I purchased an old SnoScoot (80cc single cylinder 2-stroke – w/reed valve) that had been neglected for many years. I got it running (rough) a few weeks ago, however, now it won’t run. I am convinced it is fuel starvation. I have cleaned the carb so many times that I lost count. Originally, it was pretty gummed up, now it appears clean and all of the jets look clean. The bowl is always full when I pull the carb. The reeds have also been inspected and cleaned.
If I prime it, it will run and then eventually die. If I rev it up after priming it, it will stay running as if at higher RPM is creates more vacuum and finally draws gas in. The choke does not help get it started and seems to have no effect, although I have confirmed that it mechanically functions properly. The choke is not a butterfly style.
A few days ago I was able to prime it and get it running for ½ hour of riding around the yard. It ran surprisingly well at that time and even idled well. It eventually bogged then quit and wouldn’t restart without going through the whole priming thing again. So, I know that it is capable of running properly.
Today, I pulled the pulse line off of the fuel pump, in order to test it. I put my thumb over it and turned the key. I confirmed that the crank pressure is good. While testing it, the machine fired and started to rage (it has never fired so easy). I had to quickly shut it off so it wouldn’t take off and crash into the wall. With the pulse line open, it would start up instantly.
Do these symptoms point directly to a cause? Is it just the increase of air that causes it to run with the pulse line disconected from the fuel pump or does it have more to do with a change in the internal engine pressure/vacuum?
Any help would be appreciated.
If I prime it, it will run and then eventually die. If I rev it up after priming it, it will stay running as if at higher RPM is creates more vacuum and finally draws gas in. The choke does not help get it started and seems to have no effect, although I have confirmed that it mechanically functions properly. The choke is not a butterfly style.
A few days ago I was able to prime it and get it running for ½ hour of riding around the yard. It ran surprisingly well at that time and even idled well. It eventually bogged then quit and wouldn’t restart without going through the whole priming thing again. So, I know that it is capable of running properly.
Today, I pulled the pulse line off of the fuel pump, in order to test it. I put my thumb over it and turned the key. I confirmed that the crank pressure is good. While testing it, the machine fired and started to rage (it has never fired so easy). I had to quickly shut it off so it wouldn’t take off and crash into the wall. With the pulse line open, it would start up instantly.
Do these symptoms point directly to a cause? Is it just the increase of air that causes it to run with the pulse line disconected from the fuel pump or does it have more to do with a change in the internal engine pressure/vacuum?
Any help would be appreciated.
is the spark plug wet or bone dry when you run it?
Dry plug
After it bogs and dies, the plug appears to be dry. It doesn't seem to be getting sufficient fuel to stay running. I can prime it with as much gas as I want and it will always fire right up. I have never had the feeling that it was flooded.
After it bogs and dies, the plug appears to be dry. It doesn't seem to be getting sufficient fuel to stay running. I can prime it with as much gas as I want and it will always fire right up. I have never had the feeling that it was flooded.
does that have a vacum petcock on it? what year and model is it, so I can go look at the microfiche of it??.
Vacuum Petcock?
I don't know if it does or not. I am not near teh machine to look.
1990 Yamaha Snoscoot
SV 80EM
Thanks for your help
I don't know if it does or not. I am not near teh machine to look.
1990 Yamaha Snoscoot
SV 80EM
Thanks for your help
have you looked in the airbox of it to make sure theres no mouse nest in there?
does the fuel flow feely from the petcock?
another thing I would try is to prime the engine, then with the carb fuel line off the carb, start it and see that you have good fuel flow to the carb, sounds like its either a petcock or fuel pump problem to me. The fact that you said it ran good and idled well once there tells me the carb circuits are working. the choke not making any differance is not right , have you removed the plunger from the carb and shot carb cleaner thru the orfice in there and it comes out in bottom of carb right?
does the fuel flow feely from the petcock?
another thing I would try is to prime the engine, then with the carb fuel line off the carb, start it and see that you have good fuel flow to the carb, sounds like its either a petcock or fuel pump problem to me. The fact that you said it ran good and idled well once there tells me the carb circuits are working. the choke not making any differance is not right , have you removed the plunger from the carb and shot carb cleaner thru the orfice in there and it comes out in bottom of carb right?
I cant really tell of the microfiche, too generic of a drwing. I went back and re read your post and something else comes to mind, how is the gastank vented? a clogged or plugged vent would do the same thing.
I can't totally rule out that this carb doesn't have some internal obsruction somewhere. The carb is so small, it is very difficult to see inside and get cleaner in all the little ports. All the jets have been removed and cleaned, including the choke and all appears to be in order. The fuel bowl is quite large and is always full to the rim when I take it apart. I would think that I could rule out the fuel pump. The air box was removed and it is free flowing. However, I'll try to start it with it off, just to rule this out too.
Gas tank is vented like a MX bike. A large vent tube right out of the center of the fill cap. It is clear. The fuel lines are all new and you can see gas, with no bubbles or air what so ever.
Gas tank is vented like a MX bike. A large vent tube right out of the center of the fill cap. It is clear. The fuel lines are all new and you can see gas, with no bubbles or air what so ever.
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you should be able to shoot carb cleaner thru all passages and then blow compressed air thru circuits of carbs, for instance the pilot jet circuit, with the jet out, you can squirt carb cleaner by the little plastic hose on the cans thru the circuit and see it come out the bleed hole in front of the carb throat, same with choke circuit, it will come out in the bottom of carb in the bowl area, if you cant do this the carb isnt clean. the choke circuit should be able to stall the bike out if its working.
