory, i run a 65.Put the car on a level surface and do the float levels get a set of clear holley site plugs for the front and rear carb to adjust height.Swap back the original ones when finished. Don't use a high pressure fuel pump.

[b5blue]

I'm trying to recall the correct fuel pump number....it's a Carter, maybe M4845? They are only 35.00 or so so don't be fooled into a Hemi or Holley pump for 100.00 or more as they run too much pressure 8-13lb. You need a brass adapter to fit the steel line to the output that runs to the vapor separator, a detail that drove me nuts as I bought this pump only to find it would not accept my steel line fitting. (I sent it back only to have to re order it and get the adapter) I found even many other pumps that fit big block run more pressure and because of having 3 floats to balance you need 5lb's at the right volume capacity. I not certain this is your problem but keep it in mind. 

[8WHEELER]

Did you ever upgrade your small fuel lines to the 440 HP & Hemi bigger fuel lines? and with the vapor
separator return line? this is probably not the problem, but I have seen things less obvious be a
problem that you would not think it should be.

But it is most likely a lean condition, very common to have to tweak a six pack after first installing it.
But once its dialed in, hold on..........

Dan

[8WHEELER]

I think the engine bay looks very good, do you know you have the wrong drivers side valve
cover on the car? not a big deal, but it should not have the spark plug wire stands on it.

If you know this, disregard this observation   

Dan

[70charginglizard]

I think the engine bay looks very good, do you know you have the wrong drivers side valve
cover on the car? not a big deal, but it should not have the spark plug wire stands on it.

If you know this, disregard this observation   

Dan

Hi Dan.

Thanks for the observations. Although I have bigger fish to fry at the moment. But if you have a correct driver side 440 6 pack valve cover that you know is available and for sale I'd be more then happy to take it off you hands. 

[maxwellwedge]

Almost sounds like a vacuum advance issue but you said it didn't surge with a 4-BBl setup. If the car runs well under full throttle your fuel pump is fine. Do you have the linkages properly adjusted to the end carbs? Power valve ok in the center carb? Do you have the distributor vacuum hooked up to the right port on the carb?

[70charginglizard]

Did you ever upgrade your small fuel lines to the 440 HP & Hemi bigger fuel lines? and with the vapor
separator return line? this is probably not the problem, but I have seen things less obvious be a
problem that you would not think it should be.

But it is most likely a lean condition, very common to have to tweak a six pack after first installing it.
But once its dialed in, hold on..........

Dan

Hi Dan.

Thanks for the input.

Although ...for the purpsoe of this discussion...I'd be really suprised that my fuel delivery system would be causing this. Especially since this has always been a big block car from day one. I think it's more vacumn related myself. just need to find it. (Think I have with the booster leak on the interior boot leak)  

I just want to persure all simpler avenes first before I dig into something as labor intesive as the changing out the fuel lines.


for the purpose of understanding your concerns....why you think a 440 six pack car would require any larger fuel delivery fuel lines then it did when I was running the 383 2bbl. Especially when after the 383 I upgraded to a 440 with a 750 cfm edelbrock carb running those same fuel lines and never once did it have this condition with that set up.

I've even tried cutting off the fwd and rear carbs completely from the six pack (buy plugging off the vacumn that make then function) and ran it off only the middle 2bbl and still seem to have the same problem.

So with that in mind.. what do you think the difference would be between a 440 2bbl and a 383 2bbl when it comes to the fuel line capacities? (other then the cubic inches)

I've been told that the 440 six pack cars can run completely indipendent of the fwd and aft carb
(which I would think would require no more fuel delivery then a 383 2bbl and be of a lower cfm then my previous 440 4 bbl set up I had just before the 6 pack set up) of coarse that is all subject to opinion I supose. More reason to have more cool mopar carb discussions on this matter I suppose...lol

[maxwellwedge]

What else is different when you went from 4BBL to the six-shooter? Did you change or upgrade anything else that could be a variable?

[Troy]

Stop making so many threads covering the same problem!

You forgot to mention your leaky new brake booster in this thread. As I said in the other thread, I do believe the vacuum leak could cause this stumbling. Assuming the car ran well before you removed and replaced brake components I'd start with anything that you disconnected and reinstalled (including said booster).

