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tuning my first holley double pumper

7K views 44 replies 10 participants last post by  spinn 
#1 ·
so as you ready the title i have a holley 4160 double pumper 650 on my SBC 400.
it is balanced and has edelbrock aluminum heads and speed pro pistons running about 10.5:1.
dual plane performer rpm air gap intake. headers and 3.73 gears.
it has a crane mutha thumper cam in it.
it runs 12 inhg at idle and about 5-6 inhg in gear.

so i changed the power valve to a 3.5

should i do any jetting? my car always smells rich.

i am at 580 ft above sea level and really only drive it in the summer.

it has 67 jets in the front 73 in the back. same as stock.

holley tech info says that factory jets should be good from 0- 2000 ft average of 70 degrees.

any thoughts from those that are expert carb tuners? i have read everything that i can get my hands on for holley tuning.

appreciate the pointers.

Jon
 
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#2 ·
Jetting has nothing to do with smelling rich at idle, jets aren't doing a thing at idle.

You would have to change idle feed restricters in the metering block, and idle air bleeds in the main body to get rid of the richness at idle, or just live with it.

If you have an HP carb, these things may be easily replaceable, but the standard DP's they are a fixed pressed in orifice.

DP's come set up rich at idle as they are expecting it to be put on a competition engine with a race cam and high compression that need that richness at low rpm, and not a street engine.

I don't know what your initial and total ignition timing is, but high initial timing will allow you to close the idle speed screw and idle mixture screws down some, and eliminate some of that over-richness.....something like 16-20° initial timing, with 34-36° total mechanical advance.

That Thumpr cam isn't helping the rich stink at all, it is contributing to it.
 
#3 ·
As Erik says, you're going to always have at least some fumes at idle with that cam (cams with alot of overlap). But also as Erik says, double pumpers have richer idle circuits. Turning the screws in reduces the amount of mixture at idle but doesn't really make it leaner. (Well sort of does).

The idle-feed restrictions in double pumper metering blocks are larger vs a vacuum secondary piece. And.....the PVCR (power valve channel restricions) are usually SMALLER in the double, cause they anticipate a race motor using bigger jets.
If you have a vacuum secondary primary metering block around maybe try it. The idle air bleeds of the double pumper body might not be in the range for it or just might be. You can play around with it though (again as Eric says) with the air bleed mods. If you keep your metering block and try just drilling the idle air bleeds to lean it, go a tiny "bit" at a time....it ain't hard to get it out of whack.
 
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#5 ·
yes sorry it is a comp cam.

i have a mallory distributor with vaccum advance straight to the intake not ported vaccum to get more vaccum at idle. as i said i get 12 inhg at idle and 5-6 inhg in gear. mallory was pretty much straigh out of box as far as advance curve.
 
#8 ·
Exactly what Fbird said, you can buy whatever Carb you want, it won't fix anything. As a victim of the Thmpr line of cams I know first hand, get the timing either locked at 36* or a very short 10* curve, 26* initial, 36* total... I found it better with full manifold vacuum advance as opposed to ported, it cleaned up the idle beautifully. Every combo will be different tho.
 
#10 ·
. How does it drive? 67 primary and 73 secondary sounds like small jets for a 400 with low vacuum cam... I would think something more like 70-76 primary and 76-80 secondary...

. May want to pick up a jet kit from Holley or Mopar or borrow one... I would lend you mine if you were close by... I let my friends borrow it, then they just replace the jets sizes in the kit that they end up using for their final tune...
 
#12 ·
F'bird is right about the timing however in a street car I'd really hesitate to have no advance curve- I'd go 25 or so at idle with it going up to 34-36. This gives you a little protection at low rpmlugging which may happen unintentionally UNLESS you have a 3000+ stall. Then I'd just lock it as he prescribed.

That will fix a lot of your problem. If you have an auto trans though buying a dp carb was likely a mistake. A vac secondary carb works better on the street, with a dp you end up having to run small pump cams that net you the same volume as a single accelerator pump would put out on a vac secondary carb. DP carbs have a place on the track but this sounds like a street carb.
 
#13 ·
well timing was set at 25 degrees and the mech advance will add 24 degrees.

bad news is there is not a way to lock or even limit the mech advance on this unit per mallory tech support. unless i want to drill and tap it somewhere.

i am strongly considering changing this cam. i think it is just too much for street use.

i tried adjusting the idle bleeds but it really didnt help vac reading.

i am pretty agrevated with it at the moment.
 
