I'm currently working on a 1990 FZR250 that won't start. It sounds like it's really close to starting but it just refuses to start. Fuel is getting into the cylinders along with air and all 4 plugs are firing. Bike is making popping noises from the exhaust and has backfired out the carbs too. I think the ignition timing is off. The guy that sold the bike did prove that it would start as of a couple months ago. Any suggestions for what might be wrong and how to test it?
Welcome, Check plugs and leads are in good condition and connected correctly, as in Lead 1 goes to Cyl 1 etc. There is a good thread on this already in this forum.
https://www.2fiftycc.com/index.php?...eads-spark-plug-configuration-inline-4s.8176/ https://www.2fiftycc.com/index.php?threads/trim-your-spark-leads.8032/
any idea if these bikes will crank over without a fuel pump? or is there a relay or something of the like that will prevent that?
If you have fuel in the carbs then the pump shouldn't matter. Do you know what the valve clearances are like?
no, i don't have any good idea what the clearances are like. that might end up on the list of things to check. anything else that could've gone wrong over the last couple months?
Try draining the carbs (screw on bottom of float bowls) and filling the tank with fresh fuel. Maybe a sniff of either spray (aerostart or startyabarstard) will help get the fires lit.
sadly the last person to touch the carbs ruined the drain screws by over tightening them on 2 and 3 which does not fill me with joy, already made liberal use of aerostart and only really got popping noises
One quick inspection you can do is check the condition of the JIS screws on the carbs, float bowl screws and slide diaphragm covers - if they've been tampered with or are damaged you may need to go through the carbs to check them out. From the factory the screws are very, very tight, especially the ones mentioned above, so the float bowl screws may not have been overtightened by the previous owner, unless they removed them. BUT before you do that, check that the manifolds [carb boots] are done up properly, both to the cylinder head and around the carb. Also worth going through and checking other basics, before contemplating disassembling the carbs, once you loosen the float bowl screws, check the fuel height with some clear tube onto the float bowl drains and the idle mixture screw settings. Check the pinned threads in the Yamaha 4 cylinder 250 subforum.
thanks. the manifold boots were tightened properly as far as i could tell, i will check the carbs out when i can.
As @maelstrom mentioned, popping can be plug leads incorrectly connected - 1&4 are paired to the same coil and 2&3 are paired to the same coil - usually their lengths dictate where they will go, although potentially 1 and 2 could be swapped same goes for 3 and 4. But if nothing has been done to it since it was known running, concentrate on fuel supply firstly. You don't mention which model. They will run on gravity without a pump with sufficient fuel in the tank - 2KR tank sits low inside the frame so needs a pump for a less filled tank. Check filters inside the tank for blockage [remove the connection on the bottom of the tank - obviously not when full], also if you have an inline filter, check that one. Hope this helps
it's a 3LN3 and the fuel flow seems about right, though the fuel drained from the float bowls we could drain was kinda yellow
Silly question, but you did drain the carbs completely and put fresh fuel into it before attempting to start it didn't you?
fresh fuel. fresh plugs. check for spark on each plug. I know I am like a broken record, but 9/10 it solves most issues.
A great trick I learned for butchered JIS screws... Take a ball pein hammer and tap the screw head so it squishes the damaged sections flat again. Then insert your JIS driver and tap that in to the screw head to correct the shape. Apply lots of pressure and remove the screw. Sometimes I have more success with a small drive bit and ratchet than a screwdriver - you can still apply pressure, but you get more leverage than a screwdriver.
i'll try to get the other 2 carbs drained and see if i can get my hands on new plugs, the ones in the bike did all seem to be sparking strongly. thanks for the tip on the screws i'll see if i can get them out
