Trying to get the tuning on my Holley 4160 sorted out. I finally rebuilt the thing last weekend and the slant runs much better. Everything was re-set to the specs in the Holley rebuild kit. But I still have an on-throttle bog. Not from a standstill, but when coasting, and getting back on the gas, I get a major bog (can kill the engine in certain situations if you hammer the go pedal) for about 1 second, then it takes off (like a raped ape! ).

Background info:

Vehicle is an '87 D150, approx 3800 lbs.

'87 225 .080 over, 10:1 compression. Offy intake, holley 390 turned 90° (primaries away from head), clifford headers, big valve (Ford 302) head w/ minor porting (mostly cleanup). MSD 6AL ignition. Mild (~.400 lift, 240 dur) hydraulic cam. Base ignition timing is currently 8° BTDC, I do not have a dial back timing light and have not marked up the dampener to check total timing

Holley currently has #51 main jets, a 25 (If memory serves) shooter. Red pump cam--I need to double-check the hole position. And I forgot the powervalve number... I'll see if I can find it; if it is stock I believe it is a 6.5 from what I have found searching the forum. Natural secondary spring. No secondary metering block, just a plate.

This coast-to-on throttle bog is the only drivability issue I have. Plugs are a nice medium tan color. I do have a vacuum gauge hooked up, ad teh bog seems to occur in the 4-6 in-hg range.

Any suggestions? Am I barking up the wrong tree with the secondary springs? Should I be looking at the power valve or pump cam instead?

TIA (you out there DI? )

-S/6

_________________
The "Silver Bullet"
87 Ram D150

One way to make sure it isn't the secondaries is put the "Black" spring in...this will effectively lock out your secondaries (it takes a V-8 a fair amount of rpm to get that one to "open")...

After that you can check your pump cam (sounds like when the throttle is already open there isn't enough cam profile to pump more shot in there to cover the Bog)...

You might try to go up a color on your cam, the pink one has a long duration to it (you still get some gas after 40-60 degrees of throttle shaft rotation, but it's a big shot too...).

The power valve is suppposed to be set jst above your "cruise" vaccuum setting so it kicks in at "passing speed" then goes back to sleep when you go back to cruise... (for me my cruise is about 15" hg so a 13 PV would be nice but they don't make them...so I either go with a 10-9 or if running for mileage, I use a dual stage power valve with gives me partial enrichment at 12" then the rest of the whole wopper at 5").


Remember to make one change at a time and note the difference...

-D.Idiot

I had a similar setup and my 390 liked the PV that comes on the earliest (16?), yellow spring for the secondaries, and a fairly aggressive accelerator pump cam. My jets were somewhere around 55 and 58? I was very surprised that I could use That cobination on a slant, but it worked the best on my engine. I had a 264/440 Isky camshaft and about the same other components you have. Drivability and performance were very good and my milage was about 16mpg's which is about what to be expected from my combination. I never dyno'ed the car though.

Okay, correction: I have the orange pump cam in the #2 position (it sure looked red before! )

I changed the natural spring to the long yellow spring, and the bog is 90% gone. Now I am debating whether I need a different pump cam or to try the short yellow spring.

Two dumb questions:
1) I do not see how to even mount the pump cam in the #1 position, the cam appears to only slide on the throttle shaft one way??? (I am looking at this with the carb mounted, and the linkage is facing the firewall so everything I see at this point is by use of a mirror....so what am I missing?)

2) Where does the white spring fit into the 'lineup'? The instructions that came with the spring kit do not even mention it, saying the short yellow is the lightest spring. The white spring feels lighter, but that doesn't really say much.

BTW-as I read in many previous searched posts--that quick change secondary spring kit is worth every penny.
-S/6

Here is the Holley color code for their secondary springs.
White - Lightest
Yellow (Short Spring)
Yellow
Purple
Plain (Steel grey)
Brown
Black - Heaviest

This info came with the spring kit:

"If there is a bog or hesitation when the secondaries open, the spring tension is too light, go to the next heavier spring".

This is sometimes true. I think you also need larger jets; 56 pri and 58 secondary. Also, I think it would be worth trying a different power valve. Mine ran like a striped a$$ ape with the previously mentioned setup.

Andyz--do you by chance remember which color pump cam you were using?

Since it only takes 2-3 minutes with the quick change kit, I'll probably swap in the purple spring this evening to see what happens (I swapped in the long yellow last night).

Thanks for the info on the white spring. The instructions in my spring kit seemed to 'forget' it was there!

I'm hesitant to up the main jet size, as my plug coloring is good right now. In fact, I would almost go so far as to say 3, 4, and 5 are a little rich (darker tan/brown than 1,2 and 6)

I am also hesitant to up my PV as currently at idle in gear, I only pull about 8-9 in-hg on the vacuum gauge (13-14 in-hg at idle in park---I have searched for vacuum leaks to no avail.)

