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basssound

Rev 3 carb settings and issues.

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He'llo everyone, first time posting in here as I'm new to trialling. 

I've got myself a 2006 Rev 3 250, I really enjoy riding it but I've noticed a couple of things. 

First off the carb would dribble all the time from the atmosphere tubes so I did the BILLY T mod with the plate tang, replaced the vent pipes with long ones going over the carb. 

Whilst I had the carb stripped and cleaned in the bath, I checked the needle to find the rubber hard with a dip in the cone so fitted a genuine needle and body. 

The carb also had the standard 30 pilot and 150 main, I've read the I should try the 27.5 pilot and 145 main so I've fitted a 27.5 but I'm waiting on the 145, I've refitted the 150.

Now I'm noticing the bike seems to want to stall easily when I'm slipping the clutch to start moving... This didn't happen until I modded the carb. 

What should the basic settings be when rebuilding the carb, what should the air fuel screw be set to, it's set to 1 ¾ turns out. 

Also there's a brass overflow pipe under the carb, should the be a pipe on that like the vent pipes? 

Lastly, the throttle cable on top of the carb, the metal bend into the top cap, should that be tightened or left loose as I've read something about air getting in at the point and messing with the air fuel ratio. 

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Noodle on throttle cable is loose on purpose so the cable can swivel. The brass tube on bottom of carb is float bowl overflow and it's important it ends below the float bowl. If you put a long tube on it higher than the bowl and the float bowl overfills it'll end up in the engine. The air screw at 1 3/4 is about right but you may have to adjust for conditions. The 27.5 pilot is kind of the default as the older bikes came jetted a little rich as opposed to all bikes now that seem to come jetted lean for emissions. The Billy T fix of nippering a hole in the vent tubes above the height of the float bowl works well and should preclude the necessity of routing the vent tubes up higher. In fact once the tubes have the holes above the float bowl the ends should be routed as standard down the back of the engine cases. Adjusting the tangs on the float lever is not always as straight forward as it seems. The travel adjust is important but the level adjust needs to be thought through. I assume you set it level when the tang just touches the float valve plunger. If you let the weight of the float assembly sit on the plunger it'll compress the spring in the plunger and give an incorrect level reading. One thing to consider is that with a slightly off pilot mixture most people will adjust their idle higher. So when they change the pilot they readjust their idle to a similar RPM but the slide is actually in a slightly different position. You nay need a slightly higher idle with the current jetting.

Keep working on it. Carb adjustments take time and many iterations to get right. Well worth it.

 

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The float arm was upside down when I stripped the carb, the perpendicular tang was pointing down. 

I turned the arm and refitted, the arm sat perfectly parallel to the carb body whilst on the needle but not compressing the needle spring. I then adjusted the travel tang so that it was 1/16th above the left tower at max lift. 

I did notice the bike performed better with a higher idle but I thought that would be wrong as the higher idle may push me out on tighter turns but that's just my very novice bike handling, this is only the fourth time I've ridden a motorbike. 

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If the air screw hasn’t been touched and you’ve gone leaner on the pilot and are now experiencing less strength in the motor, try going in on the air screw 1/8th turn at a time (richer) and re test. You can also try coming out from where it is now. One will be the right direction to follow. Make sure engine is fully warmed first and idle is set right. The main won’t be having any affect at smaller throttle openings. That only comes into play after half throttle. You will be able to dial it in though easy enough. 

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On 7/12/2020 at 4:51 PM, basssound said:

The float arm was upside down when I stripped the carb, the perpendicular tang was pointing down. 

 

That's a little disturbing.

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On 7/14/2020 at 11:41 PM, pindie said:

The main won’t be having any affect at smaller throttle openings. That only comes into play after half throttle. You will be able to dial it in though easy enough. 

Mmmm... As soon as you get off the idle the main jet is now in the equation.... Key word is IN the equation  

Why?  Because the fuel has to flow up through the main jet orifice to get to the needle jet orifice as the slide moves up taking the needle with it...

As the needle and slide get higher the main jet starts to have a bigger influence / role to play

All jets (Pilot / Needle / Main) are in the equation once the slide and needle jet start to move up although at different contributions 

Be it a Mikuni or Keihin carb the logic is the same

 

 

 

s-l1000.jpg

Edited by billyt

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Wait a minute. Did you mean the travel adjust tang was pointing to the bottom of the carb? That is where it’s supposed to go as it limits the float travel while the carb is bouncing around. If that’s the case your float arm is now in upside down.

We need pictures?

3ED23053-4A08-4276-95DC-78A77570C473.jpeg

Edited by dan williams

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Dan... Wont be the first time someone has installed the brass tang upside down.  Seen that and worse on the VM 26mm Mikuni's on the Beta.

How about a float install without an axle pin, or some holes drilled in the floats to make them lighter and the worse was connecting the gas directly to one

of the brass atmospheric vent tubes and then could not figure why the gas was flooding out of the carb when he turned the gas on ?   

 

Edited by billyt

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The 'adjust this tang to set the float travel' in the above picture was facing down and not up, it's up the above picture.

