Are all the guys with Mikuni triples just posers??

[Bruce Woolmore]

just wondering, cos I got ZERO replies when asking what jettings they run - whats the bet that they all run the same jets i.e. those supplied as the Mikuni defaults? :-)

[HS30-H]

My installation was set up on a rolling-road dyno ( the only way to really get it right as far as I'm concerned ).

We changed the Air Correctors and Main jets, but apart from that the stock settings were just about spot on for my particular engine spec.

Later on I changed to a different exhaust system and noticed a drop in power and torque across the range. Took the car back to the rolling road and once again we changed the Air Correctors and Main jets - making a great improvement.

I'm running 3 x 40PHH-S with 32mm chokes on a Harada inlet manifold, Option 76 Degree cam, larger valves, raised compression and some porting of the ( E88 ) head. Exhaust system starts at an Option manifold running into a full stainless twin-pipe up and over layout.

Anyone who bolts on a set of triple sidedraughts and expects them to work properly "out of the box" is fooling themselves. This is one of the main reasons why this kind of layout gets a bad reputation. Truth be told its usually the installer / user who is at fault - not the carbs.

Apart from the correct jetting and synchronising, a properly engineered linkage is also essential.

Apart from that, I think I probably AM a poseur too.....

Alan T.

[Gav240z]

Well the PO of my car was running tripple Mikuni's but he sold the car to me with the Dual SU's.

I've been considering webbers or Mikuni's but I have faith that the old SU's are pretty good and after all there stock :classic: .

Now my engine setup is raised compression probably 10:1, ZX valves (E88) head L28 Block(F54). I've got a mild duration cam not sure exact specs. Good set of extractors and good flowing exhaust system.

The car however could run alot harder I feel. I've been reading about using different needles and nozzles. Mainly off the earlier Z's. But I feel very lost with this stuff as it's new territory for me.

Oh and yes it does have a habbit of pinging from time to time even of premium pump gas. think it's 98octane here.

Alan would you have any recommendations regarding my current fuel set up. I would really like to keep the SU's on there does this limit me in anyway?

After reading what you wrote and having another friend tell me I think a Rolling Dyno would be the best way to get it right as it were but time on those is expensive and alas my student budget might get burnt for a while afterwards.

Sorry can't help with the tripple mikuni's Bruce I'll try get in touch with the PO of my old car gotta pick up the original l24 off him soon. I'll try keep in mind to ask about how he had the car setup.

[justaZcarguy]

Hey Bruce,

Sorry for not looking at your previous post, I have been out of town for a bit.....

I am running Trips on my '74. LOVE 'EM! I can't quite remember the needle size that I am currently running, I have the head getting redone and need to throw the engine back together, I have torn these carbs down to basically nothing and reassembled them...

I will look this weekend and check the sizes, I need to get the setup ready anyway, you are always welcome to call me at home with any questions, just let me know if you want to number...

The local guys here at Z-Therapy know quite a bit about the triple Mik's, they run them on on of the race carz.

Let me know if I can help out....

Brian

[Bruce Woolmore]

thanks for the feedback guys - Alan I'm running 44s, not 40s, so your settings may not translate, but how about posting those main/air settings anyway?

(btw I suspect your 40s with 32 chokes would be round about ideal for a fast road car, thats what my Dellorto'd car ran)

Brian, if you are running NEEDLES in your Mikunis you're way too sofistkayted for me ;-) - be real interested in your choke/main/air/pump sizes are too!!!!

cheers

[HS30-H]

Bruce,

On my current setup ( 40PHH-S ) the Main Jets are 160s and the Air Corrector / Main Air Bleed are 210s. All other settings and sizes are stock for the 'S' model 40PHH.

I do hope that you are not going to read anything too much into what other people are using. This data really ought to be used only as a base-line from which to start from when setting up your particular engine. The stock jettings from Mikuni were a pretty god baseline, but they really ARE just a baseline, and a proper set-up on a rolling road dyno with AT LEAST a few sizes of Main and Air jets on hand is mandatory. The operator of the rolling road will almost certainly be able to make a vast improvement over what any of us can do without him, and the old-fashioned method of do it yourself through plug reading still necessitates having the alternate jets on hand..............

Gav,

In my opinion, if you can't cover the cost of a proper rolling road dyno session and the cost of the jet changes, then going for triple carbs will be a waste of time. I figure that the dyno session is part of the investment, and pays dividends in the long run. I've lost count of how many people I've talked to who take a look at the triple carbs on my car and suck through their teeth at them. Many of them go on to say that they had endless trouble with theirs, but admit to having just bolted them on with a crap linkage and expected them to work properly!