Troy

[70charginglizard]

Almost sounds like a vacuum advance issue but you said it didn't surge with a 4-BBl setup. If the car runs well under full throttle your fuel pump is fine. Do you have the linkages properly adjusted to the end carbs? Power valve ok in the center carb? Do you have the distributor vacuum hooked up to the right port on the carb?

"Do you have the linkages properly adjusted to the end carbs?"

Linkage connection to fwd carbs-



linkage connection to aft carb-



"Do you have the distributor vacuum hooked up to the right port on the carb?"

distributer vacume line connection to center carb-

[70charginglizard]

Stop making so many threads covering the same problem!

You forgot to mention your leaky new brake booster in this thread. As I said in the other thread, I do believe the vacuum leak could cause this stumbling. Assuming the car ran well before you removed and replaced brake components I'd start with anything that you disconnected and reinstalled (including said booster).

Troy

Thanks Troy...I just mensioned that above-

"I think it's more vacuum related myself. just need to find it. (Think I have with the booster leak on the interior boot leak)"  

but I know what your saying. I'm just flustard and a post whore when that happens to me. lol

[oldschool]

sounds like a vaccum advance problem to me.try unhooking the vaccum advance hose and plugging it. then go out and drive it and see if it still does it. thats why i dont run a vaccum advance on any of my cars.

[maxwellwedge]

Are the linkage rods properly adjusted - the rod needs to easily slide into the hole (at both end carbs) with the center carb at curb idle with the choke fully open and the carb totally off the fast idle cam. The linkage swivel on the center carb needs to be all the way against the end of the slot and the end carbs fully closed when you are checking the rod engagement into the end carbs. I appears like the hoses on the center carb are ok and aren't "swapped" - can't fully tell.  

[Sublime/Sixpack]

I've been told that the 440 six pack cars can run completely indipendent of the fwd and aft carb

FWIW It's my understanding that the outboard carbs come into play even at idle so the fuel in their bowls doesn't go bad. The float level in the outboard carbs need to be adjusted to the correct level and their idle mixture screws need to be set correctly for the engine to idle properly and run smoothly when running/driving on the center carb. All three carbs come into play when just driving around easy.

I'm not sure why your engine is surging but you've had a number of good suggestions from members here. I'm thinking that you have a lean condition. Possibly from a vacuum leak, or maybe the carbs are running lean because of the elevation where you live. You do live near sea level don't you? 

Make sure your float levels are set properly, and maybe experiment a little with the idle mixture screws on all three carbs.

If you really suspect the new brake booster and live in the country or have acess to a chassis type dyno you could disconnect the line to the booster, plug it, then run the car up to the speed where the surging starts to rule that out.

Probably the best thing to do (for your sanity) is find someone in your area that is familiar with mopars and sixpacks and has a chassis dyno, drop your car off to him for a dyno tune.

[8WHEELER]

Kelly
I was simply trying to make sure of everything you upgraded during the 6pk install, and trying to rule
out any possible problems ''old or new''. If you had upgraded to the new system with the return line,
it is possible that if that was not working properly, that can also cause a problem. Like I said, just
trying to help eliminate possibilities, but as I said before, it sounds like a lean condition by a carb
setting, or some source of a vacuum leak.

Buy the way, being born a big block 383 does not give you the larger fuel lines, and if you can show me
a 440 2bbl I would be interested to see it..................

I don't know why you are so overly sensitive, that will not get you anywhere, I am just a local guy
trying to help. Looks like I learned my leason................ Yes I have a valve cover, but I am keeping it.
And a six pack valve cover is nothing special, just a standard 70 HP engine valve cover, with no spark
plug wire holders, or simply grind off those stands, I was not trying to ruffle your feathers................

Dan

[firefighter3931]

sounds like a vaccum advance problem to me.try unhooking the vaccum advance hose and plugging it. then go out and drive it and see if it still does it. thats why i dont run a vaccum advance on any of my cars.

Disconnect it and go for a spin to see what happens. 

If the brake booster has a vacuum leak that can also be an issue as well. 



Ron

[quapman]

If the center carb throttle shaft is sloppy, it could cause a vacuum laek as well. Heck, even undertightened base bolts could be the culprit.

[70charginglizard]

Kelly
I was simply trying to make sure of everything you upgraded during the 6pk install, and trying to rule
out any possible problems ''old or new''. If you had upgraded to the new system with the return line,
it is possible that if that was not working properly, that can also cause a problem. Like I said, just
trying to help eliminate possibilities, but as I said before, it sounds like a lean condition by a carb
setting, or some source of a vacuum leak.

