Topic: How much fire out of exhaust is OK?

[fire_strom]

 
So I have my exhaust system off the bike right now and have been tinkering a little. When I run the bike there is quit a bit of flame coming out of the exhaust ports. Most of it is blue. A little yellow once in a while but only at first. This is at idle and when I hold revs a bit. No choke, not really warmed up. Pretty much even between all 4 cylinders. Does this mean anything like rich or lean? I was mostly only out of the number 2 cylinder before I adjusted the valves and set the point gap. Like I said, now it is pretty even, so did I make it better or worse?
The bike is a 76 CB750f with a foam uni-filter and at the moment no exhaust. Stock jetting, 7500' elevation. The exhaust that is going to go on s a stock header and a Dunstall DB silencer 1138.

I might try to catch a little video and post it here. I never have done the video thing but flames might be a good reason to.

Scott

[ev0lution7]

you need to have some exhaust or you can BURN an exhuast valve... as the hot gas excapes it exchanges with the c00l air.. and it can burn a valve and put a hole in it ALWAYS! run at least SOME exhuast!!!

[fire_strom]

I have only had it running on the stand for a very few moments at a time. Never even around the block or anything and never under load. Thanks for the heads up though. I'll quit it, except to film it. Unless even a few moments is too dangerous?

[ev0lution7]

its your motor not mine 

i just know that my buddie against my warning did that on a HI PO... chev 350 chevel and it led to an early demise of 3 of his exhuast valves they ended up destroyed like half the valve eaten away becuase of the premature damage...


great looking flames though!!!!!!!!!!

[mystic_1]

Here's how I understand it:

Raw exhaust gasses contain very little oxygen.  With no exhaust at all, when the exhaust port closes and the gasses come to a stop, raw air (which contains a good amount of oxygen) is pulled back in.  The oxygen reacts with the hot exhaust valve and seat.  You need at least some exhaust (several inches or more) in order to prevent this.

mystic_1

[merc2dogs]

Burnt valves are only indirectly caused by running an open exhaust. The actual cause is that reduced backpressure leans out the mix enough that it runs super hot, and that's what burns the exhaust.
 Tune the carbs for it and you can run all day with wide open ports. (larger jets)
 It's caused by the open exhaust, but the air simply being able to reach the valves isn't what does it.

Ken.

[moham]

I wouldn't stop until you can roast wieners or at the very least toast some marshmallows...

[333]

If it were a natural gas stove, it is burning just right.  That blue flame(on the stove, not the bike) means it's getting just the right amount of air, to achieve the highest heat.

I don't know what color flame equates to proper jetting on the bike.  But do it one more time and get some video.  I know it's bad for the bike, but it will look so cool.

[fire_strom]

Maybe I better just draw a picture.