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Tillerman6

New carb anyone?

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On 6/6/2021 at 5:53 PM, Tillerman6 said:

Tony 27- 

Had a time with the OKO install today.  First thing was that the fitting on top of the new carb has a fine pitch thread that is different than what was on my TKO throttle cable.  That may not sound like much, but I don't have another cable kit to draw parts from, so I had to mill off the old fitting and cable ferrule and keep the inner stranded part of the cable intact.  That went well, but not everybody has a milling machine and a lathe, so depending on what threads are on the end of your existing throttle cable, you might have to do some scrounging for parts. The OKO fitting has a large Inner Diameter that fits over the carb end of the cable, so that was a plus, but the main thing is not to have to wait on another delivery.

So with that done I started getting the OKO carb body mated up with the new rubber boot from Claus Studios.  This was a bit more of a challenge as the opening on the OKO is larger than the TKO by about 4mm.  I ended up making tapered plugs that were oversized for both ends of the new boot.   These tapered plugs are inserted and left in the boot while the whole assembly is warmed up and then boiled with a lid on it for about 2-3 minutes. I had more trouble with the carb end than the airbox end and I would say that if you clamp the carb end first  and leave the tapered plug in the airbox end till the last second, you stand a better chance of getting everything assembled correctly.  I also had to take all the mounting bolts out of the airbox and let it float around as much as possible.  After the carb is hose clamped to the boot, and the boot is hose clamped to the air box, you can insert the front end of the carb into the rubber manifold and I'm hoping the airbox will still bolt back down to the frame.  The instructions with the kit are OK, but don't say what to do in case you can't get the new boot stretched over the carb intake diameter.  I had to take the hot boiling pan and all out to the bike to keep it hot enough so that the boot didn't shrink down before I could get it in place.  You only have about 5 seconds to get this done.

There are also a couple of considerations that you might want to think about if you are going to install an OKO on your TY 250 A. 

#1 is that with the standard (furnished) metal float bowl- it is large enough that it touches the top of the gearcase.  However, if you ordered the clear plastic float bowl, there will be more room under because there is no access plug for changing the jets.

#2- It might be necessary to have on hand another throttle cable kit.  _ I was lucky to have the machinery to re-work the one I had- there is another work around - you could re- tap the carb cap to accept the threads of your existing throttle cable.  

I should have the bike running tomorrow if all goes well- wish me luck!

 

 

Well, it's tomorrow now and the bike is running well- I got to the middle part of the tuning instructions that came with the OKO 26mm and adjusted the air bleed screw to maximize the rpm while keeping a minimum setting on the idle speed screw- now it pulls well up to half throttle- my test area around the house is not suitable for WFO testing, so I will have to wait on that, and right now it seems to still be a tiny bit too rich on the idle jet (because of my home altitude being higher than the factory 700 ft) but I'm a bit lazy about changing the jet size right now.  With that boot being barely large enough to stretch over the intake, it takes a lot of patience to get it back in place if it comes off or has to be removed. I have had to un install the rear wheel, seat and air box to get the carb body and boot all situated and happy, so it's not too much of a fun idea to be changing jets right now.

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So with part of the tune up sheet completed- the procedure has you peak the rpm's with the air bleed screw and then count the number of turns out you are- Mine were somewhere beyond 2.0, so I opted for the 50 size idle circuit jet that was included in the kit.  Hard to tell for sure, but I was able to adjust the air bleed screw down below 2 turns out and still had a good idle and good throttle response.  Just FYI - the carb for the TY 250 is a 26mm and comes with a 52 size idle jet installed.  If you live at higher elevations than the factory (700 ft) it might be better to go ahead and install the smaller 50 idle jet and save yourself the time it takes to swap them out.  I was not familiar with jet sizes or what was installed originally when I called Roger at USA-OKO 443-821-6154 but he helped me figure things out straight away. Overall I would give them a 4 out of 5 at least for their customer service and a good product.  If you want to check out the installation page it's here:

www.usa-oko.com/installation.html

 

 

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Here's what one of mine looks like. 26mm OKO from Roger. Stretched Yamaha intake hose. This carby was fitted a couple of years ago when this bike had an A model motor.

Fitted a B model motor in the bike a few weeks ago and the carby didn't need any adjustments.

20210610_073451.jpg

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3 minutes ago, feetupfun said:

Here's what one of mine looks like. 26mm OKO from Roger. Stretched Yamaha intake hose. This carby was fitted a couple of years ago when this bike had an A model motor.

Fitted a B model motor in the bike a few weeks ago and the carby didn't need any adjustments.