So when the bike wont run anymore and you pull the bottom bolt for the fuelbowl out it will be full? Is this only after you try and repeatably crank the engine to start? or is it immediately after stalling? see there could be a problem with the petcock or pump if its after your just cranking it, it will fill the bowl or if the engine runs the bowl dry then stalls, thats why I asked.
I have done this. All the passsages flow thru, even the choke. When the machine is running, after priming and reving to mid RPMs, then the choke will bog the motor, so I immediately, flip it off. However, once it dies, the choke seems to have no effect. Again, if the fuel is not flowing then choke won't help.
I'll fart around again tonight and provide my findings.
Thanks a ton for your input!
I'll fart around again tonight and provide my findings.
Thanks a ton for your input!
ok, well you didnt mention the choke stalling the engine out before, you said it had no effect.
you have a petcock or fuelpump problem. If carb cleaner comes out thru all the passages in carbs, then theres nothing left in there as long as the needle valave works and doesnt hang up in the neddle jet tube, inspect the needle valave carefully for wear marks on its sides and see if the brass tube it sits in has wear. The fuel pump may move gas while cranking but not while running, theres nothing in there but a diaphram and when the engine runs the pulse signal is that much stronger then cranking and could be opening up a tear, or it may have sediment in it, have seen that before, also blow backwards in the fuel line into the tank, have ya ever checked the fuel filter in tank? sometimes they can run and pull all the sediment to the filter blocking off flow then when the machine stalls the sediment falls off and will let a little more gas get thru till the siphon starts again.
I would encourage you to run the machine and let it do its stall out thing then immediately remove the fuel bowl and see if theres gas in it or if its dry., Dont crank the engine once it stalls out, just remove the bowl.
you have a petcock or fuelpump problem. If carb cleaner comes out thru all the passages in carbs, then theres nothing left in there as long as the needle valave works and doesnt hang up in the neddle jet tube, inspect the needle valave carefully for wear marks on its sides and see if the brass tube it sits in has wear. The fuel pump may move gas while cranking but not while running, theres nothing in there but a diaphram and when the engine runs the pulse signal is that much stronger then cranking and could be opening up a tear, or it may have sediment in it, have seen that before, also blow backwards in the fuel line into the tank, have ya ever checked the fuel filter in tank? sometimes they can run and pull all the sediment to the filter blocking off flow then when the machine stalls the sediment falls off and will let a little more gas get thru till the siphon starts again.
I would encourage you to run the machine and let it do its stall out thing then immediately remove the fuel bowl and see if theres gas in it or if its dry., Dont crank the engine once it stalls out, just remove the bowl.
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Sorry for the confusion. It is hard to type everything that you would like to say. The In tank fuel filter is brand new as well as all the lines. Fuel Tank and oil tank have been complete removed and flushed. The machine was torn down to the frame for restoration. AEverything has been visually inspected and or replaced.
I'll open up the fuel pump tonight, however, even after the motor is primed and then stalls out, it will always have a completely full bowl. I thought the same thing as you, so I once opened it up to inspect it immediately after it stalled (no cranking). It was full of fuel.
I'll open up the fuel pump tonight, however, even after the motor is primed and then stalls out, it will always have a completely full bowl. I thought the same thing as you, so I once opened it up to inspect it immediately after it stalled (no cranking). It was full of fuel.
MrViper700,
Any thoughts on why the machine wants to run with the pulse line disconnected?
Any thoughts on why the machine wants to run with the pulse line disconnected?
Hmmmm, I would look at the petcock then, see if it free flows fuel with just gravity on it in a bowl. I have not worked on one of these little machines in about 4 or 5 years, they are pretty rare now, but if it has a vacumm petcock on it that could be the problem.
when you removed the pulse line and it started right up makes me think that the machine was overly rich, the added air made the mixture more in line with good combustion. Thats why I asked about plug being wet or dry.
As for explaining things, believe me its harder to try and solve the problem from a keyboard then actually getting to see and work on the machine....LOL!!
I think I remember there being a bowl vent on those???, maybe check that as well, was on a hose that went to the case or something???, been a long while since I had one in front of me, youll have to be my eyes on this.
when you removed the pulse line and it started right up makes me think that the machine was overly rich, the added air made the mixture more in line with good combustion. Thats why I asked about plug being wet or dry.
As for explaining things, believe me its harder to try and solve the problem from a keyboard then actually getting to see and work on the machine....LOL!!
I think I remember there being a bowl vent on those???, maybe check that as well, was on a hose that went to the case or something???, been a long while since I had one in front of me, youll have to be my eyes on this.
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You are pretty good, these is a carb vent/breather. It is a small brass fitting on the engine side of the carb. Some guys use them as a primer, others have plugged them completely. From Yamaha, they are supplied with a 3-4" black hose that is bent in a U, I assume bent to lesson the chance of junk being sucked into the carb. It doesn't seem to make much difference whether I plug it or leave it open. (See photo)
For give me, when you say petcock, are you referring to the needle/seat?
For give me, when you say petcock, are you referring to the needle/seat?
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when he says petcock he is talking about how you turn the fuel on and off at the rear of the frame under the seat........... the sno-scoots are gravity fed.
Tod
PS - your restor job looks nice - I wondered why it had a silver frame.
Tod
PS - your restor job looks nice - I wondered why it had a silver frame.
Any news fleabags??