40PHH Mikuni tune advise

[luvemfast]

Hi, i've done a search, but can't find the info I need.

I have an L28 (N42 F54) with the following specs.

Ø88mm flat top pistons (2mm oversize, which makes it a 2883cc)

0.49 inch lift 74° cam

balanced bottom end

recurved and mechanical advance dizzy, set to 15°

Extractors to 2.5" exhaust

 

I am running triple 40PHH Mikunki's, what jets do people you recommend?

 

Currently running

Choke ø36

Main Jet 160

Air Jet 200

Idle/Pilot 57.5

Pump 45

Block OA

Bleed pipe T

 

I have a selection of jets to choose from

Choke ø32, ø36

Main Jet 140, 145, 150, 160, 190, 200, 210, 230

Air Jet 180, 200, 210, 230, 240

Idle/Pilot 55, 57.5, 60

Pump 40, 45, 50

 

I sorted a flat spot down low by going smaller idle/pilot jets (60 to 57.5)

Looking for help at top end, seems like it wants to go, but is lacking fuel or air, or both.

Can someone give me an explaination as to what effects the main and air jets will have on performance?

 

Thanks, Simon

[luvemfast]

No one?

There is heaps of info on Webers and even Dellorto's.

Find it strange for such a popular carby that there's no one who can help.

[Leon]

In a nutshell, mains affect mid-range and top end. Bigger mains make the mixture richer. Air correctors affect top end, where a bigger air corrector makes a leaner mixture. A wideband 02 sensor is very helpful in the tuning process. The Weber sticky has very good info: Linky. There should be some pertinent Mikuni info as well.

[zbloke]

If you have not got this already then it might be of some help to you, click on the link to go to the PHH service manual on the Mikuni site

 

http://www.mikunipower.com/PHH01.htm

[randy 77zt]

get a wide band o2.i think with a wide band o2 i could tune a carb faster than me fiddling around with software tuning an efi system-you really need the data from the wide band

[Bahraini240z]

What is a good A/R to set at WOT?

[Leon]

Generally, slightly rich with lambda of ~0.9 (13.1 AFR). Specifically, it's what the dyno says.

[luvemfast]

Been reading the triples sticky. Even though its not specifically for Mikuni's, there is still some useful info there.

Thanks for your help with that, might need to get a wideband O2 set up.

[Bahraini240z]

Since we are tuning triples, how can we adjust them using a single wideband gauge? My point is, one of the triples could be running richer and causing the overall reading to be rich.

Edited September 17, 2010 by Bahraini240z

[sticky280zx]

normally on tripples (like everything else) you do the same thing to everything since in theory everything should be the same and balanced so they fire the same. Ie 4 cyls running rich and 2 lean...i would start with the same thing in each, and change all 3 little by little untill you get it tuned with the 02, or just take it to an amazing shop like robello or someone that really knows what theyre doing with multiple carbs, austin healeys, mg's, etc race shops that use dual or tripple carb setups.

[Leon]

Since we are tuning triples, how can we adjust them using a single wideband gauge? My point is, one of the triples could be running richer and causing the overall reading to be rich.

 

How do people adjust them without a wideband gauge or dyno? You do the best you can. Doing everything the same on each carb is a given, but ideally I would love to have an 02 sensor for each cylinder. Using one wideband is not ideal, but it's a lot better than not having one at all. A competent person can get the carbs dialed in pretty well with a WB02. A dyno is even better.

[Bahraini240z]

Thanks guys, that makes sense. Sorry for my ignorance, never been into the carbs business before. My othe Z is running on an Fcon V-pro, huge technology difference

[srgunz]

Based on my experiance with your carbs try those 180 airs first and drive it with the mains you have installed.

Next pull the 160 mains and go to the next smaller (150). Drive again.

Repeat with the 145 main.

Repeat with the 140 main.

Let us know. I think you will be going in the right direction.