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Runs Like Crap With Air Cleaner On - why?

7K views 30 replies 11 participants last post by  T-bucket23 
#1 · (Edited)
when I put the air cleaner on (new 14" x 3" air cleaner) it runs like crap at wide open throttle and "sputters". when I take the air cleaner off and road test her, she tears up the road, smokes the tires and gets rubber when shifting gears - no "sputtering".

It's a vacuum secondary carb - just rebuilt Holley 750 with added secondary metering block instead of metering plate.

UPDATE 1: It's not the secondaries. I disabled them so they won't open, road tested again with the air cleaner on (running only the primaries) and same problem. "sputtering" at wide open throttle. So to recap, with only the primaries operational, and the air cleaner on, the engine runs like crap at WOT. when the air cleaner is off, she runs great. I give up. HELP!!!!

UPDATE 2: New update. I road tested again. left the air cleaner assembly on and cut away about 25% of the filter element. It still ran like crap at WOT. I removed the entire air cleaner assembly. She ran great. Next I left the air cleaner baseplate installed (and secured it in place) and left the filter element and top lid of the air cleaner off then road tested. She ran great. so it's nothing to do with the air cleaner baseplate obstructing anything. It's simply to restrictive and it "redirects" the airflow into the venturi's from the side rather than from the top (when the lid is in place). Very unusual. All this might be cause because the secondaries are not opening under WOT? I ordered a new spring kit for the vacuum diaphram and will install a lighter spring and then roadtest it again with the air cleaner off, and then on again.

Any suggestions?
 
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#3 ·
red_rider52 said:
Linkage hitting the air cleaner?
no - I checked. looks ok. I don't feel anything hitting it when I'm driving it. I checked it pretty good when it was parked and sitting still. I'll check it again.

One thing I didnt do is actuate the throttle when the car is sitting still - parked and the air cleaner nut is loosened. if it's hitting the linkage that's when it would be noticeable. I'll try that. unfortuneately everytime I stroke the throttle it dumps fuel into the intake manifold form the shooters.
 
#4 ·
leejoy said:
no - I checked. looks ok. I don't feel anything hitting it when I'm driving it. I checked it pretty good when it was parked and sitting still. I'll check it again.

One thing I didnt do is actuate the throttle when the car is sitting still - parked and the air cleaner nut is loosened. if it's hitting the linkage that's when it would be noticeable. I'll try that. unfortuneately everytime I stroke the throttle it dumps fuel into the intake manifold form the shooters.
A few pumps isn't going to hurt it.

check to see if the air filter lid is getting too close to the tops of the bowl vent tubes that stick straight up. If there is insufficient clearance, we used to cut the tubes to a 45* angle (High sides to the rear) to give them more air or drill a 3/16 hole on the front side near the top of the tube. What happens is that the air rushing past causes a vacuum around the tubes and sucks a vacuum on the float bowls..... :nono:

Rather than modify the carb.....If it will fit, use a 4 inch tall air filter.
 
#5 ·
Doc here, :pimp:

I had one with a brand new Edelbrock Air-cleaner installed, and It did the exact same thing..

Turns out under inspection, the tube for the breather on the bottom of the Air cleaner, when tightened sat very nicely into the choke linkage and jammed it..

All needed to d to rectify the problem was turn it a 1/4 turn and bolt it back down..

You might want to look..

Doc :pimp:
 
#8 ·
xntrik said:
A few pumps isn't going to hurt it.

check to see if the air filter lid is getting too close to the tops of the bowl vent tubes that stick straight up. If there is insufficient clearance, we used to cut the tubes to a 45* angle (High sides to the rear) to give them more air or drill a 3/16 hole on the front side near the top of the tube. What happens is that the air rushing past causes a vacuum around the tubes and sucks a vacuum on the float bowls..... :nono:

Rather than modify the carb.....If it will fit, use a 4 inch tall air filter.
holy smokes.................you might be onto something. If you're right, I'm buying you lunch and a beer. I'll go look at it now, but I thought both bowls (front and rear) have the same vent opening on my Holley model 4160. It seems like it's a secondary issue not a primary - but I will go look.
 
#9 ·
docvette said:
Doc here, :pimp:

I had one with a brand new Edelbrock Air-cleaner installed, and It did the exact same thing..

Turns out under inspection, the tube for the breather on the bottom of the Air cleaner, when tightened sat very nicely into the choke linkage and jammed it..

All needed to d to rectify the problem was turn it a 1/4 turn and bolt it back down..

You might want to look..

Doc :pimp:
I'll check again, but i dont have a choke - I took it off, so that's not the problem, but it might be choking one of the bowl vents like the other reply said.
 
