Freshman Rider
Currently Offline
Posts: 72 
Likes: 3
Joined: Oct 23, 2017 9:12:34 GMT -5
|
Post by jaciche on Jul 2, 2018 8:29:25 GMT -5
My scooter has 950 miles on it now. I set the valve clearances to .005" at 500 miles. Starting around 850 miles, I noticed that my scooter backfires while decelerating. It doesn't backfire every time i slow down, but more often than not. I also noticed that if i roll off the throttle very slowly or only am riding at a slower speed and less throttle, it wont backfire when I slow down. The backfire always happens AFTER i have completely released the throttle and it's back at the idle position, but the RPM's are still dropping. Last night, I turned the idle air mixture screw out 1/8th of a turn to richen it up a bit. That didnt seem to help, maybe a little bit by having fewer backfires while riding.
Also FWIW: When my scooter is cold and i just start riding it, I hear some ticking noises as the engine runs across the entire RPM band. I'm guessing this noise is coming from the metal parts around the valves. Once they bike warms up, the noise goes away. Maybe my valve clearances are now more that .005" 
Do you have any ideas on what I should look into next to get rid of this issue?
|
|
|
|
Post by pistonguy on Jul 2, 2018 12:01:38 GMT -5
She is just a tad lean on the low end when you chop the throttle. you can adjust the Air screw or may need to upjet 1 on the Pilot Jet.
A Classic Case of Throttle Chop..
You don't have to Chop the throttle feather it off and most of it will not be there .
.005 on the Valves, I have never set mine that loose. not sure were you got the information on that but its incorrect.
I run a tight .003 on the Intake and .004 on the Exhaust.
There seems to be allot of bunk information on the 150 Valve lash but always remember the spec given has Idiot insurance built in it
|
|
Freshman Rider
Currently Offline
Posts: 72
Likes: 3
Joined: Oct 23, 2017 9:12:34 GMT -5
|
Post by jaciche on Jul 2, 2018 12:20:20 GMT -5
She is just a tad lean on the low end when you chop the throttle. you can adjust the Air screw or may need to upjet 1 on the Pilot Jet. A Classic Case of Throttle Chop.. You don't have to Chop the throttle feather it off and most of it will not be there . .005 on the Valves, I have never set mine that loose. not sure were you got the information on that but its incorrect. I run a tight .003 on the Intake and .004 on the Exhaust. There seems to be allot of bunk information on the 150 Valve lash but always remember the spec given has Idiot insurance built in it
Ok, is there anything wrong with setting both valves at .004"? What's the advantage of having the intake valve clearance set to .003"?
I forgot to mention that i put a bigger main jet in the carb when I took it off for a cleaning. A 105 was in there, I replaced it with a 112 since it ran like it wasn't getting enough gas while cruising from half to full throttle. I am considering putting a 110 in there at the end of this riding season. The main jet change probably is a contributing factor to the backfiring that I'm experiencing.
|
|
|
|
Post by chewbaca on Jul 2, 2018 15:51:46 GMT -5
a smaller valve clearance allows the valve to open earlier, farther and close later
it will also help with longevity of the head by not letting the valve seat slam shut.
The cam will slow down the valve just before it makes contact with the seat
but can't do so if it hits to early.
.0027 maybe is the exact number on one particular scooter and .0029 is it for another scooter. but it's really difficult to be that accurate with a fealer gage
and sometimes a scooter is all the way out at .0035 or something
so the books say .004
because that's going to work for almost all scooters even if its not the best
it all depends on how much your personal cylinder and valve head expand with heat.
oh I almost forgot. popping can be caused by an exhaust leak.
At idle the idle enrichment kicks in and higher rpm=vacuum will pull fuel+oxygen leak= popping.
