Topic: a little help with my CR's

[nokrome]

Hi guys,
  the motor,
      850
      stage 3 ported head
      webcam 63a
      CR 29's yy8 needles 3rd from the top, 132 mains, all other jetting stock
      very free flowing 4 into 1

   the problem,
       the bike pulls hard and smooth until i get a little past the 3/4 throttle point then it starts to sputter, if i twist the throttle a little more it will catch up and take off again, this will happen consistently in any gear.
        i was running 128 mains and got it to the point were it started to sputter and did a plug chop, definite lean condition, that's when i decided to step up to the 132's, that didn't seem to make much if any of a difference.
        i think my next move is to step up the mains again since I'm not getting any too rich bog down once the motor starts to take off after the initial sputter.
        does it sound like I'm going in the right direction or should i be looking at something other than the main jets? I'm a little confused with this because i have worked up all the way from 120 up to 132 mains without very much if any change in the symptom.
                    thanks

[Sam Green Racing]

You could be taking air in, those jets are masive and shouldn't show a lean condition.
What altitude are you at?

Sam.

[mlinder]

He's at, basically, sea level.

You get the advance sorted there? Never heard back from you on that. How ya?

[Sam Green Racing]

Hi Mark, we were on 115  at sea level, if everything is set up right, I still think he could be taking air in, perhaps round the boots.

Sam.

[nokrome]

He's at, basically, sea level.

You get the advance sorted there? Never heard back from you on that. How ya?

  i did retard the advance about 3 degrees, it seems to be fine.

Hi Mark, we were on 115  at sea level, if everything is set up right, I still think he could be taking air in, perhaps round the boots.

Sam.

  i have checked for leaks around the boots at idle, every thing seemed to be fine, (hard to check going down the road at 3/4 throttle  )
   this really seems to me to be throttle position related as opposed rpm related because it will rev smoothly to 9000-9500
    in the lower gears (it will rev to that point before i get to the 3/4 position)

[mlinder]

What's your final advance on that, Phil?

Anyway, you mentioned plugs showed lean?

Hi Sam. Yeah, but all these bastards are different.

[Rod]

At that stage of throttle opening, the needle profile x main jet interaction is key and normally that's where I'd look. But the step change from 120s to 132s without a big impact on mixture doesn't seem right.

By the way, have you tried raising the needle in any of the changes you've made?

[nokrome]

What's your final advance on that, Phil?

Anyway, you mentioned plugs showed lean?

Hi Sam. Yeah, but all these bastards are different.

 i am at about 30 degrees total advance,
 yeah, i took it out on the road and wound it up until it just got to the point were it started to stutter and chopped it, showed lean (i had 128's installed at that time)

At that stage of throttle opening, the needle profile x main jet interaction is key and normally that's where I'd look. But the step change from 120s to 132s without a big impact on mixture doesn't seem right.

By the way, have you tried raising the needle in any of the changes you've made?

  i raised the needles to 3rd from the top, and have experimented with raising them higher without much change,
  i agree that going from 120's to 132's without noticeable difference seems odd, it makes me think that i am developing an air leak at higher rpm's but like i said, i can rev smoothly past those rpm's in lower gears at lower throttle openings and once it gets past that spot it takes off again.
 

[mlinder]

Honestly, with the cams and compression you have, I'd still drop down another 4 or 5 degrees. If the ignition timing is wrong (too much advance), it doesn't matter what kind of jetting you do. The mixture will not burn properly. You won't be able to jet properly.

Mike, Sam, kos, whoever, let me know if I'm wrong, here.

[Sam Green Racing]

Mark/nokrome, I'm not sure if Honda made any recommendations on setting up the ignition timing with a 970 or similar kitted motor but when they offered race kits for their earlier models (CB92/95/72/77 and 350Ks) they recommended 5 degrees more advance over stock timing.
If you don't have a degree wheel, this can usually be achieved from the F and T marks that you set your timing and tappets with as they are normally 5 degrees apart. In this case, set the static timing as if you had another T the other side of the F mark.
I would start with, cam chain tension, tappets, ignition setting then carb sync, you're then ready to move on to plug chopping.
If all that fails, get the bike on a dyno with a good operator.

Sam.

