Zongshen 155z Running but wont rev properly and backfires

[my67xr]

That plastic insulator between the manifold and head are the mounting hole's and the bore of the spacer central ?
Is there another one between the carby and manifold too?

Also running it without an oiled foam air filter will make it run quite lean, that defiantely won't help the way it run's

 

[grech_nathan]

Yeah it is central and how would that make it run badly tho? And yeah there is another on on the carby, I've had the filter on it and it still runs the same


Sent from my iPhone using Tapatalk

 

[my67xr]

The air filter help's to restrict the airflow and give's you a richer mixture.
Oiling them as well as trapping dust before it goes through your engine restrict the airflow a bit more too making it richer again.
I'm lucky to be able to even start my bike without an air filter, let alone rev it


Have you checked the float level on the carby ?

Thought that spacer between the manifold and head might have been one for the manifold to carby, with them being different it might not be sealing against the head too well and making a vacuum leak.
Did you try the test i mentioned above to see if there's any vacuum leak's

 

[grech_nathan]

The air filter help's to restrict the airflow and give's you a richer mixture.
I'm lucky to be able to even start my bike without an air filter, let alone rev it

Thought that spacer between the manifold and head might have been one for the manifold to carby, with them being different it might not be sealing against the head too well and making a vacuum leak.
Did you try the test i mentioned above to see if there's any vacuum leak's

Yeah I've tried spraying wd40 an it didn't change anything I even put new gaskets on it and it's still the same


Sent from my iPhone using Tapatalk

 

[my67xr]

Try holding your hand over the air filter side of the carby to block it completly and kick it over a couple of time's.
Your hand will get wet from a bit of petrol.
Then try starting it, it will take a couple of kick's to get it to start and run, but if run's any better, then kicking it over with your hand over the carby might have dislodged something from your pilot circuit.

How many turn's out is your mixture screw set at ?

 

[grech_nathan]

Try holding your hand over the air filter side of the carby to block it completly and kick it over a couple of time's.
Your hand will get wet from a bit of petrol.
Then try starting it, it will take a couple of kick's to get it to start and run, but if run's any better, then kicking it over with your hand over the carby might have dislodged something from your pilot circuit.

How many turn's out is your mixture screw set at ?

I used carby cleaner and cleaned out the hole carby and the screw is about two turns out


Sent from my iPhone using Tapatalk

 

[my67xr]

Your engine is a Z155HO / Z160HO isn't it ? a 1P60YMJ ?
If it;s got the oil filter on the side cover then i thought it wouldn't have that pin for the decomp?
The later engine's don't use them

What are you valve/rocker clearance's adjusted to?



Is that a Mikuni copy 22/26mm carby on it?
What jetting are you running in it ?
If it's still got the standard 15 pilot jet in it it wont start that easy, and will have a bog off idle and when you try to accelerate.
I'd change it to a #20 pilot jet and retune it to suit.
Did you retune the mixture screw since you've rebuilt the carby ?

I used carby cleaner and cleaned out the hole carby and the screw is about two turns out

Yeah but there's cleaning the carby, and then there's cleaning the carby.

When you did it, did you remove the mixture screw and spray carby cleaner in through the small port's on the air filter side of the carb, and check that it flowed out through the mixture screw hole ?
Then put the mixture screw back in and spray it again checking that the carby cleaner came out the pilot jet hole?
Did you check all the little hole's through the jet's were open, including the hole's across the pilot jet?
Then there's the emulsion tube, did you take that out and check the hole's across that are all open ?
Also the little hole at the bottom of the thread's where the pilot jet screw's into in the base of the carby, is that open and can you see light though the hole into the main bore of the carby ?


And watch out kicking it over like that too, you'll end up breaking the kick start gear's or even worse and crack the case
Kick it over from just past tdc, that way the kick start gear's will last longer

 

[cookem37]

Did you find the solution as mine is doing this