Mikuni Help

[Guest R&D Z Factory]

I currently have a 260z with the L26, Soon the head will be shaved to add a slight increase in compression.

 

I have a question on Mikuni carbs, I see many complete sets floating around, but I also see many single carbs floating around, Could I infact buy these all seperatly, Im just worried I would buy the wrong items, Im currently Looking at a set of Mikunis that came from a 22r toyota, they are the Mikuni PHH44's

 

Could i technicly buy these 3 carbs, then buy a manifold, and either fab up linkage or purchase some, thanks guys, I did a little bit of searching but only found most threads on tuning etc.

 

 

 

Also, are there manifolds that will bolt from the block side to these carbs?

 

heres some pics of a 44s

 

 

 

 

 

 

 

Thanks again,

-R

[JMortensen]

The most important thing is that they all need to be the same carburetor. Obviously same size, but also same type. Mikuni made several revisions to the design of the carbs over the years. I'm not sure how to tell which are which. Measure the BACK SIDE of the carburetor near the butterflies to tell the size, not the front. Above and beyond that, they might not all have the same jets, so you'd probably have to buy new jets as well. Probably going to need new jets anyway since what runs on a 22R isn't likely to work for a Z.

 

Linkage is pretty easy. Buy the linkage for the carbs to the manifold, and then forget the linkage to the gas pedal. Just do a cable. Lots of ways to set up a cable, and its so much nicer than trying to get all the linkage pivots from the pedal to the manifold to move smoothly.

[duragg]

I'm having a heck of a time tuning 3 carbs on a Z that are all identical and have a fresh rebuild.

 

Buying used carbs from a variety of sources is guaranteed to be a hassle. You'd have better luck training 3 housecats to do tricks than getting carbs with varied backgrounds all singing the same song.

 

Maybe Mikunis are far easier than Webers?

But sounds like impending headaches.

 

GL.

 

TJ

[Guest R&D Z Factory]

Thanks John, Ive allways admirired your Track Z ownage, I just recently Purchased a 260Z, Ive allways been a newer age nissan owner, S13, S14 etc. and now I have added a Z to my collection. Im not sure what I wanna go with it, Maybe early class autoX or something, or DD becouse of the way cops act around here.

 

Hopefully I had work the Indv. Carb Issue, Ive just allways loved them over the SU's and unfortionalty when i bought my chassis it was incomplete, but besides the carbs I would say my chassis is one of the cleanist around. I checked everywhere. No rust whatso ever, the only place that has a hint is the battery location, and even then there is little to non. Only thing its that Green thats really not of my taste in colors...

 

On the Carb issue, Its just i see these carbs going for very cheap, And im wondering if i could pull it off, if it would be worth it or more of a pain in the ass, and If there was a large amount of manifolds for the mikunis around for sale.

 

 

Thanks John, see if you can help my situation,

 

-Robby

 

 

oh while im here, heres some pics of my chassis when i bought her.

 

 

 

[JMortensen]

Maybe you should price out all the other bits so that you have an idea of what the whole thing is going to run. You're going to need a manifold, linkage, air cleaners, air horns, jets, probably a good idea to get at least one rebuild kit too. You can try http://www.wolfcreekracing.com, they have all kinds of Mikuni parts. For manifolds the common ones are the Mikuni, TWM and the Cannon. Of the ones I've seen the TWM looks the best. I have the Cannon and it's casting was very poor quality FWIW. I don't much care for the shorter Mikuni runners, although others here do. Maybe if you start by checking what the other costs are going to be you can figure if it will be worthwhile.

[Guest R&D Z Factory]

Yah sounds good, Thanks Jon

 

It might be a real pain, Ill see what im gonna daily soon, and if I get my s13 240sx running well, I can dig into the Z, If not It might be a better idea to pick up a set of Roundtops, how much to those usualy run, I might need the linkage becouse I have flat tops,

 

thanks Jon

 

-R

[rztmartini]

nice S15 front! is that on a s14 or s13?

