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Mikuni Carburettor Id Thread - Phh

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Ok, so I've been looking at a lot of places recently to source some Triple Mikuni 44 carb bodies and I keep coming across different versions of these.

 

So I figured I'd start a thread with photos of each style so that we can all more easily identify these carbs.

 

Contributions and corrections are welcome along the way.

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Solex-N40NPHH-A15 carbs.

 

As the numbering suggests these are 40mm sidedraft carbs.

 

These were fitted to the S20 motor found in the KPGC10 GTR

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These are earlier style 44 MM Solex / Mikuni's. Nicknamed "Mag" Solex carbs.
Mikuni/Solex - NPHH-2 (Type 2)

 

These look like the 50mm versions, but are in fact only 44mm. Also found on Datsun Roadsters with the U20 motor sold in Australia (Solex/Mikuni N44PHH-A5a is the designation).

Z432-R photo taken from Alan Thomas (Facebook post). These carbs have been fitted later (not factory fitted).
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General FYI:
Be careful the screws are different and the throttle shaft is clocked differently. Also be careful with the threads. Zinc is really soft and the thread pitch is totally different.

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432-specific S20 parts: Unique to the 432 and 432-R. The original triple Mikuni N40PHH-A24 carbs

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The 44mm "Type 2" were indeed fitted to U20 engined Roadsters in Australia and Japan. American U20's only got SU's.  Because of this, a  lot of pics you see of American roadsters which have had Mikunis fitted will show the later (more readily available) carbs.

 

Out of interest, the upgraded carbs and a "hotter" cam gave a 15hp improvement over SU's, up from 135 to 150hp.

 

I've got a small collection of 40mm Mikunis of various types, will get some pics tonight.

 

Roadster carbs :

 

post-100293-0-43786900-1481861539_thumb.jpg

 

 

Edited by 1600dave

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Sadly, all mine are 40mm, but here goes.

 

First up, type "T". To the best of my knowledge, these are OEM Toyota Carbs.

 

Part numbers 21100-88254 (front) 21100-88255 (rear).

Factory standard on Toyota 18RG Twin Cam Engines

 

post-100293-0-35499800-1481972016_thumb.jpg  post-100293-0-89243700-1481972038_thumb.jpg

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The 44s are usually identified by the number of the screws in the top cover. S4 (early 4 screw carbs) and S5 (later model 5 screw version).

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Type "S5". At least in the 40mm version, both these and the "S4" use a sleeve to reduce the diameter of the body from the front of the carb back to the main venturi (I've taken them out of the S5 carb pictured) . The "T" type carb does not have this feature, the bore of the carb is pretty much the same size as the bore of the sleeve in the others.

 

 

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Edited by 1600dave

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And the rare and elusive "Type S4" in 40/46mm size  :o

 

This was a broken S4 40mm body that I performed a bit of "exploratory surgery" on to see if it is possible to convert 40's to 44's.

 

This one is out to 46mm without hitting anything / boring through into any air / fuel passages. Boring the rear of the body in to the main venturi and running without the "sleeve" at the front should get a 40 to approximate a 44.

 

Doing this to a S5 may not work as well, it has more air / fuel passages that look closer to the bore of the carb. And a type "T" would be very difficult due to needing to bore the front of the carb out as well (and on an angle) du to not being able to simply remove the "sleeve"

 

Its not that simple though, from what I can work out I will need (at least) custom throttle butterflies and custom venturis. Venturis as its not (easily) practical to bore right through the carb without re-doing how the inner venturi mounts (you will bore the existing mounting bit away). The main benturi will need to be a 40-type, possibly re=profiled to some of the larger sizes. Butterfly needs to be custom as it looks like it will need to be on a different angle to what it is in 44mm carbs to get it sitting right with regard to the progression holes. 

 

Anyway, I haven't gone further with this so don't go whacking your 40mm carbs in the lathe then complaining when you can't convert them to 44's because I've overlooked something. I was just messing around because I had a busted carb body (and because I have a stash of 40's and no 44's....)

 

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Edited by 1600dave

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You're probably unlikely to encounter these in the wild given rarity. But these were fitted to the Toyota 2000GT MF10

Mikuni Solex 2 type N40 PHH

 

Many 2000GTs have had replacements in the form of Type S and Type 4 carb bodies, so if you find a pair of these they are worth good money now to a 2000GT owner who wants to go original.

 

These look externally like the other Type 2's (44) and similar to the 50mm version, but obviously smaller.

 

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MF10-10401 and later cars received Mikuni Solex type 3 N40PHH

 

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MIKUNI SOLEX 36 mm carbs. Often fitted to A-series engines.

Likely to be found fitted to vehicles like Datsun B10, B310, 510 or Toyota TE27, KP61 etc..

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"Nismo" Mikuni / Solex 44 (Type 5).

 

These tend to be known as Nismo colloquially because they were offered through Nismo catalogs in the late 70s, early 80s in North American markets.

 

They have the externally adjustable float with the provision for it to be mounted on either side (dual fuel feed lid), unlike regular s5's.

They also came with larger outer venturis too.

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These are a slightly earlier style, I believe available in the Sports Option Catalog.

The only way I can usually tell the difference is the Wing Nut holding the lid for the jets, and the cover also has Kogyo cast in it.

