2008 2t With Keihin Carb

[jmlfin]

The tank that I used was brand new, bought it as I tanked the gas. Mixed the oil and in it went. But as said, its working now (I believe) although not anymore under my feet so I dont have to worry this anymore.

Just wanted to explain thoroughly what I experienced and stress that although this happened to me, Im not complaning Beta in general as I have always find it being one of the best. My friends bike was perfect from the beginning, many though have had problems with carb settings and float level as the bike stalls when in angle. Actually I noticed my problems first time when I pumped the front suspension and in a second it just died... every single time it was either in angle or suspension was pumped and not like after a while but not more than than a blink of an eye. Just simply stopped running. We cleaned the carburator several times, checked the needle position and adjusted the float level. Changed different gas, even drained the fuel system and filled it from another gas tank. And also changed the oil mixture from 2% to normal 1.5%. Nothing helped. We opened the reedvalve, changed carb throat just to be sure (btw, this is so thick that its hard to even imagine it would brake under stress of taking the carb of or putting it on. Maybe after many years or when -20 frost but not in normal conditions). Im not that technical, but I believe we did almost everything there is to do with my bike. We also checked the crankshaft gasket and timing. Local importer was very helpful as said, so I believe nothing more I could do about this.

[dan williams]

Well it sounds like you worked the problem. Sorry you couldn't get it resolved. Here's where you get an idea of the engineer's mindset. For me that sounds like an irresistible problem. The kind of thing I find fun and can focus on to the exclusion of almost everything else until I have it figured out.

[jezza]

You can access the clamp nearest the airbox from the side by positioning said clamp so that it faces the triangular cut out on the frame just above where the rear brake assembly bolts to the frame. Put your hand underneath to hold the clamp as it is loosened to stop it rotating away from your screwdriver. The other clamp nearest the carb can then be loosened and the airbox to carb rubber boot slid back towards the airbox and clear of the rear of the carb.

Squirt a bit of WD40 (other lubricants are available) on the joint betwixt airbox and boot to aid slideage.

[worldtrialchamp]

The Keihin PWK28 fitted to modern trials bikes has only one atmospheric port open, the other one is blanked off by the casting.

I have done this mod to several bikes fitted with Keihin PWK28 carb. It stops the bike gagging when at extreme angles eg splatters, steep descents

On the LHS of the carburettor, the vertical atmospheric port inside the float bowl area is pre cast by Keihin but the horizontal port on the LHS is blanked. Just drill it out with a 2.5mm drill until it meets the existing vertical port (you'll feel it)

[podracer]

Hi,

Some say installing a Keihin carb on a 2006 Rev3 270, will help the bike solving the fuel leaks, and also bringing a clener and crisp throtthle response down low....

Must be a reason why BETA updated it on the newer rev3's... and removed the mikuni...

Correct me if Im wrong...

Dos this Keihin carb will need any mods to my 2006 rev3 to install it with the OEM carb boots ?

If so, were I can get a good deal on one of these...

Thanks

Edited March 21, 2015 by podracer

[worldtrialchamp]

no, it's not a case of just swapping carbs. the manifold, snorkel, throttle cable all require changing. The mixture screw is also on the opposite side on a Keihin. There is a company selling conversion kits for these but I can't recall where....might have been in Australia or New Zealand. someone else here might know. best to get some expert advice. ...

[podracer]

Hi,

Does anyone knows the OEM specs for this 2008 Keihin ;

Main Jet # , Pilot #, Needle position and air screw settings ?

Many Thanks.

[oldgrumps]

What size vent tubing is that 3/16 or 1/4 inch

[dan williams]

On 5/5/2008 at 6:18 PM, jmlfin said:

The tank that I used was brand new, bought it as I tanked the gas. Mixed the oil and in it went. But as said, its working now (I believe) although not anymore under my feet so I dont have to worry this anymore.

Just wanted to explain thoroughly what I experienced and stress that although this happened to me, Im not complaning Beta in general as I have always find it being one of the best. My friends bike was perfect from the beginning, many though have had problems with carb settings and float level as the bike stalls when in angle. Actually I noticed my problems first time when I pumped the front suspension and in a second it just died... every single time it was either in angle or suspension was pumped and not like after a while but not more than than a blink of an eye. Just simply stopped running. We cleaned the carburator several times, checked the needle position and adjusted the float level. Changed different gas, even drained the fuel system and filled it from another gas tank. And also changed the oil mixture from 2% to normal 1.5%. Nothing helped. We opened the reedvalve, changed carb throat just to be sure (btw, this is so thick that its hard to even imagine it would brake under stress of taking the carb of or putting it on. Maybe after many years or when -20 frost but not in normal conditions). Im not that technical, but I believe we did almost everything there is to do with my bike. We also checked the crankshaft gasket and timing. Local importer was very helpful as said, so I believe nothing more I could do about this.

Going back to this as a friend had a GasGas with a PWK28 that did the same thing. Bounce the front end and the bike would die. Nose down and the bike would sputter and die. Fixed by replacing the carb. I had hoped to do a postmortem on the carb but the dealer who replaced it already disassembled it for parts.

Very curious.

[dan williams]

Just wanted to add something that happened with a Keihin on a GasGas. Bouncing the front gagged and sputtered the engine and was very like the issues mentioned above. Turned out the choke was partially on. So while trying to diagnose the bounce sputter issue I had never considered a leaky choke circuit. So if your bike gags on downhills or while bouncing the front end have a look at your choke valve.