20210610_073451.jpg

Feetupfun, 

Yes mine looks just like that now except for the OKO logo being in black ink or laser embossed.  You may be at an altitude closer to the OKO distributor's location at 700 feet which is why you didn't need any jetting changes.  I live at 2000 and go up the hill to 4500 or 5000 when the snow melts, so it seems like my tests were showing a too-rich mixture on the idle speed jet test with the air bleed screw.  There was one K50 slow speed jet in the kit, so I put that in today- no issues with the slow speed test now.  Roger at Mid- AtlanticTrials is great to work with and very knowledgeable 

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14 minutes ago, Tillerman6 said:

Feetupfun, 

Yes mine looks just like that now except for the OKO logo being in black ink or laser embossed.  You may be at an altitude closer to the OKO distributor's location at 700 feet which is why you didn't need any jetting changes.  I live at 2000 and go up the hill to 4500 or 5000 when the snow melts, so it seems like my tests were showing a too-rich mixture on the idle speed jet test with the air bleed screw.  There was one K50 slow speed jet in the kit, so I put that in today- no issues with the slow speed test now.  Roger at Mid- AtlanticTrials is great to work with and very knowledgeable 

Yes most of my riding is near sea level and the highest riding in my state is about 4000 feet.

When I said it didn't need adjustment when I fitted the B model motor, I meant that changing from one motor to a different motor did not require any adjustments to the carby.

Both of the OKOs I fitted to TY250 motors did need adjustment when originally fitted.

Edited by feetupfun

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2 minutes ago, feetupfun said:

Yes most of my riding is near sea level and the highest riding in my state is about 4000 feet.

When I said it didn't need adjustment when I fitted the B model motor, I meant that changing from one motor to a different motor did not require any adjustments to the carby.

Both of the OKOs I fitted to TY250 motors did need adjustment when originally fitted.

Needing a few adjustments is probably par for the course.  If all I have to do is the one slow speed jet, I will feel lucky.   The B model motor I think is about the same bore and stroke, but other stuff like the expansion chamber or air box might be different. Do you remember what you had to do to the OKO's to get them dialed in? and who did you buy them from?

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2 hours ago, Tillerman6 said:

Needing a few adjustments is probably par for the course.  If all I have to do is the one slow speed jet, I will feel lucky.   The B model motor I think is about the same bore and stroke, but other stuff like the expansion chamber or air box might be different. Do you remember what you had to do to the OKO's to get them dialed in? and who did you buy them from?

Over the past few years I've fitted five 26mm OKOs, all from Roger. Some didn't require any change. Some needed the pilot jet swapped and one needed a different slide needle. For that one I bought a range of Keihin needles to try.

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1 hour ago, feetupfun said:

/Over the past few years I've fitted five 26mm OKOs, all from Roger. Some didn't require any change. Some needed the pilot jet swapped and one needed a different slide needle. For that one I bought a range of Keihin needles to try.

 

1 hour ago, feetupfun said:

Over the past few years I've fitted five 26mm OKOs, all from Roger. Some didn't require any change. Some needed the pilot jet swapped and one needed a different slide needle. For that one I bought a range of Keihin needles to try.

So what is the best way to tell if the main jet and needle position is correct?  The bike pulls strong if you give it lots of throttle, but if you ease it on slowly it will 4 stroke on the way up on flat ground.  I have not changed anything except the pilot jet from a 52 down to a 50.  I wanted to just change one thing at a time.   Or I could wait for the new ignition to come in and install that before I do anything more to the carb.  

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1 hour ago, Tillerman6 said:

 

So what is the best way to tell if the main jet and needle position is correct?  The bike pulls strong if you give it lots of throttle, but if you ease it on slowly it will 4 stroke on the way up on flat ground.  I have not changed anything except the pilot jet from a 52 down to a 50.  I wanted to just change one thing at a time.   Or I could wait for the new ignition to come in and install that before I do anything more to the carb.  

Jetting a bike using internet forum messages is a bridge too far for me

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9 hours ago, feetupfun said:

Jetting a bike using internet forum messages is a bridge too far for me

Can't blame you for that.  I think in general terms, changing the main jet to a smaller size may help with the higher altitude performance overall and dropping the needle would enforce the influence of the smaller main jet, but the actual performance is still the last word. Hopefully, if I have to make any changes at all from this point it will be just the main jet.  I think the spare one provided is only a tiny bit smaller than what came in the carb stock.  I will probably wait till I get the RSS electronic ignition installed and see if that has any influence before I try going back up the hill again.  Those points are worn down to the point where I don't trust them for any extended trips into the hills even though they run fine down here. 

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1 hour ago, phiggs said:

Just found this on the internet, as a guide to re-jetting for changes in altitude and temperature.