My last oddety is a slight idle surge in gear. It will idle happily along at 9 in-hg, then after approx 10-15 seconds drop to 8, and surge bewteen 7 and 9 in-hg. If I apply the parking brake so the truck does not move in drive, when I apply the brakes I get an immediate 2" rise in vacuum, then it drops off 3-4", then settles in around 8-9 and will begine the surge as described above. Bad power brake booster? The power brakes still work fine, and I still get 1-2 good power assists from the brakes with the engine off so it seems to be holding vacuum. ??? The vacuum line itself is good (I replaced it last week for grins). I should probably note, this idle surge was so bad before I rebuilt the carb that it would kill the engine after idling about 30 seconds in gear (it surged from 10 to eventually 0 in-hg before the rebuild)

I double checked the float levels last night, and they are right on; just barely dribbling from the sight plugs while the engine idles (in park).

The wonders of tuning a holley....

_________________
The "Silver Bullet"
87 Ram D150

You say when you apply the brakes it rises then loses vacc... is your power brake booster about to give up the ghost?


In the mean time if the yellow tall spring is taking away the bog, it's opening up the secondaries sooner giving you more gas...I would suggest going back to the plain spring and trying the Pink pump cam in the #1 position (same shot as orange in #2, but metered over a longer profile). I would hesitate to up your jets if your cruise plug color is still tan, if you have surging though you might stick in a set of 53's and see if that does the trick.....

Eventually you will want to splurge for the Holley 34-6 secondary metering block so you can change your secondary jetting, the plate is good for small car slants, but needs help on hi-po/heavy vehicle slants.

-D.Idiot

Thanks for the advice DI . If there is one thing I have seen from reading other posts here, it is don't argue with your Holley tuning tips, just do it!

No high-speed/cruising surging. She's solid as a rock at any cruising speed. Brake booster--I simply don't know. It is the original booster, I suppose after nearly 20 years of service it could finally be letting go. I will dig through my FSM and see how to diagnose it.

I have been searching for a pump cam kit with little luck (all 10+ parts stores I have been to are out of them ). I'll probably just have to order one. Looks like I may as well go for that secondary metering block as well, thanks for the P/N!.

-S/6

Edit: One last question, what size jets would you recommend for the secondaries once I get the metering block?? If I use the relative jet size difference from andy's setup that would put me at a 54-55, good place to start?

_________________
The "Silver Bullet"
87 Ram D150

It's not a matter of just doing what I say (hey I'm human I make mistakes too, and sometimes guys don't tell me everything that's going on), it's just getting the correct info so I can get you a close answer based on the problem and seeing if we can get a solution going.

Each setup is kind of different, I tend to run two jet sizes over in the secondaries as I like my cruise to be "on target" then when the secondaries open up I need the "Rich" setting to get the power then go back to "normal" during cruise...


will check in tomorrow, this swingshift stuff is fun, but not helpful...


-D.Idiot

Thanks agian DI. I am going to attempt to round up the above parts tonight, but I will probably need to order them. And I am out of town wednesday through next monday, so if it doesn't happen tonight, I won't be able to tinker further until early next week.

-S/6

I had a pink cam I am pretty sure.

Well, I had a chance to get some tinkering and tuning done this weekend.

I ended up with the blue accelerator pump cam in the #2 position, and the purple secondary spring. Throttle response is now instantaneous at any speed, and the transition when the secondaries open is almost undetectable. Basically, drivability is excellent, but I still have one nagging problem: surging while at idle in gear. It idles at a steady 14 in-Hg in park or neutral. In gear, idle drops to 10 in-Hg, slowly lowers to 9 in-Hg, then begins surging between 5 in-Hg and 9 in-Hg (those numbers being the absolute peaks of the surges, typically between 6-8 in-Hg). No amount of idle adjustment has cured this problem, and the idle screws are responsive. I believe I eliminated the brake bosster as a problem, as the idle surging in gear occurs if I set the E-brake and do not touch the brakes... Any ideas?

Second question. What is the order of Holley pump cams from lightest to heaviest? Holley's website says White, Blue, Red, Orange, Black, Green, Pink, Brown. The pink cam made my slant fall flat on its face upon acceleration, even in neutral. The pink cam also looked much smaller in profile than the orange cam. I was also under the impression the Black cam could only be used with the 50 cc accelerator pump, and it would cause damage to the 30 cc pump Anyway, the cam order listed above does not look correct when I look at all of the pump cams in the kit I bought.

Anyway, my eventual choice to go to the Blue cam was based on comparing the cam profiles of the various cams, and the blue cam looked 'fatter' all-around than the orange I had originally, with a more aggressive throttle tip-in (so it appeared). Is the blue cam in fact lighter than the orange I had on there? I know my slant is very happy with the blue in #2.

Sorry for the long-winded post.

-S/6

PS The secondary metering block kit is still on order.

Don't know why the vacuum is so low at idle, but from the Hg range you gave, I'd say the power valve is turning on and off and you're getting into some rich/lean positive feedback loop that once it starts, it just keeps itself going...........

Either change the power valve to force the carb rich or lean, or temporarily disable the power valve on the primary to isolate the problem (and prove my theory right or wrong)..

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Don't over look the distributor...
If the mechanical advance springs get set real light, that will cause the surging you discribed. Look at the timing with a light, is it steady at low idle speeds?
DD

I will check the timing. I admit is has been a while since I put the light on it.

The PV is a 6.5, so I guess it s also possible the vacuum fluctuations are opening/closing the power circuit when the surge is large enough.

I am very happy with how my slant is performing other than the idle issue though. (Where's that dancing banana smiley when you need it? )