[Guest R&D Z Factory]

s14,

 

me and the old gf's

 

[SuperDan]

A recommendation.

http://cgi.ebay.com/ebaymotors/Dellorto-DHLA-TWM-triple-intake-manifold-Datsun-Z-ZX_W0QQitemZ230039284052QQihZ013QQcategoryZ38634QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[Tony D]

The most important thing is that they all need to be the same carburetor. Obviously same size, but also same type. Mikuni made several revisions to the design of the carbs over the years. I'm not sure how to tell which are which. Measure the BACK SIDE of the carburetor near the butterflies to tell the size, not the front.

 

What I will add is there is no real reason to actually measure the bore if you have them off! 40's will have "165" stamped on the throttle plates, 44's will have "175" stamped there. A little brain scratching and you will come to the obvious conclusion what the numbers stand for...

 

But the point about measuring at the back IS VERY IMPORTANT if you are junkyarding and find a set. Early Toyota Carburettors used a unified casting that shared external dimensions with the 40 and 44 carbs. In these carbs (early 70's) the 40mm versions had a 44mm bore on the air cleaner side of the carburettor, and used 44mm Booster and main venturis, while having a 40mm throttle plate and bore behind the main venturi. This was great from an interchangability of parts for racing vehicles because you could use 44mm trumpets, for maximum unrestricted airflow to the main venturi. To make them "legal" 40mm carbs there was an insert sleeve that went in the front portion of the throat of the carbs to neck it down to what later 40mm Phh carbs had cast into them. On a 44PHH you will see a vestigial casting bump left over from the days when there was only one casting for 40 and 44 carbs. That bump can't be seen in the photos above, but it's there, and it would have been machined for a setscrew and jam nut to secure the front necking down sleeve for a 40PHH application (same nut and screw type that is in there for securing the booster venturi).

 

As far as that oddbal OEM Toyota carb, there is no way to mix up a 40 from a 44. In the production run the 40PHH eventually went to another type of casting that had a squarish float bowl cover, and that is the kind you find mostly out there. The older 40's with the same float cover as the 44 are few and far between nowadays.

 

Try to find at least one with the vacuum advance tube on it, they are there on Mikuini Kits on the #1 Carb that feeds #1 & 2 Cylinders, and on the front carb in OEM Toyota applications as well.

 

The other major difference is the "OA" and "OB" jet block difference, and I have personally never found one old enough to have the "OA", every one I have seen in 40 or 44 has had the later "OB".

 

People don't realize the Mikuini people got the License from Solex in France around 1960! They made those carbs for almost 10 years before the Z was around. Those early carbs with "Solex" on the tops are the ones to check for "OA" blocks, but then only if it's in the first few years of production, but 66 or 67, most everything had "OB" and those are the majority of carbs that are out there, unless you are snooping around an confirmed old-school Japanese Racer active since the late 50's...in Japan! LOL

 

Anyways, as for "Type" the Solex/Mikuinis are NOT like Webers where there were a million types of machining variations due to different internal passages. They were an OEM application Carburettor, and the production tooling was kept is VERY tight tolerance compared to what they ran at Weber. Believe it or not Weber bodies have much more variation in the internal passages than you would think compared to a 'cheap jap carb'! Basically if you get ANY body from a 44PHH, you can get the bits to standardize it to the other two. Check Main Venturi Size (usually 32 or 34mm) and Booster Venturi Diameter (usually 10 or 12mm). Those are the main body components that can really screw your mixture up from carb to carb if not identical. Jets, pump squirters, and small bits are obvious things that you know might be different, but the booster venturi sometimes gets overlooked, because people didn't realize there was more than one available!

 

If buying used, if at all possible LOOK IN THE FLOAT BOWL! Literally take the cover off. If you see corrosion, look closely and be aware that brass jets like to seize irremovably (is that a word?) into the body, so if you have a seized accel pump jet because of corrosion.... It also is an indicator of car in handling the carbs received over their lifetime. Carbs taken off a running engine are best, those that have sat around for years (without the gas being drained, water sitting in them....) can be a crapshoot.

