yamaha jog 50 with 70cc kit won't start...ideas?

it runs \o/

60 jet ftw. may try a little smaller and just see how it goes.

only issue I have atm is that when the motor stops a bunch of fuel runs out of the carb, though I imagine that is because the carb is 'downhill' of the engine and that's prob fuel left in the manifold. I'll figure it out tho.

thx everyone for the advice & help ")

 

hello mate I just recently put a 70cc big bore kit on ny Yamaha jog and i had trouble getting it to start but after many failed attempts it started but then after about 5mins it cut out and wouldn't start again so in the end I got a professional to look at it and he said that the air cooling system on my bike wasn't sufficient enough to keep the engine cool and was advised to revert back to 50cc which i have now done.

 

thanks for the info, tho it turns out I don't think it has a 70cc kit after all... it also ran and now it doesn't again for no apparent reason. ugh.

Might try the carb from the other bike and see if it works with that..if so, perhaps it needs a new carb.

 

mine was working fine then cut out and wouldn't start. i was advised it was the stator so I bought a new one and it still won't start (I've got no voltage coming from either of the wires on the stator) its got a new cdi reg/rect and new ht coil. i just dont understand what's wrong with it.
The stator is definitely the first thing to look at isn't it? with regards to no spark

 

As far as I know mine's getting spark (it was before, haven't tested last couple of tries but it runs fine on easy start), but if you're not getting a spark then I guess stator is a good place to start. Do you know for sure you're not getting a spark? Take the plug out and rest it on the cylinder (so it's earthed) and turn it over and you should be able to see whether you've got a spark or not for sure.

Have you got the service manual with the wiring diagram? That should show where to test that you're getting a signal otherwise.

 

hi yes I am definitely not getting a spark I'm going to take the stator back to the shop tomorrow morning to get it tested and hopefully replaced but we'll see. I'll post the outcome when I know whats what. no i havnt got a wiring diagram will look for one. cheers for the advice pal

 

drop me your email in a pm and I'll send you the service manual. forums won't let me upload it here.

 

ok so today I tried putting the carb from the neos on and it ran fine, so it's definitely something to do with the carb. Tbh I'm thinking that whilst whatever's wrong is probably not that difficult to fix and I'll figure it out at some point, right now I don't know what it is and I want to move this project forward so thinking probably get a new dellorto 17.5mm carb..then my jets should fit and i should also be set if i want to go for a 70cc kit or other upgrades later on too (on either bike). A 17.5 should run ok on a 50cc if jetted appropriately, right? Anyone know if I'll need to fiddle with pilot jets too or just mains?

the other carb did a wierd thing where while it was running fuel kept dribbling out of the drain bit, which it doesn't do on the other bike, so am not sure what that's about but it didn't seem to affect running, tho obviously would be something which needs looking at if that carb were to stay on that bike.

 

yeah my carb leaks fuel from there too, you should check the rubber washer that is attached to the screw inside the drainage hole

 

if fuel dribbles from the drain tube when running its because the screw nut is not sealing fully.

i was down the breakers when a chap truned up with the exact same problem a dribbley carb from drain port, he handed me the screw and asked what i thought, you could tell right away the tip had corroded and was not fully sealing the drain port so when the carb got put under pressure from teh pump flowing fuel it was forcing it past teh drain screw and out.

its a very much common thing from old carbs that have been left to gunk up and been left with a ting spurge of fuel, the fuel attracts water vapour and that in turn starts to oxidize the tip of teh drain screw

also anther area is the small black rubber O-ring used, they tend to get compressed outta shape of knipped and then start to cause a leak

 

hmm ok - I wonder why it doesn't do it on the other bike then? That's the "working" carb so wasn't really wanting to fiddle with it but dribbling fuel is also not really kosher. I'll check the drainage screw/o-rings etc.

thanks

 

could be a higher pressure from the pump , more crank pressure more pump force and its just over riding the auto shutoff valve on float, its a pain when that happens and you have to then go in to finger the problem and rectify it

 

which pump do you mean? is that do with the petcock or part of the carb?

That sounds like a closer fit to what's going on really. There looks to be an overflow chamber in both carbs and it did seem like the one on the "working" carb was getting overflowed and hence it was dribbling out. I did check the drain screw was in tight at the time but didn't really think about the o-ring so was going to wait till I'd checked before replying on that.

