Engine not firing up instantly

Deaf250scooter · 03-27-2024, 09:07 PM

Hi guy!

I am an owner of MP-250-A Scooter (250cc). My scooter looks like beat up but have all functioning instruments and lights (everything works). It's just the plastic bottom side guard and windshield broken off cuz it's cheap and brittle. I just replaced starter, starter clutch, battery, and new carburetor and cone air filter. scooter have 4,300 miles on ODO and it's 10 years old. (New carburetor don't have vacuum connection so I capped vacuum tubes except for vacuum operated fuel pump connect from rubber intake nub.. Basically Carburetor is a straight carburetor)

My only issue is that engine don't fire up quickly when it sits overnight. Valves had been adjusted .004 in Intake and .008 Exhaust. It take few tries before it finally run. After 20 min ride, parked at store and shopped 15 min then back to scooter. Tried to fire up and it won't fire up quickly, I had to twist throttle few times to prime fuel then fire it up. It ll run and die. I tweak throttle just little while starting and it fired up and running. Had to throttle a bit to get RPM up till it steady at 2,500 rpm. I just want to fix that I can fire it up quickly and go rather than struggling to start.

I wonder in the past, I rode scooter 65mph on highway to work (30 min away both ways several time) and does it cause issue with valve?

I was wondering if Valves need lapping and will it fix the air leak issue?

Let me know

Purpose · 05-19-2024, 11:36 PM

I'm a novice, and been watching several youtube videos for instruction on scooter maintenance. It is my guess that the exhaust .008 is too much of a gap from the .004 intake. Most videos have a diference of .002 between the intake and exhaust. Maybe try setting the exhaust to .006.

Thumper · Yesterday, 04:24 AM

This sounds like a push rod engine?

If so you should be OK with 0.002" to 0.003" on intake side, and 0.003" to 0.005" on the exhaust side. The extra gap on the hot side is to make sure that heat expansion doesn't close the gap while running. It could lead to escaping exhaust gas (failure to fully close) which can burn the valve seat.

krat · Yesterday, 02:15 PM

Probably none of the above.

Most China scooters have an electric choke and you probably disconnected yours while screwing around with installing the new one. One of those wires and one of those tubes you thought were of no use actually did have a purpose.

My 50cc and 150cc both use the same electric choke. Your 250cc is likely no different especially if it has the diaphragm type carb.

ProDigit · Yesterday, 09:29 PM

Quote:

Originally Posted by krat

Probably none of the above.

Most China scooters have an electric choke and you probably disconnected yours while screwing around with installing the new one. One of those wires and one of those tubes you thought were of no use actually did have a purpose.

My 50cc and 150cc both use the same electric choke. Your 250cc is likely no different especially if it has the diaphragm type carb.

Electric choke?
Never heard of it, and I've had about 7 Chinese scoots and bikes.
All of the ones I have, are choke by cable.

03-27-2024, 09:07 PM	#1
Deaf250scooter Join Date: Mar 2024 Location: Rural Kansas Posts: 1	Engine not firing up instantly Hi guy! I am an owner of MP-250-A Scooter (250cc). My scooter looks like beat up but have all functioning instruments and lights (everything works). It's just the plastic bottom side guard and windshield broken off cuz it's cheap and brittle. I just replaced starter, starter clutch, battery, and new carburetor and cone air filter. scooter have 4,300 miles on ODO and it's 10 years old. (New carburetor don't have vacuum connection so I capped vacuum tubes except for vacuum operated fuel pump connect from rubber intake nub.. Basically Carburetor is a straight carburetor) My only issue is that engine don't fire up quickly when it sits overnight. Valves had been adjusted .004 in Intake and .008 Exhaust. It take few tries before it finally run. After 20 min ride, parked at store and shopped 15 min then back to scooter. Tried to fire up and it won't fire up quickly, I had to twist throttle few times to prime fuel then fire it up. It ll run and die. I tweak throttle just little while starting and it fired up and running. Had to throttle a bit to get RPM up till it steady at 2,500 rpm. I just want to fix that I can fire it up quickly and go rather than struggling to start. I wonder in the past, I rode scooter 65mph on highway to work (30 min away both ways several time) and does it cause issue with valve? I was wondering if Valves need lapping and will it fix the air leak issue? Let me know
	1

05-19-2024, 11:36 PM	#2
Purpose Join Date: Feb 2024 Posts: 10	Valve gap I'm a novice, and been watching several youtube videos for instruction on scooter maintenance. It is my guess that the exhaust .008 is too much of a gap from the .004 intake. Most videos have a diference of .002 between the intake and exhaust. Maybe try setting the exhaust to .006.
	0

Yesterday, 04:24 AM	#3
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,298	This sounds like a push rod engine? If so you should be OK with 0.002" to 0.003" on intake side, and 0.003" to 0.005" on the exhaust side. The extra gap on the hot side is to make sure that heat expansion doesn't close the gap while running. It could lead to escaping exhaust gas (failure to fully close) which can burn the valve seat. __________________ -2022 5 speed Templar X Orange, OEM 51T rear sprocket, 14T front sprocket -NOS 2020 KTM 250SX (2-stroke motocross), less than 10 hours on it
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Yesterday, 02:15 PM	#4
krat Join Date: Nov 2019 Location: KY Posts: 259	Probably none of the above. Most China scooters have an electric choke and you probably disconnected yours while screwing around with installing the new one. One of those wires and one of those tubes you thought were of no use actually did have a purpose. My 50cc and 150cc both use the same electric choke. Your 250cc is likely no different especially if it has the diaphragm type carb. __________________ %90 of the Chinese motorbikes ever made are still on the road. The other %10 made it back home.
	0