I am getting a lean spike AT the moment the vac secondaries open. The motor stops pulling at this moment and then it pulls hard again. Is this a sign of the spring being to lite or to stiff? I'll have to check but I think I have the one in the middle in there now.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Too light usually, but is the check ball in the secondary diaphragm housing where it belongs? If that's missing the secondaries will open too quickly. I'd look there first. If that doesn't fix it you may want to check to see how far the secondaries are open at rest. There is a hidden screw that adjusts the secondary closed position.

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Joshua

A stiffer spring will delay the opening, and may be what you need, or atleast need to try. THis may help, but may also just delay the piont it goes lean at. If you delay this and it only waits to a higher RPM before it goes lean then tuning the rear will probably be needed.

Also the accel pump can help this, but it depends on if it only does this when you kick it. You also may want to make sure your rear float level is up high enough. You can even try higher than the bottom of the site hole as long as it dont start flooding from it.


Even though the carb does not have four corner idle ajustment ( atleast I dont think it does) ajustment to this circuit can help. Be sure the T-Slot is showing about a .020 gap when the rear plates are closed. It may take air bleed changes if nothing else will cure it, this could be idle and/or main bleed changes.



One thing you should probably do is check the linkage to make sure the back half is in sync with the front. What you do is open the front half way (without the engine running) then take the secondary and open it with your hand. The little V link that hooks the front to the rear and slides in the rear shafts slot may need to be ajusted/bent. The idea is to bend this link until the rear opens to the same amount as the front so that no matter what throttle possition you are at the secondary will be equal to the same angle as the primary when the vacuum diaphram opens it.


Jess

I've locked out the secondaries for now and I am back to tuning the primaries. I have reduced my lean spike by half by moving from a 31 to 35 shooter nossle. (orange cam) I now have a little lean spike from 12.5 to 16.9 for .33 seconds. (it used to be up to 22.5) I moved to a 37 shooter and the AFR and time didn't change. That surprized me, but what really surprized me was that I didn't get a rich dip at all. Is is posible that I am dumping all 30cc in .33 seconds regardless of the 35 or 37 shooter?
The differance between the 35 and 37 shooter can't be seen on the log, but I think I feel/hear it loading up a pinch with the 37 and not with the 35.
The most important question I need to ask is this. Is it posible to elimanate an off idle to WOT lean spike completely?

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

you're trying to get MPEFI response out of a carbureted engine.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Sounds like you need to 're-qualify' the bolt/plunger at the end of the acc. pump/lever (has the spring on it)... I would check the following:

Motor off, get feeler gauge set, open to .01, .015, .020)...

Pull throttle lever open to WOT... with other hand slip feeler gauges between the head of the bolt/plunger and the acc. pump lever... if you can get a .020 in there or bigger... time to get a wrench and tighten it... you'll be in the ballpark if the .015 fits and isn't looser... and it shouldn't be tighter than .010 or you'll need another acc. pump lever and casing)...

That should help crispen things up... next up since you're dump a lot of fuel off the bat... time to check the pump cam profile...

The best way to imagine the pump and 'shooter' is the pump cam will tell it 'how much' to squish the fuel... and the shooter is 'how fast'...

So:

If you need a lot of fuel 'fast' picking the widest shooter (37,40...) and a big cam (Brown)... that will dump a lot of fuel fast... if you want to dump the same amount of fuel over a longer period then using the same cam, but a smaller shooter will help ( like using the brown cam with a 25 shooter....) more like a nozzle on a hose when you turn the water off the water at the faucet... if you open the nozzle a little it will trickle the water out until the pressure is gone... if you just open it up.. you get one big burst of water that just 'peters out'...

If you are getting enough fuel but need say a longer duration shot... (say the #37 is just a bit much and the orange pump cam is in the #2 position on ...you might seeing if the proceedure above tightens up the pump shot a bit quicker... then I'd work on maybe stepping up the cam to green #2 and the 35... or for the 'really longer/stronger'- only if you still need pump shot after 50-60% throttle opening try the 35 with the pink cam in #1)....

