Z155HO Major Running Issue

[morgsim]

Hi guys, I've acquired a DHZ 160cc which is the same as a PitsterPro(?) I believe.

Its got what I think is the Z155HO motor (possibly Z160HO I guess but its a few years old so I assume its the 155).

It starts easily, it revs up in neutral or in gear with the clutch in...all seems fine except it sounds a little like the timing is off or something (backfires out carb a bit). But the real issue is as soon as you let the clutch out and try to move it just stalls, its literally impossible to make this bike move itself no matter how much revs you give it...almost like you're trying to take off in top gear.

I've tried almost everything I can think of, basically all electrics have been tested/changed (new CDI, plug, coil pack, wiring)...multi meter readings off the stator seem OK. I've stripped and checked/cleaned the carb, set the timing correctly and done the valve clearances.

Any help would be appreciated beyond belief, especially if someone can diagnose this for me. If you need further info to help I will supply no problem.

I'm usually OK with pit bike repairs but this one has me stumped.

 

[my67xr]

The engine would be the same as what's used in the Pitsterpro.

Does the engine look like this Z155 ?

Or does it look like the Z155HO / Z160HO ?

To check the timing,
take the cam cover off the left side of the head, and then remove the stator cover.
Turn the engine over to tdc on the compression stroke and check the timing mark's are lined up.
The making on the flywheel will line up with the marking at 12 o'clock in the case, and the cam gear marking will line up at 9 o'clock in the head
That is how it should be for the timing to be right.


Or possibly the valve/rocker clearance's are a bit tight ?
Have you checked the valve/rocker clearance's ?
While the cover's are off the cam and stator, take the rocker cover's off the head.
The rocker's should have a little play there, in and out.
If they are tight then that wont help the way it's running

I would check the clearance's anyway while you are there,
Do it at tdc on the compression stroke, inlet .003" and exhaust .004"
Once done turn the engine over 2 full revolution's to check it's ok
Recheck the clearance's and then you should be good to reassemble it.



What carby do you have on it ?
And do you have an oiled, foam filter on it?
With it stalling on take off, it could also be the pilot circuit, or the pilot jet might be partly blocked?

 

[morgsim]

Thanks for the reply.

As per my post timing and clearances have been done (twice actually) and I am pretty sure they are right.

I'd probably put my money on it not being a carb problem either, the pilot jet works ok when idling and revving it up at a standstill and the "stalling" feels like worse than just fuel starvation.

I'll check the motor tonight for what type it is, ideally I need to get a video to show exactly whats wrong...everyone who looks at it tends to agree its like its not sparking at the right time yet timing is supposedly correct.

I had a feeling it was going to be hard to translate this fault description into text.

The owner before me actually took it to a bike shop and after a few hours they diagnosed it as a faulty CDI, I replaced that to no avail. It really seems like its some kind of issue with the spark timing, is it possible the stator is outputting incorrectly on the trigger wire to the CDI under load?

 

[headsmess]

usually being gutless as soon as it gets some load IS a sign of being lean.

try raising the needle all the way, ie, e clip on the bottom notch, that should at least richen it up in the mids/transition.

how old/used is it? the carb could be full of shellac from old fuel, or just be gunked up...lots of annoying little orifices to block up. just one blocked hole and its got lousy transition from low speed to main jet. give it a good overnight soak in carb cleaner, the most violent of violent solvents then blow, and make sure you get EVERY hole...

type of choke? flap over the hole or a separate plunger type? if its the flap type, see what happens when its on. plunger type usually just rev up... sorta hard to tell whats going on when they do that. try blocking the carb off a bit.

electrical is not an issue as it as load doesnt affect it in any way...just speed.

whats the plug look like? try a different one anyway.

shove a 1mm drill through the jet

and see what happens, just out of curiosity of course, what happens if you take the main jet off...

and just maybe perhaps the exhaust valve is leaking.

 

[my67xr]

Lol headmess, hope you dont mean a 1mm drill bit through the pilot jet ?
A Mikuni copy 22/26 pilot jet has a .30mm bore, and a .9mm main
Good to see you back anyway!!
Did you ever finish that custom quad you were building?


When you cleaned out the carby, did you take the mixture screw out when you blew it out?
Double check the pilot jet is open through the middle and the small hole's across the jet.
Also look into the base of the carby where the pilot jet screw's into, at the bottom of the thread's there will be a small hole that goes through to the carby bore, make sure it's open
Poke a strand of copper wire (from some car wiring) through the jet's, if you notice any dry flake's come out then there's dried up gum in them restricting the flow

What were the reading's you got off the stator ?
Compare them to the reading's listed here- http://www.miniriders.com/electrica...urce-coil-pulse-coil-regulator-rectifier.html

I have seen the main loom for the 8 pin cdi have a wire poke out the back of the black 8 pin socket that plug's into the cdi
Make sure there isn't any loose one's

 

[headsmess]

ha ha, nah, through the main. if its still gutless with that opened up wider than stock, something else is an issue.

pilot sounds fine if its starting and idling, my suspicion lies in the main jet, and/or the size of the needle jet (why i say try it with no main jet at all...if it runs, even revs a bit...the needle jet is waaaaaay off, which wont surprise me, being a copy with lax QC... raising the needle all the way up will help a bit, but still wont let the main jet do its job properly.)

yeah, the quad was finished... then i pulled the 140 out and stuck it back in a two wheeler. been sitting in a shed for a while now. life gets in the way of having fun only just got around to putting some decent rubber on the pitty! now that really makes a difference through the turns!