BSP engine running lean

W5R

New member
Im having an issue with my bsp engine that i cant seem to figure out what to do about it, any help is appreciated. Here is the deal...

I have a brand new box stock project engine, it is set up for bsp rules for a track that i race every weekend. This track has its own rules for box stock, which is the max jet sizes we can run are .028 main and .019 low speed, so those are the jets in my motor, but my engine is running way too lean and building alot of heat, sometimes up to 440 degree's with no tape on the blower housing at all. The plug is brand new and after 2 races, its still white as can be on the porcelain and only a tiny bit of black around the plug itself. When i ran AKRA with another engine that was identical to this, the plug was always a nice chocolate brown color, but then again it was jetted completely different and timing was much more also.

What can i do about this problem without raising the jetting in the engine? Or am i just basically stuck with having to run it lean like this? I cant imagine it being very good for my motor to be running so lean that the plug is actually white. The engine is wicked fast the way it is, but theres no way it can be healthy for it to be that lean or that hot! This is with stock airbox and filter, 3/4" weinie pipe, stock flywheel and timing, basically everything bone stock except for a bsp cam. I have tried tweaking with the low speed idle mixture screw on the back of the carb and i have it maxed out as rich as i can get it, but still too lean.
 

Yakattack

Member
Idle mixture screw only effects idle no where else... With a .28 main jet it will always be lean...
I am surprised you can get it to full throttle with out breaking up?
What about the etube is it tech? You could try the gx140 etube!
 

alvin l nunley

Premium User
There was this father/son team I use to help with their KT100 in Southern Calif. The son was the driver. I taught them how to use the EGT (exhaust gas temperature gauge) and the son was really good at it. He won the KT100 Championship two years in a row. And that’s the Southwest regain 7 series.
In his third year he got a ride with a big builder.
So one day we’re sitting in the pits and the builder comes over and wants to look at his plug. The son gives him a wrench and the builder pulls the plug. The builder’s eyes get really big and he says “this thing is way to lean!!” The plug is bone white.
My friend looks over at me and just kind of smiles. How lean could it have been I’m thinking. He gets fast time, wins first place and the year’s championship. You don’t do that running “too” lean.
I do agree that making a jet size rule is about the stupidest thing I can imagine, but if it’s running good, and not getting slow on the top end, what’s the problem. The people that make spark plugs, and publish pictures of them show how they look when they are burning right, never say they should be “chocolate brown”.
An engine that’s running good is not “too” lean, but the jet rule, like I said, is, IMHO, just wrong. Five points change in the air density calls for a 5% change in mixture. If you’re running good with the .028” jet, and the air density go’s up 7 points, you need a .029” jet. if it goes down 7.5% you need a .027” jet.
Swings of 14 points in air density are not all that common, but you can see the problem you could have if they do. It would be interesting to know what the air density is where you race, and how much it changes thru the day, or thru the year.
What about the plug? Can you find a colder heat range plug to run?
What fuel are you running? If it’s gas, what octane? Have you ever done a CC check on the engine?
If the engine is running good, then I wouldn’t worry about the CHT. Thing is, if you’re right on the edge of going lean, knowing what the air density is, and if it’s changing, would be my concern.
And being how I am, I would be explaining about air density to the people who make the rules.
comments, compliments, criticisms and questions always welcome.
 

W5R

New member
Are you allowed any other modifications to carburetor?

Idle mixture screw only effects idle no where else... With a .28 main jet it will always be lean...
I am surprised you can get it to full throttle with out breaking up?
What about the etube is it tech? You could try the gx140 etube!

No modifications at all allowed to the carb, cant even change the jets, this track is a true box stock class, stock everything including flywheel and timing.

The motor is a beast, which surprises me with the way its running so lean like this. I just chalked it up to the jetting not being rich enough and i guess thats it. Cant really do anything about it without coming up illegal. I mean i could change the jets if i wanted, but i dont want to cheat, i wanna keep it legal. Theres enough people thinking im cheating as it is, the last thing i need is to prove them right lol. ill just leave it alone and hope it doesnt blow up i guess. Even if it blows, i only have $140-150 in this engine, i put it together myself and it does a good job at spanking the competition at the local saturday and sunday races.
 

