Sluggish take off power

[1969_Mach1 333]

I was able to close the gap on the primary transition slot by backing off the choke fast idle screw. Actually I took that screw off because as much as I had it turned out, it was hitting the secondary vacuum arm. The primary transition slot exposure did not disappear, but I was able to get it closed to with in 0.15, so now I can open both Prim & Sec transitions slots to 0.30.

 

I have read numerous times to have the Sec transition slot exposed no more than a perfect square or 0.20, why use 0,30?

 

On this Carb there is a screw on top of the dash pot for Vac Sec, called Secondary Adjustment.  The screw is turned out a 1/2 to Quickfuel specs. If turned more in the Secondaries will kick in sooner. As in my case with Cleveland heads, should I just leave it alone or turn it in a 1/4?

 

Thanks!

 

For transfer slot exposure below the throttle plates.  I have read numbers of 0.020" to 0.040", and in the middle of 0.030".  If you can get the primary side adjusted with the secondary side at 0.020, then that is fine.  The reason for some transfer slot exposure below the throttle plate at idle is to eliminate any delay in the transfer circuit start up when the throttle is slowly opened.  If too much is exposed at idle, as you slowly open the throttle, there is potential to completely exhausting (using up) the transfer circuit before the main circuit starts.  In this case a lag, or surge, or laziness, can be felt during slow acceleration.

 

I am not too familiar with adjusting a vacuum secondary.  But you might be on to something.  I know if they open too fast the motor will feel lazy until the air speed through the secondaries is fast enough to draw fuel out of the main circuit.  I'd be a little careful with that adjustment.  If they really open too fast you can get a lean backfire out the carb when they open.  If you want to tinker with that adjustment I think I would first adjust it to slow down the secondary opening and see how the engine responds.  If it's worse, then try going in the other direction.

 

Do you know what type of boosters are in that carburetor, down leg, annular, straight leg?  Those cannot be changes without overpriced special tools.  I am just curious, there are benefits and drawbacks to each.  For example, regarding sensitivity to air flow and flowing fuel at lower RPM (air speeds), annular are most sensitive, straight leg are second, and down leg are least.

 

 

I am not familiar with the cam requirements of a Cleveland.  If it were a Windsor, it's more than mild but not too aggressive.  I've used custom grinds in the past, some good, some not.  Many people are happy with custom grind cams.  I've resolved to off the shelf cams for the simple reason they have also been developed using some R and D testing and are not just computer designed.  Off the shelf cams might leave a few HP on the table but I'll sacrifice that for more drivability.  Lot's of lift is fine for performance, but it is harder on valve train components.

[prayers1 153]

It has Annular boosters

 

I'm gonna try it today as you suggested with both Transition Slots (TS) approx 0.30. Pull the mixture screw out to 1 full turn and see what happens.

 

My initial complaint was an off idle boog, If you recall I can only go 3/4's out on mixture and my Prim TS was at least an 1/8 exposed.

Without knowing what was causing that, I thought I was running too rich (strong exhaust smell) so I changed my idle air bleeds  from 70-74 and Prim from 68-70.  Smaller makes it run richer, less air into the system.

 

I'll see how it runs with the new TS setting, I might have to got back to factor air bled settings.

I already have my initial at 16, so I can't go up in timing to get more idle rpms.  With the primary throttle plates closed to get approx 0.30,TS I hope I'll have enough to allow it to run and adjust the mixture. If not I'll record how many turns on the Prim idle screw I have to go.

 

Thanks for checking up on things!

[Mach1 Driver 560]

John, you might want to read this about timing:

https://www.fordmuscle.com/archives/2000/03/timing/

 

The above states that the preferred vacuum source is timed, and it was developed to optimize fuel economy and reduce emissions. That's why barnett468 always says to disconnect it, plug the line and leave it that way. I've seen his timing method several times on this site- try "Another stalling/acceleration issue", post #4. 

[prayers1 153]

Mach1 Driver - Thank you for forwarding that web page "Timing is everything" It is a good read and has a ton of helpful information.

I do not have vacuum advance on a on my dist.

 

1969_Mach1- I bolted everything up today and kept Sec TS around 0.30.  By keeping my Idle speed screw set to a 1/2 turn puts me around 0.30.

