rev limiter

R

rewilson64

Member
new engine at the begining of the season. I was hitting the rev limiter at end of straight. now with no changes I am not hitting the limiter. 1/8 dirt oval. why might this be happening
 
Kart might be bound up, tires might be going away, carb might need cleaning, valves might need adjusting, air cleaner might be dirty, fuel filter plugged, etc, etc lol
 
You didn't do enough to keep the dirt out and your engine ingested enough dirt to wear it out in 1/2 a season.
 
pretty sure I kept it clean, oiled filter used filter sock, and nylon over cover. I will try to clean carb, and check valves thanks
 
Tires, tire temp , track condition, driving smother or less controlled, chassis set up tight or loose , fuel air bleed screw adjustments, old fuel , in addition to the above mentioned. One thing that had stayed constant . The Rev limiter coil has not changed.
 
Track conditions change?
Most dirt tracks will change quite a bit during the course of a night of racing. Not uncommon to have to change gears a time or two to keep up with a track that picks up speed as the night goes on.
If the engine is down on power, that could be a problem -- check the fore-mentioned items first, then do a leak down to see just how well sealed your engine still is.


-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
27 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
If you had been checking the compression on a regular basis, that might tell you something. If you had been checking the air density on a regular basis, that might have told you something. In the summertime, after the sun goes down, the air density can go up and that will lean your mixture out.

Often I have been told that air density doesn't affect these little engines, but the rest of the racing world would disagree.

Now I'm not saying that these two things are your problem, but they're certainly two key problems you should be eliminating from consideration in your pursuit of a reason(s) why you're going slower.
 
Jimbo said:
You didn't do enough to keep the dirt out and your engine ingested enough dirt to wear it out in 1/2 a season.
Click to expand...

Possible, but very doubtful.
I've got a group of backyard 206 customers who take horrendous care of their equipment and they're on year 6 or 7 on their engines now with absolutely no maintenance other than changing oil once a week and replacing the air filter when it is so plugged up that the engine doesn't run right.
Certainly, I'm not suggesting that anyone treat their 206 (or any engine) in this manner, but when I hear a guy say that their 206 is worn out, I'm thinking it probably just needs the valves and seats touched up and a new head gasket. These engines seem to run better and better when they've got plenty of run time on them and have a simple top-end freshen-up.

The OP may simply have an inlet needle stuck - that will cause a lack of rpm for sure.
A plugged or partially plugged pilot jet can cause a lean condition as well (= lack of power.)


Although air density does play a factor, I doubt that the air has consistently gotten worse as the year has progressed. Seldom is A/D that predictable.
I will never discount the value of air density in properly tuning a race engine, but with a fixed jet, you're carb. tuning on these sealed engines is limited to clip position on the needle (should be ample,) air bleed screw, and float height.
 
CarlsonMotorsports said:
Although air density does play a factor, I doubt that the air has consistently gotten worse as the year has progressed. Seldom is A/D that predictable.
Click to expand...
Although I agree very much with most of your points, let me tell you something about air density and how it can change.

Many times I have been to the track and the air density hardly changed at all, throughout the whole day, but there are times when it does. At one particular track, Paris in Southern California, I've seen the air density change seven points from late afternoon to early evening after the sun went down. Atwater, in California, is another place where the air density can change a lot. Unfortunately, at the race I'm thinking of right now, I really didn't know much about air density. It must have changed (dropped) a bunch from early in the day to qualifying time because my practice times were a lot faster than my qualifying time. I did check the compression pressure after qualifying but it hadn't changed.
 
Al, tell me how A/D can get consistently worse throughout the season and that'd be news to me.
We're not talking about throughout a single race day, but through half of a season.
Please read the OP's concern over losing power (not hitting the rev limiter) over the course of the season. I will personally guarantee that his lack of performance is not due to a consistently decreasing air density.

On dirt oval, kart/tires locked down might be a better answer as to why it won't turn the same rpm as earlier in the season.
We'll just have to wait for the OP to come back on this thread and let us know what he found. :)
 
CarlsonMotorsports said:
Al, tell me how A/D can get consistently worse throughout the season and that'd be news to me.
Click to expand...
Nothing was said about "throughout the season", what was said was "beginning of the season" and I assume until now. Early in the season it could have been cooler, which many times means higher air density. hot summer weather many times means lower air density. Something else; hot afternoons mean lower air density can happen, cool evenings can mean higher air density, which can mean increased power, but you wouldn't know if you don't have an air density gauge. In the late 90s I had an air density gauge, but I don't have my notes, so you'll just have to take my word for.

A race comes to mind, in San Diego, where the air density was 103 and the temperature was 82°, really hard to tune a Yamaha with those conditions. You seldom see that hi an air density with that high a temperature. Being in San Diego, near sea level, the barometric pressure can get up there. Air density is the combination of barometric pressure and temperature. I've spent the last 20 years trying to convince people of the importance of air density with little success.
 
alvin l nunley said:
I've spent the last 20 years trying to convince people of the importance of air density with little success.
Click to expand...

Hey Alvin, maybe you could post the simple equation how the HP changes with air density and people would understand this better. I think you might of posted this sometime way back, not sure. We get it and always have, its the difference between winning and loosing if done right.

Steve
 
I found an interesting ap for iPhone. It uses the GPS feature to get the current weather conditions. Then you can use those conditions to find the relative density and relative HP. Or you can play around with different parameters and it will show the effect on relative density and relative HP. Check it out at the ap store.
 
steve baker said:
Hey Alvin, maybe you could post the simple equation how the HP changes with air density and people would understand this better.
Steve
Click to expand...
There is an equation for correcting dyno readings, torque x RPM / 5252.1, to a standard atmosphere. I've never thought of it as a simple equation, but then I'm no mathematician. The purpose of the correction factors is to show what HP readings, taken at 5000 feet. would look like if taken at sea level, or for any change in air density. The correction factor is arrived at use barometric pressure and temperature.

I don't know of a calculation that uses an air density number for correcting horsepower. Air density and correction factor calculations use the same atmospheric conditions, barometric pressure and temperature, but HP correction factor numbers use three decimal place precision.
 
alvin l nunley said:
There is an equation for correcting dyno readings, torque x RPM / 5252.1, to a standard atmosphere. I've never thought of it as a simple equation, but then I'm no mathematician. The purpose of the correction factors is to show what HP readings, taken at 5000 feet. would look like if taken at sea level, or for any change in air density. The correction factor is arrived at use barometric pressure and temperature.

I don't know of a calculation that uses an air density number for correcting horsepower. Air density and correction factor calculations use the same atmospheric conditions, barometric pressure and temperature, but HP correction factor numbers use three decimal place precision.
Click to expand...

I'm confused
 
steve baker said:
http://www.csgnetwork.com/relhumhpcalc.html
Click to expand...
Thank you, this software has shown me that my dyno spreadsheet arrives at the same correction factor when using the same barometric pressure and temperature. My spreadsheet uses the same SAE 1990 standards. This is the first time that I have been able to verify the accuracy of my spreadsheet. Do you have any idea where I can find the formula for calculating the humidity correction factor?
 
Anybody use a weather station? Generally available, reasonably priced, easy to use. At track info, where the "dyno" that matters lives !!!
 
You must log in or register to reply here.
Back
Top