|
|
|
|
Post by pistonguy on Jul 2, 2018 18:45:06 GMT -5
a smaller valve clearance allows the valve to open earlier, farther and close later it will also help with longevity of the head by not letting the valve seat slam shut. The cam will slow down the valve just before it makes contact with the seat but can't do so if it hits to early. .0027 maybe is the exact number on one particular scooter and .0029 is it for another scooter. but it's really difficult to be that accurate with a fealer gage and sometimes a scooter is all the way out at .0035 or something so the books say .004 because that's going to work for almost all scooters even if its not the best it all depends on how much your personal cylinder and valve head expand with heat. oh I almost forgot. popping can be caused by an exhaust leak. At idle the idle enrichment kicks in and higher rpm=vacuum will pull fuel+oxygen leak= popping.  Chewy's on it again and Spot On!! |
|
Freshman Rider
Currently Offline
Posts: 72
Likes: 3
Joined: Oct 23, 2017 9:12:34 GMT -5
|
Post by jaciche on Jul 3, 2018 8:06:44 GMT -5
a smaller valve clearance allows the valve to open earlier, farther and close later it will also help with longevity of the head by not letting the valve seat slam shut. The cam will slow down the valve just before it makes contact with the seat but can't do so if it hits to early. .0027 maybe is the exact number on one particular scooter and .0029 is it for another scooter. but it's really difficult to be that accurate with a fealer gage and sometimes a scooter is all the way out at .0035 or something so the books say .004 because that's going to work for almost all scooters even if its not the best it all depends on how much your personal cylinder and valve head expand with heat. oh I almost forgot. popping can be caused by an exhaust leak. At idle the idle enrichment kicks in and higher rpm=vacuum will pull fuel+oxygen leak= popping. I'll adjust my valve clearances during the next oil change which will happen after 210 more miles. After hearing your responses, it does make a lot of sense about there being a harsh change between when gas is supplied from the main jet versus when it goes back to being supplied from the pilot jet. I'll try to keep backing out the idle mixture screw 1/8th at a time, but I think a bigger pilot jet size will be needed. When i ride slowly with a little throttle and roll off the throttle, it never backfires. I will check the exhaust for leaks too. |
|
|
|
Post by hillbillybob on Jul 4, 2018 6:55:28 GMT -5
There is an air cutoff valve (ACV), on the right side of your carburetor. It is operated by vacuum, through the line that crosses over the top, front side of your carb. It's purpose is to prevent backfiring during deceleration. You said you had the carb off....check to see that this vac line is sound and secure.
As far as the valve lash goes, I say leave them as they are. You will not hurt your engine running a .004" gap. I check mine annually, but the last adjustment needed was on June 15, 2013 at 2,502 miles. Today, the scoot has 14,256 breakdown free miles on it. I run .004" intake....and .005" exhaust. I've been doing this a while, bought my first bike in 1965....so I'm official a freakin geezer....and I still say "ticking valves, are happy valves".
|
|
Freshman Rider
Currently Offline
Posts: 72
Likes: 3
Joined: Oct 23, 2017 9:12:34 GMT -5
|
Post by jaciche on Jul 20, 2018 14:07:11 GMT -5
I think I found the problem. I started my scooter for the first time in 2 weeks and listened to it idle. It sounded like something along the exhaust was loose and leaking. I found that one of the exhaust stud nuts is completely off the scooter. Are there any local hardware stores in the US that have these or do I need to order some online?
Edit: It looks like i'm going to have to order one. Could I throw a 6mm lock nut washer on there to serve as a band aid until I get some new exhaust nuts delivered?
|
|
|
|
Post by chewbaca on Jul 20, 2018 21:10:40 GMT -5
you can get a coupling nut from most hardware stores
that will do an excellent job
|
|
|
|
Post by pistonguy on Jul 21, 2018 6:29:01 GMT -5
I think I found the problem. I started my scooter for the first time in 2 weeks and listened to it idle. It sounded like something along the exhaust was loose and leaking. I found that one of the exhaust stud nuts is completely off the scooter. Are there any local hardware stores in the US that have these or do I need to order some online? Edit: It looks like i'm going to have to order one. Could I throw a 6mm lock nut washer on there to serve as a band aid until I get some new exhaust nuts delivered? Double Nut It. |
|
Freshman Rider
Currently Offline
Posts: 72
Likes: 3
Joined: Oct 23, 2017 9:12:34 GMT -5
|
Post by jaciche on Jul 23, 2018 8:26:16 GMT -5
Alright, I already went to the hardware store and put 2 locknuts on there with a lock washer. Double nutting should hold it. Having the exhaust header pipe loose on the engine side was the issue. I've ridden it for 30 miles since i tightened up the nuts on the exhaust studs and I have not had a single backfire. Thanks for your help. I wish I had checked the stock nuts to make sure they were tight in the first place! |
|
|
|
Post by cyborg55 on Jul 30, 2018 23:09:07 GMT -5
That was a great call chewy,,, keep up the good work
|
|
