Quote:
Originally Posted by Laird Scooby
The jet in the carb is in the lower body of the carb and from what you said earlier, the needle had come out of the piston - the piston rises and falls in relation to airflow into the engine and manifold depression, hence the CD in the carb designation denoting "Constant Depression".
You need to get the ignition correct before you start meddling with the jet and needle in the carb. Most common cause of the dwell angle changing all the time is wear in the bushes in the distributor (that's bushes NOT brushes!) that the main distributor shaft runs in. It's a common problem with those era of Bosch distributors.
If some muppet has cross-threaded the contact breaker screws in the dizzy base-plate, you need new screws minimum. Then remove the base-plate and re-tap the holes (correct size) and hope that cures it, if not, you need a new base-plate.
That said, your better option for the long term would be to obtain a dizzy from a later 240 with electronic ignition (Hall Effect) with the sensor in the dizzy, the ignition amp module and convert it, no need to worry about contact breakers then or a varying dwell angle. This is a fairly common upgrade/modification (i believe Alan has it on his RB) so there should be information somewhere on the forum exactly how to do it.
Failing that, a reconditioned dizzy.
A question though - is your mechanic monitoring the dwell angle with the engine running while trying to adjust the carb? If so he's over-analysing things as the dwell angle naturally changes with engine speed/load courtesy of the mechanical advance weights and also the vacuum advance mechanism. Dwell angle should be checked/adjusted while cranking the engine, not with it running.
Also if he's not familiar with that particular carb, he could be adjusting it the wrong way from the start.. The throttle butterfly is factory set and shouldn't be altered, there is an idle air volume screw to adjust the idle speed and then the mixture is adjusted with another screw.
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Ah! Dave may well be right in referring to the little screws that hold the CB points in place rather than the clamp bolt. Either way the solution is the same (and essential): tap the thread and replace the screws. You really must make sure the ignition timing is spot on before it is worth meddling with the carburettor set up. There no way your mechanic could diagnose a worn jet if the timing is not set properly.
Once the timing is right, I'd still advocate that you set the carburettor up from scratch as per pp 67-72 of the green book I sent you previously, the first page of the schema looks like this:
... it really is quite simple if one is methodical. I always find that eliminating one thing at a time is more productive than a mechanic guessing at worn jets and so on. If you follow your mechanics guesswork you may well have to pay for half a dozen things to be fixed before you happen upon the right one by chance.
Have you checked the motor is well operating mechanically? I think you mentioned that you had changed the cam belt (well done), but did you check the valve clearances (easy job) and cylinder compression (another easy job)? If you did not then it would be really sensible to take a step back and check those two items first (about an hour's work for both) before looking for spurious leaky jets.
Well done - just be methodical, eliminate one thing at a time and you will soon work out what is wrong.
Alan