Boxerworks.com

Have a 73 R75/5
Bike has open Epco megaphone exhausts on it. I have both carbs (Original Bings) in what I think is good tune. The left cylinder is harder to start when cranking. If I hold my hand behind both exhausts, there is a noticeable "popping" on the left cylinder. Also left cylinder header is a lot bluer than right (obviously running hotter).

I keep getting told that it is most likely carb issue with left carb. I am thinking its left cylinder exhaust valve not seating well. My thoughts being an exhaust leak causing the popping on compression stroke (hence hard to start) and the escaping gasses/heat from combustion causing excessive blueing.

Am I right on this or does anyone have any ideas on that?
I don't have a compression checker so I was going to try to see if Autozone or local parts store had one. maybe test compression on that side. Bike runs really strong besides and does not smoke at all.

Need lots more investigation. Check your valve adjustment. Knowing whether or not your timing is hitting a double image would also be helpful.

It is REALLY easy to determine if this is being caused by ignition or carb. Switch plug wires and see if the problem switches sides. Switch carbs and see if the problem switches sides.

That sounds just like what I went through with my ‘88 RT when I first got it, except it was on the other side. Turned out the entire cylinder was ate up, valves were shot on both sides. (Yeah, nickasil will wear out)!

You can tinker and tune for years and never fix it. I’d start from the bottom and check everything. One of the great things about these bikes is they’re so easy to work on. You can take the heads off and on in one afternoon.

Pull the spark plugs and with a flashlight you can get a good look at the valves as you roll the engine over and the valves move open. But that won’t tell the whole story! I’d have a valve spring compressor handy and pull the heads. Check the cylinder walls, and remove the valves so you can inspect the seats. This is the only way you’re going to prove that your problem is not inside the engine.