Cota 247 Carbie

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Hi my 1976 Cota 247T I just fitted my carbie with a complete AMAL carbie kit - jets, needle, o-rings, gaskets the lot. Now I have had my carbie off countless times before but when I took the bike for a quick test run it was fine until the throttle jammed open (thank god I had fixed the kill switch).

I pulled the carbie off and the slide was working perfectly so I refitted constantly testing slide as I went and when I did the manifold bolts up that last little bit the slide stuck - back off the nut 1/4 turn and snap the slide comes home and works perfectly. Obviously the carb is being distorted by the tension on the manifold bolts but I can't understand why it is doing it now - I did fit a new gasket - maybe it's on backwards - any ideas?

[David Lahey]

Yes - if you overtighten the nuts, the body distorts. The gasket is so thick that it is easy to pull the flange into a curve. If you look back a while in the forums you should be able to read about Hagsta having similar problems with the throttle slide in his 247.

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David - I can't find the post but I'll take your word for it. BTW- carbie refurbish has fixed all my power problems, now it really does feel like a 250 two-stroke. The bottom end response, which I thought was good is fantastic now. Popping the front wheel with ease :)

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However all was not quite perfect. While it appeared to run well it had the annoying habit of stalling every time I stopped to open a gate - or put on my helmet. I wasn't easy to restart and eventually I checked the plug and it was clearly running very lean. I tried adjusting the idle jet (Pilot air adjusting screw) in but that just made it harder to start. I removed the new idle jet and compared it to the original - they are the same length but the old one was clearly narrower (I deduced due to wear) by about 0.3 mm I reinstalled the new idle jet and removed the carbie and recalibrated the float level (the new float has tangs that can be bent). But still no better I went for a test run up and around a large steep hill and all was fine until I returned home and stopped to close the gate and the engine abruptly stopped - no splutter just ran down in revs and stopped (again).

So I replaced the new idle jet with the old and it's fixed

[David Lahey]

I've got an idea what is wrong but more info needed. Does it idle properly at any stage in the proceedings ie hot/cold? Does it stop only when you put it on the stand?

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It was idling ok but fragile (if you know what I mean) it just didn't feel strong I felt like I had to constantly give the throttle a tweak. No nothing to do with stand (I think) it it would die at times without being on the stand - it would run down in revs very quickly and die - throttle had no affect at that stage it as just too late. And it would do it hot or cold - although harder to restart when hot. I checked the plug many times for flooding but not the case.

[David Lahey]

I might be wrong but it sounds like you haven't set the idle RPM since fitting the new parts to the carby.
There are two adjustment screws on the side of the carby.
The top screw is the stop for the throttle slide, and usually needs to be adjusted when changes are made to the carby. As you screw it in, it lifts the slide (opens the throttle), and vice versa.
The other screw is called the "idle mixture screw" or "idle air screw". This works by throttling an air path in the pilot circuit. As this screw is screwed in, it reduces air flow, which increases the "suck" through the pilot jet at idle. So screwing it inwards makes the idle richer and screwing it outwards makes the idle leaner.
To set the idle to where you want it, you need to adjust both these screws. I would suggest setting the idle mixture screw to 1.5 turns out from fully inwards to start with, then start the motor, warm it up fully and then come back to the tools. Adjust the throttle stop screw until you get the RPM you want it to idle at.
Then move the idle mixture screw very slowly inwards till the motor start to run unevenly (too rich). It may only take 0.25 turns of the screw to do this, or it may need more. Every bike is different. Then move the screw outwards very slowly. The motor should idle more evenly as you move the screw outwards, and then as you continue to move the screw outwards, a point will be reached when the idle will become uneven again (too lean). You should then choose a setting somewhere between both extremes that gives the nicest idle, and no hestation from the motor when you snap the throttle open from closed while riding.
Now you have set the idle mixture, you may fine that the idle speed is then different to what you want. If so, adjust the throttle stop screw again.

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David

Yes I have used the idle adjust screw many times (which was also replaced as part of AMAL kit). I have got to know the AMAL quite well on the Cota (although the distorting of the barrel due to manifold nut tightness was a surprise ) I have removed all jets and cleaned (several times) and now removed and replaced everything.

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Next day - I just went outside started the bike (easily) it idled happily and allowed me to go through the process of adding helmet, jacket and gloves and the died Maybe I am barking up the wrong tree - it could be electrical - as its just as if an imaginary hand hits the kill switch - but only at idle. DOES ANYONE WANT TO BUY A COTA 247

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I just discovered a slight leak from the seal (new) around the banjo bolt (drain) could that be causing a critical loss of the vacuum at low revs? Fitted new gaskets and checked seal - no better. So I again checked float level and lowered the level a little - no difference. It runs well but cuts out after about 90 seconds at idle. I have read lots of other forums and many say you shouldn't let a 2 stroke idle for too log anyway - but my plug isn't fouling and yet it is hard to start after it stalls. I am running a B7HS plug just slightly cooler than the recommended B6HS and it has had maybe 3 hours use could it be something to do with the plug? I am all out of ideas nearly ready to get a box of matches and toast the #$*^@#*^ thing. I found this post about a guy with a Kwaka trail with similar symptoms and attempts to correct - with 110 posts over 5 months and in the end he still couldn't get it to idle property http://www.dirtrider.net/forums3/showth ... ight=lemmy