FAQ REJETTING FOR ELEVATION AND TEMPERATURE CHANGE (jetsrus.com)

One carb manufacturer recommends -5% in jet size for every 3000 ft additional height.

.

 

Thanks phiggs- good to know stuff!  I almost wish I had a cylinder head temperature gauge to monitor.  It's not un heard of to burn a piston while experimenting with smaller jet sizes. 

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On 6/7/2021 at 12:53 PM, Tillerman6 said:

Tony 27- 

Had a time with the OKO install today.  First thing was that the fitting on top of the new carb has a fine pitch thread that is different than what was on my TKO throttle cable.  That may not sound like much, but I don't have another cable kit to draw parts from, so I had to mill off the old fitting and cable ferrule and keep the inner stranded part of the cable intact.  That went well, but not everybody has a milling machine and a lathe, so depending on what threads are on the end of your existing throttle cable, you might have to do some scrounging for parts. The OKO fitting has a large Inner Diameter that fits over the carb end of the cable, so that was a plus, but the main thing is not to have to wait on another delivery.

So with that done I started getting the OKO carb body mated up with the new rubber boot from Claus Studios.  This was a bit more of a challenge as the opening on the OKO is larger than the TKO by about 4mm.  I ended up making tapered plugs that were oversized for both ends of the new boot.   These tapered plugs are inserted and left in the boot while the whole assembly is warmed up and then boiled with a lid on it for about 2-3 minutes. I had more trouble with the carb end than the airbox end and I would say that if you clamp the carb end first  and leave the tapered plug in the airbox end till the last second, you stand a better chance of getting everything assembled correctly.  I also had to take all the mounting bolts out of the airbox and let it float around as much as possible.  After the carb is hose clamped to the boot, and the boot is hose clamped to the air box, you can insert the front end of the carb into the rubber manifold and I'm hoping the airbox will still bolt back down to the frame.  The instructions with the kit are OK, but don't say what to do in case you can't get the new boot stretched over the carb intake diameter.  I had to take the hot boiling pan and all out to the bike to keep it hot enough so that the boot didn't shrink down before I could get it in place.  You only have about 5 seconds to get this done.

There are also a couple of considerations that you might want to think about if you are going to install an OKO on your TY 250 A. 

#1 is that with the standard (furnished) metal float bowl- it is large enough that it touches the top of the gearcase.  However, if you ordered the clear plastic float bowl, there will be more room under because there is no access plug for changing the jets.

#2- It might be necessary to have on hand another throttle cable kit.  _ I was lucky to have the machinery to re-work the one I had- there is another work around - you could re- tap the carb cap to accept the threads of your existing throttle cable.  

I should have the bike running tomorrow if all goes well- wish me luck!

 

 

What I've done with both my Jarvis & the TY is use the Dellorto threaded adjuster which screws into the OKO carb top perfectly & a Sherco cable for a Keihin carb as I use a modern throttle, it does run a slightly different route to the standard carb due to the cable coming out on a curve rather than straight up. Hopefully we can find some time to build the new airbox over the next month or so & I can get some decent testing done

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Follow up- The OKO is running now and so far I've only made a couple of small changes.  the pilot jet is changed down to the smaller size that came in the kit and the needle is dropped down 1/2 step with the tiny washer .  I think these changes were needed because of the higher altitude I have than the OKO distributor.  I'm at 2100 ft and they are at 700 ft.  I was able to use the same cable kit parts from Venhill for the throttle cable and the throttle end is soldered on with regular electronics solder and flux.

The throttle itself is the Domino slow throttle and the overall length of the cable is 49 inches.  I did not measure the outer cable housing as it is in segments so that the cable length adjusters can be used.

I am not in love with the standard air box for the TY 250 A.  So I hope your efforts turn out better than that.  But as weird as that thing is, it would be pretty difficult to replace and still have all the features that it has.  

i guess the biggest ones are that it is part rear fender,  - splash resistant, holds the air filter, and incorporates the fitting for the special air pipe leading to the carb.  So if you change any of these items or try to move them, it will change everything else and it will not be easy to do. 

However,  I do hope you will post some pics of what you do and I might still be tempted to copy your efforts if they are successful. 

The Mid-Atlantic Trials website has an accessories page that lists several options for air filter products that adapt to the various OKO carbs, and they are all simpler than the stock arrangement, being so light weight and just mount with a hose clamp, but I'm not sure of any details beyond that. 

It would be really nice to simplify the air filter and do away with the stock air filter arrangement altogether, but I have not seen anyone do that and still have an air box around the air filter to protect it from water and mud.  Best of luck and please keep us posted!

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2100 feet shouldn't be enough to affect the jetting that much, I'd suspect engine variability (ie. compression, exhaust being a bit oiled up, etc) would explain differences more than that

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