I have a Chinese quad, not sure of the displacement or brand. Plastic says 150cc but cylinder is stamped 200 (rounded, cant remember exact) but I do know its a air cooled vertical push rod engine, 4 speed, unknown if it has reverse.
What it does
Starts quickly hot or cold but only with choke on, will idle with the coke on and will rev with the choke on, soon as you open the choke it idles or revs just a bit and stalls. No black (rich) smoke out the pipe, doesn't lean pop out the carb.
Naturally I assumed the pilot/ idle jet was clogged. Fully disassembled and soaked carb, did find the pilot jet clogged and bowl was dirty. Everything else flowed and was clean. Float level set good etc.
Engine stil runs the same, no change even with a unplugged pilot jet now. No response from idle mixture screw.
Ive checked the engine mechanically and found
The oil is clean, compression is 125 PSI cold, cylinder leakage is less than 5% and the engine makes no ticks or knocks or any abnormal noise.
It really seems like a carb issue, and whatever its problem is its had it since it was new, this quad is old but in "like it was never used" aged condition (if you get what I mean) the tires have no wear all the nubs present, the frame paint has no rust or abrasions, the piston crown is like new clean, exhaust has never really had the paint burned off etc.
I leaning toward a new carb and/ or jets. just wondering if anybody has run across something i'm overlooking.
It seems to have a keihin clone, thinks what's called a PZ. I believe it's 27mm, i have not measured it yet. I wonder if the chinese didn't fully drill a passage out or something. I feel really confident all passages are clear. I really wish i knew what the real carb model this was cloned from so I could attempt to find a flow chart, description of operation and jetting/ adjustments etc.
I'm open to any ideas even if they're not likely.

 

You probably still have dirt in a jet or passageway. I always clean both jets and passageways with compressed air, checking the jets by looking through them afterwards. Some main jet needles are adjusted by putting the circlip into a different groove on the needle. A lift of needle may help if a thorough cleaning doesn't.

 

ya i would say the jets are still plugged.. Sometimes it takes several cleanings before you realize you missed some of the little holes in the jets.. Took me 5 cleanings on one carb before i noticed them

 

Pilot (idle) jet is clogged...using choke bypasses the pilot jet and dumps more fuel into the mixture...


Pilot jets can be hard to find/remove/clean...

 

You can buy a new pilot jet from <jetsareus.com> Before it drives you nutz. That is if a Keihin one will fit.

 

Read his post again, it stalls as soon as it gets off idle unless choked.

 

"Starts quickly hot or cold but only with choke on, will idle with the coke on and will rev with the choke on, soon as you open the choke it idles or revs just a bit and stalls."


I did read the post but it's contradictive...so I assumed the orange part of the description was misstated and meant when the choke is closed...which would lead to a plugged idle jet. Getting it to idle without choke, when warm, is always the #1 priority...how it acts on throttle can be a subsequent diagnosis...

 

Well the short way of saying is it only runs or revs with the choke on period. Warm or cold once the choke is off it will idle for a second and die, like its running out of fuel. If you open the choke and rev/ full throttle it will for about the same second and stall.
I have soaked, poked and blown air all throughout this carb and no change in the way this thing operates.
Id have to assume this carb must have been manufactured incorrectly etc. Wouldn't surprise me.
For the price, Ive ordered two new ones from ebay, one exactly the same and one slightly different, looks like one has a accelerator pump. I may still need to jet it but I just want the darn thing to idle or do something different than what its not.
Ill post the results when the parts come in. I do appreciate everyone's input!

 

Do me a favor...with the carb float cover off...turn on the fuel and tell me if fuel is getting into the bowl...it can be messy but we need to establish the carb is getting fuel to the bowl...the flow should be good...


While there...you can test your float valve operation by manually pushing up on the float...push up & fuel flow should stop, release and fuel should flow again...


I'm going to say you'll have fuel...because if your quad is running with the choke (really an enricher - unless it's a butterfly actually closing the intake) then there would need to be fuel in the bowl as the enricher draws from the bowl...


Please do this in well vented area...

 

I will check the flow of fuel, I have not done that yet, however there has always been fuel in the carb when Ive taken it off. But that doesn't mean its not filling up in the time it takes me to disconnect and remove it.
It is a butterfly choke that's spring loaded, so with choke on and you rev engine it will open dependent on how much the engine is sucking etc.
Ill check tonight when I get home.