What could cause loss of revs?

1

In my restricted X30 I’m usually hitting between 15,000 - 15,200 revs at the top of the straight at 99-100km/h. I don’t think I’ve ever seen anything less than 14,900 at my local track.

In my final race of the day I was doing consistent lap times until the last 2 laps of the race where they instantly dropped by 5 tenths. I was pretty surprised to see such a huge drop off in time as the kart still felt good and the previous 3-4 laps were all within the same tenth.

I looked at my data afterwards and in those last 2 laps my top revs dropped from the usual 15,100 to 14,500, and I was maxing out at 97km/h compared to the 100km/h I was hitting those first 8 laps. I was in clear air the entire race.

What could’ve caused this?

2

Start by checking engine. Reeds, carbs etc. anything that is obvious and responsible for the engine performance

3

I checked the reeds, they looked fine.

Took the carb apart and was actually missing the high speed needle washer. Which I guess would mean the needle was a touch deeper than usual? If this was an issue I’m guessing it would’ve been evident the entire race day and practise day prior?

4

The washer is there to keep uniform pressure on the o-ring

It cannot get any deeper than the taper is so no difference without it

Could also be a stator issue if nothing is wierd, I’ve experienced that with a couple stators. Everything else is perfect but it won’t rev out

1 Like
5

Did your EGT change with the rev drop off?

6

No one really runs EGT here in Australia, at least at my local. Most folks here use the Lambda sensor, which I also checked afterwards and it showed normal readings. Water temp was consistent and well within normal range as well.

7

I’d be open to getting an EGT sensor if you guys think it’s valuable. I’ve sort of just followed what’s been recommended by my local kart shop re Lambda, not even really sure how the EGT works tbh but am always looking to learn.

8

Ah right no worries then.
Do you have data to look at?

9

Check compression and the condition of the spark plug. Rebuild the carb. Barrow a coil to test with.
Check the toe-in plus the rear axle for side-to-side movement, axle bearing issues, or maybe your chain.
Also look at your throttle cable to see if the carb is getting opened completely.