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Backfiring
by: jerseyboy - Dec 31, 2014 14:31:45 GMT -5
Post by jerseyboy on Dec 31, 2014 14:31:45 GMT -5
No its all good bro..just make a video of it starting,idling,then rev it up to 7k and let it decel so we can hear how it sounds.
Easy enough.
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Post by alleyoop on Dec 31, 2014 19:04:32 GMT -5
Not a problem Lain, most folks cannot distinguish from POPS or BACKFIRES or BRAT sounds a motor may make.
But it is very important to know which sound it is making and WHEN because that will tell you what the problem is so one can fix it.
Backfiring is not good that can damage your exhaust valve period.
POPS are RICH and or LEAN conditions depends when it POPS. They can occur at low rpms, accelerating and or during decel. If they occur at low rpms and or accelerating to much fuel if on decel to lean.
Brat sounds are LEAN condition and you will get this sound at higher mph.
From all you say I would say it is getting to much fuel right off the bat.
Check the Vacuum hose going to the PETCOCK, pull it off at the INTAKE MANIFOLD and see if it is wet.
Also when you did the bbk did you change any of the JETS the one causing this would be the PILOT JET NOT the main jet.
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Backfiring
by: geh3333 - Dec 31, 2014 23:50:28 GMT -5
via mobile
Post by geh3333 on Dec 31, 2014 23:50:28 GMT -5
Oh,,cool..I bet your issue will be gone after you get the new head on there with two exhaust bolts snugged up right. A good tuned motor will pop some on the decel..totally normal..alot of times you wont even hear it unless you have a free flowing pipe. Will be standing by. Tom He actually already replaced the head and still has the popping . it does sound as if its a rich condition " that is because when it is popping". My scoot use to pop on decel but I have it running just right now. |
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Backfiring
by: jerseyboy - Jan 1, 2015 10:54:37 GMT -5
Post by jerseyboy on Jan 1, 2015 10:54:37 GMT -5
Yeah,,
I really cant say mine is popping on decel but its more like a rumble of seperate BRAT sounds that are different levels..too me it sounds like a darn racing Briggs..lol..its running so good Im afraid to do a BBK on it...there is no reason a stock block and head cant push taller gears if tuned right IMO.Im 180lbs and it pulls me along just fine.
Maybe hes got the chain one tooth off on the timing??
Would it still run with one tooth off??
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Post by lain on Jan 1, 2015 12:29:45 GMT -5
Yeah,, I really cant say mine is popping on decel but its more like a rumble of seperate BRAT sounds that are different levels..too me it sounds like a darn racing Briggs..lol..its running so good Im afraid to do a BBK on it...there is no reason a stock block and head cant push taller gears if tuned right IMO.Im 180lbs and it pulls me along just fine. Maybe hes got the chain one tooth off on the timing?? Would it still run with one tooth off?? No, it isn't a tooth off. I've tried setting the cam a tooth off in either direction before just to see what would happen, it just makes it run really horribly, so I mean I know what to look for if it is off, but it is on point. I ordered a new Keihin carb since they look like a tunable version of my carb. When it comes in I will work with tweaking the mixture screws to see if that helps at all. The backfiring and smoking only happen the first startup of the day now it seems, after that it runs very well all day long. I should have a video soon, sorry yesterday was very busy, it was my B-Day and new years eve, and I was hosting a party so I couldn't be messing with the scoot too much yesterday. |
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Post by lain on Jan 1, 2015 13:30:31 GMT -5
[...] From all you say I would say it is getting to much fuel right off the bat. Check the Vacuum hose going to the PETCOCK, pull it off at the INTAKE MANIFOLD and see if it is wet. Also when you did the bbk did you change any of the JETS the one causing this would be the PILOT JET NOT the main jet. Yes, the vacuum line seems a little wet. No, I did not install a new idle jet, however I did upjet the main jet to #  . Before the BBK my plugs always lasted forever and checked out as running normal, after installing the BBK the plugs keep coming out wet and smells sort of like a permanent marker, but stronger. The things I changed when installing the BBK are as follows; the piston, rings, cylinder, head, variator weights, main jet, and gaskets. Is there anything in the stuff that I changed that could have changed the way the idle gas amount works? |
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Backfiring
by: geh3333 - Jan 1, 2015 14:21:34 GMT -5
Post by geh3333 on Jan 1, 2015 14:21:34 GMT -5
U still have the stock pilot jet , so you should not be running to rich at idle " especially since u have a stock carb that cannot be adjusted and they are usually set lean ". However your plug is wet ? Are u having trouble starting the scoot " that is when u first start it " ? If so the wet plug could be a result of fuel building up because of an ignition issue , thus the exhaust smoke at startup. When I say ignition issue I mean an issue with the air fuel ratio causing the ignition procces to not take place . I suggest waiting for the new carb to come in this way u can actually adjust the fuel supply at idle.
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Backfiring
by: geh3333 - Jan 1, 2015 14:32:52 GMT -5
Post by geh3333 on Jan 1, 2015 14:32:52 GMT -5
Also , when u replaced the head , how were the valves ? If I'm not mistaken u mentioned your exhaust valve was in bad shape , or u thought it may have been. If this is so this means you were prob running way to lean and the wet plug is probably the result of what I posted in my last post. I def suggest waiting for the new carb , you do not want to burn up the new exhaust valve . I hate the fact that they install a carb that cannot be adjusted . you may need to up the pilot on the new carb but u may be able to get away with just adjusting the air fuel .
