Carb leaking fuel...

[JT2Fast4u]

Hi. I'm trying to get my Grandson's bike running. It's a 1987 Yamaha BW-80 (Big Wheel model). It had been sitting for awhile before this, so I cleaned out the tank & petcock. Put new gas in it, & also cleaned the air filter & the carb. & all the jets real good, & blew them out with compressed air. But the problem I'm having is when your trying to start it, I get gas leaking out of the overflow hose on the bottom of the carb. It only leaks while your kicking it, it doesn't leak at any other time. I have tried setting the float numorous times now. I tried it set to spec., tried it lower than it should be & also higher then it should be, & I still get the same results. Leaking while kicking it. It gets good spark & the plug seems to be getting wet with gas, but It won't start. It acts like it doesn't even want to start, except after maybe kicking it 20-25 times it will sometimes let out what sounds like a PPSSSSSS type of sound. Like compresssed air or simular type of sound. I haven't been able to tell if that sound is coming from the pipe or the carb because it only happens every so often. But anyway, If anyone could give me some suggestions I would sure appreciate it very much. Thanks in advance... JT2Fast4u

 

[Jon K.]

Does the float bowl have a brass tube extending up into the bowl chamber? If it does; this is the overflow pipe.

I have seen them split down the side. This might cause the sloshing of fuel while kicking to allow the fuel to leak out at a lower level than intended.

Make sure your vent hoses on the carb are open.

Is the exhaust pipe plugged with a bird nest or something? PPSSSSSSS could be a snake in the pipe! Make sure you properly identify it before removal! :eek:

 

[Rhodester]

A possibility may be that the rubber needle tip on the needle and seat assembly is old, hard, and will not seat properly. I'd clean up the seat with carb cleaner and a Q tip, replace the needle, reset the float level (the float isn't somehow logged with gas and sinking is it?) and clean the carb real good with carb cleaner. If your bike is like the PW80 then it's jetted too rich from the factory. I had no top end RPMs at all until I went down 1 size on the main, raised the needle clip 1 position and opened up the air box a little. It was a whole new bike after that. It's still too rich on the main jet, but I haven't found a leaner size to try yet.

 

[Jon K.]

(the float isn't somehow logged with gas and sinking is it?)

There you go!

I'd bet Rhodester has got it!

 

[JT2Fast4u]

Thanks for the idea's &suggestions, Jon K. & Rhodester, I appreciate it very much.

Jon K...... Yes, it does have the brass tube extending up into the carb. & I blew thru the overflow hose while covering the top of the brass pipe with my finger, & no air escaped. So that seems to be fine. Also, both of the vent hoses are clear on it too. I haven't checked the exhaust pipe yet, to see if it's blocked up yet. That will be my next step now. Thank you very much for the suggestions.

Rhodester... There is no "rubber" tip on my needle & seat assembly. It is all metal, no rubber at all on it. Could this be the reason why it's leaking then? I know "most" of the ones I have seen before, do have the rubber tip on them. Are they suppose to have it? If so, then that could very well be my problem then. I know that the tip isn't scratched in any way at all, it "looks" great, also, I tried blowing thru the fuel inlet while moving the float up & down, & it doesn't let air thru when the float is moved up on it thou. I have also cleaned the carb. & all the jets completely Twice, with carb. cleaner so I know everything is clean. I will replace the needle assembly thou. The float isn't "logged" with any fuel or anything, I put them in a bowl of gas & they didn't sink, nor did I see any bubbles either. So I'm assuming they are ok. I haven't tried changing any of the jets yet. The main is a 87.5 & I believe the needle clip is in the top position. So maybe I need to change that to get it started. Do you think I would need too, to get it to start? At this point I'm willing to try anything. Thanks again for your suggestions... JT2Fast4u

 

[Rhodester]

I haven't been into the PW80 carb in a while so it's hard for me to remember what the needle design looked like. I have a factory manual and it reads that the needle and seat should be replaced as a set. It looks from the picture that the needle is indeed solid brass. Does the seat have any rubber down inside of it? Have you taken the float and shaken it to see if it has any moisture in it? If so you'll want to replace it. The standard main jet on the PW80 is a 125. I'm 1 size down from that (whatever that is...).

 

[JT2Fast4u]

Hi Rhodester...Thanks for all your reply's, I really appreciate it. Tonight I took off the exhaust pipe & it's all clear. It's a little dirty with some oily carbon deposits, but nothing out of the ordinary. So that eliminates that, as suggested earlier. The seat doesn't have any rubber down inside of it, I checked that tonight also. The float is good too, no moisture, no leaks, or anything inside of it. Tomorrow I will order the needle & seat set, & also get me a repair manuel as well. I'm sure it will come in handy too. Is their anything else I can check or do, while I wait for my parts? Also, can you tell me what the gap on the spark plug should be set at? Thanks again for all your help, Rhodester, it's very much appreciated. :o) JT2Fast4u

 

[nickyd]

I would - and this is just my opinion - turn the gas off - spray a little carb cleaner down the throat of the carb and give her some kicks and see if she even trys to run.

at least first see if she has life in her - before you kick your leg off worrying about the carb.

Now once you've ruled that out - what everyone has said before is spot on.
Float Floats? Yes
Overflow tube not cracked? the drain screw is tightened right? the one that feeds to the overflow drain line?
Is the needle jet assembly severly worn? it could be to the point that it won't seal off the incoming gas - you might be able to push it up there by hand and get it to close but if its gouged the float may not be "strong" enough to raise it up to full closed (Assuming you have the level set correctly).

A bike with an overflowing carb should run - I saw my buddy's YZ 250 do it last week - we pulled the carb trail side and pulled the float/reassembled and she was fine....sometime they just get hung up....pull the float apart and put her all back together (but it sounds like you've done it a handful of times.

keep us posted - you got me interested now!

