Still having problems with backfiring on decel By DevilDog (Read 2,133 times)

[DevilDog]

Brand new crate engine 150cc gy6 using the original carb. that came with the scooter (Roketa Sicily). It has plenty of power but backfires loudly on deceleration. I have put a new exhaust manifold gasket on and it still backfires. I also have check all the vacuum lines and installed new NAPA in-line fuel filter. Not sure what is going on here! The old engine never had this problem. Sounds like a vacuum leak to me but who knows?!!

[rob63]

May sound a bit silly for a brand new engine, but have you checked the cam timing and valve gaps ?

[Alleyoop]

Check the Vacuum hose going to the CARBS ACV valve which is on the THROTTLE CABLE side.
It may not be connected.
Alleyoop

Here is a picture of the ACV valve which for Backfires on Deceleration(when the throttle is being closed). What it does is cut off AIR so more fuel is fed when you let off the throttle.

[DevilDog]

All hoses are connected and I have not checked timing or valves yet just want to rule out simple things first. How can I tell if my acv is working?

[Alleyoop]

You really can't test it the only thing is to take the cover off and check the Diaphgram to see if it has tiny holes or is ripped.

Did you check your Exhaust where it connects to the Motor that is a very common place that causes backfires. It could be loose or one of the nuts vibrated loose or came off.
Alleyoop

[Alleyoop]

One other thing if the IDLE is set to low that will also cause backfires. IT should be idleing at least 1500-1800 rpms.
Alleyoop

[DevilDog]

Exhaust gasket is new, all snug and tight. I cant really tell what my idle is at because I don't have a tach. Been kind of adjusting it by ear. Just got done replacing all the vac lines and no change at all. Maybe it is time to buy some carb cleaner and spray around looking for a leak. I would like to get this fixed before my engine mount comes in ( The stock one got bent when my engine blew!). Has anyone had any problems with their enrichener leaking? Mine is new and maybe not seated in quite right.

[Alleyoop]

To find a leak Use a Spray Bottle with WATER. Then go around spraying individual places if your idle changes you found a LEAK.

But on the IDLE bit, turn the idle up using the IDLE SPEED screw until the REAR TIRE starts to spin then back it off until it just wants to spin.

Take a picture of the Carb area and the Enricher and I will tell you if its seated right.
Alleyoop

[sprocket]

I agree with alley...air getting into the exhaust or the AVC valve..the enricher needs to seat right or it won't function properly.

[DevilDog]

Checked for vac leaks with spray bottle and found nothing. I guess I will have to pull the carb and check the acv valve.

[Alleyoop]

How about some pictures BRO. More eyes are better than 1
Alleyoop

[DevilDog]

Carb

[DevilDog]

Carb

[DevilDog]

Carb

[DevilDog]

Carb