Linkage comments / question
 

Well, I have been working though a acceleration hesitation and I think I am on to something. I have a 2X4 tunnel port set up on a 427 SO. Since getting it back from the builder, it has stumbled at low RPM response and steady driving speed (this little stutter). Well I increased the mixture to run richer to get more gas to the thing below 3000 RMP and that helped, but man...red lights were hell to sit through and just to rich. When I got it to do well moving, idle at a stop light was horrible. Then, I started thinking about the linkage. It is on a progressive linkage, new from the builder, so I thought I would go look at it. It seems like a LOT of travel before the second carb comes in. So until I romp on it, I was running on 2 barrels for a 580HP motor. So, I took the linkage and put a bolt in it to take out the slack of the progression and man did that car wake up. No hesitation. Runs much better. Now a couple of questions. I have to redo the idle mixture on the 2x4. On the idle mixture screws (4 of them on 2 Holleys), what is a good starting point when adjusting them. I have heard all the way in and then out 1.5 turns. Is that correct? Also, do they make different sized link arms to change the actuation of the progression? Is there a kit that I can get to fine tune the progression. I know there is some adjustment on the arm itself, but it is still out of range with it all the way set to the end. Thanks

Buzz

Buzz,
Read this all the way though, understand it, and you will be well rounded on Holleyology:

http://www.bob2000.com/carb.htm

Let's see a photo of each side of the setup you have so we're
all on the same page.

Just off hand, it sounds like you may need to look at your accererator pump adjustment.

I looked in your gallery. Where did you get those hub caps? My friend is looking for a spare one.

Please tell us what the list number of your front and rear carb is.

http://www.clubcobra.com/photopost/d...C04231-med.jpg
http://www.clubcobra.com/photopost/d...C04233-med.jpg


Steve

I had a similiar problem with mine, particularly the subtle "stutter" you mention at cruise speed and also the off idle stumble.

For off idle stumble I finally (due to input from CC members) increased my base timing to 15-18 deg. I was SURE that was to much, but man it really "woke things up" and was a HUGE over all improvement. For the stutter I slowly (several times) increased the main jets (yeah FOUR of them with twin carbs) until the stutter went away. I wound up with 72's. But I STILL had a hesitation on accelleration at speed. So I took a vacuum reading at idle AND at cruise rpm and installed a power valve 1 or 2 points BELOW that vacuum reading. Again I had to try different power valve ratings until I "nailed it". I can actually FEEL the power valves kicking in with just a slight increase in throttle, like going up a hill or passing. Myvacuum was 11" and I think my final PV rating was 9.5.

No stutter, no hesitation! It was all about timing and correct carb settings. The fuel air idle ratio screws didn't seem to help much for the above problems EXCEPT for the idle itself. I'm out about 3/4 turns I'd say. REDUCING the main jet size cleared up the "loading up" problem while setting at a stop light AND the stutter. The PV is really a MAJOR player in the Holly carb.

My linkage opens BOTH primaries at the same time, there is no "progression". The secondaries are vacuum. I played with the "pump shot" but like the idle screws found that they didn't change things "that much". More advance was the real ticket!

advance at idle is 18, all in at 3000 at 38. I thnk the key is getting rid of the "progression". I basically starves your engine until you get the 2nd carb to kick in

Buzz
Good luck.;)

Steve...didn't mean to not respond you you, but just didn't shoot pics just yet. I'll get to it when I can

Buzz

Buzz,
Gotcha :)
Where did you get those knockoff type hubcaps?
Steve

they are the stock earlly SPF cheapo make believe fakies that came on the early SPF cars as the "standard" for wheels. I would like to change over to some real wheels at some point. They look ok, but really that are kinda "cheezy"

Thanks. My friend has them on his Classic Roadsters Cobra. I get a kick out of seeing people get fooled by them. :D

I know where there are some, I think. I year ago, a guy with a Classics came over to me and told me had some if I was interested. I may be able to see if he has any. BTW, you guilted me into taking pics (smiles). I did not get the numbers of of them, didn't take the time to pull it all out. One has the number filed off as well..I remember from looking once before when I had them off. Pics will be in my fold in a minute. I just put a small bole in the slot for the progressive linkage. I did have to file down the top of the arm to get it to duck under the fuel line, ( I know, I need to replace the like,,,,it has cracks...new hose is in the bag in the garage, but right now worried about my squeak and what I am finding in my oil filter right now)! AAARRRGGGHHH


So, check it out

Buzz

Buzz,
For comparison. Our linkage is very similar. Mine has the progressive slot, and the engine does not stumble.
http://www.clubcobra.com/photopost/d...13075carb2.jpg
http://www.clubcobra.com/photopost/d...C04235-med.jpg

Did you steal my car, Steve? (smiles) That looks awful similar....

Buzz

Don't tempt me. I'm not above doing things like that.:cool:

Is your front carb delivering a good squirt of fuel from the accelerator nozzles?

yeah it is...

Are the power valves appropriate for the vacuum your engine produces?