Buy the way, being born a big block 383 does not give you the larger fuel lines, and if you can show me
a 440 2bbl I would be interested to see it..................

I don't know why you are so overly sensitive, that will not get you anywhere, I am just a local guy
trying to help. Looks like I learned my leason................ Yes I have a valve cover, but I am keeping it.
And a six pack valve cover is nothing special, just a standard 70 HP engine valve cover, with no spark
plug wire holders, or simply grind off those stands, I was not trying to ruffle your feathers................

Dan

Dan.  

Peace man.
I was not trying to ruffle yours either.

thats why I put a thanks for the input, lol and a two thumbs up on my reply to your post.

I was just trying to explain the fact that I had a 750 CFM 4bbl on this motor prior and never had any issue with fuel starvation at freeway speed. The 440 2bbl comment was to let you know that I did vacuum off the two outbd carbs and ran it out on the freeway as a 2bb as well to be sure it wasnt a fuel starvation issue basing it off the fact that my 440 4bbl edlebrock system wasnt doing this.
Something my old buddy Mr Woodward always tought me is to look at the simpler solutions first then start to dig into the more complicated things. Good advice to me. Just seemed like your sugestion to replace all of my fuel lines seemed to be a pretty radical suggestion at this point in time. 'I wasnt trying to tell you that you were wrong. Just explain my side of that discusion. ok

[70charginglizard]

I will try running it again today guys with the vacuum advanced unplugged and see what that does.
Thanks 

[70charginglizard]

I've been told that the 440 six pack cars can run completely indipendent of the fwd and aft carb

FWIW It's my understanding that the outboard carbs come into play even at idle so the fuel in their bowls doesn't go bad. The float level in the outboard carbs need to be adjusted to the correct level and their idle mixture screws need to be set correctly for the engine to idle properly and run smoothly when running/driving on the center carb. All three carbs come into play when just driving around easy.

I'm not sure why your engine is surging but you've had a number of good suggestions from members here. I'm thinking that you have a lean condition. Possibly from a vacuum leak, or maybe the carbs are running lean because of the elevation where you live. You do live near sea level don't you?  

Make sure your float levels are set properly, and maybe experiment a little with the idle mixture screws on all three carbs.

If you really suspect the new brake booster and live in the country or have acess to a chassis type dyno you could disconnect the line to the booster, plug it, then run the car up to the speed where the surging starts to rule that out.

Probably the best thing to do (for your sanity) is find someone in your area that is familiar with mopars and sixpacks and has a chassis dyno, drop your car off to him for a dyno tune.

Yeah I'm a sea level guys. I was only turning them off as a temporary test to see if perhaps it was a fuel starvation issue. There plugged back in now. I agree though. It may have to go to the dyno shop to be sure everything is tuned in correctly after I fix the booster issue and check for anymore vacuum leaks anywhere and if it's still occuring after that point. I may just do that anyway to be sure everything is properly sinked in.  

[jerry]

they make different springs for secondaries.i run what my car came with from factory. around 65 mph running a 4:10 rear i notice the six bbl starting to kick in.change your springs. this has nothing to do with fuel line size.

[mauve66]

if you can "feel" the outer carbs come in then they are coming in too late, the transition should be seamless

[maxwellwedge]

they make different springs for secondaries.i run what my car came with from factory. around 65 mph running a 4:10 rear i notice the six bbl starting to kick in.change your springs. this has nothing to do with fuel line size.

I have a few six-pack 4.10 cars - 4-Speed and Auto. If your end carbs are starting to come in at 65 MPH your springs are way lighter than the stockers....or you are really running 4.88's   

[Sublime/Sixpack]

 

[jerry]

white springs 30" tall tires 65 mph = lift off.

[70charginglizard]

sounds like a vaccum advance problem to me.try unhooking the vaccum advance hose and plugging it. then go out and drive it and see if it still does it. thats why i dont run a vaccum advance on any of my cars.

Disconnect it and go for a spin to see what happens.  

If the brake booster has a vacuum leak that can also be an issue as well.  



Ron

I think that was may have been it Ron. I pulled the vacuum line like you said and ran it down to snohomish for a spin today and with the vac advanced unplugged it seemed to eleviate the surging. and when I plugged it back in and ran it home I started noticing it again.

Wonder why it didn't do it before the six pack conversion? It's the same distributed.