I have heard a few different things on this subject and just wanted to clarify and make sure my info is correct...this is what I heard that when a quad is jetted wrong and is running rich that the pipe will turn red causing it to backfire with a orange/red flame...when the quad backfires and a blue flame comes out it is running lean....Is this info correct if not please clarify...because I aways thought that when a pipe is red (in my case a 450r) when I first got it it was red and people say that the Honda 450r runs lean from the factory and that is what I always thought, but I have had people disagree with me and want to find out for sure...Thanks

 

Normal......do a search on it "pipe glowing red"

 

Well when I first got my Honda the pipe glowed at idle, but I am talking about say someone is riding and the pipe is red all the time and it is shooting flames...Is this a rich or a lean condition? That is pretty much what I am asking I just want it to be clarified because I have heard both and just want to be positive on the subject.

 

I was right that it was lean and always thought it was that way until I came in here one day and was corrected by someone who knows a good amount of stuff so it made me think to myself...Thanks

 

shooting flames?[img]i/expressions/face-icon-small-shocked.gif[/img]

 

It is the deceleration when you are running lean and because engines run hot when lean it causes the glowing and deceleration causing flames...I just wasn't sure of myself when I was told I was wrong and wanted to make sure my information was correct...Thanks for the help.

 

I am getting your sarcasm [img]i/expressions/face-icon-small-wink.gif[/img]

Usually this is due to a rich condition that deposits unburned fuel in the headpipe where EGT's then ignite the fuel. I suppose it could happen with a lean condition but that would not be the first guess.

I am glad you figured it out. [img]i/expressions/face-icon-small-smile.gif[/img]

 

You should never have flames coming out of a pipe with an engine on gasoline. (Unless you have a 6" headpipe.) About the only way this can happen is if you had a bad gasket or a hole in the pipe. There is not enough O2 after the piston pops the mixture off to support a flame. Nito, sure, but not gasoline.

A red pipe is normal if it's thin metal and the mixture is close/lean. When it starts to turn orange or orange white is when it gets dicey.

 

Dr. T - Every time I have ever had a rich condition on one of these machines they have reacted the same. At night, whoever fllowed me could see blue and yellow flame in my pipe on decelleration. In fact, the quicker I cut throttle, the more flame their would be. I agree that a glowing headpipe is normal. Obviously this is getting a visual on a backfire or a series of small backfires.

I don't remember the temp at which gasoline ignites.........octane plays a role in this but if you have unburned fuel exiting the exhaust valves and it hits an 1100 degree pipe, that is a cause for a backfire.

I am intrigued by the notion that there shouldn't be enough oxygen for fuel to ignite at that point. I never thought of that before. As high as the exhaust gas velocity is, if there is any head pipe gasket leakage, it will be sucking cold air in like crazy providing enough oxygen to ignite. If there is no leak........I agree, I don't see how a backfire could take place....

Thanks for another brain stretching thought! [img]i/expressions/face-icon-small-smile.gif[/img]

One more thing, on later model cars that have 02 sensors and CatCons, if a thermostat goes bad or certain engine codes get tripped the fuel injection goes to safe mode or "full rich" to protect itself. If you drive it that way, you will notice the pipe from the exhaust manifold to the CatCon glowing bright red due to the excess of unburned fuel. It will actually melt down the honeycomb, almost completely plugging the CatCon which exacerbates the problem........all caused by the elevated EGT's associated with the fuel injection safe mode.

This gives you a little background as to why I look at this the way I do. I consider the source of heat on a lean condition to be centralized in the combustion chamber itself. My question would be; if a lean condition was elevating EGT's that much, how hot must the piston, cylinder and valves be? Wouldn't they be cooked?

This is not an argument, I am just throwing out a little support for my position to see if it holds up to scrutiny.

Ron

 

This is what we did old school, if poping and back firing flames (lean) richen mixure (main or richen air screw) or if its a 2 pcs or 3 pcs pipe, cold air can be sucked in and cause backire flame also we used to go to a pep boys and keep a exhaust exspander if this happens to snug up the fit once the pipe got warm and exspanded and sealed the air leak.
Old school jetting (didnt have dynos everywhere) was up the main and open the throttle till was blubbering then back off 1 size down on the main and do a plug check (will get ya in the area)