Backfire after I let off the Throttle By zombieninja (Read 11,595 times)

[zombieninja]

So not every time but a lot of times while I'm riding I'll let off the throttle and my scooter will backfire. Most of the time it isn't very loud but every once in a while it will scare me. Not like a car or anything, just sounds like I ran over something. I recently replaced my ignition coil with a better one and also upgraded my cdi. I don't know if maybe that was the cause. Also it seems like my scooter is idling fast. Not after it cools down only when I first start it. And I know it is supposed to do that but it just seems like now it does it more. The wheel seems to spin quicker and the scooter pulls a little if off the center stand (only when warming up). Other than that my scooter has 9200 miles and runs perfect. Well sometimes it can be tricky getting it started. If anybody can help that would be great. Thanks

[Deleted]

usually lean conditions or an exhaust leak cause backfires. unless your idle is set high then the high idle can be caused by lean too.

**edit** i see you said that only when cold does it idle high. thats normal and doing it longer could also be that if its colder out the enricher takes longer to close and that is causing it.

[jvino]

Yeah the idle mixture screw might need tweeked probly a little start there and let us know. Wow 9200 miles that is impressive. Is that on a stock engine?

[zombieninja]

Yeah its stock. I just bought a new carb for it. Haven't put it on yet tho. Today is oil change day!!! Its so nice out 70° I bought my son a helmet (he's nine now so I figure he can ride on the back this summer) he loves it. He asked me if he could try to kick start it today. I let him try. He gave up after the third try. Hey thanks for your help by the way. If it wasn't for you guys I would be clueless at times.

[Bashan]

Your avatar will haunt me. Everything the guys said is correct. There's also a valve on the right side of your carb called the air cut valve. It's sole purpose is to stop backfiring when you shut down the throttle. So make sure the vac connection is tight, on both ends.

[zombieninja]

Thank you. I'm planning to put my new carb on this week sometime. I'll let you guys know if it works. I can't adjust the valve screw on the one that's on there now. Its pretty bad. I hope this works. If not, try, try, again.

[Alleyoop]

I see it is a 50cc scoot, those do not have an ACV valve so if it is backfiring when you let off the throttle it is one of two things.
1. You have a bad air leak
2. It is running really lean

But since you ordered a new aftermarket carb which has the Fuel Ratio Mixture not capped you will be able to adjust it. The ones that come capped are set really Lean so hopefully all you will need to do is Adjust the carbs Fuel Ratio Mixture and get rid of the LEAN CONDITION.
Here is how to adjust the NEW CARB:
Alleyoop


scooterdoc.proboards.com/thread/1499/4ts-carb-tuning

[zombieninja]

The help I get on this forum never seizes to amaze me. I'm glad I found this one and not an inaccurate board full of tweakers. If anybody has any more useful information for me I'll be glad to have it. Thank you all. How about a video on how to install my new carb? That might help.

Oh yeah. I was thing about buying all new fuel and vacuum lines. Where can I get good ones and how much do I need? I was thinking about blocking out the ERG/Pair. Also other than the line what else would I need. Vacuum caps? T splitters? If I'm gonna do it I wanna do it right. Might as well replace the lines and all the components along the lines. I will look at my manuals of course but if there are parts I may need or other forgotten about pieces please let me know. The "ERG" thing is just a maybe. I would prolly need a push one way or the other.

[jvino]

Don't quote me but the lines I think you can get from like an auto zone. But the great stinky might no a better place and more direction on your question. Good luck though I am impressed on how many miles are on that how many times have you had to change the belt in it?

[Alleyoop]

Here is a Video on how to take a carb off replacement is just the opposite.
One thing on this Video he takes the ENRICHER off the carb but to replace a carb you just need to UNPLUG it because the new carb comes with one already installed and all you do is plug it in.

But it will show how to do it, it really is not hard: Just remember where the Vacuum lines go and the fuel hose.
Alleyoop

[zombieninja]

Apr 2, 2014 8:34:43 GMT -6 jvino said:

Don't quote me but the lines I think you can get from like an auto zone. But the great stinky might no a better place and more direction on your question. Good luck though I am impressed on how many miles are on that how many times have you had to change the belt in it?

Three. 3. Once when I bought it, the one it came with was garbage. The second time was when I was installing a new variator @ about 5,000 miles. The third and more recent time was about a month ago. There were some times in between when I used the crappy one it came with but that one finnaly broke. I pretty sure it had a lot to do with the variator I had to replace.

Thank you for the video. Very helpful. Its been raining so I haven't been able to switch it out yet. Scooter is still doing the same stuff. No better, NO worse. That's a good think if you ask me.

[Alleyoop]

Forgot to mention check the exhaust pipe where bolts up to the motor, if it leaks there it will backfire when letting off the throttle as well. Vibration sometimes loosen the nuts and sometimes they actually come right off.
Alleyoop

[jvino]

Alleyoop is defentally right the back fire could be the gasket on the pipe. Might need a new donut on there. thanks for the video also alleyoop.

[zombieninja]

Well I finally got around to changing the carb today. It was really nice out today so I didn't have any excuse not to. I watched the video Alleyoop provided. It helped a great deal. It gave me the confidence I needed to dive in. I pulled off the fuel/vacuum lines and muscled the thing out. It all went back together pretty easily. I found attaching the lines and throttle cable was easier to do before trying to stuff it back into place. Might be different for others but that's what worked for me. I got it all put back together and kick started it back to life. I tried to use the electric start first but I didn't want to wear it out. I figured the bowl would need some time to fill up and it did. I had some problems at first. I couldn't get the idle right and it wasn't as responsive on take off. I almost came back in and asked for some help. I opened it back up gave it a look and realized I hadn't pushed the exhaust side all the way into the manifold. Messed around with the idle screw some and realized the cable didn't have enough slack. Adjusted the two bolts and BINGO!!! Scooter runs better than ever. No more backfire. Responds well and I believe its gotten a little quicker. I didn't mess with the fuel/air screw any. Is there any reason I should? The manual I have says that's how I should set my rpm's. I'm pretty sure the carb came pre adjusted tho. It was basically just plug and play. Came with a new fuel filter also. I only paid 26$ for it on amazon. If anybody made it through this long post and has any more advice I'd appreciate all I can get. Thanks for all the help.

[Alleyoop]

Glad your up and running good job
Alleyoop