-D.Idiot


Another thing to ponder is 'how fast' is your timing 'ramping up' from idle to full timing... you need a slower curve to get up to cruise rpm for street




[/quote]

No, you'll always go lean when you open the throttle as the air is faster than the fuel.

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Joshua

I ve been fiddling with this carb for quite a bit changing things, logging, reading the logs and changing again. Throughout my testing I have found that this combination seems to work best.
Primary jets 57 (still a little rich, maybe 55 or 56)
Secondary 60
Silver spring
Orange cam
35 Nossle
PV 8.5 (didn't seem to make any difference from the 4.5)


I realize that I am not going to get rid of the lean spike when the primaries open and the second lean spike when the secondaries also open, but I have been tring to minimize the hieght and length of the spikes. Basicly the first spike jumps to 16.5 AFR and lasts about .4 seconds and the next spike jumps the same and lasts .6 seconds. Overall the car doesn't pull hard for a full second.
In regards to the secondaries I have openned them a little which seemed to help lower the height of the lean spike a little, but had really no effect on the lenght of the spike. I ve tried different vac springs and small adjustments just move the lean spike up or down the time line. Very lite springs are bad and cause huge wide spikes.
I am thinking about a work around for track time and with start another thread discussing launch type.

http://www.slantsix.org/forum/viewtopic.php?t=27803

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

Is the check ball in the secondary spring housing where it belongs? If not the secondaries will flop open and cause a bog.

Do you really have a noticeable bog when taking off from a stop?

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Joshua

I haven't driven other cars with carb except mine (carb 2.2) and still tuning it..

I find that idle jet 55 is just right but makes mine bucks a little if I open too slowly but is that OK? Idle jet of 60 is too rich.

Cheers, Wizard

I have one of those quick change two screw thingies. I would guess to find this ball I'd have to dig deeper?

Bog, nothing I would really get to excited about on the street, but at the track, maybe. I feel that these two bogs are costing me about .5 in the 1/4.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

The whole lid has to come off the vacuum secondary chamber to get to where the check ball belongs. My old 390 was missing its check ball from the factory, but the carb was smaller so it didn't hurt the performance much at all. If you have an exploded view of the carb it's pretty obvious where the ball goes.

With that big a shooter if you're still getting a bog I'd have to say the carb is a little on the large side and the main circuit isn't coming in soon enough. If you foot brake it and bring the RPM up a bit does it still bog?

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Joshua

Brennan,

My friend just finished his SL6 rebuild, .060 over, .550 lift cam custom pistons etc.
He is using a 600 Holley double pumper, turned 14.06 in the quarter last weekend. His car has no bog what so ever, it just scoots!

Does your car actually physically bog on the line or just a blip on the air/fuel meter?
At what rpm do the bogs occur?

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Hey brennan,

which screw hole are you in on the Orange cam?

CJ

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Part of Tyrde-Browne Racing

I dont think you will totally get the lean spike out, the air moves faster than the fuel is a good descripsion of what is going on. Also the Innovate meter reads so darn fast. But tuning can minimize things. You can richin things up, and jugle the main & PVCR size and help this quite abit, but you loose the good lean cruize that is needed for driving. One thing you can try is going smaller on the main air bleeds, you can do this with the wire trick I was talking about before. Wrap the wire around the vent tube a few times and stick th eends down inside of the main air bleeds. This can make the main system come in quicker, but it will also richin it up and may require lowering jets after testing.


The surface on the inside of the intake effects this also. Its is refered to as the taul effect ( how much fuel clings to the walls of the intake). Basically if the walls will hold a lot of fuel, you have to get them saturated before fuel starts coming off of them to add to the fuel mix. This is why the surface finish of the walls changes things.


You might also try a 1" four holed spacer. Spacers can really change the way the carb meters fuel alot, plus the extra plenium volume effects how fuel stays in suspension in the air because it can slow the air down to help it make turns that are needed inside the intake.

Without doing individual cylinder O2 testing it may be hard to find what is needed to correct this. It may just be one or two cylinders that go very lean for a instance and this will require going over rich to fix just so the lean cylinders are right.


Verying float level can have hugh effects on this. You dont have to put the level at the bottom of the site glass/hole, but you do have to keep it low enough not to flood.


Jess