#15 · (Edited)
You do not want 50 mechanical.

It you twisted it to 25 for just the idle, did it clean up?

FBird is not wrong about the locked timing, with that type of cam.

Do not change the cam, enjoy it. You should eventually get it straight. If the compression is there it will be fine. It might only make 12" of vacuum people work with less.
 
#17 ·
I just want to make sure I am hearing this correctly...we are recommending to a member to lock the base timing at 36 degrees initial on a 10.5:1 compression street engine running on maximum 92 octane fuel?

Not sure how many of those reading this thread have tried this but all I have ever seen from this scenario is a detonating overheating mess in traffic with any kind of load.

Might work with race fuel but it sure doesn't work with pump gas and I've tried this with big and small overlap cams and everything from dual carb tunnel rams with 300 advertised duration cams and narrow overlaps dow to 252 duration towing cams, maybe fine for a drag car on race fuel...but thats it.

The general recommendation is 12-16 degrees initial and 34-38 total all in by 3000-3600 rpm...why? Because thats what works! You can add some vacuum advance on top of that but at higher compression you may only be able to add 10-12 degrees at cruise.

Where is this recommendation coming from, I've never been able to make this work on the street. Maybe there is some magical formula I am missing, the last engine I tried this on was 10.5:1 Ford 351W with ported 69 heads and a 290 advertised duration comp cam with 110 LSA, running even 28 degrees initial locked timing it was horrible, more timing only made it detonate with any amount of load or throttle and no starter I tried would start it without backfiring even with a kill switch start procedure.

School me, I'm willing to learn. :cool:
 
#18 ·
.
. Are you running power brakes? Since you haven't mentioned them, I assume not...

. This 235/249 cam with narrow 107 LSA requires a bit of extremes in ignition timing... as the guys are saying...

. To get around rich smell, exhausts out under back bumper are best solution... don't use an open crankcase vent tube, run it into the air cleaner... in the beginning, nobody bought a thumping cam for the sound, it was just an undesirable artifact of a big cam for more big power... lopey, dirty, crappy idle... then kids wanted to copy the sound...

. A higher stall converter will allow higher, smoother idling with more vacuum...

. Need to take a reading of your steady speed cruising vacuum and see if power valve is lower than that so it stays closed while cruising...
 
#22 ·
I would do some healthy experimentation. Try the different timing curves, play with the jets, whatever secondary adjustments you can make, etc. See what does what. Live dangerously, raise those floats, turn that screw, flip that switch...NOT THAT ONE! ...

Get to know when things like timing is retarded or advanced. VERIFY your TDC.

Get to know when it is lean, or rich. You know what rich smells like , how about lean? You know what signs to look for? Plugs , exhaust, carb throat, etc.

Most power or lack of complaints are because the thing is lean or not enough timing.

Adjust your own valves(running). That is like fine tuning your cam at the very end of the combo completion.

Go to these forums and share your story. You get some fresh perspectives all the time. I'm not going to think any different of anyone, one way or the other.
 
#24 ·
your post above is how I do it too. Another reason I would be against locked out timing,and it does depend on the engine,is a standard transmission,light to moderate throttle say around 1700-2000 rpm with locked out timing might rattle. The 10 or 12º buffer might be beneficial.
And as I so annoying harp,not all cars are drag cars, though I assure you my cars accelerates as well as any street car that occasionally goes to the drags. I just have my car geared for its purpose(nothing to do with cam specs)lol
 
#27 ·
This little buffer zone is very important IMO on real "street cars". If you only take it down the interstate at 3500 rpm to get to the track- that's not full street duty. driving through the suburbs during rush hour will not take kindly to locked out timing, a lot of "off idle" driving then and it will bite you in the ***. BUT that is also to say you should be running 12 initial either. If its a big cam and has some gear to it with decent fuel then 20+ initial timing should not seem unusual.

THERE IS NOT A ONE SIZE FITS ALL ANSWER. And while locked timing is not the best solution it can work pretty well in a lot of cases but NOT ALL. As with so many other things- it depends.
 
#25 ·
Well heres the thing.

If your running a modified advance curve of course the timing will be at 20-28 degrees once the engine is running at speed plus whatever vacuum your going to get.

My point is, all your basically doing is eliminating a feature of the ignition system that makes the vehicle easier to start for the sake of not having to recurve the distributor.

I get it...its easier...but its not better per se. Especially from a starter and kickback point of view not to mention the possibility of a carb backfire without a kill switch wired in to prevent ignition before the engine is rotating at full speed.

