ESE's works engine tuner

[ApolloMotoMoto]

Do the rules allow you to jetison the Mikuni? A PWK28mm is a fine dirt carb as on KX85 etc and will be easier to jet / have better throttle response. Can easily handle 35hp on an RZ350. I avoid the Chinese copies.

I will second the recommendation to ditch the Mikuni for a Keihin PWK if the rules allow for it.

[Flettner]

I will second the recommendation to ditch the Mikuni for a Keihin PWK if the rules allow for it.

No problem with rules, just cost. The Mikuni was free and appears to be about the right size at 34mm.
In fact there is no rule against FI, but that would introduce unreasonable cost at this point.
This is one of four (two stroke) carburetors that came off a Subaru 1800cc engine powering an Autogyro, flown many hours in England then around most of NZ. I collected them out of a bin as the craft was re fitted with a LINK EFI, waste not want not. All jets appear standard accept the needle, I ordered a new needle from Sudco, what the carburetor would have been sold with in the first place, a 5FP17. Figured Id at least be in the ballpark.

The aircraft needle was a 6FJ40, not the right needle for a 34mm I think?

[F5 Dave]

KX125 has a PWK35 . Big carb for a 100cc dirtbike used for Enduro I would have thought. I had one surplus but I sent it to another chap casting an engine as a mock up.

My spare 28 was lent to a bucket racer, but i haven't seen him for 15 years so safe to say I might not be getting that one back.

[Flettner]

125cc Dave, but thankyou anyway.

[ApolloMotoMoto]

This is one of four (two stroke) carburetors that came off a Subaru 1800cc engine powering an Autogyro, flown many hours in England then around most of NZ. I collected them out of a bin as the craft was re fitted with a LINK EFI, waste not want not. All jets appear standard accept the needle, I ordered a new needle from Sudco, what the carburetor would have been sold with in the first place, a 5FP17. Figured Id at least be in the ballpark.

The aircraft needle was a 6FJ40, not the right needle for a 34mm I think?

Playing with fire all over the place aren't we?

So, what makes you think this Autogyro carb runs the same emulsion tube as the MX setup would?

Same question for the Needle Jet

So, you have the potentially appropriate Jet NEEDLE for that carb on an MX bike...

Idle Jets and Main Jets are fairly simple to sort out;

What about the air corrector, does it have a removable/tunable air corrector "jet" accessable inside the bell mouth?
(not talking about the screw-adjustable corrector; I am talking about a removable and tunable 'jet' that feeds that emulsion tube with the air it will use to emulsify the rising fuel...)

The Needle JET (the orrifice right at the base of the carb throat, right were the needle first ...penetrates....) has a 2-stroke shroud on it, sure, but is that shroud height ideal for MX riding?

Is the Needle Jet ORRIFICE SIZE the proper corresponding diameter to match that 5FP17 needle?

Is the emulsion tube you are threading main jets into the correct emulsion tube for MX riding at ...ground level.... ?


Interesting questions those....

[ApolloMotoMoto]

For reference;

This is the Needle JET: https://ibb.co/mH0pY0N

[wobbly]

Once you have figured out what you have and consulted the chart - I have just ordered a manifold from MikuniOZ.com
Plenty of stock , reasonable pricing for parts and freight.
You dont have an issue with the Air Corrector or the shroud height ( yet ), as they adjust the fuel curve with increasing rpm - nothing to do with going rich at low rpm/WOT

[Flettner]

Playing with fire all over the place aren't we?

So, what makes you think this Autogyro carb runs the same emulsion tube as the MX setup would?

Same question for the Needle Jet

So, you have the potentially appropriate Jet NEEDLE for that carb on an MX bike...

Idle Jets and Main Jets are fairly simple to sort out;

What about the air corrector, does it have a removable/tunable air corrector "jet" accessable inside the bell mouth?
(not talking about the screw-adjustable corrector; I am talking about a removable and tunable 'jet' that feeds that emulsion tube with the air it will use to emulsify the rising fuel...)

The Needle JET (the orrifice right at the base of the carb throat, right were the needle first ...penetrates....) has a 2-stroke shroud on it, sure, but is that shroud height ideal for MX riding?

Is the Needle Jet ORRIFICE SIZE the proper corresponding diameter to match that 5FP17 needle?

Is the emulsion tube you are threading main jets into the correct emulsion tube for MX riding at ...ground level.... ?


Interesting questions those....

It is a standard flat slide Mikuni 34mm twostroke carburetor. It was adjusted by the original original owner, from new, to run on a fourstroke although Its not a fourstroke carburetor, emulsion tube is still what came standard with the carburetor when originaly sold ..... as a twostroke carburetor, all that was changed was the needle and main jet to run on the gyro. also the float valve but that's been changed back to a low pressure unit.

[Flettner]

Once you have figured out what you have and consulted the chart - I have just ordered a manifold from MikuniOZ.com
Plenty of stock , reasonable pricing for parts and freight.
You dont have an issue with the Air Corrector or the shroud height ( yet ), as they adjust the fuel curve with increasing rpm - nothing to do with going rich at low rpm/WOT

A 5FP17 is whats in it now.

[wobbly]

Well that , right there is the major difference between a 4T and a 2T.
The 4 stroke needs a heap of fuel as you wind on the throttle - explicitly why they have ,in most cases, an accelerator pump.
A 2T does not need or want the extra fueling at all.

[Flettner]

Well that , right there is the major difference between a 4T and a 2T.
The 4 stroke needs a heap of fuel as you wind on the throttle - explicitly why they have ,in most cases, an accelerator pump.
A 2T does not need or want the extra fueling at all.

No that's what I put in it, it had a 6FJ40 in it when it was in the aircraft.
Sudco told me they are sold standard (for twostrokes) with a 5FP17 needle, so I bought four of them (I've got four carburetors), that's what I've been running. I've never run it with the 6FJ40. The 6FJ40 is a much fatter needle. Perhaps I should try it? When I can ride again.

[husaberg]

Spankme seems to have fixed the attaching files and photos.

For Neil an explanation of the 4t vs 2r needle jet ie emulsion tube.



this too



https://www.kiwibiker.co.nz/forums/a...hmentid=301846
https://www.kiwibiker.co.nz/forums/a...hmentid=301845
https://www.kiwibiker.co.nz/forums/a...hmentid=301762
https://www.kiwibiker.co.nz/forums/a...p?albumid=4844

[Flettner]

I managed to post a test picture.

[TZ350]

.
Just testing to see if I can post pictures again.



Yaeee Looks like I am back in business too. That is a picture of the turbo that is going on my 70cc EFI 2stroke project.

The aluminium housing for the hot end is something Speedpro helped me with to tighten up the AR ratio. Hopefully it will work better with my smaller engine.

[jonny quest]

Flettner, you can jet a carburetor pretty close on the stand.

What does it do when you hold throttle just above idle? Does it race up in rpm? If yes, your pilot and needle root are good.

What about 1/8 and 1/4?

Just listen carefully, does it blubber and then race up?

You'll get bad dips on dyno if it has to accelerate through these rich conditions.... even though you are testing wfo... it has to go through these rich conditions which causes false main jet readings.