OSSA roadracer

So I finally pulled the ossa roadracer project out off the shed. I have a new employee who is bike crazy like the rest off us here. So I am going to let him build it and race it. My way off getting some new young blood into this sport. He is only 24 years old so hopefully he likes it and stays involved.

My questin is what size carb does this bike need? It has a huge AMAL flatslide on it right now. I know nothing about amal carbs so we want to change it to a mikuni. So what size and any idiea off jetting to start.

Second questin is what size tires are you 2 stroke guys running on bikes like this. I know what size's I run on all my big heavy 4 strokes but am not sure about what this little bike needs. It already has 18" wheels at both ends.

And finally I know this is a 2 stroke and I know I only have raced 4 strokes with big heavy valves and pushrods and stuff so go ahead and letts hear what you guys have to say.

Brad Phillips

 

[QUOTE=Vintage Bling;.


kr124a dunlop rear, kr825 front. for a mild motor 34 is fine, my taco had a 38mm but also had barlow porting and pipe.

 

It needed it to carry all that weight around

What type of primary drive does it have? although the Spanish 2 strokes of that era were very similar one of the biggest differences was in this region. Montesas had gear primary whereas Bultacos like Scott's were chain. If it has a chain put a new one on and check it regularly, I've seen those break on several occasions and toss the rider down the road and more than once it has taken a following rider with it. I'm always a little bit nervous when I'm close to a 250 Bultaco.

 

.........and i was always nervous when you were behind me.......which was alot!!!!

 

Is this a 250 or 175? For a 250 with a new rider, I'd go 36mm mikuni. I've got some notes from the 36 mikuni conversion on my Bultaco Astro 250. Those might get you in the ballpark.

 

If you are building an OSSA road racer you will need to get a pro to weld an inlet manifold mount onto the inlet side of the barrel. This will allow you to run a bolt on rubber Mikuni manifold. The porting can then be done to match the size of carb you use. If you run a decent pipe and improve the porting you can go up to a 38mm carb. 36mm Mikuni is a decent compromise. Stock was a 33 mm IRZ, so you could use a VM34 with the stock inlet porting.

parillaguy

 

Amal flat slide? I'd like to see that gizmo.

 

Thanks guys for the info. I think we will stay stock for a little while with the porting intill we sort out the rest off the bike. making a manifold for the carb is no big deal I have done that to a bunch off my MAR trials bikes to run a mikuni.
Carl I would like to see those notes to at least get in the ballpark this is a 250. The motor that is in it right now is a early 4 speed wildfire motor. It is a bit wore out so i think we will build a later model 5 speed motor I have for it.
The bike already has a pipe on it off unknown build. I am going to pull the top end and see if it has had any port work done or not.
David I will let ya see this carb sometime. Maybe you could use it on one off those brit bikes you have.
Another questin is who services skitsu tacks?

Thanks Guys

 

Scitsu tach.

Dawson-Harmsworth Ltd, in England makes them and they also service them.

http://www.scitsu.com/service.htm

 

Brad-
email me at jay.c.anderson at boeing.com and I'll send carburetion info.

 

Scitsu tachs have a rechargeable battery that often fails when not used and charged regularly. Also some have poor quality resistors that can fail. Give it to an electronics guy to fix. Sending it back and forth to/from the UK costs a fortune these days.

parillaguy

 

Good choice! I was always taught that an Amal was a metered leak.

 

When I did the Mikuni conversion on my Bultaco, my favorite comment from a teenage neighbor: "What did you do with the AMISH carburetor it came with?"

 

Ossa's were semi popular Flat Trackers back in the day. Dick Mann rode one for a while. In fact I beleive he had some sort of ownership role. I think he was instrumental in developing the Yankee 500 which was bascially two OSSA 250's fused side by side. Ossa also made a DMR (Dick Mann Replica) which is highly sought today.

Go to the Tuners section of Flattrack.com. People there are always willing to help.

http://www.flattrack.com/index.php?option=com_fireboard&Itemid=46&func=showcat&catid=9

 

A Gardner is a metered leak.

Amish carbs are the best. They are very non-confrontational . . . .

 

I run a 36mm on my stock Stilleto 5-speed that is shoe-horned into a 175 Wildfire chassis.

Good to see another OSSA out and about.