Hi. Our boy's Beta 80 (2014 b/w) starts and runs sweet from cold, but as it warms up, it's as though it's retarding. It feels tight like it's going to seize, has no power off the bottom, and sounds a bit rough. It revs out though. Fast 'blipping' of the throttle in neutral fails ("bwoooor"). Slightly slower blipping is fine, but it's like it can't wait to get back to tick over (i.e. no run-on of the revs). Leave it overnight, and the next day it's fine for 5 minutes, then same again. We have tried re-positioning the CDI to get it away from the direct heat of the cylinder / exhaust. No change. We have tried a brand new CDI. No change (no change in fact out £180!!). All manner of experiments have been made with regard to carburetor jets / needle / mixture screw, and fuel / air supply is all fine. We don't want to give up on it, because it is clearly capable of running ok, like when it's cold, but there are times when I want to dig a deep hole and bury it. Is there something that should be (but isn't) telling the CDI to alter the timing when hot? We have a 2018 s/w Beta 80 and apart from occasional touchy carb settings this generally runs well and as expected. Any help / guidance gratefully received. Thanks.

I know someone with I think a 2014 (might have been a 2015) with some issues with running correctly caused by manufacturing debris in the fuel tank getting into the carburetor.  If you don't already have one I might put a fuel filter on it and check/clean out the carburetor as a first step.  

Good luck.  

18 minutes ago, jonnyc21 said:

I know someone with I think a 2014 (might have been a 2015) with some issues with running correctly caused by manufacturing debris in the fuel tank getting into the carburetor.  If you don't already have one I might put a fuel filter on it and check/clean out the carburetor as a first step.  

Good luck.  

Make sure you blow out the overflow ports/hoses as well when cleaning the carb. If I over oil my 2015 evo 80s oil filter it runs burbly rich but it it runs rich right from cold to hot.

@jerv888

One more thing.  If it has been this way from the beginning you might want to order up some jets and re-jet at the same time as my daughters Beta 80 runs so much better now that its jetted.   

None of these bikes adjust ignition timing based on temperature. Certainly not something with razor thin profit margin like a tiddler. Your problem is either a faulty ignition or more likely carb/mixture possibly an air leak. Is the current jetting set to stock values? Are you certain the carb is assembled correctly? Have you tested for air leaks with hot start? Are the reed valves intact? Is there anything blocking the exhaust?

It’s important to start from stock jet values with a properly cleaned and assembled carb. It’s very easy to chase around in circles if you don’t have a known starting point.

Not diagnosing but just reference, a cold engine requires more fuel in the mixture to help vaporization. Do you have to use the choke to start it cold? If not that would indicate a blocked air passage or a choke circuit that is not shutting properly.

is your fuel tank venting properly or are you running lean?

My guess is the cork crankcase stuffers are expanding and rubbing against the casings,it'll ride like you're back brakes sticking on.

I think this is a known problem and sadly requires an engine strip .

I've a 16 80 that does it occasionaly at the minute I'm getting away with it as it's only used for playing. 

I heard leaving the fuel on causes the cork stuffers to expand when it fills the crankcase so make sure it's always switched off when left.

Must be plenty know about this.

 

Have you tried a new plug? It sounds like others have said, lean/clogged pilot circuit but if you’ve not tried a different plug it is worth a shot. 

8 hours ago, breagh said:

My guess is the cork crankcase stuffers are expanding and rubbing against the casings,it'll ride like you're back brakes sticking on.

I think this is a known problem and sadly requires an engine strip .

I've a 16 80 that does it occasionaly at the minute I'm getting away with it as it's only used for playing. 

I heard leaving the fuel on causes the cork stuffers to expand when it fills the crankcase so make sure it's always switched off when left.

Must be plenty know about this.

 

Thanks everyone for all of the very useful and informative replies - much appreciated. I have tried new plugs, back-to-standard jetting and tested the carb for correct functionality. I think I am going to get in there and check out these cork stuffers. Riding with the back-brake on is how I should have described it in the beginning because that's exactly how it feels, AND, because of the really annoying fuel tap on these (and this one in particular as it must be a Friday afternoon one with the tap tight against the coolant / head pipe) the fuel is always left on....

Cork stuffers? Wow. Never heard of that.

3 hours ago, dan williams said:

Cork stuffers? Wow. Never heard of that.

That’s top Italian design!

per litchi de la “cork stuffers”?

17 hours ago, breagh said:

My guess is the cork crankcase stuffers are expanding and rubbing against the casings,it'll ride like you're back brakes sticking on.

I think this is a known problem and sadly requires an engine strip .

I've a 16 80 that does it occasionaly at the minute I'm getting away with it as it's only used for playing. 

I heard leaving the fuel on causes the cork stuffers to expand when it fills the crankcase so make sure it's always switched off when left.

Must be plenty know about this.

 

Almost nothing surprises me anymore about this bike but cork? Luckily, I have always shut my petcock after every ride. Whoever spec'ed that lousy little slippery knob poor excuse for a petcock should be kicked squarely/firmly/repeatedly in the mommy/daddy button.

If the tap is that bad to use and the results of leaving it on are so bad then I'd be draining the tank or putting a clamp on the petrol pipe between events.

On 4/30/2019 at 3:40 PM, dan williams said:

Cork stuffers? Wow. Never heard of that.

Yes sounds like a juggling pin or foofoo valve fault???‍♂️?