W5R

New member
There was this father/son team I use to help with their KT100 in Southern Calif. The son was the driver. I taught them how to use the EGT (exhaust gas temperature gauge) and the son was really good at it. He won the KT100 Championship two years in a row. And that’s the Southwest regain 7 series.
In his third year he got a ride with a big builder.
So one day we’re sitting in the pits and the builder comes over and wants to look at his plug. The son gives him a wrench and the builder pulls the plug. The builder’s eyes get really big and he says “this thing is way to lean!!” The plug is bone white.
My friend looks over at me and just kind of smiles. How lean could it have been I’m thinking. He gets fast time, wins first place and the year’s championship. You don’t do that running “too” lean.
I do agree that making a jet size rule is about the stupidest thing I can imagine, but if it’s running good, and not getting slow on the top end, what’s the problem. The people that make spark plugs, and publish pictures of them show how they look when they are burning right, never say they should be “chocolate brown”.
An engine that’s running good is not “too” lean, but the jet rule, like I said, is, IMHO, just wrong. Five points change in the air density calls for a 5% change in mixture. If you’re running good with the .028” jet, and the air density go’s up 7 points, you need a .029” jet. if it goes down 7.5% you need a .027” jet.
Swings of 14 points in air density are not all that common, but you can see the problem you could have if they do. It would be interesting to know what the air density is where you race, and how much it changes thru the day, or thru the year.
What about the plug? Can you find a colder heat range plug to run?
What fuel are you running? If it’s gas, what octane? Have you ever done a CC check on the engine?
If the engine is running good, then I wouldn’t worry about the CHT. Thing is, if you’re right on the edge of going lean, knowing what the air density is, and if it’s changing, would be my concern.
And being how I am, I would be explaining about air density to the people who make the rules.
comments, compliments, criticisms and questions always welcome.

It wont do any good to explain air density to the owners of the track, they have had this class going for years since clones came out, they were actually one of the first tracks to start racing the blue clone motors, this is where it all started at. The track im talking about is J&M Motorsports in Columbia, ky, they have their own box stock rules and it seems to work great, box stock racing has taken over at this track and all of us akra racers went back to box stock because of the kart counts in akra being so low. Its fun racing though and i like it.
 

Yakattack

Member
If it is a true box stock class... You could find a young foo etube that was out of spec that day to richen it up!

In a couple of our $99.00 motors from Princess Auto like your Harbor Freight...called power fist...we have found out of spec etubes....with a .36 jet they would run a afr of 10.5 from 1000-6000rpm not changing...as soon as we put a ruxxing etube in it would go lean at idle 15.0 to a afr of 12.35 at 6000rpm...
After we found this and inspected the middle hole was visibly larger than a ruxxing etube...
Stock carbs on the power fist were Zon-Chen...
 

Kart43

Member
Leave the engine as is I would not worry about the temp. we have never hooked our temp probes to any of the engines we run, don't care about the temp really.
 

W5R

New member
Its not really the temp that concerns me, because my akra engines are running 420-450 conistently. What has me concerned is the extreme lean condition. Ill try changing the E-tube
 

jake17j

Member
if you have a bsp cam in aren't you cheating anyway ?there is a heck of a difference between a bone stock cam and the bsp grinds.
 

W5R

New member
Bsp cams and cl1 cams are legal, something like the mod2 and bigger cams are not. Guess i should have put that in the other post, my fault.
 

alvin l nunley

Premium User
i am not changing the jet, it has to remain as 28 main and 19 low

I wonder what genius came up with that rule!!
Apparently that person doesn’t know much about jetting. For sure they don’t know anything about air density.
Seems there are people that think that with just “ONE” more rule, they can make everybody a winner.
Comments, compliments, criticisms and questions always welcome.
 

Kart43

Member
You might want to see if your high speed air bleed might shrink up a few thousanths . ;)

I was going to suggest this but no modification was indicated, but then the E tube is going to be changed, so I have no idea what modifications are allowed.
 

W5R

New member
I was going to suggest this but no modification was indicated, but then the E tube is going to be changed, so I have no idea what modifications are allowed.

Just so you dont get the wrong idea, i am not changing the stock e-tube to an e-tube from a different kind of engine, i am going to get some stock e-tubes and go thru them to see if i can find one that is a little out of spec from the rest, like someone said above. Im hoping that may make a difference but it likely wont. I have no idea what the high speed air bleed even is, where is that and what does it look like? What does it do?
 

SHAVED APE

New member
Look at the opening to your carb, it's the small opening to the right . the size of the brass insert in this opening regulates the ammount of air that the e tube sees and is adjusted to change the A-F ratio . Larger = leaner Smaller = richer in simple terms ;) If you measure yours and and have a friend make you one smaller , you trick the carb into being richer ,not as much air mixing with the fuel as it is pulled up the E tube. Hope this helps .
 
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