[mlinder]

Mark/nokrome, I'm not sure if Honda made any recommendations on setting up the ignition timing with a 970 or similar kitted motor but when they offered race kits for their earlier models (CB92/95/72/77 and 350Ks) they recommended 5 degrees more advance over stock timing.
If you don't have a degree wheel, this can usually be achieved from the F and T marks that you set your timing and tappets with as they are normally 5 degrees apart. In this case, set the static timing as if you had another T the other side of the F mark.
I would start with, cam chain tension, tappets, ignition setting then carb sync, you're then ready to move on to plug chopping.
If all that fails, get the bike on a dyno with a good operator.

Sam.

Aye, but a hot cam and higher compression (I think his 850 is higher compression than stock) can often need a little less advance. The later k's had more advanced.. er, advance (about 5 degrees?) than the K0, probably having something to do with the cam of the K0.

He's set to more advance than the late K's, if I remember correctly. I'd still set it to 25 degrees and go from there to eliminate that from the variables, and once everything is dialed in, advance in 1 degree increments to find the sweet spot.

[nokrome]

Mark/nokrome, I'm not sure if Honda made any recommendations on setting up the ignition timing with a 970 or similar kitted motor but when they offered race kits for their earlier models (CB92/95/72/77 and 350Ks) they recommended 5 degrees more advance over stock timing.
If you don't have a degree wheel, this can usually be achieved from the F and T marks that you set your timing and tappets with as they are normally 5 degrees apart. In this case, set the static timing as if you had another T the other side of the F mark.
I would start with, cam chain tension, tappets, ignition setting then carb sync, you're then ready to move on to plug chopping.
If all that fails, get the bike on a dyno with a good operator.

Sam.

  cam chain tension and valve lash have been gone over and set several times, im positive that it is where it needs to be, carbs have been synced and double checked

  my electronic ignition has pre-programmed curves, i am on the least aggressive curve which has a 33deg. total advance, i am able to retard that up to 5deg more by rotating the pickup mounting plate. if i retard it much more than where it is now it will pop at idle and have noticeable lower power when under load
   honestly, i dont feel like this is an ignition issue, it will rev smoothly and pull hard to red line as long as the throttle doesnt reach a certain position. this is the main reason that i am thinking it is a jetting issue, does this make sense or am i missing something?

Mark, the 850 kit is rated at 10.5:1

[mlinder]

Mark/nokrome, I'm not sure if Honda made any recommendations on setting up the ignition timing with a 970 or similar kitted motor but when they offered race kits for their earlier models (CB92/95/72/77 and 350Ks) they recommended 5 degrees more advance over stock timing.
If you don't have a degree wheel, this can usually be achieved from the F and T marks that you set your timing and tappets with as they are normally 5 degrees apart. In this case, set the static timing as if you had another T the other side of the F mark.
I would start with, cam chain tension, tappets, ignition setting then carb sync, you're then ready to move on to plug chopping.
If all that fails, get the bike on a dyno with a good operator.

Sam.

  cam chain tension and valve lash have been gone over and set several times, im positive that it is where it needs to be, carbs have been synced and double checked

  my electronic ignition has pre-programmed curves, i am on the least aggressive curve which has a 33deg. total advance, i am able to retard that up to 5deg more by rotating the pickup mounting plate. if i retard it much more than where it is now it will pop at idle and have noticeable lower power when under load

Probably because it's too rich...

   honestly, i dont feel like this is an ignition issue, it will rev smoothly and pull hard to red line as long as the throttle doesnt reach a certain position.

more than just jetting makes engines run correctly. Like, say, ignition timing..

this is the main reason that i am thinking it is a jetting issue, does this make sense or am i missing something?

see previous..

Mark, the 850 kit is rated at 10.5:1

Ah, not terribly high, then... Did you go with stock thickness gaskets? Was head decked?

[sebatje]

What type off coils are you using and contact points or electronic ignition? In my shop we have a lot off these problems on 1 cilinders going from 50 to 80cc. High compression makes your fuel more difficult to burn.

[mlinder]

He's got a nice elec ign. Good coils, too, if I remember correctly.

[sebatje]

correct float height?
setting air mixture screw?
can you reach your choke lever when you are riding? maybe you can turn it on for a little bit when riding. In this case you don't have to change jets while trying to find a solution.

[nokrome]

thanks for all the help guys, due to an unrelated issue the motor is coming out and the weather around here is starting to get ugly, i might be done for the season
      to be continued........

[Sam Green Racing]

Funny thing about regret is...... its better to regret something you have done than to regret something you haven't done.

You may regret not putting it on a dyno.

Sam.