1969 big twin idling rough

[byacey]

My 40952R idles OK, and then it sounds like it backfires every once in awhile, sometimes killing the engine.This also occurs at higher throttle openings (advanced ignition, the throttle butterfly isn't opening yet at this point). I enrichened the idle mixture, and this seemed to help. I am running it on 25:1 mixture right now. Is this possibly creating the problem?

 

[lark2004]

Re: 1969 big twin idling rough

well, can't say for sure, but the mix should be 50:1 for your motor.<br /><br />You might have sheared the flywheel key. Maybe. the only way to tell is to pull the flywheel off.<br /><br />The key will shear off if the flywheel hasn't been torqued down properly. It needs 105ft/lbs, no less.

 

[byacey]

Re: 1969 big twin idling rough

No, the flywheel key is fine- I had it off a couple of times today. Another funny thing is it seems to happen less when the engine is in gear under load. I'm going to add some gas to the tank and see what happens with a higher oil/fuel ratio. 50:1 goes against my better judgement, is 40:1 OK?

 

[lark2004]

Re: 1969 big twin idling rough

I guess so, the factory made these engines to run 50:1 back then, with today's oils, its absolutly fine.<br /><br />The reason for 50:1 is that the engines run on needle rollers, in the 1963 and ealier motors, the cranks ran on bronze(oilite) bushes. which needed the higher oil concentration.<br /><br />Have you rebuilt your carb?

 

[byacey]

Re: 1969 big twin idling rough

No, I haven't had the carb apart yet. What are the chances of opening the bowl for an inspection without damaging the gaskets?