 

I had all 4 A/F screws at 1 full turn, the car started up and idled around 700 to my surprise. I let it warm up and tried to increase the rpms with just the A/F screws, hoping I can richen it up, but that didn't help much, I had to raise the rpms w/ the idle screw to around 850.

 

I hooked up my Vac gauge and Timing light w/ rpms, I couldn't raise the A/F but had to lower it around 3/4 of a turn, I tried all different ways for about 5-10 min, the rpms kept jumping around.

 

I was able to raise my Vac by a 1/2, it is now 12 1/2  and my idle speed screw is now set at 3/4 of a turn or approx 0.40.

 

I did a quick drive around the block and felt a difinite improvement in off idle response, it's not that neck snapping feeling but the Bog is much limited. I believe there is more tweaking to be done.

 

1969_Mach1- Thanks for all of your help! I now have a better understanding of the transition slot & carb set up.

[1969_Mach1 333]

Happy to help.  Basically as you open the throttle under normal driving, the job of the transition circuit is to provide fuel to the motor in that range after the idle circuit is exhausted and before and the main circuit starts up.  But the transition circuit need to be initialized at idle and then not be exhausted before the main circuit starts up to provide a seamless operation.

 

Nothing wrong with 3/4 turn off seat for the 4 idle A/F mixture screws.  My Holley with 4 idle A/F mixture screws always end up around there.  One last thing to double check after getting the idle adjustments ironed out is the accelerator pump linkage adjustment.  In the idle position there should be no play in the linkage.  Any play in the linkage will delay the accelerator pump.  Then at wide open throttle you should still be able to move the accelerator pump arm a little more with your finger.  This check insures the accelerator pump diaphragm is not bottomed out at wide open throttle.  Obviously do the wide open check with the engine off or with the carb off the engine.

 

If you have time, do some research on the different types of boosters (some call them booster venturi) used in Holley type carburetors, down leg, straight leg, annular, truck type, and I think a couple more.  The benefits and drawbacks of each type.  It's good info to be aware of when selecting a carb.

 

I think also looking at some timing adjustments like Mach1 Driver suggested might be helpful as well.

[prayers1 153]

I have messed with the timing curve more than I can remember. Right now Initial is 16, Mech 21 all in at 37. Clevelands can take a lot of initial.

 

I'm trying to match my curve with the stall speed of 2600 rpms. A person who runs a Cleveland and same Converter said this:

 

"I've run that converter and it's pretty dern tight. More initial would help with street manners/vacuum. If it were mine I'd try 18 initial 32 total and start tuning from there. Since you have an AOD and 3.55's (I now have 4:11's) be careful with the advance curve. You don't want it coming in super fast as it will be easy to lug the engine down with that combo."

 

In my opening statement I enclosed a copy of the MSD Advance Curve choices, I am set now with Graph (D) using the BLUE Stop bushing & (2) blue springs @ 21* all in at 2800 rpm's.

 

I was told to have it all in by 2500 rpms, therefore I was thinking of changing to the BLACK Stop Bushing which will get Mech at 17* all in at 2500 rpm's = Total 33*.

OR

Use Chart (E) and change to a Silver & Blue Spring and keep the BLUE Stop Bushing, this would get me 21* all in at 2500 rpm's = Total 37*.

 

Which do you think best fits my application?

 

[larryc94 38]

The last combo,  also on a C you want at least 36* total

 

I realize you had good people pick your cam and on paper it should work well for blasting away from light.  Your stall is 2600 rpm and you say it start flying at 2000 rpm.  But the problem is you can't drive like that all the time.

 

You need to pull away from a light some what normally and build power off idle and not wait to hit 2000 rpm build power you feel.

 

Some times there is a communication break down of what your asking for and you expectations. These are street driven cars that are going to operate majority of the time idle to 3000-4000 rpm

 

I'm on my second cam, the first one had too much overlap.  You could here the reversion when the air cleaner was off and you rev'd the engine.  It was lazy down low, poor throttle response ect .  C cams need less overlap and at least 114 LSA.