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Post by lain on Jan 1, 2015 14:51:04 GMT -5
geh3333 Yeah, the exhaust valve was so broken that i could see into the exhaust port when the exhaust valve was close, very tiny holes but holes nonetheless. Could oil blowby also cause this? I have been consuming a lot of oil when running. I have to add oil every couple weeks or so if I run everyday.
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Backfiring
by: geh3333 - Jan 1, 2015 15:12:01 GMT -5
via mobile
Post by geh3333 on Jan 1, 2015 15:12:01 GMT -5
geh3333 Yeah, the exhaust valve was so broken that i could see into the exhaust port when the exhaust valve was close, very tiny holes but holes nonetheless. Could oil blowby also cause this? I have been consuming a lot of oil when running. I have to add oil every couple weeks or so if I run everyday. I think you had or have a couple problems , if I'm right you didn't change the rings yet right ? I believe you are running way to lean and you also have a prob with oil passing the rings . just be sure to hone the cylinder before installing the new rings or you will have the same issue with oil blow by. Its excessive heat that caused that to happen to the exhaust valve , and this is caused by a lean condition . the oil blow by will cause the exhaust to smoke and will of course cause the loss of oil . |
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Backfiring
by: JoeyBee - Jan 1, 2015 15:12:58 GMT -5
via mobile
Post by JoeyBee on Jan 1, 2015 15:12:58 GMT -5
From all you say I would say it is getting to much fuel right off the bat. Check the Vacuum hose going to the PETCOCK, pull it off at the INTAKE MANIFOLD and see if it is wet. . Could you explain some of the symptoms of why moisture would be in the vacuum lines? Is running rich the only reason why it would happen? I'm asking because when changing my carburetor the other day I noticed a little moisture in the line that runs to the fuel petcock. It happened when I was running the stock carburetor and jet so I'm guessing it was running lean. The stock carburetor has the restriction screws on the bowl so I don't know the size of the main jet. |
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Backfiring
by: jerseyboy - Jan 1, 2015 15:27:54 GMT -5
Post by jerseyboy on Jan 1, 2015 15:27:54 GMT -5
Fuel in the vacuum line would be from way too much fuel going into the motor from to big of a main jet or improper set floats thus the line will suck up some of that extra fuel..moisture well maybe from running in wet conditions...only other way fuel will get into the vac line is if something goes wrong with the petcock housing or diaphragm my guess..
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Backfiring
by: tvnacman - Jan 1, 2015 15:41:57 GMT -5
Post by tvnacman on Jan 1, 2015 15:41:57 GMT -5
Fuel in the vacuum line would be from way too much fuel going into the motor from to big of a main jet or improper set floats thus the line will suck up some of that extra fuel..moisture well maybe from running in wet conditions...only other way fuel will get into the vac line is if something goes wrong with the petcock housing or diaphragm my guess.. I have not seen it , but the diaphragm at the fuel pet cock can leak . Putting extra fuel in the vac system . I'm still thinking it might be timing . Swing by a service station and see if one of the guys have a timing light , see if they will shoot it for you . John |
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Backfiring
by: alleyoop - Jan 1, 2015 16:32:53 GMT -5
Post by alleyoop on Jan 1, 2015 16:32:53 GMT -5
If the Vacuum line coming from the PETCOCK and or FUEL PUMP is wet that means the Petcock and or Fuel pump is bad and allowing gas to be sucked out of the VACUUM line as well as the Fuel hose, so in that case TO MUCH FUEL.
And for starting and low rpms the MAIN JET has nothing to do with starting and or feeding fuel at that point so forget about the main jet. It is sucking in extra fuel from someplace and the only other place would be the VACUUM LINE.
So let me repeat IF THE VACUUM LINE is wet from FUEL the VACUUM PETCOCK or FUEL PUMP whichever is on there is BAD. And that would explain why it runs good after warm up as well because since you have a BBK it needs more fuel and the extra fuel it is sucking in from the VACUUM is helping it after warm up due to the PILOT JET been plugged and set LEAN.
my .02
Alleyoop
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Backfiring
by: JoeyBee - Jan 1, 2015 16:41:06 GMT -5
via mobile
Post by JoeyBee on Jan 1, 2015 16:41:06 GMT -5
If the Vacuum line coming from the PETCOCK and or FUEL PUMP is wet that means the Petcock and or Fuel pump is bad and allowing gas to be sucked out of the VACUUM line as well as the Fuel hose, so in that case TO MUCH FUEL. And for starting and low rpms the MAIN JET has nothing to do with starting and or feeding fuel at that point so forget about the main jet. It is sucking in extra fuel from someplace and the only other place would be the VACUUM LINE. So let me repeat IF THE VACUUM LINE is wet from FUEL the VACUUM PETCOCK or FUEL PUMP whichever is on there is BAD. And that would explain why it runs good after warm up as well because since you have a BBK it needs more fuel and the extra fuel it is sucking in from the VACUUM is helping it after warm up due to the PILOT JET been plugged and set LEAN. my .02 Alleyoop It wasn't fuel. The moisture had a neutral smell to it. And when I tested the petcock by sucking on the line the moisture did not have a taste either. Everything is running fine now. I only have 300 km on my chinometer. Just curious of why it happened. |
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..BAD TO THE BONE..
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