Cota 247 Running Lean and Overheating

[keychange]

It wasn't clear at the time but this post really is a continuation of viewtopic.php?f=16&t=5688 Cota 247 Carbie May 01 - 2010
One of my earlier posts I reported that I thought my timing might have been too retarded and so I started fiddling and as result lost all spark entirely . I had tried rigging up a timing light on 12 volt battery and onto spark plug to see if there was any chance of getting an accurate indication of when the points open - alas I am not sure why but I think I might have fried the condenser.

Correct me if I'm wrong the condenser input wire in isolation should not be a dead short to the stator body should it? - Coz it is.

I eventually pulled the engine out of the frame so I could clean it properly and work on a bench and save my poor old back. So it might be a while before this thing is running again

While I've got you here - when I bought the bike it had an aluminium bash plate (see below) - which Greg Harding noted was set between the engine and the frame thinking this was incorrect. With the engine out I removed the plate and I am not sure it will fit below frame and if it does with the required spacers it could reduce clearance by a centimetre - does anyone have experience with this kind of bash plate.

[David Lahey]

Yes it is meant to be between the motor and the frame. Unusual and provides no protection for the frame tubes but that is where it was made to go. I've seen similar bashplates made for fitting between motor and frame tubes on Cota 348s too.

With your timing checking gear set up as you have described it, it is much more likely that you have fried the high voltage winding of the HT coil, than the condenser.

Yes the condenser should conduct to earth on the stator plate. When the motor is running and points are closed, the magneto creates a magnetic field in the low voltage side of the HT coil. At the moment that the ignition spark is required, the points open which breaks the low voltage circuit which causes the low voltage magnetic field to collapse. The rapid change in flux in the low voltage side of the HT coil generates a high voltage in the high voltage circuit of the HT coil. The condenser is only there to prevent a spark between the points contacts as they open and is not part of the HT circuit so it is very unlikely that you damaged the condenser by connecting a battery to the spark plug.

If you want to use a battery and light bulb to check the timing, you should connect it across the points (the low voltage part of the circuit)

I usually disconnect the points/condenser from the HT coil and connect the 12V light bulb and battery between the non-earthed side of the points and to earth. The light bulb glows dimly when the points are open (some resistance to current flowing through the capacitor) and brightly when the points are closed (almost no resistance when flowing through the points).

[David Lahey]

To make it easier to work on the ignition, you can lie the bike over on its side.
Motorbike workbenches also are good for getting bikes up to a nice working height.

[David Lahey]

The reason for the lack of spark may be something like the points being adjusted too far one way or the other (not opening, or not closing)

[keychange]

Hi

A new set of points and the spark is back :) - now to put it all back together. At least it is all clean, for the first time since I bought it I have really scrubbed it clean, chain, sprockets everything is glistening - I hate working on dirty engines

[scrivo]

Andrew,
This link may help
http://rmmontesa.webs.com/techarticles.htm#545034310

This also applies to other points ignition bikes. David's descrition of HT coil is one of the best I have seen

[cedric van heerden]

We are very lucky to have David in Gladstone, not only is he a wealth of information, he is brilliant setting up bikes and sections. Thank you David for all your help.
Cedric

[keychange]

I seem to take one step forward and two steps back. As reported I had good spark - I set the points to 0.40mm and then set timing to 2.5mm BTDC - I then started the bike and checked with timing light and all good. By now I had replaced rear shocks so took for a run and right back to where I started with this bike - no top end, it just dies on open throttle (I have already replaced all carbie gaskets, jets and needle) .

Removed carby (yet again - I swear I could reassemble blind folded) cleaned everything with compressed air and checked float level. Re-faced manifold end of carbie using wet & dry on a sheet of glass - tested for air leaks. Cleaned fuel tap on tank - checked fuel flow, replaced air filter.

Power is non-existent on open throttle back off and there is a rush of power but that doesn't last - there is a surging of power on half throttle - really strong surge. Feels like it is starving for fuel yet plug shows rich - i can't think of anything else to change or replace on the carbie - I am out of ideas - I improved this last time by retarding the engine about 10 degrees but I don't think that is doing the engine any good - should I try advancing - it'll have to wait I can't get it to even kick now so I think the plug (maybe 6 hours old) is buggered

In the days of the Spanish Inquisition they used to burn heretics - this heretic is about to seek revenge

[TriCub]

Can you give us a bit more info.
Has the bike been running ok in the past?
When did it start to run badly and was it an instant decline or gradual?
What sort of carb is fitted to the bike?

I take it that you have a battery powered timing light. Have you tried using it when the motor is under load, they can give a good indication of spark by just by whatching it, strap it to the handle bars and go for a ride and watch for it flashing.(Don't watch to closely or you'll fall off and don't blame me if you do) Is your spark stoping when the motor cuts.
Also is the timing staying steady when you give the motor a good free rev?
When you lose power does it miss fire or back fire or make any other strang noise?
Have you tried a new condensor. I have seen bikes that would start and run ok until they went under load and new condensors fixed them, but they usually bang and pop out of the exhaust underload.

[keychange]

Thanks TriCub

It's been a saga ever since I bought it 3 months ago viewtopic.php?f=16&t=5640 - viewtopic.php?f=16&t=5688 .

After lots of work tt was running quite well until a few weeks ago I spent a day with Greg Harding - once it was hot it started idling high ( as if throttle slide was sticky) and then became more and more difficult to start - at one stage 3 of us took turns kicking the B*^***d . In an earlier effort to get improved performance I had retarded the motor (at the time I incorrectly posted that I had advanced ) and while this appeared to improve some aspects I thought that this could be causing the high idle and what I think was overheating causing the hard restart.

I had a spill requiring shock replacements and took my time and I went back to basics checking everything eventually I gave up working on my knees and removed the engine in order to check timing. I double and quadruple checked points gap. My timing light requires 12 volts so no I can't try it on the move unless I lug a car battery with me - but I did test at higher revs and flywheel mark moves clockwise a few degrees (retarded) which I thought would be normal with a an engine with no auto-advance.

I take your point about the condenser - I was suspicious of this before I changed the points (which maybe coincidentally brought spark back) .

There is no banging or backfiring just complete loss of engine at full throttle - as if the ignition is turned off (I have removed kill switch - stator wired direct to coil) - I have reported same sensation in the past and that was when I replaced all carbie (Ahmal) parts. I will get a new condenser - nothing to lose.