Hy boys

I was always wondering, how much better a more modern than the 40 years old Amal 627 carb would be on my M49 Bultaco.

After succesfully fitting an Oko to my Honda TL 250 (ok, quite similar to the Keihin, as it is a copy, but was tricky to find out the good jettings), I did it again an bought for 80$ form ebay (Taiwan) a 24 Oko. I once read an article in todotrial, comparing Oko and Mikuni to a modern GasGas 250, main jet 120, slow 45. This is my starting point now in the 1968 M49 Bulto.

Has anybody experience with an Oko and jettings on a Bultaco? Any advice is welcome, as it could be time consuming and frustrating to try & error...

(On my TL 250 4 stroke Honda, I was longtime too rich and on the wrong path, till I went radically leaner on the main jet).

Pat from Switzerland

pics on

http://www.twnclub.ch/classic_trial_files/patrick%20BultoM49_files/M49_tuning.htm

Edited June 30, 201115 yr by Trial Pat

I do not know the M49, isit a 250cc displacement? All a guess, but i am thinking a #40 pilot and a #110 main to start on that bike.

Get airscrew within 0.5-1.5 range 1 being ideal.

Can not help with the bultaco jetting but curious as to what jetting you found worked best on the Honda tl250. Am considering the same update. thanks mark

Hy Mark

For the Honda it is 38 slow and 100 main, clip in top position (leanest), Maybe 98 or 95 main is also good, but my jetting set is from 100 - 122.

(original Keihin is 38 and 115), air screw abaout 1 1/2. I stared with 115, then 120, but in the middle was no power, so was long time on the wrong path...

Manifold fits, some oil spray helps to fit the carb in. to the airbox an old Montesa conic rubber balg fits perfectly.

Oko starts easier than old Keihin, a bit moore power I think, more reliable.

Good luck and keep the Honda running!

Pat

Thanks very much Pat, that info will save me a lot of trial and error time. Good luck with the bultaco project. Mark

Thanks very much Pat, that info will save me a lot of trial and error time. Good luck with the bultaco project. Mark

oh, I forgot, there are 2 Oko models, one with a powerjet (additional fuel corredponds to about 10 jet size) and one without.

I think without is better, as the thinny jet soon will be cloughed. I just put a small wire into the rubber hose connecting the power jet, which makes it out of order.

May be it works at the beginning, but I want no trouble during a trials competition, when it gets cloughed...

Pat

Edited July 1, 201115 yr by Trial Pat

Hi Pat,

I have a OKO 28 on a 325 Sherpa M125 its lot better than the worn Amal very good response from down very low, although I'll probably go back to a Amal to keep it original and really when they are not worn there is not too much performance difference

The jetting is main 115, pilot 35 but as yours is a 24 I don't know if this would help much. I might try this 28 OKO on my M49 one day to see how it goes.

Ross

Hi Pat,

I have a OKO 28 on a 325 Sherpa M125 its lot better than the worn Amal very good response from down very low, although I'll probably go back to a Amal to keep it original and really when they are not worn there is not too much performance difference

The jetting is main 115, pilot 35 but as yours is a 24 I don't know if this would help much. I might try this 28 OKO on my M49 one day to see how it goes.

Ross

Hy Ross

Thanks for the hint. I will keep it in my mind as a starting point, if the 120, 45 used for 250 Gas Gas does not work.

Regards

Pat

There was much interesting discussion about the OKO carb for the Bultaco.

How about the Dellorto PHBH 28mm or 26mm, round slide type, there is some information

here in the Bultaco departement, but I found no hints about jetting and how

good or bad this carb work with the engine.

It would be very interesting to read something about this carb too. At least

here in Germany the DellOrto PHBH is much easier to get, (even jets) and

the carb is much cheaper too.

There was much interesting discussion about the OKO carb for the Bultaco.

How about the Dellorto PHBH 28mm or 26mm, round slide type, there is some information

here in the Bultaco departement, but I found no hints about jetting and how

good or bad this carb work with the engine.

It would be very interesting to read something about this carb too. At least

here in Germany the DellOrto PHBH is much easier to get, (even jets) and

the carb is much cheaper too.

We are currently experimenting with a PHBL26BS Dellorto on a model 199A (325cc) at the moment!

Big John

We are currently experimenting with a PHBL26BS Dellorto on a model 199A (325cc) at the moment!

Big John

These are good/interesting news. I'm looking forward to Your report.

Patrik

Hy Bulto fans

After 2 hours trial & error I'm quite sattisfied with with my M49 (1968):

45 slow and 110 main jet, air screw 1 3/4 on the 24 Oko. Feels quite strong and does no more shut the engine on down hills without gas. Next will be a club trial and check the spark plug for the colour. Maybe also experiment with the needle position to optimise.

Grüsse aus der Schweiz

Patrick

PS: Habe USD 80 inkl. Post in ebay bezahlt, kam in einer Woche von Taiwan. Plus CHF 40 für 2 Düsensätze . Weiss nicht, wieviel ein Dellorto so kostet.

Edited July 16, 201115 yr by Trial Pat

Hy Bulto fans

After 2 hours trial & error I'm quite sattisfied with with my M49 (1968):

45 slow and 110 main jet, air screw 1 3/4 on the 24 Oko. Feels quite strong and does no more shut the engine on down hills without gas. Next will be a club trial and check the spark plug for the colour. Maybe also experiment with the needle position to optimise.

Gr

OKO or Dellorto?

To be honest, if you rode two identical bikes, one with OKO, the other with Dellorto, both adjusted and jetted correctly, I bet you wouldn't be able to tell any difference.

I have two 340 Sherpas, one with a Dellorto and one with an OKO. Both run very well although it is difficult to make a direct comparison as one has a modified exhaust.

The point is, either of these, being new carburettors, will be an improvement over an original Amal or Bing if that carb is worn out.