I hope you can help me, I'm having trouble starting my 1932 W32-6 (500cc side valve).
I've have my magdyno professionally rebuilt, in the process replacing the three brush dynamo for a two brush dynamo on the advice of Tony Cooper who did the rebuild. Also on his advice I've remove the mechanical regulator coil and replaced it with a modern semiconductor solid state encapsulated regulator for motorcycles using the Lucas E3 type dynamo.
Since the rebuild I have had the bike running and have travelled about 3 miles. However today it would not start; it would only bake fire through the carburettor. This happens irrespective of the position of the ignition control and the air level.
Why will it run one day and not start the next? How can I diagnose and fix this problem.
Thank you for any helpful advice.
Hi there,
Based on your description, I'd suspect either: the carb; or perhaps the mag timing has slipped\jammed so that it is way, way advanced; or a stuck valve ?. Spitting back through the carb is often a sign of a weak mixture.
I imagine that you have already done most of this below, but this is what i would do, more or less in this order:
Starting with the easiest thing first, I would:
- check that there is a good free flow of fuel to the carb.
- confirm you have good compression, that the valves appear to be opening and closing correctly, with correct clearances.
- verify that the points gap is correct; the ignition timing is correct (also - is the advance retard cable\mechanism working correctly) ; that the mag is still producing a good, blue spark. Replace the spark plug.
If all seems in order there:
- check for air leaks at the manifold\gasket (if its a flanged carb, then overtightening the bolts can result in it warping and admitting air).
- check the float level & verify that the float is not leaking\damaged and is free to move correctly.
- dismantle the carb and check that all the jets are clear, especially the pilot.
This is what I would do, but those with greater experience may have better suggestions.
Keep us updated on how things go.
Cheers,
Bevan
Thank you for all your help. Yesterday I had another go at starting the bike. I made no alterations other than trying the ignition level and air lever at different positions (which I had done before).
After two minutes of the same back fire and failing to run it came to life! I quickly put my helmet and gloves on and set off for a ride. For the first mile and a half the engine was popping, but at the two mile mark the engine smoothed out and I started to enjoy a well mannered bike. After four miles I realised that the vibrations were undoing the nut on the ignition lever, hence I returned home before I lost the nut and created another job.
When I got home the bike was running fast at ideal, can I resolve this by turning in or out the air screw on the carburettor?
The bike started when the ignition was fully retired and the air level was full closed. I would like to think that this was to answer to my problem; however I know that I had tried this combination before with no luck.
What do I take from this small victory to the journey to understanding my bike and having an easy to start smooth running bike, ....... well just these points:
1, Air fuel is getting through to the engine
2, The new spark plug works fine
3, The engine timing works
Congratulations on getting the bike going ! All old bikes do have their peculiarities, so hopefully you've identified the correct technique for yours.
It is a bit surprising that it started on full retard. I realise my '29 ohv Sloper is a different beast to yours, but it won't start on full retard; in fact I can stop it by fully retarding the timing. It might be worth just checking that you have indeed got the timing setup correctly.
Also, it is possible that the pilot jet may have been blocked but this has now cleared. It could be useful to check if there is any residue in the float bowl which could get sucked through and clog the jet up. I am assuming you have a fuel filter ?
My bike needs to have the carb well flooded and with the air lever fully closed before it will start from cold. Having done that, I also turn it over with the valve lifter in, so that it sucks some fuel through. I then ease it over tdc and do a long swinging kick, only releasing the valve lifter once the engine is spinning. It will then chuff into life near the bottom of the kick. I confess that I haven't fully mastered the hot start technique, which can be troublesome at times. The carb gets incredibly hot, so I may look to fitting an insulating spacer. Or it could also be a sign of a failing magneto. Time will tell.
My carb has no throttle stop screw and I'm guessing yours does not either. I have a throttle cable adjuster a short distance from the handlebar which I use in conjunction with the air screw to get the lowest steady idle. In fact, I have it set a little fast since I don't want to risk stalling it at a busy intersection.
I would be interested to hear how things go, so please keep us posted. A photo or two would be interesting.
All the best,
Bevan