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Discussion Starter · #1 ·
hi my 65 mustang stock motor c 4 box,with flowmaster headers elderbrok performer manifold, electric fan, hooley 600 vac secondary carb, distributor is standard vac and mechanical advance with pertronix. its ran a 15.1 @ 90 mph and is healthy enough im trying to tune a stumble out at around 1500 to 2000 rpm mark when you are cruising then accelerate. ive gone through carb checking vacumn settings and different diaphram springs, accelerate pump etc.
i solved the problem of it pinking i found the vacumn advance was over advancing so adjusted the grub screw inside.
i have tried and been advised on different ways of setting timing these include, setting 8 degress at tick over, setting to 32 at 3000 rpm with vac connected (so this is max it will ever achieve) and the latest way set at 32 again but without vac with theory been when you accelerate vac in carb dissappears so it want over advance unless you rev it at a stand still, also this way occasionally can get it to pink which suggests it will over advance this way. with this setting it has helped flat spot.
need to know which is correct way as im going around in circles.
a friend has also offered me an elderbrok carb how do you rate these to the holley ive already got?
the car is daily driver well untill theres is salt on the road ( good old uk).
thank you in advance.
 

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For timing, factory specs in my manual are 6 deg. initial and the mechanical advance adds 24 deg., at 4,000 RPM. The vacuum advance is listed as adding another 22 deg. at 14 in. of vacuum. First check the mechanical, with vacuum disconnected. You should see a smooth increase in advance as the RPM goes up. Keep increasing the RPM until there is no more increase in timing advance. This should be 32-38 deg. depending on gas octane, compression, etc. Then check advance at 1500-2000, where your problem is. Timing should be about 20-25 deg. without the vacuum connected. The vacuum hose should go on the fitting above the idle screw on the carb, not to manifold vacuum. Also, check how much fuel is coming out the "squirter" in the carb when the throttles are opened. Too small nozzles or plugged nozzles won't allow enough fuel from the accelerator pump, causing a hesitation on initial acceleration. Try something like a #28 or 31 squirter if yours is smaller. Set the RPM at a steady 2000 RPM and slowly close the choke plate by hand, to richen the mixture. If the RPM goes up a lot and the engine sounds smoother, the mixture is too lean-float level, main jets or air bleeds need changing. A slight RPM increase when closing the choke is normal and good, meaning it's not too rich at part-throttle cruise. (Of course, closing the choke too much will drop RPM and flood the engine; just watch for an increase in RPM as the choke is closing). If by chance the secondaries are opening too soon and causing the bog, disconnect them and test.
 

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Discussion Starter · #3 ·
hi thanks for reply.
without vac. connected setting at 34 degrees at 4000 rpm, reducing to tickover then gives 14 degrees advancing, meaning the mechanical advavce is allowing just about 20 degrees advance, it does increase smoothly, with vac advance i can adjust the amount via the grub screw, but with this setting with connected it goes up to 40 but i do realise that once your driving you loose the vacumn, this does help the flat spot but can pink slightly. (obviously with vac connected setting max vac. at 32 then give 8 degrees at tickover flat spot slightly worse)
the squirter is a 31 i have no hesitation from stand still i cured this by going from 28 to the 31, its purely when accelerating from cruising, i do have vac connected to timed spark as you said.
using the choke plate is very good idea i did not think of that.
anymore ideas with timing???
thanks jon.

<font size=-1>[ This Message was edited by: jonnys on 11/20/06 6:01pm ]</font>
 

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Best driveability will be when you have your initial timing plus mechanical time set between 32 and 38 degrees when your mechanical timing is fully advanced--which sounds like 4000rpm. I would recommend setting your timing to 36 degrees @4000 rpm for testing. Do not connect your vacuum advance at anytime during this part of the test.

