ESE's works engine tuner

[TZ350]

My rotary valve Suzuki ones are the primary type and look like how you discribe them.



All my Keihin carbs from 28-38mm came from read valve 2-strokes and the OKO's have the bleed type too and they all look like this.



My RD's 250/350's and 400's and some 24mm Kawasaki carbs I have all had bleed ones that look like this.



And the jets cant be removed from some of my other carbs.

The OKO must be used on 4T as well, but I do remember reading that 4T and rotary valve engines work best with the bleed hole setup.

The original Suzuki carb was a primary type and as my OKO is the bleed type I hope your right.

[twotempi]

The Dellorto carbs I use have the option of either a bleed type with a flush nozzle, or a primary type with shrouded nozzle.

Which type should be used for a piston-ported engine ?? Most seem to use the primary type.

Or would a bleed type with a shrouded nozzle be even better ??

To achieve this I would have to make the shrouded nozzle part the the nozzle jet screws into from the underside of the carb.

I have read various info on this subject but haven't got a definitive answer although some immediate previous posts by Wobbly say that that a primary type with shrouded nozzle are the ones to use.

Any opinions on a bleed type with a shrouded nozzle ??

[TZ350]

Any opinions on a bleed type with a shrouded nozzle ??

The Honda MC18 does it that way ...

[TZ350]

Something else I scraped off the net:-

I should point out here how the air jets and fuel jets interact. I can do this most easily with a little graph.



This graph is 100% a figment of my fevered imagination, and is only to be used as a general guide, not an absolute definitive end all be all word of truth. That said..

1. air jet way too small
2. air jet a little bit too small
3. air jet just right
4. air jet a little bit too big
5. air jet way too big

So basically what happens is if you have the mixture right at low rpm, and it's too rich at high rpm, the air jet is too small and you need a bigger one. Or if you have it just right at high rpm and it's too lean at low rpm, you have an air jet that's too small and you need a bigger one. Or if you have the mixture just right at low rpm and it's too lean at high rpm, the air jet is too big and you need a smaller one. Do I really need to type the fourth combination? When you put in a bigger air jet, it leans things out everywhere, but more at higher engine speeds. And when you put in a smaller air jet, it richens things up everywhere, but more at higher engine speeds. Then when you get the right air jet, it might be too rich or too lean everywhere, so now you have to go and put in a smaller or bigger fuel jet to fix things up again. So you control the shape of the graph with the air jet, and move it up and down with the fuel jet.

I scraped it from here:- http://www.braigasen.com/fcr_tuning.htm

[koba]

In hindsight, what I did back then, is a collection of blunders, with a hit every now and then. Looking back, I knew nothing then.
Looking back in ten years' time, I will probably say the same about now .

That whole post drips wisdom.

[wobbly]

I think that as time progressed the 2T carb manufacturers realised that you can very easily tune the fuel curve to suit by simply changing
the needle, the tube diameter and the air corrector.
Dellorto,Keihin and Mikuni offer both for differing applications.
Having to deal with a myriad of bleed holes, there size and position and number of them all make a difference, and ends up being a full on nightmare to make every variation needed.
Keihin led the way and for years have deleted the removable tube altogether,as do many of the Mikuni 2T carbs.
The OKO carb will for sure have a range of tubes and needles available,and with luck you may be able to track them down.
You can for sure tune both types of system, but the bleed type really is brian damage.

The FCR carb was designed for 4T racing, and is considered a real bitch to tune correctly, but it has a primary shroud and all the same circuits as a normal 2T Keihin, with one extra.
Its idle circuit has FOUR adjustments, idle fuel jet, idle fuel screw, idle air jet, idle air screw.
I use them as a down draft on several 2T engines to get the carb dead straight on the manifold and they work a treat.

[husaberg]

To get the result you are after with a number of differing methods.
The nature the overlaping curcuits of the traditional carb is why some people turned to the Lectron EI type.

The sudco site and cataloge used to offer some great info Haven't been there for a while.
It sounds like these Oko carbs might actually be better than the original Keihin they were based on.

I noticed on the RS125 nf4 the Keihin (Which i guess is a PWK) seems to handle a fair amount of downdraft anyone know how much?
or if it is just a the angle of the pics i have looked at?.

Copied links from when i was ridding the cr500 of the old Keihin spooge.


Also Robinson covers fueling with the airjet and differing needle jet types posted below

Jetting the Pilot:
http://www.cr500riders.com/cgi/yabb/...num=1067267855

The jets to buy:
http://www.cr500riders.com/cgi/yabb/...num=1132092467

2-Stroke Tuners Handbook:
http://www.edj.net/2stroke/jennings/...rshandbook.pdf

PJ Carb exploded view:
http://www.sudco.com/vol33/129-130.pdf

PWK Carb exploded view:
http://www.sudco.com/vol33/125-128.pdf

Sudco Needle Jet cross reference chart:
http://www.sudco.com/vol33/135-136.pdf

Oxygenated fuels:just for fun
http://www.cr500riders.com/cgi/yabb/...num=1066795536

[husaberg]

Now i Can't find that much about the engine but i do note the updraft on the carb.
The frame is Mg alloy.

It was later Water cooled.
The rider (Santiago Herrero) was yet again leading the 1970 250 world Championship when he died.

