Cutting out at high rpm, and ignition timing question

noah9988

Well-Known Member
Local time
10:07 PM
Joined
Jul 3, 2021
Messages
414
In my quest to go dangerously fast on a bicycle, I have hit a wall. My current setup is the best I've gotten it, but when I hit 9000 rpm the engine cuts out. It's not 4 stroking, it just feels as though it doesn't fire for a few revolutions then it fires again. It really won't turn more than 9000 rpm.

Now I know you're thinking I'm crazy for reaching 9k and wanting more, and the engine is protecting itself and me from an untimely demise, but I can't help myself. I know the engines got more in it. I've tried tightening the plug gap to about .015 and a bigger main jet, didn't help. I've been playing with the timing and have found that advancing it improves the overall performance greatly. I have heard the opposite, that the timing is overly advanced and retarding it will improve performance, also that retarding helps in the high rpms. I don't think advancing it more will solve the cutting out issue though, so if there's something that could cause that I'd like to hear about it.
 

Kehkou

Active Member
Local time
8:07 PM
Joined
Jul 21, 2022
Messages
134
Location
The Duke City
In my quest to go dangerously fast on a bicycle, I have hit a wall. My current setup is the best I've gotten it, but when I hit 9000 rpm the engine cuts out. It's not 4 stroking, it just feels as though it doesn't fire for a few revolutions then it fires again. It really won't turn more than 9000 rpm.

Now I know you're thinking I'm crazy for reaching 9k and wanting more, and the engine is protecting itself and me from an untimely demise, but I can't help myself. I know the engines got more in it. I've tried tightening the plug gap to about .015 and a bigger main jet, didn't help. I've been playing with the timing and have found that advancing it improves the overall performance greatly. I have heard the opposite, that the timing is overly advanced and retarding it will improve performance, also that retarding helps in the high rpms. I don't think advancing it more will solve the cutting out issue though, so if there's something that could cause that I'd like to hear about it.
Which CDI are you using? It sounds like preignition to me. Yes, you want the spark retarded at high rpm to after TDC or you will get preignition. That's why the magnet is mounted in the 1 o'clock position.

Yes, you will get a lot of "you're crazy", "buy xxx engine instead", "buy a motorcycle" etc. , but I understand pet projects just for fun ("just buy a battery powered headlamp" lol, NO!).
 

Chainlube

Well-Known Member
Local time
7:07 PM
Joined
Jan 5, 2020
Messages
7,001
Which CDI are you using? It sounds like preignition to me. Yes, you want the spark retarded at high rpm to after TDC or you will get preignition. That's why the magnet is mounted in the 1 o'clock position.

Yes, you will get a lot of "you're crazy", "buy xxx engine instead", "buy a motorcycle" etc. , but I understand pet projects just for fun ("just buy a battery powered headlamp" lol, NO!).
Forget that :poop: retarding the timing never means "AFTER" TDC, it only means not the total advance that is already built in to the engine. Say the total advance is 12 degree, then you want to shave down the key until you have only 8 degrees. Don't quote those #s, I forget the exact amount of advance built in. YMMV
 

noah9988

Well-Known Member
Local time
10:07 PM
Joined
Jul 3, 2021
Messages
414
The weird thing is that when I retard the timing it's so down on power that it doesn't even get up to 9k rpm so I can't test if that's the issue.
 

noah9988

Well-Known Member
Local time
10:07 PM
Joined
Jul 3, 2021
Messages
414
Also my spark plug is gray. Always gray. Unless it's rich, then it turns black. I used an e3.32 and an ngk br6hs. Using amsoil dominator at 32:1. I also used octane booster because of my high compression, although I think it's down to 150psi now. Oh, and I put in some seafoam cleaner and upper cylinder lube. I had some and thought it was a good idea for more lubrication.
 

Chainlube

Well-Known Member
Local time
7:07 PM
Joined
Jan 5, 2020
Messages
7,001
The weird thing is that when I retard the timing it's so down on power that it doesn't even get up to 9k rpm so I can't test if that's the issue.
It's a fine line when you retard the timing, if you shave down the key.
 

Chainlube

Well-Known Member
Local time
7:07 PM
Joined
Jan 5, 2020
Messages
7,001

noah9988

Well-Known Member
Local time
10:07 PM
Joined
Jul 3, 2021
Messages
414
Which pipe do you have on your bike?

If you have any fab skills, this one might get you there.
I got the mz65. I was wondering if it's possible that the ports are holding it back? Maybe the transfers? I didn't do anything to them. I opened up the intake a bit but mainly raised and widened the exhaust. Perhaps the exhaust duration is too high?

I'm using a pwk 21 with a custom made intake that's 35mm in diameter and 3-4" long, which might not be doing it any favors.
20220731_151156.jpg

I also got pictures of the plug.
 

Attachments

  • 20220731_151334.jpg
    20220731_151334.jpg
    100.8 KB · Views: 39
  • 20220731_151357.jpg
    20220731_151357.jpg
    95.1 KB · Views: 39
  • 20220731_151509.jpg
    20220731_151509.jpg
    101.8 KB · Views: 40

ixxGunnerxx

Member
Local time
10:07 PM
Joined
Jul 2, 2022
Messages
35
In my quest to go dangerously fast on a bicycle, I have hit a wall. My current setup is the best I've gotten it, but when I hit 9000 rpm the engine cuts out. It's not 4 stroking, it just feels as though it doesn't fire for a few revolutions then it fires again. It really won't turn more than 9000 rpm.

Now I know you're thinking I'm crazy for reaching 9k and wanting more, and the engine is protecting itself and me from an untimely demise, but I can't help myself. I know the engines got more in it. I've tried tightening the plug gap to about .015 and a bigger main jet, didn't help. I've been playing with the timing and have found that advancing it improves the overall performance greatly. I have heard the opposite, that the timing is overly advanced and retarding it will improve performance, also that retarding helps in the high rpms. I don't think advancing it more will solve the cutting out issue though, so if there's something that could cause that I'd like to hear about it.
are you using an Rpm Tester,to see if this is the 9k? ( or Dino? )
Rpm Test with the Wire that Goes around the Spark Plug Wire if so , Make sure you Rap it around as much as you can .. ( even thought this is not going to fix your Problem .. But .. more raps of Wire will give a more accurate REading
ok , so Getting over 9k Rpms .. , try Putting a new Magnet in heat will kill that Magnet ( i assume you know this ) , but also, the Cdi box, have a capacitor in it ,, that Fill , and discharges .. it might not have time to be Building up That Capacitors, up fast Enuff to provide Them Rpms ... so there is a spark, but they're not Enuff Volts to Light all the Fuel air mix . ( some nas will let you know if its SPark ) .. So maybe Use a Cdi from a 2-stock Racing motorcycle (Crotchrocket ) or maybe try to Find a Bigger/stronger magnet. that cdi Going to Charge that Copasator Faster.. if its not spark ,, its a Balance in the crank , or the Air Flow is getting Bottle Necked .

GOod luck , not sure if any of this helped .. i know i hate it when someone post something i already know , or have Treid , good Luck And GOd bless ...
 
Top