#10 ·
leejoy said:
holy smokes.................you might be onto something. If you're right, I'm buying you lunch and a beer. I'll go look at it now, but I thought both bowls (front and rear) have the same vent opening on my Holley model 4160. It seems like it's a secondary issue not a primary - but I will go look.
no - that's not the problem. both bowl vents arent even close to the air cleaner housing. Oh well - onto the next theorem.
 
#12 ·
Vortech 4.3 said:
over tightening the nut ?

maybe you can put the lid and base on without the filter ?
I was thinking the same thing, but why would that cause a problem? both bowl vents are nowhere near the air cleaner housing - plenty of clearance. My next step in figuring this out is disabling the secondary throttles from opening, leaving the air cleaner assembly and filter on, and road testing again just using the primaries. I'm thinking it's the secondaries starting to open that's causing the sputtering. If the sputtering goes away at WOT, its' definitely something with the secondary circuit and I will have to rebuild the carb again. If it still sputters, it's something still with the air cleaner.

Lee
 
#13 ·
to any of you following this thread. I road tested again today with more interesting results. I disabled the secondaries and road tested with the air cleaner on. Ran like crap again at wide open throttle. removed the air cleaner and she ran great. so it's not a "secondaries" issue. It happens when running only on the primaries. for some reason when that air cleaner is installed she runs like crap at WOT. what the heck is going on?

Lee
 
#14 ·
If it's a stock type filter try another brand. Instead of a K&N check out the AMSOIL foam filters. I like them better -- they seem to breathe at least as good as a K&N and you can't ruin them by getting the wrong oil on, they use motor oil. Easier to clean too -- no special kit or fluids to buy.

Sounds like you need to adjust the carb with the air filter on. It should be running a bit richer with the restriction of the air filter. I bet the carb was set up without a filter and that's exactly what's happening now -- it's way rich at WOT. A low restriction filter (like the AMSOIL or a K&N) might fix it right up.

No, I'm not an AMSOIL dealer, but got a filter from a dealer friend to try and noticed the difference right away! That was after a K&N was ruined by spilling motor oil on it. You can't clean a K&N once it gets a petroleum based oil on it. It stops up at the area the dino oil contacted it just as if you stuck a piece of sheet metal over it.
 
#15 ·
I'm still having problems with this. I will roadtest the car again this weekend. My next trick is to put the air cleaner on but cut away about half of the paper element and then run it again to see what happens. I don't know what else to do at this point.

Lee
 
#17 ·
weirdbeard said:
Yeah Thats what I was going to suggest! That or a different air cleaner. It is alway a good idea to tune your carb with the air cleaner in place. If you switch to a high flow filter you should re tune because you might run lean. You probably already new that. ;)
when you talk about "retune", do you mean try different jets or power valve? what else is there to retune at wide open throttle other than jets and power valve? Help!!!!!
 
#18 ·
Try a different air cleaner!!!! I had the same problem on my 408 windsor, when the aircleaner was on it ran like crap, when I took it off , and ran like a raped ape. My problem was the air cleaner was too restrictive.

By the way even when I had the air cleaner on, jetting smaller didnt help. Try changing filters and going to 1" taller.
 
#19 ·
brainsboy said:
Try a different air cleaner!!!! I had the same problem on my 408 windsor, when the aircleaner was on it ran like crap, when I took it off , and ran like a raped ape. My problem was the air cleaner was too restrictive.

By the way even when I had the air cleaner on, jetting smaller didnt help. Try changing filters and going to 1" taller.
dear brainsboy

thanks for the tip. I will try that. Now I don't feel so bad since you had the same problem. I may have a little problem though. I have a standard hood on that 72 nova and nothing taller will fit under the hood. I'll figure out something though - a less restrictive air cleaner I guess, but the one on there now is totally new and clean.

that samurai of your is a riot dude. Have fun.

Lee
 
#20 ·
ok - new update

for those following this thread, check this out. I've done tons of testing on this and here is what I have learned. The "sputtering" problem appears to be caused by the "removal of the choke plate". I bought the Holley 750 carb used, without a choke plate and never installed one. I felt no reason for it. I only drive the car in the summer and just give it time to warm up. Anyway with tons of road testing I have learned that when the choke plate is installed (not even connected to the linkage!) the "sputtering" at wide open throttle problem disappeared. Can you believe it. It runs better with the choke plate in!!!!!

We are talking about a 468 BB Chevy with a huge cam, dual plane intake, Holley 750 with vacuum secondaries, 2" headers, ported heads, roller rockers, MSD ignition, etc.

Apparantly something with the choke plate acts as an "air straightener" when the air cleaner assembly (14" x 3") is on. without the choke plate installed, and the air cleaner assembly on, she runs like crap at WOT. I believe the top lid of the air cleaner is to close to the carb choke tower and at WOT the high velocity and CFM flow rate is to much to turn down 90 deg under the air cleaner lid and enter the venturi's, so the airflow profile gets "turbulent" and the resulting air/fuel mixture gets inconsistent and the ratios change.

