Keihin 28mm Worth The Swap ?

[hammer]

I was considering installing a Keihin 28mm carb on my 08 2.9 is it worth the cost and trouble to do the swap.

[copemech]

Hummmmm, well, unless you are really into Big splats, Big rocks and riding on a national expert level and need more top end power, probably not worth it.

They are a bit fussy as well.

[trialsnutterman]

I'd say yes definitely.

It makes the bottom end alot smoother when setup right, which has got to be good for any standard of rider.

[copemech]

Not to disagree with nutterman, as the things are technically a better mixer, and tend to be smooth off the bottom, while yet Bigger power throughout the range would be my perception.

The standard dellorto 26 phbl is not a bad brick of a carb, tends to be reliable, and I think I had one as well refined as could be, rivaled the Kiehin in smoothness off the bottom and progression, and without the bigger power(i do not need or want) in mid and top.

Running the 38 pilot, i managed to get the fuel screw down into a controllable range at about 1.5-2 turns. This compares to most running leaner pilots and the screws out to 3-4 turns. Now this does put you in a tighter range of controllability, but you must manage it, not unlike the sensitivity of the ariscrew on a kiehin, the fuel screw can be even more sensitive based upon the temps and such.

All this might be a bit mute, cause I run the boyesen reeds as well, which also seem smoother off the bottom, and on a regular bike, I may not go past 35-36 on the jet. Lean the idle as best you can. If it gets blubbry off idle at 1/16 throttle(transition circuit) under load,you gone too far, back off.

All this fine tuning takes time and experimentation.

The Boyeseen reeds are cheap, yet if you want a carb I have a good one. Let me no!

[neo]

My Keihin28 sits in the cupboard at home. So start with a low cost OKO 26 (Keihin copy) and see how you go with that.

There are more posts than I can remember on this subject on TC.

Best of balance.

Neo

[steveo]

My Keihen 28 that came standard on the Raga sits in my cupboard too.

My OKO 26 flatslide that I put lots of time and effort into making my engine smoooooth running and gentle off the bottom sits in my cupboard as well, again to aggresive down low.

Your dellorto 26 phbl (Neo) is the carb I much prefer, along with the addition of the standard 250 induction manifold ( different to the standard Raga) and a 34 pilot, needle clip second from top, fuel screw nearly 2 out, has my motor sweet as.

Fitted a set of boysens and the motor ran sweeter on idle but introduced aggression that I found unsettling for my riding.

Lots of postings on this subject as each rider looks for different motor responces for their own style of riding I guess.

[neo]

Your dellorto 26 phbl (Neo)

Not me!! ....my PHBL is the same cupboard as the Keihin (along with my OKO 30)...Hard to believe it's effecting my tuning from there

Oh and I fitted a set of Boysens some time back too ... They're Ok but nothing to write home about ... A bit smoother and runs a bit leaner too.

Recently got myself a VHST26 gotta get it milled down a few mill first .... But stay tuned (forgive the pun) over the next few weeks

Best of balance.

Neo

[hammer]

Going to try out the 28mm, what did you guys do about the reed manifold and the airbox boot

[tony27]

I bought the airbox to carb connector off splatshop, Chris explained how the keihin manifold differed to the standard version. From memory it's only slightly modified at the opening & easily done at home

I'm running a oko kit which came with a manifold so I haven't bothered modifying the standard 1

[neo]

Going to try out the 28mm, what did you guys do about the reed manifold and the airbox boot

Honestly if all your doing is experimenting to see how you can improve thing don't worry about another reed manifold for now. Despite what some report i know the Sherco dealer in Aus has never sold a replacement manifold because the old one split. So there's no merit to that claim.

You might think that bigger is better but I know (from experience) you'd be wrong. The 26mm OKO is the best all round carb. It's much cheaper and has NO less power than any of the 28mm carbs either.