I simply don't see the need for this when a simple recurve of the distributor results in an easier starting and cooler running engine in traffic...and those little springs are what $5?

I have never seen this scenario work better than a recurved distributor especially from a convenience and driveability point of view...particularly when compression is close to max for pump gas.

I think its incorrect to recommend a locked distributor as a solution to every single members issue simply because its easy to do, I know I am not alone in this way of thinking.

With a standard trans or really loose converter plus only drag strip usage it makes sense...one less thing to affect timing and an easier to dial in at the track from simplicity.

But lets face it, thats a really narrow view of the hobby. Personally I prefer the get in and turn the key and start with an 800-900 rpm idle that can sit in traffic without getting hot or having issues with hot restarts after a short heat soak.

These ignition features were developed for these reasons once overhead valve engines were the norm and the flathead engine was no longer standard equipment.

If I were the OP I would drill and tap the centrifugal advance mechanism for a setscrew to lock out the advance at cranking speed and time the engine for 12-16 degrees while cranking by grounding the high tension wire. Then remove the setscrew and recurve the distributor to suit the requirements of the engine and the stop watch and the plug readings to avoid detonation which you can only see and not hear on a loaded high gear roll on.

Yea its more complicated but it works and you don't need to resort to kill switches and deal with all the other issues created by locking out the distrib.

I think I will create a seperate thread where this can be debated and discussed, sorry to hijack your thread OP...but this locked distrib issue has become a mantra and in my opinion its not always the best solution.
 
#29 ·
a lot of misunderstood misinformation in that post, so I went though it point by point and came up with the proper adjustment:

DO NOT add vacuum timing into mechanical to get total- EVER.

You are recurving a distributor- the entire curve, not just the advance rate. Initial and total advance are also factored in along with the rate.

Its not “easier” its actually what you do and then some- so harder or more time consuming (not that hard though) and it is BETTER.

You utilize the spring and weight kit in addition to an advance limiter.

Again, this is a RECURVED distributor- it goes beyond just swapping springs though.

Locking it is NOT the best solution EVER, but it can be a very workable solution.

A standard trans can still operate at low rpm on the street, as will many “loose coverters” depending on how they are built.

More initial timing REDUCES the engine and exhaust temperature at idle when you run a big cam.

Still using the same features, just properly using them.

Normally the advance mechanism does NOT provide any advance during cranking- unless you remove the springs or have a lot of slop.

A “kill switch” is not an issue, it’s a little toggle or button switch that you flip when you crank the car- not the end of the world.
A locked distributor is NEVER the best solution but it can be a very workable solution and is often better than your 12-16 degrees initial with light springs solution.
 
#26 · (Edited)
4Jaw that is how I get it to run nice with the most power, lock it out. The Ecurve also has a retard built into the lockout. Win win.

You would use a starter retard system for the start of coarse. And still use the vacuum advance in situations using it.

Most people building with mild camshafts (in my mind .400-.480 lift flat)would still use a 2800-3000+ stall , for driving around. That is to get a modern launch and retain all driveability. Consider it part of the basic muscle car chassis package. Your econobox or minivan probably has a 2500+ stall factory.

The old style stock stall is useless in a performance application.

I don't mean to jump to topic to stalls, but it has to do with the discussion.
 
#28 ·
I would however use locked out timing where someone bought one of those stupid 300º plus advertised duration flat tappet cams in an engine with lower compression than ideal.Its a bandage for poor match of parts and it does work. Of course the same engine with a solid flat tappet cam would idle better,make more power and not need the extra help.BUTT,that 300º voodoomagicmotherthumping hydraulic flat tappet cam sounds soooooooo nasty.!.!
 
#30 ·
well let me show your the distributor that i am using and see if anyone has any ideas on how to limit this advance.

the distributor i have is the mallory 85 series. the mechanical advance is right on to under the rotor cap.



i am concerned about locked timing as in reality this car will probably never go to a track. and if i go above 25 degrees then it wont crank, and i have a gear reduction starter.

i really dont want to have to run a ignition disconnect switch if i dont have to.

4 jaw can you clarify what you were saying?
 

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#31 ·
No, it is not the BEST solution. A proper curve that fits is best. My position is that it can be done and works.

If you wanted to get to a patent 36 total quickly, you could lock it to the proper total and run it to see if you liked the result. Then design your curve accordingly for the hot start.

Search for the HEI picture that show you how to lock the plate. Its on the 6 O 'clock pictured arm.
 
