Over heating header, predator 420

[LaithSaah]

Hello!

I just finished a go-kart build with a rear engine 420 with a flywheel, cam, pushrods, springs, con rod, intake, and exhaust, and I am having a bunch of issues with my exhaust overheating. I'm also running stock carb with a large jet and a cone filter. My head temps during hard runs only really hit about 240 F, and my sparkplug shows no signs of running lean (white plugs). After 5 minutes of running, the entire header is glowing red. Is it possible that my carb is too rich? While running in the 4k rpm range, there are just flames spitting out the back, and the backfires are way too loud. I can order more jets and test but I have no idea if this is just how it is or if I can fix it. Stopping every once and a while to cool the exhaust down is not the most fun thing to do... Thank you for any advice you could give!!

Have a great one!
Laith

(Photo 1 is just a picture of the project, Photo 2 is after a mile drive back to my house at about 80% throttle

 

[bob58o]

How hot is the header getting?
I’m not sure about the color of glow vs temp of steel.

Brown Yellow/Purple?
500 F?

 

[Denny]

It don’t matter Bob it’s still too hot! Hot is hot. Too much fuel burning still in pipe.

 

[LaithSaah]

How hot is the header getting?

I am pretty sure it is around 500, Thermal gun clocked it at like 480 when it wasn't as bright glowing...

It don’t matter Bob it’s still too hot! Hot is hot. Too much fuel burning still in pipe.

So I should lean out the jet a little?

 

[bob58o]

My understand (might be very wrong) that too lean a mixture can cause incomplete combustion which can lead to burning gas in the pipe.

Is there a lot of popping on deceleration?

 

[LaithSaah]

My understand (might be very wrong) that too lean a mixture can cause incomplete combustion which can lead to burning gas in the pipe.

So basically, should I buy a set of jets from 0.43 - 0.49? Go power sports sent over a .46, I believe. I also can borrow a precision drill set and step up the size and see if it helps...

 

[bob58o]

So basically, should I buy a set of jets from 0.43 - 0.49? Go power sports sent over a .46, I believe. I also can borrow a precision drill set and step up the size and see if it helps...

Any other carb tuning issues?
Bogging? Popping? Stalling? Hesitation?

 

[LaithSaah]

Any other carb tuning issues?
Bogging? Popping? Stalling? Hesitation?

Nope, Runs like a champ. Start with choke, right off, idles perfectly, and revs out to 7k with no problems. (besides the glowing red hot exhaust) Only reason I wanna try to figure it out is because waiting for the exhaust to cool and the backfiring are starting to get annoying

 

[bob58o]

I would try to fatten it first and see if it improves.
I’d be afraid to lean out an engine that looks like it might melt.

 

[LaithSaah]

I would try to fatten it first and see if it improves.
I’d be afraid to lean out an engine that looks like it might melt.

Will do, Thank you!

 

[bob58o]

Just some thoughts and terminology I copied and pasted

“
Afterfire - An afterfire is when fuel is burned after the combustion chamber, often causing fire to shoot out of the exhaust. This is what most people are thinking of when they say backfire. It mostly happens in high performance cars, and is a result of un-burnt fuel entering the hot exhaust system.

Backfire - A backfire is when fuel is burned while the intake valve is still open, causing it to fire back out the intake. This is something you don't want to happen.
“

“…what happens is that the mixture is lean enough that it causes an occasional misfire in the cylinder due to the lean condition, which most often happens on deceleration. When the cylinder misfires, it pumps a complete charge of unburned air/fuel mixture into the exhaust, so you actually have fuel and oxygen in the exhaust system. After a couple of times of this, you have a nice charge of both air and fuel in the exhaust system which then lights off and explodes.

Richen it up, and you'll see that the popping will go away (often you can just back out the idle mixture screws a little - if that won't do it, bump the jetting up 2 sizes).”

 

[ezcome-ezgo]

What kind of muffler you got there? It is possible it is too restrictive?

 

[bob58o]

It is a pretty color.

 

[LaithSaah]

Afterfire - An afterfire is when fuel is burned after the combustion chamber, often causing fire to shoot out of the exhaust. This is what most people are thinking of when they say backfire. It mostly happens in high performance cars, and is a result of un-burnt fuel entering the hot exhaust system.

Backfire - A backfire is when fuel is burned while the intake valve is still open, causing it to fire back out the intake. This is something you don't want to happen.
“

Didn't know this, I get the privilege of correcting my friends now lol

What kind of muffler you got there? It is possible it is too restrictive?

The problem was there way before the muffler when I just had a straight pipe, the muffler actually helped a bit so I doubt that's the problem.

Thank you guys for all the help!

 

[Denny]

May be too lean then. Break out that pin vice and go up one size at a time.

 

[bob58o]

If muffler helped, you improved by reducing the amount of air in the mix. It made it richer.

You can restrict more air (try running with the choke partially closed or duct tape on the air filter) and see if it improves.

if it improves, you know you were lean and need to fatten up the jetting.

 

[Darren]

We would watch the dyno shop tune engines by controlling the egt and moving the cherry red portion of the exhaust back and forth, very interesting, but these were 500hp 2.0ltr turbo 4 pots, they would twist drive shafts before breaking the engine.