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Discussion in 'Your 250cc Projects' started by Yetiburger, Oct 7, 2017.
ok so the two middle carb fuel levels were low. so I raised them up. how critical are the fuel levels?
I'm within sort of 0.5 - 1 mm of the correct fuel level. I will try and get this better once I get a better marker.
now however the bike won't start even with the choke on. I wound it over for a bit with a couple flips of the choke and twist of the throttle and it kind of wanted to fire. then I stopped and with the key on I got a random backfire out the exhaust.
Have put the battery on charge for the night and will have another go tomorrow.
I'd say the fuel level accuracy is down to how accurately you can read 9.2mm at the bottom of the meniscus marked on the tube 0.5mm is pretty accurate, if you do get fussy, make the adjustments and accurate measurements with the float height
Worth turning the fuel tap off overnight whilst the battery is charging, just in case
As for the choke, you should pull it on and leave it on till it starts
Ok so went into the shed to do some more work and realized I had been setting these levels with the bike on a rear stand . so I leveled the bike on its wheels and reset the fuel levels. now the bike wont start at all.
I'm assuming that the fuel levels were a little high as a result of the bike being on the stand at the back, now adjusted lower and in spec
I think @my67xr is the guru of the mixture screws, I note you have yours at 2 turns out - IIRC - it's 2.5 turns recommended
EDIT - wondering if there's a switch, kill switch that's not 100% as you seem to have difficulty getting it started from one day to the next when no changes have been made to anything, other than that, turned the fuel tap back on after adjusting the fuel height?
Wouldn't the fuel level's have been too low once you put the back wheel onto the ground again ?
Mixture screw's on the 3LN1 carby's are set at 2 turn's out standard when new, they still need to be adjusted to suit your bike though
I can't remember if you used Keyster carby rebuild kit's in them or not ?
When i was tuning my 3LN3 carb's i had to set the mixture screw's a lot leaner than the factory setting
When you try starting the bike from cold with full choke, do the exhaust pipe's up near the head start to feel warm after cranking it over ?
yeah there's no fuel tap at the moment. I think there may be some electrical gremlins somewhere due to two batteries being destroyed and what happened to the mechanic.
the carbs are 3ln1 and were rebuilt with keyster kits and litetek seals.
the bike now sounds like it kind of wants to fire but not with full choke.
I'd be interested to know what the voltage is (voltage drop) when you're cranking it over - I assume yours has the silly mod (to satisfy registration requirements) of removing the headlight switch so that they are on whenever the key is on.
You could try unplugging the headlights - also do you have a jumper battery available?
So many have been through the blown regulator/rectifier I've lost track, lazy me not reading back through the thread - have you had to replace yours?
Try the mixture screw's at 1.75 turn's out, and if it's a little better try them at 1.5 turn's out
I haven't had to replace the reg/rec yet.
I disconnected the head lights.
I took the carbs off and saw what appeared to be gas everywhere.
Removed the plugs and they looked wet.
I blew everything out with air and noticed the the throttle was a bit jammed so i fixed that. and set the mixture screws to 1 and a half turns out.
this is how it runs now. It still has to have full choke on. the throttle will kill it but if you can blip it a bit to get the revs ups touch it will take throttle.
Not sure why its hunting like that. any ideas where to head next? turn the mixture screws in a touch more?
I'd check the oil level if you've had fuel leak through the carbs into the cylinders - need the fuel tap in line, working and switch it off when the bike is sitting
Fuel pump installed? They will run without one no problems, just wondering if there's no fuel pump then pressure straight from the tank might be causing flooding when it's left for long enough
If the oil smells of heavily petrol it needs to go
Probably hunting as it's on the lean end at 1.5 turns out - try 2.25 turns out
ok but it was running worse at 2 turns out.
I disconnect the fuel when I'm not working on the bike as it isn't running through the tap.
it is running through the pump.
ok got the bike warmed well up to temp. turned the choke off and kept revving it until I got the idle adjusted up. will now idle without choke and takes throttle a lot better.
screws are 2.75 turns out.
still isn't super smooth when feeding the throttle. needs to be quite gradual to start with.
but its running a lot better than it was.
also another battery down.
also I tested the terminals while it was running and got 12.5v and when revved it didn't manage to get to 13v maybe got 12.9v.
what is the normal voltage output i would of thought it would be around 14.5v?
Most likely a dying regulator, but do the following:
Check and clean/sand the battery terminals, main fuse & holder, starter & earth leads, starter solenoid connections, and reg/rec plug. Particularly important is the earth for the R/R as it's body earth.
You should check the stator as well, resistance across each phase should be equal, and each phase should have infinite resistance (open circuit) to earth, and even AC voltage output at 5,000rpm
Reg/rectifier looks to have been one electrical gremlin causing you to burn through batteries
@Linkin has given you the perfect suggestions - reg/plug is a definite important one - should be 14.3v~15.3v @ 5K RPM
Stator coil resistance 0.36Ω ± 20% - at that low resistance check for consistency between the coils as meter lead resistance will be a factor unless you have an analogue meter which can be zeroed
That seemed to rev quite well FWIW - carb balance and tune idle mixture - we did mention that the carbs are finnicky
yeah that's definitely the best its ever run while I've had it.
I don't have a carb balancer. is it worth getting one? will i have to balance them often?
also I know nothing about motorcycle charging systems. So the stator is the electric motor looking coil behind the cover on the front of the motor. where is the rec/reg?
What do I need to check on the plug? resistance through the plug?
stator has three white wires - you test from the plug end which goes to the rectifier/regulator which is near the battery, on the frame underneath the seat - it has a 4 wire plug, 3 of which will be white - When you unplug it, you'll see the condition of the connector itself, some will show clear evidence of burning or arcing, any corrosion build up can be cleaned with vinegar then rinsed with water
On that plug to the rectifier/regulator - Test the resistance between those three white wires 1<->2, 1<->3 and 2<->3 all 3 should be consistent
With the engine running you can test for AC voltage into the back of the rectifier/regulator plug - I have actually done this with a 120V globe plugged into that plug to check that it had both voltage and current, but I had the stator unplugged from the rectifier/regulator at the time, which I've since read isn't recommended - so just test for voltage between those three white wires
hope this helps
EDIT - I know several forum members have made manometers simply out of 4 pieces of clear tube into a bottle with a coloured liquid - I made one with 90W gear oil and automatic transmission fluid for colour
@my67xr I believe documents his build of one in a thread, or perhaps it was @GreyImport - cheap simple and effective