I've bought and fitted quite a few carbs now and I'm still looking for the perfect tuning solution. So keep that in mind if you discover that it's not quite as good as you'd hoped (particularly when the bike gets really hot).

Best of tuning balance.

Neo

[copemech]

Honestly if all your doing is experimenting to see how you can improve thing don't worry about another reed manifold for now. Despite what some report i know the Sherco dealer in Aus has never sold a replacement manifold because the old one split. So there's no merit to that claim.

You might think that bigger is better but I know (from experience) you'd be wrong. The 26mm OKO is the best all round carb. It's much cheaper and has NO less power than any of the 28mm carbs either.

I've bought and fitted quite a few carbs now and I'm still looking for the perfect tuning solution. So keep that in mind if you discover that it's not quite as good as you'd hoped (particularly when the bike gets really hot).

Best of tuning balance.

Neo

Agree with this, just have to stuff it into the reed side, tight but works. On the airbox side, there is one offered now as I understand from Sherco, fits the Caby model with the Kiehin. Call Ryan.

For whatever reason, I am still running the OKO 24 on the 2.9, as compared to Neo with the OKO 26 on the 2.5(i believe), which has offered some challenges, yet I must state that even though my Dellorto was well tuned and really good, this one may be better, yet still sensitive on the day. It can get near electric motor smooth off the bottom, still has the(big bike) midrange hit and big torque(yet progressive) if one opens it up, and if there is really a loss of power of the 24 OKO v the 26 Dell, on the top end of things, I would be hard pressed to tell it! Bitch is still a bitch! I do not really want to go there! Unfortunatly for me,a 2.5 is just a smoother machine it seems, and I seem to still prefer them after my '05 bike.

With the big bore motor, with (lots) of suction, I am down to the 38 pilot(from 45) for controllability, and about 1 turn out on the airscrew(sensitive), yet on the big end,and under load, I am down to a #100 main jet, as the thing just sucks the fuel up by itself when you open up the throttle, so the basic theory prevails as one may need to adjust main jet settings by as much as 10% for each 1mm change in bore size of the carb. Which explains why a 125 main may run fine on a 28mm carb.

MC

[tony27]

Part number for the airbox to carb connector is 1555

Cope, I followed your advice on main jet size & am running the #115 main which is quite a bit smaller than in the standard dellorto. Pilot is #45 which is bigger

Any theories on why this is the case?

[hammer]

So you think the 26 oko in a better start than the 28 keihin

[neo]

So you think the 26 oko is a better start than the 28 keihin

No I actually think the OKO 24mm is much better for novice trials but the 26mm is a good compromise of smooth control and power.

But at the end of the day the choice is really yours.

Best of balance.

Neo

Edited September 26, 2010 by Neo

[copemech]

Part number for the airbox to carb connector is 1555

Cope, I followed your advice on main jet size & am running the #115 main which is quite a bit smaller than in the standard dellorto. Pilot is #45 which is bigger

Any theories on why this is the case?

I doubt that is a bad setting at all depending upon the bike, the reeds and the fuel. A quick look back at mine sitting on the shelf was very similar at a 38/115 set and 1.6 or so turns out on the fuel screw. As long as it does not get too lumpy on the transition circuit(1/16-1/8 throttle) you are fine. Mind, it seems that keeping the things as lean as possible on the slow jet and screw tend to smooth the progression of the throttle response. Many will run the 115-118 range on the main jet so the clean out better on top. As I care little about total top end performance, and seldome want or need to gothere, on a 2.9 in a section, even the 115 main could be a bit rich with the boyesens, yet all piont being, going down to the 24mm carby, the velocity is such that it sucks soo much on it's own, had to go down to 100 range on the main. I know it is totally minimal size carb in this application and such due to displacement, yet as far as control and progression throughout the normal range of riding, it does work.

Normal rider(if Neo is normal) may still prefer a 26 OKO, but for overall rideability, I still do not recommend a 28 unless you are riding top class and big stuff!