Although the single cylinder Ossa had 20 HP less than the powerful V4 Yamahas of Phil Read and Bill Ivy, the Ossa was 45 pounds lighter and its monocoque frame was much stiffer, giving it superior agility. The Yamahas swept the championship but, Herrero left no doubt that the little Ossa was quick and dependable. He finished seventh in the championship and claimed a third place in the final race of the season at Monza. He would once again take the 250cc Spanish National Championship.
1969 would be a big year for Herrero. He began the year winning his first Grand Prix at the opening race of the season in front of his countrymen at Jarama. After retiring from the German Grand Prix with mechanical problems, he returned with a victory at Le Mans. He followed this with third place at the Isle of Man TT, a considerable accomplishment considering his horsepower deficit on the infamous Snaefell Mountain Course. He triumphed again at Spa and was leading the championship points race when he was beset by bad luck. He crashed in the rain at the Ulster Grand Prix and suffered a broken left arm. Most observers considered his championship hopes dashed, but Herrero showed true grit by coming back to finish in a remarkable fifth place at Imola. At last race of the season in Yugoslavia, he held a one point lead in the championship. He started the race in the lead but crashed on the seventh lap, ending his championship hopes. He would finish third in the World Championship. He repeated as Spanish 250cc champion for a third consecutive year. http://ozebook.com/wordpress/archives/2033

250cc

Ossa

ESP 1

GER DNF

FRA 1

IOM 3

NED 3

BEL 1

DDR 2

CZE DNF

FIN 6

ULS DNF

NAT 5

YUG DNF

83

3rd

3

By guest writer Richard Fowler of Motorsport Retro. This amazing little OSSA 250cc Grand Prix bike finished 3rd in the 250cc World Championship in 1969. Its revolutionary monocoque stunned the Grand Prix paddock, yet the clearly superior design never found favour with the big manufacturers. Designed by Eduardo Giró, the son of OSSA founder Manuel Giró, the bike featured a six-speed gearbox mated to a single cylinder, 250 cc two-stroke rotary valve engine. It produced a modest 30 hp. The engine was no match for the fire-breathing V4 Yamahas of Phil Read and Billy Ivy, but with its clever magnesium monocoque chassis, the bike weighed a full 20 kg (44 lbs) less than the class-leading Japanese competition. Riding the bike was young Spanish superstar Santiago Herrero, who soon showed the world that despite its power deficit, the advantages of the innovative chassis were sufficient to bring the small team Grand Prix victories. Herrero reveled in the OSSA’s superior cornering and braking ability, throwing the OSSA into corners like it was a 125 cc lightweight. He was able to carry more speed whilst being super-accurate, and slice up the inside of his competitors under braking. It was all due to the monocoque superior chassis stiffness and weight. The 1969 campaign saw Herrero and the team win three Grands Prix against the previously unbeatable Yamahas and he led the Championship going into the final race—until a crash ended his title hopes. The tiny Spanish OSSA team again led the Championship in 1970, until Herrero crashed fatally at Isle of Man TT. Devastated by his death, the OSSA team immediately withdrew from road racing, never to compete again.

Read more: http://www.bikeexif.com/ossa-motorcycle#ixzz1nTHVoSxU

[husaberg]

Second lot of Pictures,
Someone must know a bit more about the engine. It must have still been bloody fast.

[Frits Overmars]

....Someone must know a bit more about the engine. It must have still been bloody fast.

See for yourself. It wasn't the engine that was bloody fast. It was the rider. And the handling of the bike.

[husaberg]

Thanks Frits it contrasts nicely with the Yamaha approach of the times.
Note of course this is the 125cc. Rather than the 250

Yamaha’s first 4-cylinder racing bike: Yamaha RA31 & RA31A (1966-1968)

…water-cooled two-stroke V4 125cc.
With rotary valves, magnesium engine case and Mikuni 22mm carbs, 9-speed gearbox, dry clutch,
201 lbs, 44HP @ 17,300 rpm, 140 mph top speed.


Yes that does say 17300rpm.

[gamma500]

http://www.youtube.com/watch?v=ODH2nwWO-ds


turn up the volume!

[Frits Overmars]

Thanks Frits it contrasts nicely with the Yamaha approach of the times.Note of course this is the 125cc. Rather than the 250. Yamaha’s first 4-cylinder racing bike: Yamaha RA31 & RA31A (1966-1968). …water-cooled two-stroke V4 125cc.
With rotary valves, magnesium engine case and Mikuni 22mm carbs, 9-speed gearbox, dry clutch, 201 lbs, 44HP @ 17,300 rpm, 140 mph top speed.

Now I suppose you want to see that from the inside as well, don't you?

[TZ350]

I checked my 38mm Keihin PWK carbs and they were like Wobbly said, no removable emulsion
tube. Which leaves me a bit confused because amongst my collection I am sure I have seen big Kiehin 2-stroke carbs with emulsion tubes, Oh well I will have a bit of a better look later. I also have a carb (actually a complete moter) from a Kawasaki F81M 250cc rotary valve MX engine, so I will have a look at its jets when I find it.



The OKO/Keihin emulsion tube and needle jet. The Suzuki primary type on the right.



The well around the top of the Suzuki primary type needle jet.



The complete main jetting arrangement.



I have cut the side away on one of the Keihin neddle jets to see if I could use it to richen up the bottom end of the 31hp curve.



The blue line is a 150mj, The red line is with a smaller mj. You can see why I am so keen to find a way to combine them.

I hopefull will get a chance in the next night or two to try drilling out the air correction jet and hopefully keep the 150mj's low end drive with it leaning out on the air correction and get the red lines top end.

[Bert]

something a little different:

http://www.youtube.com/watch?v=NNJkY...eature=related

I take it that the 80cc class is still strong over that side of the world.