moremazda

iTrader: (4)

I need a little help. Mine runs like crap. I have the classic symptoms of having the wrong emulssion tubes, but they are the OA's which from what I under stand are the correct ones for a rotory.

Can you guys help me out and let me know what you are running??

Ryan

WackyRotary

Hey, I used to use a Mikuni 44PHH a long time ago. When I went to a bridgeport, I changed to a 50DCO and enlarged the intake holes to match. And you know the rest of the turbo, I mean story I love my weber! But, the mikuni was PERFECT for the stock port.

But that is besides the point.

.
Main fuel 200
Air jet 240
Pilot idle jets 62.5
Pump jets 90
choke 760
I think the jet block assembly/emulsion is a
N101, 253 OB

WackyRotary

Oh yeah, I guess I should mention that I never used the Mikuni I have with a stock exhuast manifold, but I know from experience that optimial air jets change DRAMATICALLY on the length of the exhuast with the weber I used on my bridgeport. Main fuel jets are more controling of low-mid range power obviously, and have less major effect on the main higher rpm stuff.

I have a unequal length pace setter I used on the 12a bridgeport intically which I chopped and lengthened to ~120inches and made them equal length from the engine were they collect (near the muffler flange before the axle).

Doing this changed the fuel demands considerably up top. It wanted a 220-230air jet with short headers, and closer to about 175-185 when I went to long tubes.

SO, its safe to assume that when you use it on a turbo were the exhuast pulses combine REALLY close, the air jets need to be leaner(bigger) to allow more of a air leak at high rpm, and also slightly smaller main fuel jets.

I just assume the mikuni setup is jetted for streetable headers and not the stock exhuast. If it were, I am sure the main fuel would be smaller and the air jets would be bigger since the engine wouldn't be able to breath as good up top as with headers. SO I am thinking that you need to set it up with the stock exhuast in mind for a turbo because of the pulses being combined were they are.

I am not totally certain if I'm right, but the weber I have was pretty touchy to changes, and probably isn't completely right on for the a/f ratio. But its not hesitating or running excessively rich as far as I can tell on my turbo setup.

WackyRotary

Also moremazda, try this: take and remove the air jets on the emulsion tubes, put it back on without them on and drive it hard. Tell me how it does. This will simulate a much larger air jet, if thats what you need and will either fall on its face or make considerably more power.

moremazda

iTrader: (4)

Well I have tried fuel pressure from 2.5 to 5.5psi, I have tried float levels from maximum to minimum I have gone from a 200 main jet to a 285, from a 240 air bleed down to a 210, and it is always in the same place 4.5-6K uder boost it sounds like a damn machine gun, when natrually assperiated it just kind of hunt and lurch between 4.5 and about 5.5 as if it were lean, and would then pick up. After the shift (in N/A form) it would feel as if the accel pump was too small (again feeling as if it were lean) and then at about 5.5 pick up again.


The only thing different in my set up from yours is the emulssion tube/jet block. I have the OA but I can't get the bleed pipe out to look at it.

Any suggestions??

moremazda

iTrader: (4)

Okay so I pulled out the air jets and took it for a drive and NO change!! The hesitation during free rev did change (became less apparant) but the back fire is still there and I still can not floor it. AHHH!!!!

Weber here I come!!!

Ryan

WackyRotary

WHAT? There is no bleed pipe on the PHH on the Mikuni setup for rotaries was not fitted with a bleed pipe. There are two types of Mikuni sidedrafts, a homogeneous type and a independent type.

These are some direct quotes from the Mikuni PHH sidedraft manual I have.

The homogeneous type consists of a main jet, main air jet, bleed pipe, jet block. There is a few stages of flow which make it slightly more tunable across the throttle range 10-15%, up to 50% and anything up to full throttle.

The independent type(what we got with the Mikuni rotary kit)consists of Main jet, main air jet, jet block. The bleed pipe is not fitted to this type of the main system. In terms of function, it is almost the same as the homogeneous type, the only difference being that the timing of the air fuel mixture flow from the main nozzle in this system is slightly earlier in the throttle compared to the other type.

Anyway, I'm sure that may of confused you a little, but there is no bleed pipe, different blocks give you differing bleed amounts. BUT, if thats the one that came with the carb, it must be the right one.

I hope your turbo is in great working condition like mine is. Do you still have the dynamic flapper in the manifold? Did you port the smaller hole of the twin scroll on the turbo.

moremazda

iTrader: (4)

Okay if there is no bleed pipe what is the thing I am looking at in side the jet block?? Looking from the ouside of the jet block there is single circling line of holes. If you look inside one of the holes from the outside it appears as if there is another peice inside. If you look down into the jet block from where the main air jet sits, you can see a ridge of brass, and again it appears as if there is a bleed pipe.

Is it possible somebody replaced the OB jet block with an OA and a bleed pipe and then used the 200 main fuel and the 240 main air?? Will the parts for the two types interchange??

My turbo is bad, it has a tendancy to blow smoke screens worthy of a James Bond credit. I have a old school 13b with a S5 turbo (that I know is good, it put down 260rwhp on my buddies car) that is going in this weekend. If I don't get thius Mikuni sorted out I will be getting a Weber from Fast Freddies!

I did not port the smaller opening of the twin scroll and I did remove the flapper. I tapped the hole and then installed a small bolt and toruqed it to 100 lb-ft.

Ryan

moremazda

iTrader: (4)

Okay if there is no bleed pipe what is the thing I am looking at in side the jet block?? Looking from the ouside of the jet block there is single circling line of holes. If you look inside one of the holes from the outside it appears as if there is another peice inside. If you look down into the jet block from where the main air jet sits, you can see a ridge of brass, and again it appears as if there is a bleed pipe.

Is it possible somebody replaced the OB jet block with an OA and a bleed pipe and then used the 200 main fuel and the 240 main air?? Will the parts for the two types interchange??

My turbo is bad, it has a tendancy to blow smoke screens worthy of a James Bond credit. I have a old school 13b with a S5 turbo (that I know is good, it put down 260rwhp on my buddies car) that is going in this weekend. If I don't get thius Mikuni sorted out I will be getting a Weber from Fast Freddies!

I did not port the smaller opening of the twin scroll and I did remove the flapper. I tapped the hole and then installed a small bolt and toruqed it to 100 lb-ft.

Ryan

WackyRotary

The bleed pipe is intergrated into the jet block, sorry for not clarifying that. There are different jet blocks you can get, but I highly doubt who ever you got the carb/intake from altered that and didn't tell you. Did it work fine n/a style? One thing I don't like about the Mikuni is the accerator pump diaphram design which you can control the amount by setting the pump rod higher or lower, but not very precise. Webers use a piston type plunger which is a lot better in my opinion and more controlable for sudden increases in throttle to avoid the annoying sidedraft hesisation. You can get larger pump bypass jets, different accerator pump nozzles, and control them better overall to the engine its on. Otherwise the Mikuni worked GREAT on a stock 12a I had.

Its probably the turbo that is not working right in your case as you discribed it having problems. Does the turbine wheel spin freely? If not, I would scrap it and find another one in good shape. Or since you are getting a 13b, go to a weber with a 48mm bore and no choke on it.

moremazda

iTrader: (4)

The turbo is not the problem. The carb performed like this in N/A for but not to this extent. I belive that the turbo has just amplified the problem.

With this trouble and lack of availiable parts I'm just going to get a Weber. I'm giving up!

Ryan

WackyRotary