Drive your car as you wish and observe if the engine pings or acts funny. Climb a hill, pass a car, put-put around for a little while. If it pings at anytime during a normal drive, back it off 2 degrees @4000rpm and retest. Repeat as necessary to eliminate ping. Alternately, if you have no ping at 36 degrees @4000rpm, you could try 38 degrees instead. Really no need to go higher than that.

Once you are satisfied that you have the best driveability with your timing at 4000rpm, then measure your initial timing at idle with the timing light. If it ends up being 14 degrees, that is fine, if it ends up being 6, that is fine too. Note: The actual # doesn't matter if your driveability is good, but it does give you a good reference for future tuneups.

Next it is time for you to hook up the vacuum advance. Do not turn the body of the distributor again, unless you later have a lesser quality petro that causes a ping or otherwise poor driveability.

With the vacuum advance hose installed to ported vacuum (no vacuum at idle), adjust the vacuum advance screw to achieve the best driveability without ping. If you cannot get the ping out with the vacuum advance functioning irregardless of the setting of the screw, you will need to either (A) buy a better octane petro, (B) add a stop that limits the length of travel of the vacuum advance, or (C) just leave the vacuum advance disconnected (and the vacuum hose plugged.)

Leaving it disconnected might lower you gas mileage a little (1-2mpg) but otherwise will not harm your engine nor affect driving performance.

Clear as mud?

P.S. For a performance vehicle, you may want to consider recurving your distributor so that the mechanical advance comes in quicker than 4000, lets say 2500-3000 rpm. Before you consider that, you should first get a firm grasp and understanding of initial, mechanical, vacuum advance by using the tuning methods I illustrated above.

_________________
Dennis

65' STANG, 3160 lbs

393W NA, 2.78 Toploader 4 Spd, 9" 3:70 Posi
Pro Comp Heads, Vic Jr. Intake, 750dp, 236/561 Solid Cam, 9.6CR, 1 3/4" Headers, Lakewood, Subframes, Caltracs




<font size=-1>[ This Message was edited by: dennis111 on 11/20/06 8:02pm ]</font>
 

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Discussion Starter · #5 ·
thanks that has made it very clear i had so many people saying different things was getting confused. full timing is in by 3000 rpm and it only pinks once vac is connected so i will now back the screw out more.
i can now concentrate on curing the flat spot, would a bigger squiter nozzle help this??
 

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Discussion Starter · #6 ·
right then thanks 67 coug and dennis, ive now got timming spot on without vac connected ive got 34 degrees at 3000 rpm and 25 degrees at 2000 where my prob is. it is a lot better just got to drive and restrict vac advance bit more it pinks very occassionaly tiny bit tweaking required there. using the soft yellow diaphram spring also helps bit more, mixture seems about right perhaps ill try bigger squirter.

which carb do you prefer the holleys or elderbrok?

thanks again this has been anoying me for a while its not a major prob i know. perhaps i can get it into the 14's now.
 

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What carb are you running now? Be specific if it is anything but a factory 2 or 4 bbl.

I've always ran a Holley and am partial to it, especially for a car that will see the dragstrip. Some people like the edelbrock and say it is the best for primary street duty. I am not going to get into the debate, so I'll just relate my Holley experience.

The Holley has excellent tuneability and can be at home on both the street and the strip. With your automatic and sounding like you have a basically stock motor, I would recommend one with vacuum secondaries--probably a base 600 cfm. It is a carb that can grow with you as you add more performance mods (if that is your intent.) And of course the Holley is infinitely tuneable and modification parts are readily available from places like Summit Racing.

If you still have a 2bbl manifold and just want a little more performance and flexibility, you could also use a Holley 500cfm 2bbl. Same tuneability, although your mpg could be affected more.

No matter what you run, if you try to run it hard all the time it will like to use the petro. . . . . .
 

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Discussion Starter · #8 ·
its a holley 600 4 barrel vac secondary. on a dual plane elderbrok performer manifold, ive also put diaphram quick change kit on it.
 