I'm still waiting for the 145 main jet to come. 

Is there much adjustment regarding the mixture screw once I fit the smaller main jet. 

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Ok Billy the holes to lighten the floats made me laugh.

Basssound OK, I just had to make sure.

Betas turn the tightest of any bike and reward good technique but will punish bad technique and pushing the front end is a common complaint. The first thing must new riders will assign blame to is the engine/clutch. They can be a contributing factor. Especially the clutch (see clutch thread pinned to top of forum) but the usual issue is just lack of control working engine vs clutch vs rear brake. Add to that most new riders will try to steer with upper body and weight distribution and though you may cobble together a working riding style the fundamentals are wrong and will limit progress to a certain point. Watch videos of good riders and note how they keep their torsos forward and steer by bending the inside leg and arm while straightening the outside leg and arm. Even the top guys will only de-center to start a dynamic move and get their body re-centered as quickly as possible. You’ll hear a lot of BS about weight the inside peg or the outside peg in various terrain. Ignore it. If you weight one peg without the intent of changing the attitude of the bike you will have to counterweight the opposite bar to keep the bike from flopping over. You’ve now induced torsion in your body that limits your ability to respond. 

Rule one: Stay centered.

Rule two: Steer with your feet.

Rule three: Think pressure not weight.

Rule four: See rule one.

If you can find a copy of the Bernie Schriber/Len Weed book Observed Trials buy it and give it a thorough read. It may be old but the basic instruction in it is as true today as it was when it was written. You’ve just started and have much to learn. I’ve been riding trials bikes for >35 years. I also have much to learn?. But damn it’s been and continues to be a fun journey.

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2 hours ago, dan williams said:

Ok Billy the holes to lighten the floats made me laugh.

Basssound OK, I just had to make sure.

Betas turn the tightest of any bike and reward good technique but will punish bad technique and pushing the front end is a common complaint. The first thing must new riders will assign blame to is the engine/clutch. They can be a contributing factor. Especially the clutch (see clutch thread pinned to top of forum) but the usual issue is just lack of control working engine vs clutch vs rear brake. Add to that most new riders will try to steer with upper body and weight distribution and though you may cobble together a working riding style the fundamentals are wrong and will limit progress to a certain point. Watch videos of good riders and note how they keep their torsos forward and steer by bending the inside leg and arm while straightening the outside leg and arm. Even the top guys will only de-center to start a dynamic move and get their body re-centered as quickly as possible. You’ll hear a lot of BS about weight the inside peg or the outside peg in various terrain. Ignore it. If you weight one peg without the intent of changing the attitude of the bike you will have to counterweight the opposite bar to keep the bike from flopping over. You’ve now induced torsion in your body that limits your ability to respond. 

Rule one: Stay centered.

Rule two: Steer with your feet.

Rule three: Think pressure not weight.

Rule four: See rule one.

If you can find a copy of the Bernie Schriber/Len Weed book Observed Trials buy it and give it a thorough read. It may be old but the basic instruction in it is as true today as it was when it was written. You’ve just started and have much to learn. I’ve been riding trials bikes for >35 years. I also have much to learn?. But damn it’s been and continues to be a fun journey.

Thank you for the long and very factual reply, as you are saying, the main issue is me and the fact that today is the 5th time I've ridden a motorbike, all five times are on this bike... 

The reason for getting an older beta was incase I didn't get on with trialing, I really enjoy it but I'm finding issues with the bike but that's down to me. 

There are genuine issues with the bike like the idle speed will move around through the day, the piston knocks when on very partial throttle, just off the idle which is down to the completely blocked exhaust silencer wadding, that's on order. 

The flywheel has the weight fitted and the bike has a slow action throttle but I'm beginning to think I need a fast action throttle as I have to twist the throttle quite a bit to get the bike to rev, also I've removed just about all of throttle cable slack. 

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Ah good info. Idle speed wandering is often a symptom of running lean. Have a fire extinguisher handy just to be on the safe side. Try spraying starter fluid around the intake boot to make sure you don’t have an air leak. WD40 used to work as it had propane (can’t write that without hearing Hank Hill in my head?) for a propellant but I’m not sure if it still does. Short bursts while the bike is running. If the idle changes then you have an air leak. Gotta be fixed before any jetting will make sense. 

As for the knocking, Betas are famous for needing high octane. The come down knock is very common, especially that era bike. You may get rid of the knock by jetting it rich but the power gets all lazy. If you have access to race fuel or 100LL avgas give it a try. Even premium pump fuel is a crap shoot and I won’t use it after some painful get offs from a crappy running engine. I’ve run VP C-12 for years. It has the advantage of consistency. Day after day the engine behaves the same. Something that just doesn’t happen with pump gas. Another thing to consider is a set of rings. Pistons and bores on trials bikes last a long time but a set of rings will give you back engine snap you didn’t know you were missing.

Another thing new trials bike owners often do is mix the oil/fuel like a motocross bike. Most trials bikes are happy at 80:1 and some will mix at 100:1 if they’re real plonkers. The Vertigos are running 200:1 but I think 80:1 is the sweet spot.

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