 

My sec cam has less overlap wider LSA but more duration and greater lift and is some much more responsive than my first

 

I think also it's harder dealing with an auto, it's less forgiving.  A stick I let the clutch out and at a blink of an eye I hit 3k.  2.95 1st  3.70 rear 25.8 tires

 

 

Larry

[larryc94 38]

The last combo,  also on a C you want at least 36* total

 

I realize you had good people pick your cam and on paper it should work well for blasting away from light.  Your stall is 2600 rpm and you say it start flying at 2000 rpm.  But the problem is you can't drive like that all the time.

 

You need to pull away from a light some what normally and build power off idle and not wait to hit 2000 rpm build power you feel.

 

Some times there is a communication break down of what your asking for and you expectations. These are street driven cars that are going to operate majority of the time idle to 3000-4000 rpm

 

I'm on my second cam, the first one had too much overlap.  You could here the reversion when the air cleaner was off and you rev'd the engine.  It was lazy down low, poor throttle response ect .  C cams need less overlap and at least 114 LSA.

 

My sec cam has less overlap wider LSA but more duration and greater lift and is so much more responsive than my first

 

I think also it's harder dealing with an auto, it's less forgiving.  A stick I let the clutch out and at a blink of an eye I hit 3k.  2.95 1st  3.70 rear 25.8 tires

 

 

Larry

[1969_Mach1 333]

It has Annular boosters

 

I'm gonna try it today as you suggested with both Transition Slots (TS) approx 0.30. Pull the mixture screw out to 1 full turn and see what happens.

 

My initial complaint was an off idle boog, If you recall I can only go 3/4's out on mixture and my Prim TS was at least an 1/8 exposed.

Without knowing what was causing that, I thought I was running too rich (strong exhaust smell) so I changed my idle air bleeds  from 70-74 and Prim from 68-70.  Smaller makes it run richer, less air into the system.

 

I'll see how it runs with the new TS setting, I might have to got back to factor air bled settings.

I already have my initial at 16, so I can't go up in timing to get more idle rpms.  With the primary throttle plates closed to get approx 0.30,TS I hope I'll have enough to allow it to run and adjust the mixture. If not I'll record how many turns on the Prim idle screw I have to go.

 

Thanks for checking up on things!

 

Browsing through this post, I looked at some pictures of that carb, it looks to have down leg boosters instead of annular.  Maybe it's offered both ways, I didn't see any photos or read descriptions of annular boosters.

 

Also, many times a bog which feels like the motor is too rich is actually caused by a lean condition.  I have had instances with down leg booster carbs, where the main circuits are not starting soon enough.  The mixture goes lean for a brief period and the motor kind of lays over, or bog's, until the main circuit starts flowing fuel.  The good and bad of down leg boosters in a nutshell:  Good, least restrictive to air flow compared to other booster types, thus, maximizing air flow through the carb.  Bad:  least sensitive compared to other types, meaning it takes higher air speeds, thus higher RPM's, for them to start flowing fuel.  Intake manifolds with large plenum volumes and camshafts will also contribute to this condition.  I'm not trying to encourage you to replace the carb or other parts.  Just some info.  I'd be curious, if you had access to a Holley or QFT carb with straight leg or annular boosters, if all your "bog" issues would go away.  I have an inclination they would.

[prayers1 153]

Wasn't able to take the car on a test drive today. It was easy to change springs, so I went with the Silver & Blue and keeping the same Blue stop bushing.

This should give me a quicker curve all in by 2500 rpms.

This will follow Graph (E) on the MSD chart.  If you all think that I should change to a different graph, please let me know.

 

 

Your correct in that it does have Down Leg Boosters.

My bad, without looking at my carb, I went to the Quickfuels website where it stated all of their Carbs have Annular.  It must of been for a specific model.

 

Here's a picture of mine.

 

[1969_Mach1 333]

Yeah, that looks like the pictures I have seen.  Carbs setup like that can be more tricky to get working correctly on small block motors.  I am sure there are others with much more carb experience than I have here.  But my thoughts are it's because as you accelerate the idle and transfer circuits are exhausted before there is enough air speed through the venturis for fuel to start flowing through the down leg boosters.  Thus, the "bog" sensation.

