Just got a SunL150cc atv. Very hard to start, removed carb and cleaned everything out. Replaced fuel line. This Atv has a vacuum/diaphram fuel switch which is in line from the fuel tank. I tested this and it works like this; vacuum from engine opens to let fuel through to the carb. Can I bypass this? Can I connect engine vacuum and carb vacuum together? Seems to run better when vacuum is pinched off. Only adjustment to carb is mixture screw, which works best at 2.5 turns out. Why is this diaphram switch in place? Machine is very clean and seems well taken care of. Prior owner always claimed it was hard to start. Need some guidance here as this carb has little adjustment, ie no needle clip or choke switch. Kids want to ride. Thanks in advance.

 

is yours like this?
125cc 150cc GY6 Carburetor Connections

 

Yes this is the one. Had it all apart to clean and was very careful when reassembling, as not to pinch choke bladder.

 

Made some adjustments today and here is what happened. Connected vacuum from engine to carb with a barbed fitting. Ran fuel line direct to carb. Bypassed diaphragm unit totally. Very difficult to start cold. Had to feather throttle and crank it a lot. Once started idled well and ran well. Any way to aid cold starts? Does electric choke need to be checked or replaced? Not really sure that replacement would aid starting. ANy thing better carb wise?

 

The idea behind the vacuum operated fuel shutoff is a good one. When the quad is not running the fuel is shut off. Without this automatic shutoff it is very common for the needle valve in the carburetor to sometimes stick open and the gravity fed fuel system empties the entire fuel tank onto the garage floor through the carburetor overflow hose when you're not around. My garage (and many others) have a natural gas fired water heater and furnace that can ignite those fumes.

That said, those vacuum operated shutoff valves are really failure prone, and generally a real pain in the butt. I have a manual fuel shutoff valve which I bought on eBay for about $5.00, and I use it religiously. The point is, though, you really should have a fuel shutoff valve of some sort and get used to using it if you store the quad inside a building.

On the cold starting issue: Have you checked your valve clearance? These need to be adjusted periodically. Valves tighten with wear, and they tighten more when the engine is cold. So the first symptom of valves needing adjustment is hard starting when cold, eventually leading to no starting at all.

Somewhere I've seen a link on how to test the bystarter valve (what you call an electric choke). I'll try to dig that link up and post it by tomorrow evening. Maybe others have it at their ready and can post it sooner.

 

To test the bystarter valve (electric choke):

Troubleshooting

From the link select the Electric Choke test which will bring up a pdf document with pictures.

 

Thank you Lynn, I will try it today and get back to you.

 

Well everything tested out OK. I cleaned carb out again and blew air through the choke holes that were part of the electric choke module. That did it! Purrs like a kitten easy start up now runs great. Thanks for all the help. Now her brother's is next. THANK YOU