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

aha I thought that might be the pilot jet, tho I have no idea if 34 is the right size.

yep still getting a nice strong blue spark and plug was wet too so here seems to be fuel. I did wonder if i'd flooded it with the bigger jets so figured I'd let it dry out and try afresh tomorrow.

 

remove plug pop a clean rag where sprakplug lives and crank over motor a couple few times that will help expell any build up of fuel if any , leave the rag in place so fuel can evap away if need

shouldnt really need to jet up the pilot a bit of air/ful mixture screw can usually overcome an upjet on the pilot

 

good idea - I'll try that tomorrow

 

Had a bit of a result today with the Jog - I got some EZ Start and gave that a whirl - fired right up and sounded nice and smooth too which was a bonus (before it tried launching into the shed bc I had the throttle wide open - doh!)

so I guess it looks to be a fuelling issue, and hopefully means I don't have to tear down the engine. I've not tested the auto choke yet so that could be it..or I guess it might be the carb. More as I have it.

 

Just unplug the choke and remove it then put 12v across both terminals and it should extend out after a couple of mins.
http://www.pedparts.co.uk/blog/automatic-choke-unit-50cc-mopeds

 

thanks, yep someone posted how to test it earlier in teh thread, I just hadn't got around to actually doing it yet with my other projects...ditto the easy start.

cheers

 

Ah yes didn't see that. It's just that a lot of people don't realise it only works with the engine running.

 

no worries, thanks for trying to help At this point it's down to lack of user action than lack of helpful input .

Just knowing that it runs though and I don't have to rebuild the engine has encouraged me to pursue it though so testing the auto choke will be up next.

 

tested the auto-choke today and it looks like it's doing something - only seems to move about 5mm but it's a start...

 

yeah it dont move much but that 5mm is the choke closed off , its working like a boss buddy .

i would look at the chokes port give it a blow through, check the float valve is opening and closing , leave the float bowl drain screw loose pop the fuel hose back onto carb and just gravity feed the carb with some fuel if it goes in the top and out the bottom the floats opening the valve and allowing fuel to flow in.

hook it up to scoot then give it a few blasts, then chop plug out see if its getting wet . if its bone dry theres a leak somewhere between carb and manifold inlet on motor, the leak means your not getting enough vacuum draw to suck fuel from carb into motor

 

Sounds like you're very close, choke works, fires up when using easy start spray, good blue spark. I suggest cleaning the jet holes through again, put in the size jet that was recommended on earlier threads, spray some easy start and fire her up again. When it starts then gently hold the throttle at a fast tick over for a good five minutes to allow the choke to warm up. Adjust the idle screw so it ticks over on its own. Now adjust the air mix screw slowly. There are some good posts on tuning carbs. Once happy then turn off and fire up again only without easy start spray.
Let us know how it goes.

 

yeah I think another thorough cleaning of the carb will be in order. Haven't figured out which is the air screw and which is the mix screw yet but will suss it out once I've finished the stretch frame... gonna have to relocate the carb on it now anyway since it'll foul the stretch frame slightly as it stands..

On that note there shouldn't be a real issue with extending the inlet tract a bit should there? It It'll be about a 4-5" extension but means I can locate the carb in a similar position to where it is originally..just a bit more "flush". On cars longer inlet runners tend top mean more torque but I dunno whether the same applies to 2-strokes.

 

It might freeze up? This is the reason som LC engines have a water hose going to the carb to act as a heater.
If it's nearer the engine it will get heat from the engine.
Only way to find out is try it lol

 

hmm ok well I guess we'll find out. I guess I could try rubber pipe rather than ali/steel if that becomes an issue as it would insulate better.

 

so I got an ultrasonic cleaner and after an hour or so in that the carb came out looking virtually like new \o/

before:


after:


I got the bike started on easy start as before, but kept the revs up and it stayed running. Now the bike starts without easy start, albeit grudgingly, but only seems to like running at high rpm, and produces quite a lot of blue smoke. Gonna play with the jetting etc but the quantity of blue smoke makes me wonder whether piston rings are shot...thoughts?

Also having had the neos in bits I don't think this one has a 70cc kit after all - the cylinder on the neos looks identical (also iron/rusty)..which is actually good since it means I might be able to ride the jog in the mean time once I get it registered and running nice (and add some working brakes etc). Progress

update: seems bigger jets made it worse and 64 is the smallest I have currently...ordered a new set of 50-74 jets so will see how I get on with them.

further update: also ordered a cylinder kit (piston, rings etc) just in case. Chances are she could do with a fresh set.

 

You should read this article!
Its how big mainjet you should have. 12mm is about 60 for mainjet.

https://www.tuningmatters.com/how-tos/how-to-quickly-determine-the-carburetor-main-jet-size/

 

Great article - thanks for the link 60 sounds about right based on my experiences today

 

I'd use it for fire material

 

Why? Its a good base to start with instead of guessing the size.
Its always a mathematical explanation for what mainjet you should have.
Dellorto has the multiplicatior 5. Other carbs maybe has different.

 

tbh I didn't really understand what he meant...

the formula seems about right based on my findings. I'm on a 64 currently and think I need a tad smaller...12x5=60..sounds about right. I'll let you know once I've tested it.