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I have a 47 UL. Acquired the bike with the engine rebuilt. Has about 4 thousand miles on it as best as I can discern. Took me a little while to get the bike set up how I wanted and even longer to do any miles on it.
Everything is set to factory spec. Points properly adjusted, valves timing seems ok. Fitted with Champion D16 plugs
The bike fires up fine, ticks over ok when warm and accelerates ok up to about 55 /60 mph but then seems to run out of steam.
I finally did some riding on it last weekend and did 200+ miles in the saddle. Mixed freeway and back roads. Towards the end the bike started to backfire very occasionally. Not very loud but noticeable to the me. Couldn't work out what was causing it before I got home.
When the engine cooled I pulled the plugs, See the attachments. Front has a nice sooty rim but the electrode is clean as a whistle. Rear cylinder is a much more even light brown colour. I was struck by the difference and wondered whether I have a problem or whether this is not uncommon in 1200 flatheads.
On checking the bike over I found that the rear exhaust pipe had worked lose where it exits the cylinder. Otherwise it was fine
Not sure if I have a problem with the motor or not.
I know flatheads don't like sustained high speeds (neither do I for that matter ) but I do want the engine to be running right.
My next investigation was going to be a manifold leak down test but I don't have access to compressed air so this will take while to set up - or am I looking for a problem that doesn't exist?
Would welcome input from those out there who know the big twin flathead engines
Thanks
Martin
I have a 47 UL. Acquired the bike with the engine rebuilt. Has about 4 thousand miles on it as best as I can discern. Took me a little while to get the bike set up how I wanted and even longer to do any miles on it.
Everything is set to factory spec. Points properly adjusted, valves timing seems ok. Fitted with Champion D16 plugs
The bike fires up fine, ticks over ok when warm and accelerates ok up to about 55 /60 mph but then seems to run out of steam.
I finally did some riding on it last weekend and did 200+ miles in the saddle. Mixed freeway and back roads. Towards the end the bike started to backfire very occasionally. Not very loud but noticeable to the me. Couldn't work out what was causing it before I got home.
When the engine cooled I pulled the plugs, See the attachments. Front has a nice sooty rim but the electrode is clean as a whistle. Rear cylinder is a much more even light brown colour. I was struck by the difference and wondered whether I have a problem or whether this is not uncommon in 1200 flatheads.
On checking the bike over I found that the rear exhaust pipe had worked lose where it exits the cylinder. Otherwise it was fine
Not sure if I have a problem with the motor or not.
I know flatheads don't like sustained high speeds (neither do I for that matter ) but I do want the engine to be running right.
My next investigation was going to be a manifold leak down test but I don't have access to compressed air so this will take while to set up - or am I looking for a problem that doesn't exist?
Would welcome input from those out there who know the big twin flathead engines
Thanks
Martin
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