Author Topic: Over Boring needs Rejetting????  (Read 1432 times)

huason2009

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Over Boring needs Rejetting????
« on: August 03, 2009, 05:38:25 PM »
I made same change in my Pilot (1989)

Initial Settings:

- OEM Std Piston
- New 1990 Carburator (Main Jet # 138)
- 1990 Reed Cage
- Boyesen Power Reeds

Actual Settings:

- Wiseco 82 mm Piston
- New 1990 Carburator (Main Jet # 138)
- 1990 Reed Cage
- Boyesen Power Reeds


Need rejetting? (# 135 or # 140) ??


Can Help me..??

Tnx

Adnoh

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Over Boring needs Rejetting????
« Reply #1 on: August 04, 2009, 10:58:05 AM »
It most every case yes. Your went from a 80 mm to 82 mm bore you have increased your displacment from 397 to 417 cc's. Any time a rebuild has been done jetting should be done. What happens is as the engine starts to go away it starts to fourstroke which requires it to be jetted down for loss of compression. With a new rebuild compresssion haas been restored or increased. If you only went one size.25 or .50 I would say a main jet is the only thing to worry abnout. However you went from 80 to 82mm. This changes a lot of stuff. First the increase in displacment. Second, increases in static compression, Third you CR ( compression ratio). If the bike idols fine than consatrate on the mid then the main. You will need to do a compression check to compare to what you had to make sure your CR is not to high, A high static compressionlevl would be an indacator. I have found were a milled head at 160 to 165  with the 80mm bore has risen to 180,185  with the 82mm bore. This needed a reduction in the CR by changing the head cc and exhaust port duration. both of these will reduce to CR using the V-2 corrected method. What this is the area based on when the exhaust port is closed in degrees. If your head has not been modified you most likly ok but it will effect mid and topend. What you have done is effected the torgue range of the motor requireing a diffent fuel to air ratio. An increase in displacmnet is the easiest way to increase torgue. An increse in static compression has a simalur effect. The CR increse will have a negitive effect using pump gas cause pregnition and engine damage if to high. This is the reson for the head cc and exhaust port change. An unmilled head with greater squish clearence will add an additional thermal load to the piston crown haveing an ill effect on the crown temature effecting the air fuel ratio which will lead to wash the cylinder with fuel and negating and increase in preformance you gained by increas in displacment and static compression. The increase in cc of the head will also reduce the CR to an accepatle levle and effect the power stroke of the engine. However this must have a squish band recut to be effective or it gets really bad.

So check your static compression levle. Check the idol than rejet mid and top.

Most cases the neddle will need to be raised ( lowering the clip)riching the mid then final the main.

Read up on jetting and plug chops. If it pings( sound like some one hitting with a small hammer or a piece of metal is bouncing around on the engine) with the higher CR some work may be in order or race fuel raisng the octane level may be inorder to combat the pregnition.

Your elevation to which you run the egine also palys a part in this.

Take you time and get it jetted right since you have no room to play with the 82mm bore.

I am curious why you went from 80 to 82.

huason2009

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Over Boring needs Rejetting????
« Reply #2 on: August 06, 2009, 02:29:40 PM »
Tnx adnoh for your information.

I have 02 Pilot, one STD and faster than the other one (initially) , I went from 80 to 82 thinking get more HPs, and run Both Pilots in similar conditions.

The Compresion raise to 156 PSI in the 82mm bore and 148 PSI in the STD Bore.

Both Pilot runs similar now (fast).

The Plug look like Coffe With Milk in Both Pilots (As the Picture).

Both Neddle are Std (2nd Position)

And I?m Running at Sea Level  (0,000)

I think that both Pilot?s Setting are OK.

What do you Think??

Gonzalo

Adnoh

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Over Boring needs Rejetting????
« Reply #3 on: August 06, 2009, 06:03:33 PM »
Is that plug from the 82mm bore. It also look like the old plug. Not sure but you may have some spotting and tip erosion caused from over heating. Install new plug and go ride around a while than do a plug chop. If not sure ask and read some post on the subject. What brand and # on plug in pic. The new 158 psi 82mm bore should require a bigger main and a neddle change if you went  from 80 to 82 mm and from a  148 to 156 range in psi. When you get done with the plug chop take a pic and post than I will have you cut it and read it. I posted some info a while back on this. I do not know how many do it but it a lot easier for me and more accurate.

Using the old plug will miss read and may cause you to be lean.

Glad to here it halls. 156 if head is untouched should be ok for pump gas as long as it a quality gas.

Adnoh

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Over Boring needs Rejetting????
« Reply #4 on: August 06, 2009, 06:09:06 PM »
I edited your pic. Be sure to gap plug. This is why I would like to see new plug for chop.