yamaha spy big bore

i have put a big bore on my Yamaha spy and it run 4 about 10 mins then cut out then start again go for other 2 mins then cut out again then if i put new plug in it starts again then it just stoped will not start now so checked the reeds they had a hole in so put some more in and now just starts for a few secs and then cut out anyone help me

 

Sounds like one (or more than one) of the following problems:

- Faulty, fouled or incorrect spark plug

- Extreamly out of tune carb

- Bigbore kit fitted incorrectly

 

the carb is the one that was with the bike could it be cus i need a bigger one ????????????

 

I presume you have upjetted the carb??

 

no

 

then you are running too lean, as in too much air and not enough fuel....... it's possible it runs for a while because the choke is riching up the mixture and when the choke cuts out the mixture is wrong..................


On the Polini kit I fitted it said the main jet needed to be raised 5-10% and advised a reference number for a different spark-plug.

 

i will try that thanks alot

 

Some Yamaha scooters run a puney 12mm carb, when fitting a 70kit its essential that the carb is replaced with atleast a 17.5mm carb.

If your bike already has a 17.5mm carb then it needs upjetting and maybe a needle adjustment.

Transmission roller weights need changing to a lighter set too.

 

i think it is a 12 mm carb so i will get a 17.5 mm carb when got then money and i didthe rollers not long ago

 

putting on a bigger carb isn't the end of it, the jetting will still need fine tuning... there is no way round setting up, you either do it yourself or pay somebody else to do it.


anyway, carb size might not be your immediate issue, you didn't upjet, you need to upjet what you have by 5-10% and see if it cures your running issue, as it sounds like fuel starvation or ignition to me.


when it doesn't start, spin her over for a while, take the spark plug out and note if there is petrol on the electrodes/wet because if there isn't it suggests fuel starvation. If the plug is wet, it suggests it could be an ignition component breaking down, as in spark plug, coil etc

first port of call for me would be a jetting kit/examination of float bowl for dirt, checking float is working properly.

 

thanks but what gets me is it run for ten to 15 mins with the reeds with the hole in then put new reeds in and will not run

 

what jets do i need ??????

 

you say it won't start, again I will ask, when you take out the plug, is it wet with unburnt fuel?.......... because it should be, if you are cranking an engine and there is no ignition, the fuel should be visible on the plug.



also, if it isn't starting at all, take the plug out, earth it, crank the engine to see if you are getting a spark.


these are basic tests that until answered, nobody can go nowhere with this post.

MAIN JET; you unscrew the float chamber, underneath will be the main jet, unscrew it and take it out, on it will be stamped a number,if it says 62, you buy a jetting kit which starts around 62 and goes up in increments, such as 64,66,68,70,72,75,78,80............ if it says 74, you get one around 74 going up.

I have a data book but it doesn't cover your model, so I can't say what the default jet size is.
also the jets come in different thread types, and types, so you need the right size and type for that particular carb........... as well as the number range.

 

i will check it tomorrow and get bk to you thank you

 

i got a 93 main jet took it out and it run again and how will not start and yes there was unburnt fuel on the plug

 

got running again but when i rev it revs up then cuts out

 

with the jet out it starts but after a bit it cuts out if i take the plug out and put a lighter to it and put the plug bk in it starts again is this cus needs a bigger yet cus its over fuleing ??????

 

are you running an air box or open filter, have you correctly gapped the spark-plug and have you tried a different plug???

 

open filter and yes

 

what I would do is the second it cuts out, put the cap on another earthed spark plug to check there is still a spark, because if not it will be a ignition component breaking down.


Also I would ditch the open filter and convert it back to an airbox, open filters are difficult to set up on small engines.