[Six5yeti]

On 1/22/2019 at 11:05 PM, dan williams said:

Just wanted to add something that happened with a Keihin on a GasGas. Bouncing the front gagged and sputtered the engine and was very like the issues mentioned above. Turned out the choke was partially on. So while trying to diagnose the bounce sputter issue I had never considered a leaky choke circuit. So if your bike gags on downhills or while bouncing the front end have a look at your choke valve.

This might very well be what I have going on.  I've just recently acquired an 08 Rev3 250 that I can't seem to get running right.  I've gone through 48-52 pilot jets.  JHL needle position 1-5.  Always seems to be loading up. I've also followed all the articles on float adjustments and have gone from prescribed to way to low and back with no luck.  The choke operates normal and the idle falls once popping it back down but maybe it's fully closing.  Aside from this darn slow turn throttle and it not running as good as I think it should I love the bike. 

[dan williams]

The Keihins are prone to blockages in the pilot jet circuit. Particularly that tiny hole behind the slide. I find that about twice a year I have to do a disassemble and blowout of the passages in the carb. The bike just runs lumpy and lethargic off the bottom when the carb is plugged. I’m also a big fan of the carbon reeds from Moto-Tassinari model V351C. They supposedly don’t make them anymore but others have called them and they have built up a set for them. Makes the bike grunt like an old school Bultaco while still being able to rev. My ‘08 was a fun bike. Solid.

[Six5yeti]

5 hours ago, dan williams said:

The Keihins are prone to blockages in the pilot jet circuit. Particularly that tiny hole behind the slide. I find that about twice a year I have to do a disassemble and blowout of the passages in the carb. The bike just runs lumpy and lethargic off the bottom when the carb is plugged. I’m also a big fan of the carbon reeds from Moto-Tassinari model V351C. They supposedly don’t make them anymore but others have called them and they have built up a set for them. Makes the bike grunt like an old school Bultaco while still being able to rev. My ‘08 was a fun bike. Solid.

I'll try another full blown cleaning on the carb.  I'm no newb to pwk carbs as I'm pretty much the carb guru of our group but this tiny little bugger has me questioning my skills!  Torn down probably 15 times at this point each time only to make a single change and each time coming to the same result. 1/8 throttle is an absolute blubbering mess.  It's fine for doing an obstacle that I've set up for with the mid-range of the throttle being acceptable but trying to ease around or get on down the trail is killing me.  Pop pop bum bum pop pop pop. 

I can't seem to find a listing for the JHL needle I have.  Does anyone know if this is stock?

Seems to be right at the transition from pilot to needle just doesn't want to pick up.  All three 48-52 pilots have given the same result.  The 50 seems to tune in best with the air screw. I'm at 1700' btw with temps around 70F. I've just thrown a new BR7ES in to go back old school and read the plug.  Looks rich and smoking but could also be the Caster 927 I happen to have left on my shelf from a couple years ago.  The PO said he ran it at 50:1 but was never happy with the way it ran and I have since been running 65:1.  I'm pretty ocd about getting the most out of an engine. 

Speaking of vforce,  Based on another members post I bought a V351A reed cage for a KTM 50sr up to 08 (Beta engine).  The V351A comes equiped with the medium reeds which is why I went that route vs the V351B that has lesser volume reducing insert.  The cage dimensions are spot on.  You just need to modify the volume reducing insert to suite.  Using a step bit I carefully bored the intake hole and to match the Beta boot and using my dremel and rotary trim bit I smoothed everything out. 

[dan williams]

Very familiar with the '08 engine. It was probably my post on the VForce reeds. I just ground the protrusions from the face of the Beta manifold and opened up the VForce insert a bit. I've run my Zero's Technos, Rev3s and EVOs on 80:1 to 100:1 on BelRay H1R for years without problems. At 50:1 the mid-muffler and silencer could be pretty gummed up. The transition from pilot to needle goes through the slide cutaway but I don't think that's your problem. The stock jetting for the '08 was pretty close and I think the JHL or JJH needle was stock. I can't remember. One thing to consider is Beta's have high compression engines and really like their octane. They'll usually run mediocre on pump gas. Some will just jet them richer and consider it a job done but it really doesn't solve the problem. An '08 could be due a set of rings. The degradation as the rings wear is so gradual you usually won't even notice but it will lose some of the bottom end and starting will suffer. Also leaks in the intake tract can make the bike somewhat boggy so a shot of starting fluid around the manifold while the bike is running will change the engine note with a leak but I get the impression you know that. WD40 used to work but they changed the propellant from propane to something non-combustible so it doesn't have quite the same effect. When my carb needs a clean I'll usually pull the center tower off. Needs a torx security bit. I forget the size. T20 I think.

Trying to diagnose over the internet is such a drag when I'd rather be up to my elbows in an engine or at least be able to hear it in person.

[Six5yeti]

Alright.  Thank you very much by the way for hanging in here with me.  Remote diagnostics drives nuts too.  So I haven't gone down the road a air leak testing or compression as the bike doesn't have the usual tell tale "gung gungs" on decel or any perceived detonation and starts first kick every time.  The PO stated that he replaced the rings and at that point I looked for tool marks on the cylinder fasteners and was satisfied.  Does appear to have at least 2 base gaskets.  I pulled the carb down again this time removing the emulsion tower and confirmed no blockages.  The enrichment circuit is also sealing nicely.  Headed out for another round now.  Going to pull the stator cover and do a full air-leak test of the dry seal and intake tract just to rule out.  I'm also going to run a compression test.  Where should it be?  180-190psi?