#34 ·
OP you ask me to clarify, all I can say is getting a timing curve dialed in can be time consuming there is no one size fits all answer.

I can recommend setting up a distributor on the bench with an electrical drill and optical tach to dial in the centrifugal if your not going to lock it, its safer than sticking your head under the hood at higher rpm with a timing light trying to see timing tape marks. Remember the distributor runs at half engine rpm...1800 distrib rpm equals 3600 engine rpm.

Lots of good articles on the web on how to do it and recommendations as well, some people prefer ported to manifold vacuum and vise versa for the vacuum advance...manifold vacuum advance can add advance at idle to lower coolant temps and pull back as load is added which can be handy for heavy or tall geared cars with tight converters.

Gofastforless website has some recommendations that work well for street cars, electronic modules for retard and complete control of the timing curve are popular as well.

Distributor advance

In all cases I suggest disregarding what anyone might say and understand what the purpose of these timing methodologies are for yourself...they exist entirely to light the mixture at the correct time so peak cylinder pressure occurs just after TDC and that pressure point changes with rpm and load...this is a known fact.

Thats all its for, and I suggest that a locked timing curve does not accomplish this at all rpm and loads a street engine encounters...hence my views on the subject.
 
#35 ·
I once had the comp cam big mutha thumpr hydraulic roller cam and let me say that thing was a pain to try to tune around for it to be streetable and I had at the time a quick fuel q series carb double pumper carb which is the same as the holley HP brand but stupid me I sold it but that's another story.

I had a issue with not being able to keep it running in gear and I have a automatic turbo 350 with a 3000 to 3500 rpm rated range stall and 3.73 rear gears in a 86 s10. I spent countless hours and days trying to tune this thing and got to the point that I was ripping my hair out. I got it because I liked the sound and I fell for there marketing scheme in my opinion.

So after doing my homework and learning the hard way its better to build for it to run good more then that rumpty rump sound. I swapped to a smaller Lunati Voodoo Hydraulic roller 282/290/231/239 @ 50 535/550 lift and couldn't be happier. It still has a nice rump at idle but twice the vacuum and also makes my engine run a heck of a lot better and stronger and still fully streetable and was easier to tune everything.

You can make it work but the more overlap a cam has the more picky everything gets and they all have to work in hand from timing, to carb and cylinder heads and compression etc. Trust me I have made a lot of mismatch combinations over the years. My build is not perfect but close.

I have a holley 04777 650 double pumper like you have on yours and mine from stock was not rich enough on the idle circuit to keep my truck running when put into gear with out it stalling even with the right timing curve. I ended up having to open the primary blades to much exposing to much transfer slot on the front while while if I had the rears open too much I could not get the idle down while also having the front correct in relation to the transfer slot and getting a nice clean idle. It would run pig rich because of this.

I swapped out my stock metering blocks with a pair of quick fuel billet blocks and compared them to the stock blocks for sizing of everything etc and adjusted and tuned the blocks to what my engine liked as far as idle feed restrictions goes and also for jetting.

After it was all said and done with my 650 double pumper it idles at a nice and easy 1000 rpm and drops into gear at about 800 rpm and the idle is nice and clean and crisp and has great throttle response and I get 19 mpg and I jetted down to 65 front and 72 rear and it runs excellent with a nice set of tan looking plugs. I don't have a 02 censor setup yet to get the perfect tune but those cams have way more overlap then the comp xtreme energy line and comp cams says

"Applying a camshaft design originally created for sports car endurance racing, they incorporate early exhaust valve opening, long exhaust duration, and a generous amount of intake and exhaust overlap. Best of all, Thumprs will not negatively impact power output or streetability".

I disagree on that but that can be argued. Even the smallest thumpr one is not small by any means and needs a lot tuning involved.
 
#36 · (Edited)
You know Fbird I will never be the expert tuner like you but yeah I did not do it right the first time because of lack of knowledge and ignorance on my part. On my recent build I had everything else in place with plenty of timing with recommended amounts in the 20 plus initial range and limited mechanical travel even before touching my 650 double pumper.

I am not going to argue with you in what you know as I will never know what you do but I know enough not to mess up like before and butcher things. I am also not the guy who just adjusts his idle mixture screws and idle and calls it a day.

I do my homework.Problem is and when it comes to hotrodding there is always going to be differences in certain things. Locked out timing or limited timing etc. If you did not mean anything offensive then I apologize for my comment. But I do thank you and others like your for sharing your experience and knowledge as without it I would not have gotten this far as for many others.
 
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