A good rolling road session with the Hitachi SU's would also be a great benefit for many engines. I would suggest that you stick with them and just get them set up properly to suit your engine. With a relatively tame spec on the other mods, the SU's are fine.

Don't forget that the dyno tuner will optimise the ignition events as well as the fuel system...............

Alan T.

[Gav240z]

Thanks Alan will take that into account.

I think my next expense will be a rolling dyno for a day .

[justaZcarguy]

Sorry Bruce, make that Jets, I was in SU mode apparently....

And I will look into the sizes today sir....

[Bruce Woolmore]

I'll have to bribe you all, so here goes ...

i will donate a six-pack of your favourite bevvie (winner to collect!) to ANYONE with 44PHH Mikunis who has a clue what jet setup he's running!

(oh and what cam specs and compression and stuff would be nice too!)

cheers!!!!

[Sean Dezart]

The advice to use a rolling road to set up your carbs is essential ! Even for twin SUs it makes a difference - I 've heard of too many carb gurus who do it by ear - I've got a friend in Paris with triple Webers and after 6 attempts, it's still not pulling right but he will not look out a rolling road - says it will damage his engine to rev up like that !

Mine will be a 3.1 with triple 44 Delortos, set up basically to allow the car to run it a bit before going on the rolling road UNTIL IT RUNS RIGHT ! Running right means smooth power the most economically possible. Let's face it, if the engine and carbs are well balanced, the power output needn't cost gallons of fuel !

[Bruce Woolmore]

but the only two sets (including mine) have nothing but the factory default jets for Mikunis!

I'd like to think that I could get a better starting point that that.

I'm sure we'd see at least some pattern emerge if similar work had been done on the engines ..

.. and then the dyno ... VROOOM!!! (scary watching them climb the rollers, tho!)

sooo guys ... anyone for a beer?

[HS30-H]

Bruce,

With respect, I think you are fooling yourself.

What's the point in trying to be 'closer' than the Factory default jettings for a starting point? It reminds me of the saying "If you want to get THERE, don't start from HERE" ................

Since every single engine is different ( and ideal jetting even depends on your local atmospheric conditions on the day of set-up ) your engine will require a pretty-much unique combination of jetting, idle mixture setting, spark timing and advance curve.

If you get it set up on a rolling-road dyno ( as advised ) then you are going to have to change jets / air correctors on the dyno at the very least. It seems to me to be pretty-much pointless to use somebody else's jettings as a base-line if you are still going to be changing them on the dyno, no?

The stock 44PHH Mikuni jetting for the L-series sixes ( as recommended by Nissan's tech staff ) sold as Sports Option parts was as follows:

MAIN VENTURI = 37mm

MAIN JET = 160

AIR CORRECTOR JET = 180

PILOT JET = 55

EMULSION TUBE ( "JET BLOCK" ) = 8

You shouldn't need to change any of the other parts for a street ( as opposed to balls-out 'race' ) engine.

Where did your Mikunis come from? You have to be careful and check that your standard settings ( as received ) are near to the above numbers. They may very well have originally been sold for a different application than your Nissan L-series six; Mikuni supplied carbs for triple side-draught conversions by the likes of Sanyo Kiki ( SK ) and other companies from the late 1960's onwards. Make sure you are not bolting on a set of carbs that originated from something as esoteric as a blow-through turbo application or a collection of three carbs that were meant to be used singly on a four cylinder engine. There are lots of 'strays' knocking around in the used market.................

If your Emulsion Tubes are marked "OA" or "OB" on top then you would be well advised to seek out a set of six "8" types and install them instead. This will be a great help with driveability and part-throttle response. The OA and OB are best left to racers, and are not as good as the 8 for the street.

I would not be tempted to mess around with the positions for the accelerator pump stroke if I were you. There are three positions to choose from, and I would see what the dyno man says first. Altering the accel pump stroke has a great effect on transition and driveability too - but the Factory setting is the best baseline. Leave well alone unless you know what you are doing and are ready to change it back again.

The Factory-supplied settings ( if they closely match the numbers quoted above ) should be enough to get you running fairly well and allow you to attempt to synchronise the idle air mixture to a smooth and balanced level. After that, make a trip to the rolling road dyno ( with a few spare main jets and air jets on hand ) and get it done right.

Good luck!

Alan T.