Tbh that sounds like perhaps why the "not working" carb is not working. Lack of fuel pressure would totally fit with the symptoms (not getting any/enough fuel). This could be progress

 

petcock ie the vacuum petcock , its working from pos and neg pressure the crank case creates.
if you remove the vacuum line and kinda puff at it like a ciggy you will notice it acts like a pump and fuel them pumps from the outlet side. in the crank this pos/neg pressure wave is like really fast so acts like a compressor pump, if you have a compressor without an air res and you hold open the air feed you can feel the pos neg pressure wave, its the same effect that power the vacuum fuel pump.

if your running a direct gravity feed, ie the tank is higher than the carb and there is no vacuum pump, its possible there are two areas to look into, one is the fuel cap it should have a one way valve in the lid, as fuel drains it needs to be replaced with air so the one way valve allows air into the tank but if bike tips over it shuts off and wont let fuel flow out, to test this we tend to just run bike without the fuel cap on, if it runs and no hicups its 9-10 times a blocked cap vent. another area is the petcock. these days the petcock has a filter fitted to the end of it that sits directly in the tank this can get shitted up and cause no end of fueling problems more so in older bikes with old tanks that have just had a lotta crap brushed into them over time.

the last area is a sticky float valve, the float rides on a valve plunger as it rises and closes fuel flows past and over time can become glazed by fuel depostits , they can also start to stick on there own over time, you can remove the float pin and slip the whole float assembly out of the carb usually the plunger will come out with the float dangling on the small metal tab that holds it. a bit or carb cleaner and a little soak and some careful wipe with a lint free cloth can dislodge that crap and allow it to slip n slide more free.

usually its one of the three above that causes overflow/ carb leak problems, its very rare you loose a couple screws and teh float bowl falls off , unless your a honda cub owner lol hahaha or a wanky float boawl rubber seal thats been nipped and allowing fuel to piss out everyhwere lol

 

thanks again, that's super helpful

the fuel cap thing is so simple but may be a contender here. will deffo test that today.

as far as I know the float/needle etc assy on the 'not working' carb are all spotless. they've been thoroughly ultrasonic-cleaned twice. the float needle moves easily looked clean and doesn't look to have any gunk on it tho whether there's anything else wrong with it I can't really tell.

I might put the petcock assy in the ultrasonic cleaner too just for good measure, tho if you toke on the vac pipe fuel comes out of the other one (that's how I prime/fill the carb bowl) so it seems to be esentially working...tho I guess I'm still confused as to why one carb gets nothing and the other overflows.

what I haven't tried yet is checking the vacuum seal the other way around.. I.e. if there's something breaking the vacuum seal on the not working carb then perhaps it's not making enough vac to suck fuel properly where perhaps the other one is.

thanks again, I'll get to the bottom of this eventually!

 

- ok so tested without fuel cap - no difference to "non working" carb, "working" carb still runs & drips

- petcock/filter..I guess that must be working since "working" carb runs ok on it

- vac seal - I tested disconnecting the petcock end of the vacuum tube and sucked through it and did notice a slight difference in the seal vs the seal on the "working" carb (which also has a bigger vac-hose nipple so makes sense it would seal tighter). I tried clamping the vac-hose down which improved the seal but made no diff to the running (or lack of).

- I put the "working" carb back on and once again it started and ran fine, but still dribbles like a mofo. I checked the o-ring from the drainage screw and it all seemed in good shape, plus it doesn't do it on the other bike so I guess it must be something to do with the vacuum/pump pressure as you suggested.

Currently the "working" carb is on and the bike starts/runs but it dribbles (quite a lot). If I seal up the drainage hole with my finger it then leaks out of a different drainage hole with a little hose which goes in a "n" over the top of the carb which the "non working" carb doesn't seem to have.

Given that to the best of my recollection it doesn't dribble on the other bike I'm loathed to take the "working" carb apart and mess with it, since so far there's nothing to suggest I'll help matters by doing so and will probably make it worse.

So I think back to plan A - namely next time I get paid I'll pick up a nice new 17.5mm dellorto carb and then hopefully I'm starting from a less wobbly/unknown starting point. That way I can either tinker with the "working" carb to stop it dribbling and know i've still got the new 17.5 for the neos, or put the 17.5 on this bike and leave the neos well alone since it works as it is (well...apart from being in bits obvs ).

Thanks for the help everyone, have learnt a lot

edit: Just realised I forgot to specifically check the tip of the drainage screw for corrosion on the dribbley carb. will come back to that.

 

Thanks for that Minor confusion - that's given me a bunch more stuff to check. I ran out of carb cleaner but some more arrived so will give it all another once-over. I've got a spare piston and rings just in case.

tho re something bigger (like fked rings etc) surely then it wouldn't run fine and dandy on the other carb (like it does)..hmm

I'll update once I've been through all the stuff above