I’ve been having some issues with my square four during the run in stages, which I haven’t been able to quite figure out yet. I started discussing this with Paul Jameson on another thread, but decided it was best to start a new one.
My bike starts with one kick, settles to a very nice and steady idle, pulls very well from low speeds even in top gear, and runs very smoothly up to 80-90kph. Above that the engine loses its smoothness, becomes harsh and a bit rough, I feel vibrations coming through and she seems to struggle to accelerate beyond that. To reach 100kph, feels like it’s being forced, although I haven’t really tried full open throttle. I’m still reluctant to push her as I’ve only done 500 miles since the rebuild, and so until now I’ve only tried higher rpms and speeds very shortly and very few times.
I have the ignition set now where I get the best performance, having tried more advanced and more retarded from my starting point. Same with the Solex, which now seems to be on the sweet spot.
To answer some of Paul’s questions and suggestions:
- valve timing: I followed Bruce Longman’s method and my peak opening on the inlet on Nr 1 was just about at the recommended 105deg. Rechecking my notes perhaps a couple of degrees more advanced, but not less than 102-103 deg. I could of course have made a mistake and the timing is indeed off, but feeling very lazy about taking the tank and everything off To get in there again. So I’ll leave that for last if things really don’t improve. However, if valve timing is the cause, which direction should I go considering the symptoms? More advanced or more retarded?
- rockers getting caught in the housing somehow: I just took the covers off today to readjust the valve gaps, which needed to be buttoned down after the head has settled in a a number of retorques. I didn’t see any signs of anything catching, not scuffs or scratch marks anywhere and everything was moving smoothly and freely.
- coil or HT leads shorting: both coil and HT leads are new and as far as I can tell, nothing seems to be wrong there.
- distributor: I have an electronic ignition from Thorspark, so no points. It’s a Hall sensor type thing with the magnet turning on the cam and the sensor fixed. Distributor cap and finger are new. As far as I can tell the automatic advance mechanism is assembled and working properly. I have a slight play on the cam - when I turn it with my fingers I do feel a slight play, but I wouldn’t think it is so much as to cause a problem. The problem is I have no reference so I don’t really know what is acceptable or not. This could be the contributing cause, but I’ve no idea how to really check it. And I do believe the hall sensor ignition should be more forgiving of play between the cam and shaft, or am I wrong in assuming this?
Otherwise I have good fuel flow, carb has recently been cleaned and all the jets are free and the proper size. I have a washer under the float valve. Spark plugs are new and gaps adjusted according to the manual. Fuel here has 5% ethanol and I add a lead additive. Not sure what else I could tell you, so start with the questions and your always helpful ideas.