Pilot jet size and Hard starting

[larryhobman]

Hi All

I am working hard starting, long cranking times.  I have been changing pilot jets until I found one where it is good between 1.5 and 3 turns out, current setting 2.5 on a WARM motor.   The problem is when cold it is still hard to start and when it does the rpm is high like almost 4000.   When the motor is warm it fire up very quickly with no problems.   Should I make changes to the needle clip height or just deal with the cranking.

I am thinking of going with a PWK 28mm or 30mm for better throttle response.  Let me know your thoughts.

The set up is qmb139 with a 50mm piston and matching head with standard valves and an A9 cam.  The carb is a 24mm off of a 150cc with a 102 main jet and now at 40 pilot.  Standard cdi, coil and the free timing mod is done.  Performance exhaust very open and an pod air filter.  Valves are set to .003 and .004

[GrumpyUnk]

If you have a 'byvalve' or electric choke mechanism on your carb, it may be too big for the size engine, resulting in a rich mixture for the first startup and few minutes running. The pilot size seems a bit large.
When you have a 4,000 rpm cold idle, you have a signal you have 'too much' choke. The byvalve is a a separate system to feed a cold engine. It has a pintle valve, a dip tube, and a well(reservoir) built into the float bowl(most). There is also a jet built into the wall of the float bowl that allows fuel into the well. Once started the fuel flow is limited after it has used up the fuel that filled the well during normal times, by the jet. Take a look. If it is too large for your engine (100cc vs 150cc..) you'll get too much fuel. You could also be into the 'mid-range' of the carb, which is hard to get to idle with stability. If the low speed system is marginal, you will have to open the throttle more, and get the flow into the mid-range, more or less.
tom

[larryhobman]

Hi Tom,

The carb is a standard 24mm 150cc with the automatic choke. I have a modified auto-choke which basically just plugged off the choke circuit. I will swap out the electric one for it tomorrow and see. If I get a PWK carb they come with a manual choke which want be good with weather changes.

[larryhobman]

May 9, 2020 20:20:09 GMT -5 GrumpyUnk said:

If you have a 'byvalve' or electric choke mechanism on your carb, it may be too big for the size engine, resulting in a rich mixture for the first startup and few minutes running. The pilot size seems a bit large.
When you have a 4,000 rpm cold idle, you have a signal you have 'too much' choke. The byvalve is a a separate system to feed a cold engine. It has a pintle valve, a dip tube, and a well(reservoir) built into the float bowl(most). There is also a jet built into the wall of the float bowl that allows fuel into the well. Once started the fuel flow is limited after it has used up the fuel that filled the well during normal times, by the jet. Take a look. If it is too large for your engine (100cc vs 150cc..) you'll get too much fuel. You could also be into the 'mid-range' of the carb, which is hard to get to idle with stability. If the low speed system is marginal, you will have to open the throttle more, and get the flow into the mid-range, more or less.
tom

Hi Tom,

I have it starting real fast now.  I had to block off the auto choke.  I have the A/F out 2.5 turns.  An actual manual choke might be better but I do not ride when it is cold out.  Attached a picture of what I made.  It is a automatic choke with the top removed and drilled and pinned the plunger down to shut the circuit.

[ThaiGyro]

IMO...whoever put those cheap pod filters on made your situation either happen or made it worse. Put the air-box back on, and tune it...simple and more power, more economy.

If I were your mechanic, I would go back to OEM stock. Very likely more HP, similar torque.

Are you trying to build a powerful engine? What is your goal? Is this a 150cc? 125 with BBK?

Classic examples of what good looks like: Tune the CVT on a OEM stock scooter, until maxed for that power input.

Tweak the intake track until the exhaust is maxed. Then maybe a bit of exhaust tweaking and carb tuning. (Or EFI)

Not happy? Go BBK and start over...CVT, intake/fuel/ignition/exhaust.

You can do things differently...I have a Pom-Shitz-su dog that chases his tail and gets it sometimes. Sorry bro, but that is what we face everyday.

[rehabkymco]

This thread has helped me with my own scoot issues. Thank you.