.25 second delay - Carb?

[1985 CCX]

Question:

I have a slight delay ~.25 second when hitting the accelerator. Normal driving is uneffected......This only occurs when driving and you suddenly hit the gas.

What has been done:
Replace accelerator pupms
Adjust timing
Adjust air/fuel mixture
Adjust bowls
Replace discharge nozzel check valve

Any additional thoughts? Remember the delay is a quarter second so not really an issue. Not noticed with normal driving or once under full acceleration once secondaries kick in.

Thanks

[Hotfingrs]

sounds like you need bigger pump squirters....

[Argess]

It does sound like an acclerator pump issue. Either too much, or not enough. For a start, assume it's not enough.

I assume this is a Holley?

Since it's such a short delay, cheapest easiest way I'd start with, is to change accelerator pump cams. If you don't have a kit, see what happens by moving the cam screw to #2 hole vs #1

Advancing your intial timing can help a lot as well. I"m running 20Deg intial and 38 max, whihc is not unusual for these cars.

Finally, I have been advised, though can't say I tried it, but sometimes the carb woks better with the idle mixture screw set for a slightly rich mixture, maybe up to 1/4 tunr further out

[jhv48]

Things to check:

1. Make sure your secondary squirters are shooting as soon as the secondaries begin to move, if your carb has mechanical secondaries

2. Adjusting the idle air screws slightly rich will ease the transition from idle to primary circuit, but if you are experiencing a slight hesitation upon flooring the throttle, that won't effect it.

3. You are probably experiencing a brief lean condition. Try a lighter accellerator pump spring if using a vac. secondary.

4. You've done everything else that is recommended.

[zrayr]

Previous posts cover all the likely culprits, I can only add has this been an ongoing issue, or did it begin recently ?

Z. Ray

[1985 CCX]

Thank sguys,

Yes = Holley (Terrible Customer Service to Boot )
I did think throttle cam next, the settings are stock.
This has been a problem for years, just never tackled it as it was never a bother under normal driving. Recently, with all the rain, I started to try to remedy.

One note: The primary squirt, even after swapping squirters, is less intense than the secondary.

[Tom Kirkham]

What color accelerator pump cams do you have?
What size squirters do you have?
Which carb? Intake?

You will probably need to buy:
http://www.jegs.com/i/Holley/510/20-12/10002/-1

or better yet:
http://www.jegs.com/i/Holley/510/36-184/10002/-1

You also need to get a wide band O2 sensor...

[Argess]

Not sure if it should be less intense or not, but as you already changed pumps (i.e. new diaphrams) make sure the cam adjustment is correct. At idle position, loosen the long machine screw and lock-nut until clearance is obtained, then tighten back up until all slop just dissapears. You may just this type of linkage problem.

Even switching to hole #2 for the cam, I recommend re-doing the above adjustment procedure. Holley also calls for a clearance check at WOT, but if you do as above, it will undoubtedly pass. Clearance check just makes sure cam doesn't drive accelerator pump to bottom out when throttle is fully open. Hold it at WOT and make sure the accel pump lever (coming out of the pump housing) can still move.

LOL...here I am trying to help and I have similiar issues of my own...how ironic!

[zrayr]

what color is the cam, or what is the part number on the back of it.

while a complete cam tuning kit & wideband set up are nice to have, you can start with the Holley # 20-12 cam kit. If lucky, with a little experimentation, that's all you will need.

Z. Ray

[Argess]

I was playing with pump cams today. Previously I had tried black (min fuel) and then the white (typical cam and a bit more fuel), but it was still lean in cold weather and worked fine in hot weather. So, needed to richen up the shot more. TOday I installed the blue cam in hole #1. Seems to work great so far. The blue cam in #1 gives you most of the shot ealrier on, and also, most of the shot if you just give the pedal a small stab. I'm down to the fractioin of a second delay you have. However if that's all you have now, the blue cam might get rid of even that. Just a thought in case you get a cam kit.

