Mikuni 40PHH Triples

[SacCyclone]

Added a set of triple Mikuni 40PHH carbs to my L28 E88 engine yesterday. The engine was running lean with stock 57.5 pilot jets, 180 air jets, and 140 fuel jets. Popping out the #1 carb at idle and a lot of missing and hesitation through midrange. Ran great at WOT. Contacted the owner at Wolf Creek Racing who had what I need in stock and will ship out tomorrow for $4.00 each. I ordered 65 pilot jets, 190 and 200 Air jets, 160 and 180 fuel jets. I will play around with them next week and see how well I can get it to run. Also will order velocity stacks from T3, I understand it helps a lot with air flow. I will let you know what happens next. Hope to get the car up on a dyno in March or April at the track.

 

[SeanDezart]

Ooh - I love dyno graphs.

 

[SacCyclone]

 

[johnymd]

Whats the engine spec Mike?

 

[jonbills]

Whats the engine spec Mike?

Ditto - that sounds like quite big jets! I think the Mikunis are more like my Dellortos that Webers.

 

[Matt Long]

From his FB post it's an L28 with a refurbed E88 head, tubular header, unknown performance cam and a 2.5 inch single box system

 

[Lurch]

40's... Why do people bother?
Might as well be sucking through a straw!

 

[SacCyclone]

40's I got a great deal on them and was tired of SU's. At WOT they pull very well compared to the SU's. My mechanic drove it also and said the same thing, the engine came alive with these carbs. At some point I would like to upgrade to larger but need a better flowing head and a cam to go with it.

 

[SacCyclone]

Wolfcreek Racing sent off the jets today from the East Coast so I should have them on Monday. I will play around with them and let you know how they work.
John, yes it is a L28 may have been bored before I got it. Rebuilt E88 head and unknown cam. Exhaust header and 2 1/2 SS exhaust. Thats about it.

 

[SeanDezart]

Exhaust header and 2 1/2 SS exhaust. Thats about it.

Which ?

At some point I would like to upgrade to larger but need a better flowing head and a cam to go with it.

And perhaps review your header.....

 

[tel240z]

45s some cold air ported triple angle valve job je forged pistons bored l28 240z rods goes quite well 228 hp

 

[SacCyclone]

Tel240Z: beautiful set up you have going on there. Do you know what type of compression numbers you have with the forged pistons?
Sean: got the headers with another car and they are not marked. SS exhaust was custom fit on the car. Probably will run this until she stops and then build a 3.1L the correct way. Just a budget track car for now.

 

[SacCyclone]

Installed 65 pilot jets from 57.5
Installed 160 fuel jets from 140
Installed 190 air jets from 180
Still 5 turns out on air screw, at less it starts popping through intake. Velocity stacks not installed, running without air cleaners. Runs out very smooth with slight hesitation at WOT 10% of the time under load. No hesitation at WOT with no load. Runs 110% better all the way around and very smooth under normal driving conditions.
Should i increase fuels to 180 or airs to 200 or both? I have them from my order. Do I need to increase pilots again and if so I have to order them.
YouTube link:
https://youtu.be/Yn4ZZhqqn4U
https://youtu.be/a6tPwRokvxs

 

[jonbills]

Those jets sound mighty big to me Mike. I'd recommend you install a wideband AFR gauge to figure out what is going on.

 

[richiep]

As a reference point, which might help you, my triple Dellorto DHLA 40s are jetted thus:

Air correctors: 200
Main jet: 120 (so much smaller than your main fuel jet size)
Emulsion tube 7772.6
Idle jet: 58
Idle jet tube/retainer: 7850.1
Pump jet 33

Not sure how many turns are on the idle screws and would have to check venturi size (should do this while they are currently off the car actually).

Engine is N42 L28, 87mm flat-top pistons (with small fly-cuts), stage 3 Schneider cam. Compression in the high 10 to 11:1 region. 200hp 8 years ago with old **** MSA exhaust and manfold. Carb performance is fine. I just have to feed the throttle in from a standing start to avoid bogging down (no stamping on the gas!). I've only started getting the odd pop from the carbs since switching to the Fujitsubo exhaust manifold and twin system a couple of years ago. The car will be rolling roaded again once I've finally sorted my cold air feed out and got my lightened flywheel back in.

 

[Albrecht]

Velocity stacks not installed...

Doesn't seem much point in any major or minor tweaks unless you have the 'trumpets'/air horns/velocity stacks installed. Mikuni PHHs are particularly sensitive in this respect.

What jet blocks/emulsion tubes are currently fitted? I don't see any mention of them. Another very sensitive component on the Mikunis.

I'm running early 40PHHs on a fairly mild L24, fitted with #8 jet blocks (#T inners), 160 main jets, 210 air correctors and 60 pilot/idle jets. Probably would not be too far away from what you need on a mild L28, but a lot depends on compression ratio, cam and cam timing.

Definitely need the starter/choke system connected and working on most PHH setups (yours appear to be disconnected?) when starting from cold - unlike Weber DCOEs which will almost always start with a couple of throttle dabs - and if yours starts OK without it's possibly an indication you are too 'fat' (rich) on pilot jets?


I'd be wary of comparing like-for-like jet sizes etc between Dell'Ortos, Webers and Mikunis.

 

[SacCyclone]

Albrecht: Jet blocks are #8 and I need to check on the inners to see what size or if they are all the same. So 160 mains should be ok and that is what I have. I have 190 airs and you have 210 so I could play with the 200's I have set aside. I'm at 65 pilots so not too far off. I need to check and make sure I don't have a manifold leak anywhere. Boy are you correct on the choke system, took forever to start cold and finally had to use start spray to get it going. I will look for some sort of choke cable very soon. Currently at five turns out, If i start to screw them in to 3-2 turns, bad coughing out the carbs which indicates lean. I will keep playing with it and get some numbers off the dyno at Thunderhill Raceway next month. Thanks for all of your thoughts.

 

[SacCyclone]

Richiep: thank you for the numbers. My mains are much bigger as are the pilots. Full throttle under a load it seems to do fine. A couple of quick YouTube videos of how it's running now.

https://youtu.be/Yn4ZZhqqn4U

https://youtu.be/a6tPwRokvxs

 

[SacCyclone]

Today, I changed back the air jets to 180's from 190's. I also changed the fuel jets from 160's to 180's. The pilots stayed the same. The bleed tubes are "T" which may need changing to "M" which I need to locate. Performance wise, the car runs the best it has since the change. So, I think I'm close. Still have the pilot screws out about 5 turns. If I screw them down to anything less I get popping out the intake. This may have something to do with the "T" bleed screws. Idles nice and WOT is great especially with the velocity stacks installed. Occasional hesitation at about 30% throttle but happens infrequently. Still need to get it on a dyno and sniff the tailpipe. Anyway, seems good for now and I will start the search for the "M" bleed tubes

 

[SacCyclone]

Looks like I found some "M" bleed tubes tonight from a local 510 racer in the Monterey Bay area. He will send them out to me Postal this week. We will see if that smooths everything out.