Beta Rev 3 carb leaking please help.

[betabell]

I am having some problems with the carb on my Beta rev 3 250cc 2005 trials bike. I have had the bike a few months and have just been using the bike in fields, going up hills as I am new to trials. The bike starts well normally first or second kick. Recently I noticed that the carb was leaking, I think it has always done this but I had not noticed before. The carb has got the atmospheric tubes looped of the top of the carb and cut at an angle  in the end.Petrol drips out from the over flow in the float bowl. This does not happen when the bike ticks over but when you rev the bike half to 3/4 throttle.I am not a mechanic and have little experience with carbs and have been trying to lean as I go but there is little information available on the net about. Any help would be greatly appreciated.

Here is what I have tried.

I have bent the small tab on the float arm so that the fuel shuts off sooner.

I have bent the float arms where they touch the floats  

I then brought a new float valve assemble thinking it was not seating properly. This did not seam to make a difference.

I have read the Billy Traynor set up details when I set it up as described petrol just pores out.

I have taken the carb off the bike fire or six times trying to make small adjustments to correct it but I don't seam to be getting any where I must be missing something? Or maybe there is some other part that needs replacing?  

I am  getting a little frustrated and am wondering if I should just buy a new carb? 

Reading the Billy Traynor information it sounds like the float arm should only move 2mm which seams a really small amount of movement. 

James

Edited May 5, 2017 by betabell
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[totalshell]

hi.. your really lucky in that this is an issue covered brilliantluy on here in the past.. google/search beta leaking carb.. the solution involves some work but its all do able if you follow the instructions pictures.. even i managed it.. 

[billyt]

 

[dan williams]

Hi James,

 

I know you already mentioned some of this but I'm going to run stream of consciousness for a bit so bear with me. Yes the floats only need to move a tiny amount to open up the float valve to full. It's a conical seat so more than a mm or so doesn't flow fuel any faster. When you pull the carb out and take the float bowl off the seat should close when the floats are level or parallel to the float bowl sealing gasket. Don't be fooled by the difference between a closed valve and compressing the spring in the valve plunger past the closing point. The two adjustment tabs for the floats are the tab the spring clip for the valve plunger attaches to (sets float height) and the little tab that hits the side of the tower the float pivot goes through (limits float travel). There are three tubes coming out of the Mikuni. One on the bottom of the float bowl is the actual overflow. The two that come out of the sides are the atmospheric vents for the float chamber. The usual problem with the Mikuni is the atmospheric vents get fuel splashed up into them and because Beta made the tubes too long they act like siphons and pee fuel until the tank is empty. Usually this only happens when the bike is parked. Someone must have had that happen with your bike and figured they'd cure it by looping the tubes up over the carb. The easiest way to cure it is to put the tubes back where they belong down the side of the carb and nip a small hole in the tube above the float bowl. Inspect your floats for leaks. That can mess up a perfectly float adjustment. Also make sure the floats aren't rubbing on the bowl gasket. If they are trim the gasket with an X-Acto or similar knife. Billy's adjustments and fixes are really the gold standard and work perfectly unless something weird is going on. One other thing I just thought of, make sure there's nothing making the carb vibrate like a fuel line that is hitting the exhaust or the carb hitting a part of the engine. A vibrating carb is an unhappy carb.

At this point I think you might have tweaked too much at once and should stop and go back to basics. Straighten the float arms. Set the float level. Set the float travel. Check the floats for leaks and rubbing. Let the atmospheric vents go back to the bottom of the carb and nip a hole just under the bend where they come out of the carb. Make sure the carb isn't hitting anything on frame or motor. Report back here what happens.

 

You and I must be extremely diligent. Ninja Billy is watching!

[betabell]

I just wanted to say thank you for people taking the time to help me and posting advice and instructions. I am going to have another go adjusting the carb today and see how I get on. I shall follow the advice given.

James

[betabell]

   

Ok here is where I am at I have been adjusting the carb all day but it still drips from the overflow on the float bowl when the bike is reved. I have a new float arm so I thought I would start with that as the old one has been probably bent to many times. I have set it up as per instructions, I have taken a couple of photos. I have adjusted it so I have about two mm of travel but the carb still drips. If I adjust it any further it will not let any fuel through. I have piped the carb up to a test fuel tank to check that when the arm is in a closed position it shuts of fuel which it does. I can’t see that the carb is fouling on the exhaust or anything. I have taken the floats out they look a little rough in a couple of places. I have sprayed carb cleaner down the float tubes, they seem to slide nicely. I took the floats out of the carb and put them in a bowl of petrol and held them down with my finger, there was no bubbles. The floats have some lines on them but I think it is from when the where moulded. There does seem to be some surface cracks so am thinking about buying some new ones but they seem to function as far as I can see. Thinking about the whole vibration thing when I got the bike the metal tube which comes out of the top of the carb was loose and I tightened this up when I have been fiddling with the carb. So I wonder if this need some free play in it and if it was tight maybe it could vibrate disturbing the carb. But I have slackened this off and further loosened the play in the throttle cable but this has made no difference. I have nipped a hole in the atmospheric pipes. I can’t see the floats fouling on the gasket. I am out of ideas really as I say I could replace the floats but beyond that I don’t know what I can do? I could lower the float height and then adjust that for the 2mm of travel?

