high revving start up and weak bottom end

A

arjay

~SPONSOR~
Nov 19, 2002
222
0
Hi - I've had a couple of runs off road on the air-cooled hybrid project bike. Some things are going well (suspension and chassis) but I'm having a few teething problems with the engine.

It's a freshly rebuilt 87 KDX200 engine with an FMF Gold Series pipe. The jetting has been done and it runs pretty clean.

The problems are

- on starting it bursts into the mid range, revving pretty hard - with or without choke. I have to control the rev surge with the kill switch until it settles down to idle (takes around 40 seconds).

- the power the engine makes is all mid range. The bottom end power is weak then it kicks in really hard in the mid range. It signs off without an over-rev (On technical climbs it's bogging at low rpm which is not the way I remember these air-cooled KDX's to be.)

I would appreciate pointers before I start tearing into it. I'm planning the check the power valve operation, air leaks in the manifold, and the tail pipe length.

Thanks for any input.
 
J

julien_d

Member
Oct 28, 2008
1,788
1
Power valves and air leaks sound like the primary things to look for. I think you're on the right track.
 
M

mudpack

Member
Nov 13, 2008
637
0
No idea what a power valve is on a KDX200, but the air leak thing is what I'd home in on first.
 
S

sr5bidder

Member
Oct 27, 2008
1,463
0
being its a hybrid what pipe did you put on it?
double check your stator plate and make sure the timing marks are lined up correct.

after you settle your rpm's is your idle constant or does it kinda wonder?

also when you rev it does it come back down to idle nicely or hang for a while?

rebuilt how? new mains and seals and piston and rings? or just the top end?
 
A

arjay

~SPONSOR~
Nov 19, 2002
222
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Thanks for the suggestions. Will be getting on with it early next week. The pipe is FMF gold series replacement for the 87 motor, shortened by an inch at the tail pipe end to accommodate an 89 E series FMF tail pipe.
The manifold is 89, different to the original because it angles to one side to clear the shock. Many variables! The Engine was rebuilt top and bottom end. The revs settle to a steady idle, and return quickly after blipping the throttle.

If it wasn't for the crazy revving start up I would just assume that the low bottom end power and abrupt midrange was just to do with the 'sum of the parts'. But hopefully the two are connected, and there is more bottom end power to be unlocked.

Sr5 - I tried attaching a pic to show you, but you can't duplicate images from previous threads. Will get some new pics up soon.
 
S

sr5bidder

Member
Oct 27, 2008
1,463
0
or a link to the original thread??

ok so does it act different after you warm it up if you were to say pull the choke up.....does that change anything at all
 
K

King_KDX

Member
Dec 16, 2009
21
0
sr5bidder said:
you must always use the correct words for mud or he will piont it out
Click to expand...
i think julien, when referring to the Power Valve, is talking about cleaning the K.I.P.S or better known as the "All Illustrious" Kawasaki Integrated Power-Valve System or K.I.P.S for short it looks like this K.I.P.S<-click and the specific parts he was mentioning were these K.I.P.S Sub Valves<-click but i may be wrong
 
J

julien_d

Member
Oct 28, 2008
1,788
1
KIPS is a power valve system. Just because kawasaki named it KIPS, they are still POWER VALVES. I guess I'm not understanding the confusion... Power Valves have been a part of 2 stroke engine tech for quite some time.

Just in case:

A power valve equipped 2 stroke engine has 2 different compression ratios. One when the valves are closed, and another when the valves are open. This technology was introduced to improve the low end performance on a 2 stroke engine. Before the advent of the power valve, all 2 strokes needed to be kept "on the pipe" to run worth a flip.
 
K

King_KDX

Member
Dec 16, 2009
21
0
So? You were talking about the KIPS?
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Arjay, I will second the air leak, but with a clause. Was the cylinder "ported"? I have an extra CR480 engine waiting for an aluminum frame? Vintage Bob
 
P

Porkchop

~SPONSOR~
Apr 27, 2001
341
0
Hi Arjay, It sounds like an air leak, possibly an internal one. Is the fit up of slide & carb in good condition? An out of spec ignition or a stuck or malfunctioning power valve can do this, or a gummed up & stuck choke plunger? Good Luck, Porkchop... :yikes:
 
A

arjay

~SPONSOR~
Nov 19, 2002
222
0
Just got back after a few days away. Will tinker tomorrow night and see if the PV (eek, KIPS) is working. And I'll play round with air screw to see if this makes a difference.

The carb is a 35mm PWK Air Striker (from a quad I think) but jetted to KDX spec. Did a plug chop jetting to set it up. It's practically new, so no signs of wear.

There are a few minor cracks in manifold, but it looks like cosmetic perishing rather than right the way through.

The crank cases were put together without a paper gasket, just sealant. This was because the pattern Athena gasket was too far out of shape to fit. This again could be a suspect area.

The cylinder as far as I know is stock, but I did get it re-chromed.

Thanks.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
I would lay money on the crank cavity leaking. No gaskets available? Cometic, moose or drop a line to Fredette. Hit the suspect areas with brake cleaner while its running. The crank may not show, but it should rule out everything else. Real surprised the no gasket did not cause issues with the tranny clearances. Vintage Bob
 
P

Porkchop

~SPONSOR~
Apr 27, 2001
341
0
How thick is the oem or the athena center case gasket? A vacuum or pressure test may locate the hermetic leak. I would suspect the crank case, at the center case screws or the front engine mount boss. The absent center gasket will shift the sealing zone on the crank that the ignition side crank seal rides on by the thickness value of the oem gasket.( very slight amount) this may have created a less than perfect sealing situation for the crank seal to work on properly. Does the problem persist if you change the needle position to full rich? If so, does the result in performance remain consistent ? Some air leaks are not consistent & change with temp & rpm.
Good luck, Porkchop....
 
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