Can anyone confirm if these are in fact N44PHH-A11 carbs? They have the sticker I believe the A11's are like the ones just below.

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Mikuni/Solex N44PHH-A11 carbs with 4 screw lids.

 

The 2 photos on the right show the difference in lids between the earlier style (left) and later style (right).

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Just linking to this article.

http://mydatsun.com/Solex%20rebuild.html

 

I have heard Lou Mondello say this also.

 

I found out there are actually two types of PHH carbs (homogeneous main system, and Independent main system) the two main systems are very obvious in the jet block area.

 

 

I will try and get photos of these differences to add to the thread.

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RE: homogeneous main system, and Independent main system

The difference appears to be in the Jet Block area. But in order to see it, you need to remove it and look at the under side (the side facing the accelerator pump area).

This is the jet block out of my Mikuni 44 (N44PHH-A11) body.
Homogenous
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Independent
This is the the jet block out of the Type4 (5 screw lid) set of 44's. (ignore the fact that jets are still installed in this block).
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If you look at the pilots, you can see at the bottom of the homogenous type, the holes are blocked off. This is because the pilot and main system is shared.
If you look at the independent system you'll see holes at the bottom - so the pilot and main are separate from each other.

I'm going to quote an email from Lou Mondello taken from here:
http://311s.org/phpBB3/viewtopic.php?t=16501&start=150#p138683
 

Hey Will, I was reading about the Mikuni jet blocks and preferred set ups etc. One basic fundamental thing is being overlooked. There are 2 types of Mikuni S4 and S5 cars. They are homogenous and independent. The homogenous type uses the "8" jet block and bleed pipes.

 

You cannot put the OA, OB, A or B jet blocks into the homogenous carbs as they simply don't work. The metering of the fuel is wrong. Homogenous carbs are made for a bleed pipe. Same deal if you try and put the 8 jet blocks into the independent type carbs. There are two distinct versions of these carbs and they both have their own assigned jet blocks. One of the mikuni manuals eludes to this in Jinglish. Reading between the lines they specify only the homogenous uses the bleed pipes. Nissan preferred the homogenous on the production cars but independent for racing. I quizzed Todd about the preferred ones for racing but he never answered me.

 

I suspect he does not know there is a major difference. I suspect many Mikuni experts aren't aware of this either. This has caught so many people out so many times and for so long.

 

Best was to determine what your are is.... Remove 1 idle jet... use a long stiff bit of wire to see if the drilled passage goes directly to the fuel well. If it does you have the independent type. If the idle passage makes a detour to the jet block passage that holds the jet block then you have homogenous. That simple.... You should try this test on 1 idle jet from each carb. I have seen 1 independent and 1 homogenous used on a U20 with the car being woeful to drive. The homogenous ones as supplied by Nissan on the cars work very well up to 37mm choke. After that say with a 40 mm choke and a big cam, the independent carbs work better.

 

I have converted a few carbs from homogenous carbs to independent. The alloy jet block holder has to be swapped over, they are not a listed part in the manual. The fuel trend (delivery) is quite different on both types. I can see why there were 2 type made. The homogenous as supplied by Nissan (69 onwards) on the cars with "8" jet block and "M" bleed pipe were almost fuel injection exactness with a 34mm choke. The early 44 type Q carbs and all the 50's were all independent. Every 40mm mikuni I have seen is homogenous. Hope all this makes sense.....

 

Regards Lou M

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Hey guys, pretty new member, first post, bought the "One for the brave" 240 from dolls point (11162) and am yet to start the project but doing some research.

 

Among other things, at the moment looking at carby setups, have decided to go for triple mikuni/solex 44, and have learnt (Via this very helpful forum) that there are a few different versions.

 

I can't tell but hope that someone can whether this (pic below) is a homogenous or independent jet block:

 

Cheers,

 

Rob

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I believe you cannot tell from just removing the jet covers. You'll need to remove the jet block which requires you to remove the accelerator pump from the bottom of the body. Don't worry it's not too hard to do, just don't lose the ball bearings when you remove the top cover (part of accelerator pump assembly).

 

There might be a way to tell if homogenous / independent with the block in place, I believe what you need to do is remove the pilots and use a thin bit of wire and probe it down into the jet block (where pilot sits), if it goes down into the accelerator pump area (straight through) it's independent, but if it encounters resistance or has a turn, then it's homogenous. (The Mikuni Manual makes reference to this, but it's not very clear looking at the diagram vs the carb bodies themselves).

 

From what I have gathered, homogenous was used more or less with OE equipment (say Toyota's etc..) and independent (better for racing) was used as aftermarket carbs. The homogenous design is apparently meant to feel very much like fuel injection (smooth transition) where as independent may not be as smooth. This is all second hand information though and not information I've managed to verify for myself. So open to correction.

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Yeah that is a good resource, although I find it easier to understand now that I'm a lot more familiar with all the different variants and have seen photos of each kind. Trying to rely on the illustrations on that page alone is quite difficult.

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Appreciate the info for my previous question Gav, I was hoping to buy the mikuni's but missed them. Have picked up a cheap triple Weber setup to experiment and familiarise myself with for now.

 

Cheers

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