 

Many years ago I had a "bog" problem with one of those 750 cfm HP style (chokeless) main body upgrades that come with down leg boosters.  This was back when QFT was just getting started.  I contacted them and explained the condition and the motor it was on.  They then sold me another 750 cfm HP style main body with annular boosters.  The bog type problem I had was completely eliminated.  Ran great.  Sad thing unfortunately, over time the annular boosters they installed came loose.  They replaced them once.  The second time they came loose I gave up on it and went to a Holley 700 CFM mechanical secondary carb that uses straight leg boosters.  Car still ran great

[prayers1 153]

I agree with you 100%. I just recalled that a Cleveland Guru, George Pence gave a very well detailed explanation on the history and rebuilding of a 351 Cleveland on the Pantera website.

I just remembered that he highly recommends the Annular Boosters.  Now I know why!

 

Now I can go either way, by a new Carb or go EFI.  I just don't feel like ripping everything apart this Summer for EFI.

 

I was charged on getting a FiTech but after seeing so many negative remarks on various websites, I backed off.  I'd like to get an intake where I could get some injectors installed, get an Accel TBI and a Mega squirt controller. Right now I have all the plumbing, fittings, ele. fuel pump, by-pass reg and etc,,, to start the EFI. I just need the time, maybe this Winter.

 

On the other hand if I can get an Annular Booster carb, it would be a lot easy for now.

 

Which Carb do you like?

[1969_Mach1 333]

What carb is a loaded question.  My car has a 4sp trans so I prefer mechanical secondary carbs.  But in your case with an auto trans a vacuum secondary is probably beter suited.  I think the size you have is in the correct range.  I've noticed members here having success with Holley's Ultra Street Avenger series.  I've never used one but they look to have better features than their older vacuum secondary carbs.  I've used an older Holley 750 vacuum secondary list number 3310-2 with good success.

 

The only drawback with Holley compared to QFT is the adjustability.  With Holley, until you get into the HP series or other race carbs they don't have the feature of screw in air bleeds, emulsion bleeds, and idle fuel restrictors.  But, most of the time if the carb is the correct size nothing more than maybe a main jet change by 1 or 2 sizes, and increasing the accelerator pump squirter by one or two sizes is needed.  The latter is very common to eliminate off idle stumbles for some reason.  Just don't get another carb with down leg boosters.  Look for something with straight leg or annular boosters.  At least with Holley, the straight leg booster is most commonly used on street carbs.

 

Just for kicks you can try a 50cc accelerator pump kit on your carb.  It's mainly for the reason of providing fuel for a longer duration when it takes more time for the main circuit to start up.  That's definitely cheaper than a new carb and it might get you through until you can setup an EFI system.

[prayers1 153]

Thanks for the info!  I'll try a different Acc pump. Yes, it's the cheapest route for now.

 

In the meantime, I'll try to contact George Pence, show him my App and see what Carb he suggest.  When i get an answer, I'll let ya know.

 

Thanks again!!!!

[LSG 15]

   Driver, that article was interesting, but is missing information, or perhaps is biased towards emissions compliance. Full manifold vacuum is better, almost always. The only reason the timed / ported vac even exists is to make the engine idle much warmer. It was an early emissions idea to remove oxides of nitrogen. The carbs were richer than they should have been, so the rich mixture and late timing gave a very hot exhaust. 

 

  Prayers, yes, the annular discharge boosters will help, but you're still just nibbling around the edges. A vacuum dizzy, and a wider cam, will fix this. Ran a 351C for a decade, swapped into a 69 Torino. BTDT

 

                                                                                                                                                                                                                                                                                                                                                       LSG

[prayers1 153]

I threw all the info I have about my car to Pro Systems. Here's what they say:

 

Hi John,
You don't want Annular boosters in a 4150 carb IF your engine program does not suffer from low signal.  Yours does not.

Annulars help low signal programs (small cubic inch with big plenums for example..or big blocks with too big of a cam or header or plenum size).  Annulars in 4150s make these low signal programs make similar signal ratios as proper programs. 

If you use Annulars on a normal signal generating program the carb will be very jetting sensitive.  A one jet move may equate to 2 or three jet sizes.  Making it impossible to jet correctly.

It also makes them very sensitive to weather changes and minor engine changes.... so only run them if you have to run them.

The Cleveland has some specific needs and I will address their low speed issues in the build of your carb so it will be a easy deal for you.