 

But yes, you can construct a set, the components are available. Cheaper to buy as a set, but it can be done individually. I just found a set in Eastern PA and and am in the process of "discussin" stuff with the current owner.... LOL

[JMortensen]

The other major difference is the "OA" and "OB" jet block difference, and I have personally never found one old enough to have the "OA", every one I have seen in 40 or 44 has had the later "OB".

I will admit that it has been at least 2 years since I had the blocks out of mine, but I thought that OA was the common one, OB I thought fit the 50mm carbs but maybe not the 40s and 44's (not sure because I don't think I've ever seen an OB) in person, and the 8 is supposedly a more street friendly block, which I have seen in person, but never seen anyone run in their race car or autoxer.

[Tony D]

D'OH, Total Brain Fart, you are correct JM! "OA" is the common block! It's the counterintuitiveness of it all consarn it! Yes, the OB blocks came in the 50's, but were also availabe in very early 40 and 44phh's (we are talking 60-65, maybe as late as 67 or 68) By 1970, all the 40 and 44PHH's were produced using the "OA" block.

[lucky]

Don't mean to threadjack, but I'm having trouble finding info on how to tune these bad boys. I've got the triple setup on my '71 and now that the weather has cooled off I can't even get it started.

[Tony D]

connect the starter system! The discs on the top of the carb, towards the manifold pivot, and they activate an enrichment system that will allow these carbs to start and warm up the car even in -40 temperatures.

IT IS NOT A CHOKE! Once you open the throttle plate, the starter system ceases to have the vacuum required to function. It will fire the engine, and you can ease it off till the engine is up to temperature, then drive the car. You can drive with the car partially warmed if you can stand the popping, but it's ill advised as it's still lean.

The discs operate opposite the stock starter system in the SU's, so you either need to hook up another cable to the stock choke lever and run it to the front carb, or try to do it with the stock choke cable---but they don't like the bend like that. Easiest thing to do is take a coat hangar or welding rod, and bend it so it fits in all three carbs starter disc holders, and then just clamp your actuating cable in the far end.

There are setups that rotate the discs the other way _so I'm told_ but I have never seen one. They actuate by pushing them to the front of the car. You _might_ get by with hooking the stock choke cable up to the rear carb, and starting it with only one carbs starter system active, but the other two will run raggedy b utt lean till it warms up.

 

Welcome to the wonderful "Carbs are Simple" world of myths and happy reminisces! LOL

[lucky]

If you're talking about the disc with the spring attatched to it in the bottom pic up top, my choke cable is connected to all 3 of them. Even with them "engaged", it just won't fire. Could it be that since the car is jetted/tuned for warm weather that the idle fuel mixture is just that far out?

[Tony D]

The starter system jet may be clogged. it is totally independent from the rest of the jetting systems in the carburettor. There is really no adjustment to it, but I have seen the jet for it clogged with witish corrosion if the gas had water in it an the owner let it sit, or if the carbs sat for a long time and the gas evaporated leaving water in there to corrode....

 

I have started the car at -35F and it fires right up. A weak ignition system may be the culprit, the starter system makes for a VERY rich mixture, and if the sparky system isn't up to par, it may have trouble igniting it. You have to leave it run on the starter for about a minute before it starts "loading up" and you ease it half off for another three minutes, and from there I usually could drive away. But if the air is -35, chances are good you WILL need different jetting to compensate for extremely dense air! As I recall I was a jet size or two richer.... What am I saying, "carbs are easy!" Efi with that stupid air temperature pulsewidth correction is "hard"....

 

I digress! LOL

[lucky]

Thanks for the help Tony. I'm getting some local help this week, and I'll be sure to mention what you've already brought up.

[Tony D]

good luck man! severe cold and air density problems are one of the reasons I made the "EFI Switch"!

[lucky]

Thanks. I'll be going efi once I get the car home, that's for sure.

[lucky]

Just to let you guys now, the Z is up and running again. Just took a little more tweaking of the Mikunis. Now she starts up every time, even yesterday when it was -15. Kinda tricky driving it home on the ice though.