I'm wondering now if I removed the choke plate and installed a "taller" air cleaner assembly if that would work. that is my next test.

Bye.
 
#21 · (Edited)
Not being sarcastic here, ok?

Didn't I suggest a taller filter in post # 4 ?

Several months ago there was a similar thread and "carb experts" all over this site ate me up for suggesting that the choke made a difference in air flow smoothness..... go figure.

Thanks for your valuable input... I for one am still learning something after 45 years. :thumbup:

edit: I always recommend the largest and tallest air filter that can physically fit under the hood. Cold air intake ALSO.
 
#22 ·
xntrik said:
Not being sarcastic here, ok?

Didn't I suggest a taller filter in post # 4 ?

Several months ago there was a similar thread and "carb experts" all over this site ate me up for suggesting that the choke made a difference in air flow smoothness..... go figure.

Thanks for your valuable input... I for one am still learning something after 45 years. :thumbup:

edit: I always recommend the largest and tallest air filter that can physically fit under the hood. Cold air intake ALSO.
Dear Xntrik:

thanks for your help. yes you did suggest a taller filter. There is no more room under my 72 Nova hood with that 468 BB motor. I will now begin the process of deciding whether to purchase a new cowl hood or keep the hood I have and have a "rectangular" opening cut in it for a large air cleaner assembly that will be coming through it with a tall air cleaner. I will call around and see who can cut my hood and do it right. I don't want to purchase a new cowl hood and have it painted. What do you think? In order to fit a taller air cleaner (6-8" height) I will definitely need to cut the hood open. I can only fit a 3" tall air cleaner in there now.

Holy cow, when I tested with a taller air cleaner and the hood off yesterday, wow, that car ran as quick as I'd ever seen it go. She started fishtailing and spinning both tires at 60 MPH when shift from 1st to 2nd. That was fun.
 
#25 · (Edited)
leejoy said:
Dear Xntrik:

thanks for your help. yes you did suggest a taller filter. There is no more room under my 72 Nova hood with that 468 BB motor. I will now begin the process of deciding whether to purchase a new cowl hood or keep the hood I have and have a "rectangular" opening cut in it for a large air cleaner assembly that will be coming through it with a tall air cleaner. I will call around and see who can cut my hood and do it right. I don't want to purchase a new cowl hood and have it painted. What do you think? In order to fit a taller air cleaner (6-8" height) I will definitely need to cut the hood open. I can only fit a 3" tall air cleaner in there now.

Holy cow, when I tested with a taller air cleaner and the hood off yesterday, wow, that car ran as quick as I'd ever seen it go. She started fishtailing and spinning both tires at 60 MPH when shift from 1st to 2nd. That was fun.

Thank you,

I would go for the largest filter can that you can live with. That engine needs lots of air.

Removing the air horn on the carb might be an alternative and using one of those new flow director things advertised in the hot rod magazines. They are plastic and look like a big intake valve, they slip over the filter stud with the head upwards, and make the air turn more smoothly down into the carb. 3 inch filter is probably not sufficient for your engine though.

Also you might measure and consider only removing the strengthening ribs under the hood and leaving the skin intact. That might give you enough clearance for a 4" tall KN flter. Test a 4" tall one and see if it will let the engine breathe. If you could do that and still remove the carb horn, that would preserve your hood and be stealthy.

I like the looks of a cowl hood, I hate the old style gasser or pro street scoops, especially anything square. I think 3 inches is the maximum height hood for good looks. That should give you 3" that you have now, plus the hood structure thickness, and another 3 for a filter height of 6 with room to spare. I would also be sure that the filter top is the new style with filter material in it to allow as much cool air in as possible. It might actually flow better with a 5" tall and the filter material lid with clearance between it and the scoop top.

If I cut a hood, I would install a rear opening scoop which would do double duty for letting out the hot under hood air, and would still be driveable in the rain. I guess I would make it look a lot like a cowl hood. You will still be faced with the paint situation, unless black is a viable accent for your hood.

The simplest way to cut a hood is to remove it. Tape strings x'ed across from fender to fender that intersect exactly at the air filter stud, and mark their location on the fenders etc.. Reinstall the hood, reinstall the strings over the hood, and the center of your filter stud will be marked. Mark the stud location on the hood, scribe the desired radius etc, and cut away..... Of course, make sure your scoop is large enough before chopping. Watch for sufficient strength under the hood as the ribs will be removed with the sawing. You might want to weld a strap under the hood between the ribs for strength before cutting. It doesn't look great, but it works.

All in all, you might be better off going with the new cowl hood and having PPG electronicly match your paint with their paint reader computer. (Whatever they call it)
 
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