Here is Heat 1. I have Heat 2 up on my channel as well. Working on the Final.
What I can tell re-watching is that I have a good reaction time and the first 6-12 inches out of the box looks on pace with everyone else. But then from there to turn 1 it is like I am sitting still while everyone goes around me. I am very confident it is not a drastic gearing difference because if I was geared too high, I should be closing down on the other drivers on the long straights which is not the case.
I am also struggling with some engine performance issues as well as you can see in the video. I just donât have as much straight line speed or acceleration out of the corners compared to others.
Side note, maybe Heat 2 might be a better video because as you can see in this one, there was a screwdriver on the track I had to avoid right in my line on the straight coming out of my box. Here is Heat 2:
Re tire warmup: I think it was @tjkoyen who gave the observation that tire warming is most effective when you shralp the tires in bigger arcs as opposed to faster, jerkier scrubs.
Wow I see what you mean. Whatâs funny is once you get going, the pace is fine.
You and Jana should practice draft driving. Go lap with her in your nose and then switch positions. Learn to ride the heiny closer, get comfy with that, plastic on plastic. Please donât dump Jana tho.
I see in your footage some opportunity for tightening that up to better capitalize on passes.
I do see what you mean. I agree your reaction time is definitely good enough to not lose that much on the start. What was your clutch stall speed on that takeoff (next time peak at the mychron)? Were you hitting the limiter on the straights on normal laps? I couldnt hear it well, but I am at work listening at lunch.
When I get going, I am definitely quick through the corners compared to the others but I have nothing on the straights. Even when drafting, I canât get close.
I think there is something going on with my engine which may be contributing to the terrible starts as well. When I first got the engine, it had a lot of compression. Pulling the cord to find TDC was super easy as there was a clear and obvious âclunkâ at TDC. Now a days, it can sometimes be hard to feel for TDC just pulling the cord.
I was told to always pull it to TDC after running so that the engine cools with the valves fully seated and no tension on the springs. Iâll admit that when I was new, that was something I frequently forgot. That has me thinking that perhaps the valves got warped or something when I forgot a number of times? I donât know how impactful that would be given that Briggs does not even mention doing that as normal âoffâ procedure.
Thinking about getting a new head assembly and seeing if that brings back life to the engine. This engine used to be very strong and is a multiple series winner by the prior owner.
Since Iâm not a wrench my answer usually involves invoking the skills of a pro. since Don made it heâs likely inclined to fix it to be like what he did before. Obviously you canât race that.
Fair! I enjoy working on things myself but I am obviously new. I just feel like it is going to cost as much as a new head assembly to get Don to inspect the engine so part of me wants to just try the new head first!
But, I am learning that managing your relationship with a local shop / builder is an important aspect of the karting world. As a millennial, I usually prefer to just shop online, watch videos and do repairs myself but I get the sense that the shop guys almost getâŚwell âoffendedâ is too strong of a word, but very much value you going to them.
I am hitting the limiter briefly right before the braking zone on the back straight. Definitely less than it used to be. Months ago with the same gearing (though lower temps), I would touch the limiter right before turn two as well. It was quite hot this day so I was having to adjust the carb to lean out the engine which I figured contributed to the limiter difference but it may be a larger issue due to the overall lack of power off the line, out of corners and on the straights.
I am sort of new to these clutches, but this is my observation. What I hear is a lot of slip from your standing starts and I think it gets worse as the day went on. Revs come up then as the clutch fully engages the revs fall and the motor starts pulling. At speed its tough to say as you seem to have good pace except on the straights.
Crocindy also inquired about how much time is on your motor. Do you have an idea about that?
On the clutch slipping - I am curious to try some weights in the clutch. It sounds like that can really help on standing starts because the shoes will lock up more aggressively.
As for the engine, unfortunately, I do not know how much time is on it. I bought the kart used with the engine. Judging by the seals it has and the overall dings and wear to the engineâs paint, it has seen a few seasons of running. The previous owner was extremely fast on this kart and engine, winning multiple local series in the PNW with it. When I first got it last year, the engine had a ton of compression (TDC was clear and obvious) but now, it can be hard to find TDC on the first attempt. I think I need to take it back to the builder and have him do a leakdown test. I am leaning towards the valves being warped and leaking.
So I was finally able to download my Mychron data. What I am seeing from the start:
Engine is idling on the grid at ~2700 to 3200 rpm. I do blip the gas a bit so I think that is why there are spikes. In the pits, I always try to get it to idle around 2000 to 2500 (where it sounds healthiest on that day).
When the green flag drops, my RPMs initially spike from ~3000 rpm to 4425 rpm as I accelerate from 0 mph to 2.3 mph.
Then the RPMs dip a slight bit and then rise up to 4530 rpm from 2.3 mph to 11.5 mph. Speed acceleration curve appears almost perfectly linear.
The RPMs then drop significantly from 4530 rpm down to 3600 rpm from 11.5 mph to 31.3 mph.
The RPMs hover from 3600 - 3700 rpm from 31.3 mph to 34 mph and then begin to rise.
From 34 mph to the peak of 50mph, the RPMs finally steadily rise from 3700 rpm up to 5420 rpm before the entry of turn 2.
Does this data help diagnose anything obvious to you? I am concerned about the big drop in RPMs from 11.5 mph to 34 mph. It is odd to me that the speed trace is so linear. Zooming out a bit, you can see that the slope of the speed and RPM traces out of every corner appears to be similar to the standing start slope.
That leads me to believe that the issue is not particularly unique to the standing start but may be impacting me throughout the lap (even though it is the most obvious at the start). @mtbikerbob@Bimodal_Rocket@fatboy1dh Any thoughts? Another thing that I think is interesting is 3600 rpm is the engagement speed listed by Hilliard for two back and two white springs with no weights. While the RPMs jump initially well beyond this off the line, they dip down and then hover at 3600-3700 awhile before then rising consistently up to 5420 while going from 34 mph to 50 mph. Does this indicate my clutch is slipping the whole time from 0 mph up to 34 mph?