 

[yamahonky]

You could always push it to the top of a hill and try to coast start it. It would spin it fast enough it will probably start right up. If the pipe is plugged, when you coast start it it will blow and burn out any animal or other obstruction in the way! :ride:

 

[JT2Fast4u]

Ok, will tonight I tried to start the bike with starting fluid,(didn't have any carb cleaner left, after cleaning the carb 4 - 5 times already) & it still won't start. It's not even really trying to start. I was going to try & push start it, but it's an 3-speed automatic, no clutch lever. So, I'm not sure I can even push start this thing. Can I damage it by tryin to push start it? Has anyone been able to push start an automatic before? I never owned one before, so I don't know. :o/ Also, is it possible to do a compression test on a 2-stroke? I tried putting my finger over the spark plug hole, & kicking it over & it will blow my finger off the hole. But that's not really telling me too much thou. Can I put a gauge on it & kick it over? If so, what kind of pressure should I be getting out of a little 80cc motor? I just bought another carb for it off of **** too. It was cheaper then just the needle & seat set from the dealer. :o) So hopefully I can eliminate the carb. as being the problem, when I get the new one. Because this bike is really starting to piss me off. It SHOULD be at least, starting up. I just don't get it. But thanks for the suggestions & opinions so far. I really appreciate them. Thanks again... JT2Fast4u

 

[CMYVA]

I have a PW50 that was having the same problem with the gas spitting out the overflow while kicking it, it would also bog down when the choke was not on when you let off the throttle. I put a new float needle in it and seemed to fix the problem. Hope this helps.

 

[nickyd]

Ok, will tonight I tried to start the bike with starting fluid,(didn't have any carb cleaner left, after cleaning the carb 4 - 5 times already) & it still won't start. It's not even really trying to start. I was going to try & push start it, but it's an 3-speed automatic, no clutch lever. So, I'm not sure I can even push start this thing. Can I damage it by tryin to push start it? Has anyone been able to push start an automatic before? JT2Fast4u

unfortunately that is the kind of answer I was expecting.....as for the gas overflowing - it can really only be a problem with the choke/float needle(what I think) or the overflow tube...you eliminated all of that. Yes you can check compression on a 2 stroke - same as any bike. I've seen bikes run with low compression (albeit not well)...so let us know what it comes in at (i'd want to see 120's give or take)....those PW 50's and 80's are very easy to pull apart so if you need a top end, it won't be a huge chore. how are the reeds? are you getting spark? you can try to tow start it (b/c its auto..) - you won't do any damage but that may be awkward and the fact that starting fluid didn't do it makes me think you'll be wasting your time.....do you know WHY the bike was put away in the first place? I bought a PW 50 from a guy who said "my son just stopped riding it..."....I knew that was suspect b/c kids don't just stop riding - its too much fun....anyway, did the carb cleaner thing right down the intake (pulled carb off) to see if she had life before I went after the carb....the bike didn't even try to start....pulled top end and had slightly cracked piston and cracked ring (bike was run with too much piston to cylinder clearance and she rattled around until the piston cracked....)...that's common on an older bike....I hate to be captain obvious - but if you've got spark, fuel and some compression, the bike should at least run...

 

[JT2Fast4u]

Nickyd, in responce to your questions...The compression results are below, and I have no idea what shape the reeds are in. I was getting great spark. I haven't tried push starting it yet, because after I did the compression test, I didn't think their would be a need too. :o(

After doing a compression test on the bike, using a standard automotive compression tester. Here's what I got... It took me about 6 or 7 swift kicks to get the compression up to 35 lbs. So, if it's suppose to be somewhere around 120 lbs, then this must be my problem. I don't know if it matters or not, but I did this compression test with the carb. off the bike. Could doing the test this way effect the out come of the comp. test? So, it appears that I will need a top end kit for it, but I wanted to know if there is anyway to find out if the bottom end is damaged in anyway once I have the head & cylinder off the bike? Because the bike just isn't worth having too split the cases on it.

 

[nickyd]

yep - compression is way too low - doubt she will ever start without a new top end even by bump starting. as far the bottom end - check UP and DOWN play at the rod and smoothness of the crank when you rotate it. other than that I'd be curious to know what the piston looks like - specifically if it looks like she was fried (from a lean condition) - that COULD indicate a worn out ignition side crankshaft seal - NOT definately - just a thought...reason I say that is I'd hate to see you buy the top end and put the bike together and run it only to have it eat the piston up quickly. On the other hand, it could simply just be worn out - in which case, measure the bore and get a fresh piston, maybe even bore job in there and enjoy. Hope this helps.

 

[JT2Fast4u]

Well, I pulled the head & cylinder off tonight, & I found both of the piston rings broken. But, the good news is that it didn't scar-up the cylinder wall. At least, nothing that I can feel with my fingers anyway. I don't have a bore gauge, so I'll just take it into the shop & have them check it out & get me the right piston kit for it. I didn't feel any "up & down" play in the rod, & the crank seem to turn very smoothly, no roughness at all. But, I did feel ALOT of play at the piston pin. But I'm hoping a new needle bearing, piston, & pin will take care of that thou.
Also, I want to thank everyone that replied to my thread, & gave me suggestions & ideas. It's really appreciated very much. THANK YOU!!! Hopefully I'll be set now that I got my manual.. :o) Thanks again.... JT2Fast4u

 

[nickyd]

movement at the piston pin is normal - you will have side to side play from that needle bearing. here's a quick check to see if the bore is worn by hand - see if you feel a 'ridge' at the top of the bore - if so it will need to be bored. good luck

 

[yamahonky]

Glad you found the problem. Good luck.