 

They suggested this:

As can be expected from a custom carburetor, it has our adjustable air bleed configuration, it's on an HP style main body, has non-stick gaskets, drag float, jet extensions, Billet (unbreakable) baseplate, VENOM II Black Billet metering blocks, a complete wet-flow portfolio (shows all the jetting parameters for easy jet selection..BUT I AM USUALLY DEAD ON OR WITHIN 2 JET SIZES), a real sharp piece with stepped dog leg boosters, hi-flow needle and seats and big sight glass bowls. Just bolt on and go.

[nickjames138 15]

So, quick question before my Main question. Am I being rude by interrupting Prayers1's forum? My apologies if I am Prayers1. 

 

What carb is a loaded question.  My car has a 4sp trans so I prefer mechanical secondary carbs.  But in your case with an auto trans a vacuum secondary is probably beter suited.  I think the size you have is in the correct range.  I've noticed members here having success with Holley's Ultra Street Avenger series.  I've never used one but they look to have better features than their older vacuum secondary carbs.  I've used an older Holley 750 vacuum secondary list number 3310-2 with good success.

 

The only drawback with Holley compared to QFT is the adjustability.  With Holley, until you get into the HP series or other race carbs they don't have the feature of screw in air bleeds, emulsion bleeds, and idle fuel restrictors.  But, most of the time if the carb is the correct size nothing more than maybe a main jet change by 1 or 2 sizes, and increasing the accelerator pump squirter by one or two sizes is needed.  The latter is very common to eliminate off idle stumbles for some reason.  Just don't get another carb with down leg boosters.  Look for something with straight leg or annular boosters.  At least with Holley, the straight leg booster is most commonly used on street carbs.

 

Just for kicks you can try a 50cc accelerator pump kit on your carb.  It's mainly for the reason of providing fuel for a longer duration when it takes more time for the main circuit to start up.  That's definitely cheaper than a new carb and it might get you through until you can setup an EFI system.

 

So, I'm having a similar problem. My car doesn't lag too much when it's cold, but after a good drive and 100 degree weather I start getting an intense lag. Almost to the point where it feels like it's going to stall. I put a new holley 600 cfm 4barrel on a while ago and didn't have much trouble until I started messing with the timing and air/fuel. I got the timing down pretty well imo. However, I'm starting to get a temp reading of 210-220 degrees in this hot weather and my car usually stays right at 190. The major problem is the Lag from the start. Would you suggest increasing the accelerator pump squirter? I've noticed that if I floor it from a standstill it doesn't lag much, but if I just ease on the throttle from a standstill it has a decent hesitation. Thoughts? 

[larryc94 38]

I see they don't recommend the Annular boosters.  Well I went with G. Pence's recommendation on the Summit 750vs with the annular boosters and had great off idle response and low end.

 

The only reason I changed to EFI was for hot restarts, cold drivability and computer controlled timing

 

Larry

[1969_Mach1 333]

I see they don't recommend the Annular boosters.  Well I went with G. Pence's recommendation on the Summit 750vs with the annular boosters and had great off idle response and low end.

 

The only reason I changed to EFI was for hot restarts, cold drivability and computer controlled timing

 

Larry

I noticed that as well.  I don't know, they're the experts but it wouldn't surprise me if Prayers1 engine suffers from a bit of low signal to the carburetor.  Yeah, low signal is usually not associated with dual plane intake manifolds.  On the other hand it's a 4 barrel Cleveland with large cross section intake manifold runners, intake ports and valves.  I think I'd be inclined to follow the advise of a Cleveland guru like G. Pence before what a custom carb shop suggests.

 

I don't know, I am always a skeptical of custom shops like that and I stay clear of them.  They just doesn't sit right with me.

 

I hope Prayers1 realizes the type of carb they are proposing will not have any type of choke.

 

Prayers1, before spending any money on a new carb, invest in this book, https://www.summitracing.com/parts/sad-sa216/overview/  It's not extremely technical but does a very good job with how the carb operates, tuning, diagnosing, and solutions.

[ray1970 88]

At the risk of offending anyone.

G.P. is a book smart guy that can tell you anything about a 351C from 30 years ago.(if it was in print)

I dont see were he has moved on from that point..

 

Has he never built up a 351C in any form???? ....Not that I can find....

 

The one camshaft man........