ESE's works engine tuner

[Wos]

in Classic enduro Championship race at Nordhausen/ Germany... have a look on the brick

[Flettner]

Aren't you guys getting tired of having to look at my thumb for over a week now? I know I am

Whenever I post, it kills this thread ... the kiss of thread death.
😁

[Frits Overmars]

Whenever I post, it kills this thread ... the kiss of thread death 😁

If you really have that power, I can think of a few other forums you could visit

[Condyn]

Hello fellow sufferers, I have been stumped by something for a bit now. I drag race an air cooled snowmobile which uses a CVT (not sure of relevance but just to be complete I included)
I always have excessive wash width of 10mm on a 69.5mm bore, and rich plugs along with a chalky white thread base ring.
My engine responds well to jet changes, however when I go down a size from my known sweet spot EGT, the EGT increases again in a normal increment. This narrows my wash pattern, but the engine has a lean feeling on the warm up stand and my Elapsed time always gets worse. I have 130 logged passes and have rider awareness with this machine. It is a front runner (but I want it perfect lol)

This almost suggests to me that there is a mismatch with the compression ratio and or ignition timing at peak operating rpm on the cvt. Maybe something else?

-Comp ratio 15.5:1
-fuel c12
-ignition straight line 15 degrees
-spark plug Br9es
-stinger diameter 23.6x300 (no nozzle currently because it has always performed better better with full length stingers, maybe a much smaller nozzle than I have used is in order)

Am I beating myself up for nothing, or does anyone have suggestions to make my setup more synergetic?

[lohring]

The part of the text down to where it says "Jim Allen" is from Jim. The rest of the text is from Bill Givens. I like Jim's fixture, but both people have great insights. Jim mostly rebuilt small engines (26 cc) while Bill rebuilt larger engines.

Lohring Miller

[Frits Overmars]

The part of the text down to where it says "Jim Allen" is from Jim. The rest of the text is from Bill Givens. I like Jim's fixture, but both people have great insights. Jim mostly rebuilt small engines (26 cc) while Bill rebuilt larger engines.
Lohring Miller

Thank you Lohring.

[wobbly]

Condyn, what is the actual cylinder displacement - ie what is the stroke.
15.5 com is nothing for C12.
This is 2025, why are you using a straight line ignition from the 1970's.
Also a spark plug from a lawn mower.
What is the " sweet " EGT at what rpm, is this derived from a dyno run and if so what power is it making.
Many more questions to get some analysis, but this is a start.

[Condyn]

Wobbly, it is 452cc. 69.5x59.6 I use the straightline ignition because at many venues that I race, the rules state that a stock ignition must be installed. It is a vintage class from the 70’s. The egt is right at 650c at 9500 rpm, 3x bore from the piston. No, I am familiar with your logical jet selection chart, however I did not have the chance to install the probes on the dyno during the last session.

The field tests tell me that when I jet down it goes slower. I looked again with my wash light last night and I might be wrong on the wash width. It looked more narrow (around 5-6mm) I am going to take the heads off tonight to get better eyes on it. The piece that keeps me up at night is the egt continues to rise with a down jet (650 up to 670) however it makes a pop on the warm up stand at full rev and makes my pass slower by a tenth every time. Admittedly I do not always have the cht hooked up so I am not aware what the cht is doing when I jet down.

Edit, HP 104 to the crank on a low reading dyno. How low? I do not know, but I would guess 3% based on others results.

[Storbeck]

Wobbly, it is 452cc. 69.5x59.6 I use the straightline ignition because at many venues that I race, the rules state that a stock ignition must be installed. It is a vintage class from the 70’s. The egt is right at 650c at 9500 rpm, 3x bore from the piston. No, I am familiar with your logical jet selection chart, however I did not have the chance to install the probes on the dyno during the last session.

The field tests tell me that when I jet down it goes slower. I looked again with my wash light last night and I might be wrong on the wash width. It looked more narrow (around 5-6mm) I am going to take the heads off tonight to get better eyes on it. The piece that keeps me up at night is the egt continues to rise with a down jet (650 up to 670) however it makes a pop on the warm up stand at full rev and makes my pass slower by a tenth every time. Admittedly I do not always have the cht hooked up so I am not aware what the cht is doing when I jet down.

Edit, HP 104 to the crank on a low reading dyno. How low? I do not know, but I would guess 3% based on others results.

Slower in ET or slower in MPH?

Im wondering if the jetting down is increasing eghaust gas temp and therefore increasing the rpm at which you make peak power to the point that it is no longer in harmony with your clutching (CVT tuning, they're not really clutches but snowmobile people call them "clutches") , or to the point that the pipe is trying to rev higher than your ports will let it (?)

[wobbly]

Show us a hi res of the piston.
I was going to say exactly what Storbeck said - I believe that the " tuning " is OK, as the EGT goes up as per normal, but that then puts peak power into the rpm
where you would have had unused overev previously.
This would indicate that a shorter " gearing" could be used, and this would make you faster due to the torque multiplication.
To test if you are close to pushing the outer boundaries at all, I would be looking at adding some static timing with the lean EGT setting.
I believe 1* to 2* would pull back the EGT to the original " best power " rpm number.
You can find out how close you are by then leaning down again, and if the EGT flatlines, that is the deto limit.
If this is the case, then its a matter of making a decision to go back on the timing, and add some com - as I said your com seems very conservative for 110 octane.
But - the leaner/advanced setup may be faster, you wont know without the dyno data to clutch it correctly.
PS - cht tells you nothing about the tune - just the under plug temp, BUT most cht will go spastic when getting into deto - but you already knew that as the EGT had already flatlined or dropped.