Here's a link to the chart. You need to really look at how much minimum throttle you want to give, then go up the chart vertically to see the total volume of doing this. More hrottle in a light car will not change as much as the engine revs wuickly and airflow will get the mains flowing quickly. Note how the Blue cam has a bigger squirt at a small throttle opening.

http://www.carbdford.com/tech/Holley20PumCams.gif

[Bobcat]

Argess .... if you can find it , try Dave Emanuel`s book ... Holley Carburetors by S - A Design Books . Look on page 51 and you will see your graph , but to my tired old eyes , in a much easier format ( bar graph ) to read . There is also a table giving the volume for every 10 strokes of the pump in both position 1 and 2 vs degrees of throttle opening for the various cams .
This book has been a fantastic source for me ... but don`t know if it`s still in print .

Bob

[patrickt]

Originally Posted by Bobcat

Argess .... if you can find it , try Dave Emanuel`s book ... Holley Carburetors by S - A This book has been a fantastic source for me ... but don`t know if it`s still in print .

Bob

That is indeed a good book. $15 at Amazon.com http://www.amazon.com/Holley-Carbure...1490150&sr=8-1

[Argess]

Thanks Guys,....I already have the book. The problem with the bar graph is it's only applicable for changing your squirt volume for a WOT stomp to the floor.

I find in the Cobra, 1/2 throttle is enough for me in a 2 to 3rd gear run (tires), so I like the graph I linked to. But I must admit, it's a bit diffiuclt to follow some of the lines.

The fact is, I used to run with too much igntion advance. Didn't realize it, but it was a slipped damper. Kept slipping a bit at a time. I kept re-adjusting the timing evfery so often. Eventually detoantion broke a piston.....silly me. Anyway, when the advance was quite advanced, I never got any hesitation, bogging, etc., but I don't know where the timing was then. So now I have it as far as I dare go, 20Deg intial and 38 max. And low and behold, I had some hesitation. It was much worse the lower I went with the initial timing. I suspect a vacuum advance distributor would cure all the trouble, but I can't fit one easily....too big except for the Mallory, and another Mallory is not a good upgrade. Have too modify the drive gear pin and it still has the small cap.

1985 CCX may do well to advance his timing a bit before playing too much with the carb.

[Bobcat]

Argess ... one thing you might look at on your initial/full timing . The guy at 4secondsflat.com makes a set of bushings to replace the MSD dist. bushings . The largest MSD one is an 18 degree . ( 20 degree initial and 18 degree = 18 total ) . He makes a 14 and a 10 degree . I am playing with the 10 degree and have 26 initial and 36 to 37 full at about 2700 rpm . So far , the plugs show no detonation and the low end has cleaned up pretty good . No run on or hard cranking when hot either . I can`t remember ... do you have an MSD distributor ?

Bob

[Argess]

No, a dual point Mallory converted to Pertronix. Bit of a pain to adjust the spring stops to maintain 38 max when I play with advancing the intial timing.

I should get back at it. I did try 28 intial with 38 max and could feel the engine fighting me around 2500 rpm.

We seem to have hijacked this thread, but as it's all related to the original post, I guess it doesn't hurt.

[1985 CCX]

Guys,

Holley #4777-2 650 Double Pumper
Cam = red
#28 Squirters

Maybe a cam kit is in order?

Thanks

[Argess]

Looking at the chart, the red unit doess more or less the same thing at low throttle as the commoon white one. Go Blue. Kit is very cheap.

In your original post, you said you checked the timing. What is your intial advance? Might want to try a few degrees more if you have to wait for cam kit. Keep the rpms down low if you advance timing. Without messing with the dist, you my have too much total during the test.

[zrayr]

Originally Posted by 1985 CCX

Guys,

Holley #4777-2 650 Double Pumper
Cam = red
#28 Squirters

Maybe a cam kit is in order?

Thanks

also keep in mind while some of the cams have more initial action, others start slower, but have relatively enormous output.



it takes some experimentation. I was chasing a too rich phantom that no amount of jet changes could solve. It was all in the acc. pump cam.

Z. Ray