Topic: Big cam/ blue pipes question

[Don R]

 I've got a 70 750 with a K4 836 mildly ported. It also has a Kenny Harmon F cam, new stock valves, springs and ti retainers, the plugs look good, 4 cable carbs with 130 mains but the unknown origin header has a lot of blue on all four pipes, it had some when I got it used. I'm wondering if the long exhaust duration on the KH/F cam has much to do with the blue pipes. 
 My concern now, is putting a stock 300 exhaust on the bike. I know they are somewhat shielded but I don't want those turning blue too.
 Thoughts? 

[dragracer]

Blued pipes are typically a sign of a very lean condition. The pipes blue from extreme heat.  This is a carb tuning issue. Rejetting the carbs properly would have saved the color on the exhaust.

[Tracksnblades1]

I've got a 70 750 with a K4 836 mildly ported. It also has a Kenny Harmon F cam, new stock valves, springs and ti retainers, the plugs look good, 4 cable carbs with 130 mains but the unknown origin header has a lot of blue on all four pipes, it had some when I got it used. I'm wondering if the long exhaust duration on the KH/F cam has much to do with the blue pipes. 
 My concern now, is putting a stock 300 exhaust on the bike. I know they are somewhat shielded but I don't want those turning blue too.
 Thoughts?

Chrome blues at surface temperatures around 900*. Keep all that gas burning in cylinder instead of in the pipe. Quit mixing Nitromethane in it. It burns all the way out the pipe. 😎 High performance naturally aspirated engines can have EGT's over 1000*. Reputable tuners write, as I believe, the spark plug is the best thermocouple used to determine cylinder temperatures on high performing engines. The only headers mounted on a high performance engine that I've never seen turn red at sustained wide open throttle were on a boat engine. Turn the exhaust water injectors off and they would too.  Good luck...and share your secret..😇

[Don R]

 I'm thinking I preferred the F2 cam that was in it before anyway, I don't get this bike into the rpm's this one needs to work, I read it has a lot of overlap and exhaust duration for valve cooling when road racing. The bike's due for a diecast motor at some point but I can't wait for that to run the stock pipes.
 Maybe it's a good time to mount the O2 sensor I got for a contingency prize last year. 

[PeWe]

Why not a DP295 cam? Or RC

[Tracksnblades1]

I'm thinking I preferred the F2 cam that was in it before anyway, I don't get this bike into the rpm's this one needs to work, I read it has a lot of overlap and exhaust duration for valve cooling when road racing. The bike's due for a diecast motor at some point but I can't wait for that to run the stock pipes.
 Maybe it's a good time to mount the O2 sensor I got for a contingency prize last year.

Why not a DP295 cam? Or RC

Mildly Wild Ported Head...?

I don't think you need O2 sensor to tell you what you already know...🤓

[Don R]

Why not a DP295 cam? Or RC

Only because I have the F cam. There's an RC 327 in the tool box but that's about as radical as the one I have now. I agree a smaller performance cam makes sense. I know they don't make gobs of torque no matter what I do cam wise but moving the rpm range down to where I ride is a better idea.
 It's not ported huge, I just clean them up under the valve, around the guide and smooth the inside radius a little. 
 It's got one cylinder fat this morning. It insists on leaking through after multiple new floats and valves. Starting to concern me. There's a reason one pipe is blue.

[Tracksnblades1]

Why not a DP295 cam? Or RC

Only because I have the F cam. There's an RC 327 in the tool box but that's about as radical as the one I have now. I agree a smaller performance cam makes sense. I know they don't make gobs of torque no matter what I do cam wise but moving the rpm range down to where I ride is a better idea.
 It's not ported huge, I just clean them up under the valve, around the guide and smooth the inside radius a little. 
 It's got one cylinder fat this morning. It insists on leaking through after multiple new floats and valves. Starting to concern me. There's a reason one pipe is blue.

Wouldn't the increased overlap allow fresh air/fuel mixture to enter exhaust pipes thus aiding in cooling until the cam was operated in its effective tuned rpm range...?   👀  Provided exhaust has no leaks.

[Don R]

 This may be true, the cam was supposedly ground for road racing and keeping the exhaust valves cooler.

[HondaMan]

Most of the 'hot' cams for the 750 have lots of overlap time. This ends up pulling unburned fuel thru the chamber(s) quite a bit at lower engine speeds. If the spark timing is delayed somewhat, it will help to fix this up by not lighting off the unburned fuel quite as readily: it will then tend to burn up toward the carbs instead, where it gets extinguished by the next intake stroke. The 'down' side to this is the switch-like feeling of power coming on when this back-burn meets the intake timing: otherwise known as the 'roadracer's surge'. A side-effect on real wide-duration cams is the "GP pop" that you can hear on the old movies of guys like Hailwood, et al, when engine-braking into turns.

In the 750, though, you have an 'edge' to deal with this in the form of the Keihin carbs. You can install a leaner idle jet (#35 or #37.5) to reduce the overfueling. Doing both this and slowing the spark curve helps a lot.

[Sam Green Racing]

It sounds like you need the DP295 cam Don, it gives a much better spread of power right through the rev range.

[Don R]

 That's what's in the back of my mind Sam, I was playing with this one because it was in my brothers tool box and I traded parts for it.