Jump to content
HybridZ
madkaw

Triple Mikuni Help

Recommended Posts

Here's my deal. I could spend 200$ for a areomotive low pressure regulator, but then have to turn around and change it out to go FI.

The 13222 regulator is supposed to be for very low pressures , but yet not a bypass.

I might just do the run again and this time carefully monitor things. Might just take a tweek of the float levels to be good.

Probably go back after installing new HG. Might also punch out the chokes too.

 

As far as a bypass and large enough return, I'm planning on using the evap line that is on the drivers side that goes back to the vent box. It's a 1/4" and should be big enough for a return for our engines and more.

Share this post


Link to post
Share on other sites

A 1/4" return line is not big enough for a Bypass system. On carburated engines it should be equal to the pressure line size, and a minimum of AN 6. EFI engines " can "  get by with a return line one size smaller than the pressure side due to higher pressures involved.

 

Edit: I'll have a look at my stock feed and return lines on my 76 280Z. Main feed is 3/8" ( AN 6 ) I believe and return is either 3/8" or 5/16". I'll confirm later...

 

Aeromotive has some very good articles on designing fuel systems for both Carburated and FI engines.

 

Here is one article that explains the basics. In particular, read the info on feed and return line sizes and also static and bypass regulator systems. Bypass regulators are superior to dead head systems in all Racing and Hi Performance applications. They have many more articles available, but I don't have time to dig them out of my Archives.

 

http://www.superchevy.com/how-to/engines-drivetrain/0906chp-aeromotive-fuel-systems-insight/

 

Acceleration forces when Drag Racing or running Track forces have a big effect on both Fuel Pressure and  particularly Volume. Too small of fuel supply lines and return lines make the supply of adequate volume even more difficult.

 

Hillclimbs, are the worst case scenario for fuel systems. Here you have essentially an uphill Drag Race. You have both acceleration forces and gravitational forces working against the flow of fuel to the engine. You have to have a really stout fuel system to handle the stresses of Fuel Delivery in Hillclimbs.

Edited by Chickenman

Share this post


Link to post
Share on other sites

The Aeromotive 13222 non-return regulator is vastly superior to the typical Holley regulators, which is a cheap " Made in China " part for the masses. . The 13222 is a purpose built racing regulator with no cut corners and you get what you pay for.....

 

Typical Holley 12-803 FPR for carburators  ( 4.5 to 9.5 psi ) = $29.67 at Summit

 

Aeromotive 13222 non return low pressure regulator regulator ( 1.0 to 5.5 psi )  = $185  at Summit

 

Aeromotive 13205  non return FPR ( 5 to 12 psi )  = $102 at Summit

 

Still a bypass system is preferred over a Static system in just about every situation... and that's on advice from Aeromotive.

 

BTW, Aeromotive does make a Universal Bypass regulator that come with two springs. A low pressure spring for Carbs that regulates from 3 to 20 psi and a high pressure spring for EFI that regulates from 20 to 65 ps. Aeromotive Part # 13301. $142.97 from Summit:

 

http://www.summitracing.com/int/parts/aei-13301/overview/

Share this post


Link to post
Share on other sites

Aeromotive 13129 EFI regulator is a good bargain. I picked up one for my Haltech conversion on my 1976 280Z.

 

Several of our members on " The510realm "  are using them on Turbo EFI conversions and are very pleased with them. Compact size makes them easy to fit in tight spaces.

 

$128.97 at Summit:

 

http://www.summitracing.com/int/parts/aei-13129/overview/

Share this post


Link to post
Share on other sites

Pump is a high volume carter at 4 psi with a Holley regulator.

Was just re-reading this all again, and I must have missed this point the first time around.  If your fuel pump is putting out 4psi (Carter 4070 presumably?) then why are you running a pressure regulator?  4psi is pretty much perfect for these carbs, is it not?  If I were you, I would either adjust the regulator full open as a method to bypass its function completely, or remove it from the system, and see how that affects things.  It could be restricting flow enough to starve the carbs at sustained WOT.  

Share this post


Link to post
Share on other sites

Believe me Ryan, I've already contemplated this. It is only a 4psi pump, so I might delete the regulator for a while and see how things go. I've had folks mention that the small pressure differential also makes the regulator harder to operate properly. I should have a 12psi pump in there or something for the regulator to regulate properly. I have also read where guys run the pump with no regulator. I was running the RX-7 pump for a while and changed it out when I was having issues-which turned out to be that dam Mr.Gasket glass filter. The Carter is a higher volume pump though.

Share this post


Link to post
Share on other sites

Okay-so the regulator is gone. I ran the car with the fuel pressure gauge out on the bonnet and it is showing 3.5 at idle. Driving around it fluctuates slightly from as low as 3 to as much as 4. Not sure what to make of that. It seems when driving and coming to a stop the pressure rises slightly to close to 4 and harder runs it dips to 3. Kind of hard to duplicate a dyno run on the street to watch my AFRs . It did seem that the AFRs did start to creep lean around 5K rpm in 4th gear, but now I'm 100mph+.

I believe the Carter I have is good for 30gph-surely enough.

So what about float levels? Could the float level set at the ragged edge of the minimum not be enough on a long WOT run? 

I think that the pump that has ample volume should keep the pressure right at advertised 4psi, or line loss should be accounted for?

I also need to do a voltage check at the pump 

Share this post


Link to post
Share on other sites

Doing more searching and pulled up RaceTeps page which sell the 4070 carter for their triple set-ups. They run NO regulator . Now if you read advertised psi on these pumps they are described as 4-8 psi?  Gph is twice the rating as my carter which is 30gph . The more I think about , the more my head hurts-LOL. Actually, a pump on a triple set-up is feeding three bowls compare to most one bowl set-ups-makes a difference?     

Share this post


Link to post
Share on other sites

I use a Facet Red Top to feed my triple Mikunis, specs are 6.0>8.0 Psi and 45 US Gallons an hour 

 

For many years I ran it deadhead through a Filter King regulator and it ran ok, the fuel pressure used to fluctuate at idle but I put that down to the pulsing of the pump against the deadhead, I kept reading that a bypass system was better though......so......middle of last year I fitted a Fuelab 515 series bypass regulator, and it still runs ok but I have a nice stable 3.5 Psi at idle now, all fuel pipes, feed and return, are 5/16" id 

 

Even did a couple of hill climbs last year and it pulled up them just fine 

Share this post


Link to post
Share on other sites

Low float levels would shift your mixture lean across all RPMs in which your main circuit is active. The optimal setup is a high-flow pump fed through a bypass regulator, as zbloke mentions. This allows for extra capacity in the pump that can be quickly adjusted via the bypass regulator. That's the way mine is setup, I'll be logging pressure when the car goes on the dyno.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...