Sigh just when I think I have some time to work on my own projects!!
This CB750 Four came in in need of some help. It is a friend of the owners of the CL350 so I said we'd take a stab at it. She is
mostly all there, or at least was for a majority of it's life. It went in to some other shop for adjustments and came out with pods (K&N at least), megaphone exhaust, and 115 mains, much to my dissatisfaction - though I of course understand given the $$$ of a new stock exhaust!!
Anyways, she was getting 40mpg now we're at 19-20. Would a change from 105 mains to 115's account for THAT much of a fuel economy difference? After 10ish minutes or when she's full temp the revs start to soar, no tach but I'd guess 4,500rpm idle. I haven't taken it out yet so I can't say much about how it's performing through the rev range.
My first thought was to look at the choke - not making that mistake again!
Luckily (or sadly?) it, and it's owner, were both operating correctly. Throttle slides functioning as well. Along the sides of each carb intake there are shiny marks.
I originally guessed this was someone a little to dremel happy getting in there and widening something, but after seeing similar marks on all 4 carbs I believe they are actually factory. The owner says he's been messing with the idle etc to try to get it to play nice. My first step will be to put it back to a base tune and see where we stand there.
When the bike first came in hot I pulled out my IR thermometer to see how it was running. The CL350 was only running on one. Luckily #1, #2, #3, and #4 were similar temps. #1 20° colder and #4 about 10° colder, I attributed this to them being the outer two cylinders. Upon closed inspection the spark plug lead on #1 was completely loose. The little tab which applies tension to the top of the spark plug had fallen out. Instead of being a "D" shaped hole this one was just an "O". I am sure the others are weekend as well and not holding with sufficient force. The #1 cylinder was most likely missing maybe 10% of the time, but I'll have to take it out for a ride to confirm that. Anyways it seems at least new plugs are in order. Are these resistance plugs like the manual? And the coils, two coils on this bike? Removable spark plug leads or no like the CL? I will download the manual (I believe it is the the section here on the forums) and do some digging of my own.
The left exhaust is completely sooted up while the right is bone dry. That I will have to dig in to. I will also check to make sure we are in timing before going too deep elsewhere.
Anyways....always something! Hopefully this one doesn't take too long and we can get back to my 350 Four. I have decided to get a handful of my engine parts cleaned the machine shop where we have the B20 head. I am thinking walnut shells. So that will be good progress while I am working on this! At least the 750 is a Four so maybe you all will enjoy
