Put my Mikuni 51 on and now have questions
 

Ok, so I installed my Mikuni on the SA w/ a GSL-SE 13b in it, it would fire up and idle.....eh......ok, wont really hold an idle below ~1500 and it wont take a hard throttle but you can slowly throttle it up. I bought it off of another forum member, no clue what jets in it, or anything else about it. I put it on today and messed with the timing some (no timing light) and got her to fire up......

where should I start????

btw im running a mr gasket pump and a mr gasket regulator set at 3psi

have you tried playing with the idle mixture? what jets are in it?

Well this is the first time ive ever had any experience with a sidedraft....ever.....where would the mixture screws be? and I have no idea on the jetting, I picked it up from the guy i bought it from and put it on my car, didnt even crack it open

Is the motor ported at all? If not, isn't a 51 WAY too big for a stock port 13b?

It sounds as if it's running pig rich at idle, which would cause the bog/lack of throttle response. I'd buy a timing light, set timing to stock, and then pull the carb open and check what jets are in it and post back in the thread. G'luck.

yes its a stock port, how will i tell what jets are in it?

It never ceases to amaze me.... You basically answered all of your own questions in your original post.

First off... Mikuni didn't make a 51mm carb.... At least not that will fit any off the shelf rx7 manifold. They did make a 50... But they are extremely rare and command huge price tags. Likely you have a PHH 44. It is a very common carb for use on rx7's.

Now, that being said, you first and most glaring mistake was bolting on a carb that you, one, know nothing about, and ,two, didn't even bother checking the jets in. Carbs are not "bolt on" modifications. That little chunk of aluminum replaces all of the wiring...sensors... And PCM of a fuel injected vehicle, and you think you can just slap it on and away you go?

I can understand being excited about a new part for your car.... Believe me, i've got a few thousand dollars of parts waiting in my garage for my turbo build. But I would never put anything on my car without doing my research first.

You're lucky your post is titled "put my carb on and have questions" not "put my carb on and now have a blown engine". Asking questions after the fact won't do much good then...

Check out wolfcreekracing.com They are about the only people that offer parts and jets for these carbs... But don't try calling and asking them for jetting reccomendations. They deal in datsuns not rotaries and they will be the first to let you know.

Use google and find out what kind of carb you have.... Don't trust the word of somebody that may know even less than you.... Once you figure out ehat carb you have find an exploded diagram and pull the jets and chokes and post your sizes here. Then do a search for reccomended jettings and start from there.

DON'T! I repeat DON'T beat on your car until you tune the carb.... There's a good chance you can damage the engine.

Well thats why I asked :) I was hoping for someone who could direct me as to where to start haha, I know for a fact that the carb came off of another 13b that was in a second gen, once again thats all i know about it. ill check out that website. Thanks for the info.

Ive been on here a while, this is just my first experience with a sidedraft carb


How would i know the size of the carb?

Check out wolf creek they have a carb id guide... Start there.

10-4 ill check it out

I've run a 51 on a stock 12A.
Just takes some tuning.

OP: Look into emulsion tubes, then jets, if still looking for more, venturi's. Then remove the air horns or stacks especially on the street. Air Box/Air cleaner size is critical. Etc. Whether it is a 51, 50, 44 whatever. I'm not familiar with mikuni's, but i do know my way around a weber.

1. Its runing rich or the venturies are the wrong size thats why it won't hold a lower
idle. So id the carb to see what size it really is and crack it open and see what size
jets your running, emulsion tubes and venturies.

2. Your progression circuit is not working right, could be caused by the issues in
1 but could also be the AP not shooting a nice squirt when the pedal is pressed.
You'll want to verify that as well.

3. Get a full rebuild kit and rebuild it. don't trust that someone else had it working
right either.

4. That fuel pressures needs to be up around 4 to 4.5 psi for a weber/mikuni if
I remember right. Also the Mr. Gasket regulator is trash, throw it out immediately.
Ask me how I know :)

5. Do not remove the air horns (velocity stacks) as they smooth and direct the air flow into the
venturies for maximum affect. Also if you get an air cleaner make sure its has
about 2" of head room over the velocity stacks or it will restrict the air flow and
don't use the filter socks and so forth, they don't work well at all and defeat the
velocity stacks purpose.

Heres some links you should read up on:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/help-me-tune-my-mikuni-656341/

https://www.rx7club.com/1st-generation-specific-1979-1985-18/why-fuel-psi-guages-suck-my-mikuni-rocks-645103/

Ok so i took the carb apart tonight and looked at the jets

Air jets - 240
Fuel jets - 150
Idle jets - 52.5
Venturis - 41

Unfortunately i have lost one of the check balls :/

Depending on what emulsions you're running, I'd run the exact opposite jet setup. 240 fuel, and 150 air.
When I ran a weber on my on monster port, I ran F9 emulsions, 220 Fuel Jets, and 120 Air jets. The venturi's were huge, don't recall the size.

well for some reason the emulsion tubes didnt have any identifier on them?

Posts pictures of the emulsions.

Mikuni's do not have tuneable emulsion tubes... they are all labeled OA. They are refered to as "jet holders" hence the lack of tune-ability.

what engine is this on? and what carb did it end up being?

the weber jets are labeled in MM, so a 240 air in a weber is a 2.4mm hole. is the mukini the same?

anyways, 41MM venturi is a little big for a 44mm carb, but its good in a 50, and is about the right size for a 13B.

idle jet, in MM looks ok, might be a little lean, but it should run. play with the idle mixture

the air and fuel are backwards to what we'd run in a weber.... 150 might be ok, for a stock 12A, and 240 should make it very lean, IF the sizes equate to a weber.

I wonder if the air and fuel jets are backwards. Like someone inadvertantly
switched them around. If thats possible.

Tim the air and fuel jets have different thread patterns so there's no way they could have been switched

j9fd3s - its on a stock port 13b out of an 84 GSL-SE

you still haven't told us what type of carb this is.... how about some pics.

I'd bet my lunch that it's a PHH44

ya its def a 44, the 41 venturis werent any thicker thank than like 3 sheets of paper on top of each other

41mm venturi in a 44mm carb is a bit big, but for all the other values, we're using weber type numbers and they *may* not apply.

although you'd think that they would be kind of close.

in which case your air jet looks really big

Yeah check out this link on the WCR website:

http://www.wolfcreekracing.com/index...d=30&Itemid=51

It could be a 50 mm racing version but who knows.

no its a 44phh type s5, what should the float levels be set at?

Alot of your questions would be answered if you would go to ebay and get a mikuni manual. They are cheap.

If I remember correctly the float level is 12-12.5mm from the top of the carb to the top of the float when the float is touching the needle but not compressing the spring.

Details are important, get the manual so you get all the details.