   

The picture  3 with my finger in it shows the lower position of the float arm and then the next photo 4 shows the float arm in the stop full position.

  

[billyt]

Betabell

 

"This does not happen when the bike ticks over but when you rev the bike half to 3/4 throttle."   Please explain what you mean by this?

Are you saying that if the bike is in an upright position and running at idle it does not leak, and only leaks when uptight and at half to 3/4 throttle?

Are there any cracks, dirt on the viton tip need and seat?

Can you post a few pictures of the float bowl?

This is a VM26 carb? 

BillyT

 

 

Edited May 7, 2017 by billyt

[dan williams]

Whoa! That adjustment is really wrong. Pointing to that angle bit on the jet tower should be the limit of travel with the valve open. Resting upside down like that the float arms should be level when the valve closes. Parallel to the float bowl. Are your floats upside down? 

[betabell]

Hello Billyt, yes when I say it leaks I mean when the bike is upright. It does not leak on tick over but when the throttle is blipped. The needle and seat are brand new and clean.

Yes I can take some photos tomorrow after work. 

I think its a standard carb.

 

 

[betabell]

Hello Dan I think I have set this up correctly but I could be wrong as I have never done this before and am happy to be proved wrong. I thought that the float arms are at a angle because the carb sits at an angle on the bike. Not including this one I have only taken three other carbs apart and that was just to clean them not to set the float height. The other carbs I have worked on all sat level on the bike and had one float. By that I mean two floats linked together in an u shape. I was a bit confused when I opened this carb up seeing two separate floats that are attached to the bowl. You may be on to something the floats could be upside down. I do not have an diagram of what the inside of the carb should look like. When I took the floats out to clean I put them back as I found them but that is not to say they are correct.  The owner before me may have taken them out and not put them back correctly I just don't know. I will post pictures of the floats after work tomorrow.

 

Thanks billyt and dan

 

Edited May 7, 2017 by betabell
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[billyt]

Notable  The inside brass tab is bent all wrong.  Take the brass tab/tanga off and make them all flat. Before you do take  a side profile picture of the brass tang off the carb. You never bend the outside long tabs only the smaller tab in the middle.

Edited May 8, 2017 by billyt

[dan williams]

Nope,  angle of the carb slightly affects the pilot mixture on a Beta which is why they tend to stall on downhills. If you look at the main/needle jet tower it is in the center of the float bowl. The pilot is also close to the middle but still on the centerline. Pour yourself a glass of water and stick a straw in the middle. No matter how you tip the glass the water level in the center where the straw is stays the same. So with a concentric carb no matter how you tip the bike the main/needle jet combination always sees the average level of fuel in the bowl. Keeping the pilot circuit on the centerline means the pilot circuit is unaffected by leaning the bike side to side.

Your adjustment is way off. When you hold the carb as shown the float arms should be level. Flat. Parallel with the float bowl seam.

You should then be able to lift the float arms up to where they are stopped by the stop tang pointing to the right angle where the pilot jet platform meets the main/needle jet tower. 

[billyt]

The little brass tang stops the travel of the fuel shut of.  It is VERY undeniable to have move more than a few millimeters as it change the angle of the longer arms arc the further it travels there is also a chance of debris or dirt getting in.

The fuel needle is not analog its like a digital on or off.  

However the perpendicular tang does NOT stop the movement of the floats.

Both Dan and I are telling you the same thing. Dan in an American accent and me in a Scottish accent. 

Dan took the pebble from my hand a long time ago  LOL 

 

 

[betabell]

Hello guys, ok I have taken some photos as you requested. Yes Dan I had set it up all wrong, thank you for the education. As I said I don’t know what I am doing and am trying to learn as I go. Thanks for explaining about the straw and the glass of water I understand what you mean.

The floats must be the correct way round as if I reverse them I can’t close the carb float bowl. I have straightened the tangs and have tried to reset it as you said. With the height adjuster tab straight the float lever arm is not quite parallel to the bowl as you can see from the photos. I would have to bend it in the opposite direction to make it completely level. This that what I should do? I have restricted the movement of the float arm and got it to almost line up with the lower tower. I am not sure if I am now adjusting it as I should have done in the first place? And if I am getting closer?

I have put the carb on the bike with the adjustments shown in the photos. I still get the same results.

I am not sure if this helps but I thought I would put the bike on a slope to see what happens. This may be a silly thing to do and have no scientific base. When the bike was standing up hill the same thing happened- petrol dripped out of over flow when the bike was revved. When the bike was standing going downhill, the petrol poured out of the over flow.

[betabell]