Reving your engine with no load; Is it bad for the engine?

[Rick]

In the manual it usually says not to rev a 2 stroke engine with no load. However, I always see everyone do it. People rev their engines on the grid before the start. Is that bad for the engine?

[Martin Lenick]

I think it's a Rotax thing, and I adhered to it religiously. Looks like the Leopard is a bit more forgiving, but what does it matter? The only reason, beyond enjoyable smoke and noise, to rev it up on the stand is to set needles... no reason to do that with a Rotax. Perhaps it's just as harmfull to a Leopard... the discipline of selecting jets for the Rotax might be beneficial to Leopard racers tweaking their needles without putting unecessary unloaded revs on their engines.

[luke blazek]

Starting the kart while on the stand is a great way to set the idle and needles...BUT... revving the living HELL out of the engine is doing nothing productive other than wear and tear on the motor. I can understand if you just let it idle while on the stand before you get up to the grid, thats fine. But its like 16,000 nails on a chalkboard when i hear guys hardcore revving their engines on the stands while either in the pits or just chilling out by the trailers.

[PeterK]

Im no kart racer but i have relatively thorough mechanical knowledge. The most important thing is the warm up. Starting the engine and let it idle for a while is the best way to do it. Only, after the engine is warm it is a good practice to give it a few jolts of higher revs to simply burn off the excess of fuel / oil accumulated in the chamber - more so on 2-strokes than 4 strokes

[pmpnuss]

i agree with peter. From what I know of 2 storke they are prone to fouling out spark plugs I know this is true on dirt bikes they have to keep revving them to burn off the extra fuel. I dont know about high rpm revs but just a quick throttle jolt does the trick. On dirt bikes it is about every minute or so.

[pmpnuss]

The reason is because of the gas oil mixture

[PeterK]

The reason is because of the gas oil mixture

yes, gas . oil mixture is the biggest challange in 2-strokes - As is the excessive fule consumption due to limited ability to control mixture flow to the cylinder. A lot less profound with the advancement in technology still a problem making it a lot less popular choice in todays "eco-terrorism" era due also to excessive emissions. .............. LOL... shut up PeterK

[pmpnuss]

If those dam volcanoes stopped erupting we could save our planet :bugeye:

[PeterK]

If those dam volcanoes stopped erupting we could save our planet :bugeye:

but isn't it our fault they are erupting in the first place! :confused:

[Rick]

Im no kart racer but i have relatively thorough mechanical knowledge. The most important thing is the warm up. Starting the engine and let it idle for a while is the best way to do it. Only, after the engine is warm it is a good practice to give it a few jolts of higher revs to simply burn off the excess of fuel / oil accumulated in the chamber - more so on 2-strokes than 4 strokes

Hardly anyone let's their 2-stroke idle for long. I think that you could foul the plugs that way. Usually people rev their engines on the stand and then just start them right before the race starts.

Also, I think there is a difference between water cooled and air cooled engines. I notice that Rotax (water cooled) guys tend to rev their engines on the stand to warm them up and get them to operating temp. They also duct tape the radiators to keep the engines in the optimal temp range.

I don't really see HPVs revving their engines on the stand as much. Maybe it's because they are air cooled.

[JET Karting - Andy Finke]

Air cooled engines are less efficient in cooling, giving hotter areas and cooler areas. This means you have to have the clearances set a little higher in the motor.

Liquid cooled is more even, allowing closer tolerances, and adding power. This also means a MUCH better warmup is needed. It takes longer because you have the mass of all the water to get up to temp, not just the cylinder.


Andy

[PeterK]

Hardly anyone let's their 2-stroke idle for long. I think that you could foul the plugs that way. Usually people rev their engines on the stand and then just start them right before the race starts.


There is nothing more dangerous for the engine than a rapid, uneven distribution of heat. And that exactly is what happens when you start cold and excessively rev it.

You are right tho - overkilling on the idle time does no good to the engine neither.

[MotoBob]

With an experience level of ZERO in Karting, I have no idea about Leopards etc.

But…With 30+ years of riding dirt bikes most of which while two strokes dominated the market. Of course these were the big four Japanese manufacturers, but I can say revving never seemed to hurt. I don't think load has anything to do with it. What hurts is too much RPM for exteded periods. Once they were warmed to a safe operating temperature, we revved them to "clean them out". Even though a two stroke may be at operating temperature, they still have a tendency to bog if you let them run at low RPM for any amount of time. In Karting a bog could cost you some time. A bog in motocross might equal a ride in an ambulance.

[JET Karting - Andy Finke]

The BIG deal is to warm them up with small amounts of throttle and rpm. Once warm, it's tougher to hurt them.

Excessive RPM should still be avoided on the stand. 16,000+ rpm is a tough thing for any motor. I've actually seen a guy stick the kart he was warming up before a race. It wasn't so bad a stick that it wouldn't start again, but the driver only made another lap or two.

If you guy have any questions about how we recommend warming TAGs, just ask sometime when you're out there. We'd rather you had a good season too.


Andy

[PeterK]

The BIG deal is to warm them up with small amounts of throttle and rpm. Once warm, it's tougher to hurt them.
Andy

very well said Andy...

[Jeff Stamper]

Ok, Rick said that the MANUAL says not to rev the engine with no load. As much as I agree with a lot of you on this topic, you may be over looking something.No load in a manual usually means no load at all ! If you start and rev an engine with no clutch on it, the revs come up almost twice as fast as if it had a clutch ! Keep that in mind. Most manuals do not really (for some reason) take into considerstion that you are racing their product ! I have no idea why, but as far back as McCullochs, the manual refered to the engine like a lawnmower. And the best I can tell, they still do. But the warming of all engines, air cooled and water cooled is necessary. The only time I would not warm one up is when its 95 degrees out. Then the pace laps should be sufficient. The reason you need to warm things up, is that you are using 2 or 3 different types of metals that all contract and expand at different rates. This is the only reason you need to warm them up. It also includes water in those engines. Then you have to figure in the different additives people use in the water. Maybe Watter Wetter and RC 20 dont respond the same to heat ! That is just the wonderful world of high performance racing. You guys should feel lucky you dont run alcohol in these motors. Then we would be having a whole different discussion on warming them up. One more thing, in reference to the dirt bikes, usually they have a bit more clearence than the stuff we run here ( I did say usually)