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On 2006-11-21 13:56, jonnys wrote:
its a holley 600 4 barrel vac secondary. on a dual plane elderbrok performer manifold, ive also put diaphram quick change kit on it.
OK, good. How fresh is the carb? Does it need rebuilt?


How is the rest of your ignition system? Do you have fresh points, spark plugs and wires installed?

A good book on Holley carbs is recommended.


The wrong secondary spring can be the cause your problem. I would first put the stock or a heavy spring back into the carb's secondary canister and try driving the car, first to see if there is an improvement and secondly to make tuning other stuff easier.

Try one modification at a time. First make sure the accelerator pump fuel shot is steady when you move the accelerator (engine off.) With the accelerator all the way open, you should have about .020 of travel left in diaphram to accelerator pump actuating arm.

You can replace the squirter with a larger one. You also have the option of messing with the accelerator pump cams. Most cams have 2 holes which give different profiles. You can get a kit with several cams, although the stock one (white?) should be all you need to cure your problem.

You can also consider the power valve. Should probably be around a 6.5 for your vehicle. You can determine which one is correct by putting a vacuum gauge on your car and driving around normally. Observe the lowest vacuum level during the cruise (not counting heavy acceleration) and your ideal PV will usually be about 2 sizes less. For example, if normal driving shows a low of about 10 pounds of vacuum, dropping down puts you into the 7-9 PV range.

Experiment with each item until hesitation is gone then start messing with your secondary springs. Systematically go a little lighter until you start to feel the secondaries kick in. If your seat of the pants meter can feel the actual difference, you probably have too light of a spring. The transition should be smooth.

_________________
Dennis

65' STANG, 3160 lbs

393W NA, 2.78 Toploader 4 Spd, 9" 3:70 Posi
Pro Comp Heads, Vic Jr. Intake, 750dp, 236/561 Solid Cam, 9.6CR, 1 3/4" Headers, Lakewood, Subframes, Caltracs



<font size=-1>[ This Message was edited by: dennis111 on 11/22/06 8:25pm ]</font>
 

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Discussion Starter · #10 ·
i have petronix fitted in dizzy i used 8mm morroso leads and fresh plugs.
carb is year old but has not had much use.
i have set accelertor pump and have done nearly all your checks.
it has a 65 power valve and using my motor bike vac guages the lowest reading on cruise was between 13 and 14.
ive found using the black spring causes a real bad stumble but cant really feel secondaries kicking in.
buying holley book think is good idea, wanted to make sure i have ignition set up properly which i have now done as you have described.
plug colour looks good.
 

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Sorry, but I'm kind of tapped out of good ideas tonight. It does sound like you have covered most of the bases.

Hmmm, could you possibly have a vacuum leak--what is your reading at idle? How far out are the idle adjustment screws? I assume you have the stock cam.

Anyone else have some help?
 

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Lots of good advice here...The old method of advancing the timing until it pings and then back until it stops pinging and starts good(doesn't fight against the starter) has always worked pretty good for me....I restored a 66 mustang for my sister last year with a mild 289,pertronix and a 600 holley new out of the box..I had the same problem and I was able to get rid of the stumble by tuning the mixture screws and setting the accelerator pump cam into the other setting....
 

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Discussion Starter · #13 ·
cam is standard. ive set mixture screws via gas anayliser just over 3/4 of turn out. ive got a vacumn of 15 at tickover. the cam on carb is standard one (orange) set on number one so it works sooner, think will give white one a try as dennis suggested.
setting the timing as dennis suggested has deffinatly helped, you are right ive done all the basics was asking in case ive missed something obvious and you have given me a lot more ideas to try, ill but the standard spring back in and alter accelerate pump 1 st.
will keep you informed.
thanks jon. (waiting for sunny days again)


<font size=-1>[ This Message was edited by: jonnys on 11/23/06 5:57pm ]</font>

<font size=-1>[ This Message was edited by: jonnys on 11/23/06 5:58pm ]</font>
 
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