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Discussion in 'Your 250cc Projects' started by Laceysnr, Aug 8, 2019.
The sensors remove from the bottom, just take them out if you do anything.
Oh sweet.... for some reason I just thought they were fixed in there. I might give that a whirl, I really don't fancy having to get this tank off again any time soon.
Well I'm getting really stumped at this point. The tank was definitely worth doing, my previous "in place" de-rusting really hadn't gotten a lot out of the tank.
Rather than going for a liner I flushed it until water came through clear, then dropped in some phosphoric acid and rotated the tank around over an hour and a half to ensure everything got covered and time to work. It did an amazing job and the bits I could see were spotless afterwards. Washed the acid out with warm water, and then drained that and dropped in the better part of a litre of methylated spirits to mop up the excess. Drained that, refit the tank to the bike and filled it up again. Fuel is coming out nice and clear now and replaced the petcock at the same time.
All that done, I pulled and checked the plugs, then removed and cleaned the carbys once more. Compressed air gets through every hole it should, all boots etc. are tight and still it won't idle unless the mix screws are way out! I'm starting to think I just need to enrichen the mix via the needle jets for now but surely those don't affect idle? Once it was warm I could rev it easily, and back off the screws and choke a bit, but pulling the choke completely would stall it again. So definitely seems like it's not getting enough fuel, but I really have no idea why. Might be time to source an ultrasonic cleaner, and failing that, professional/experienced help.
Ensure you have the Pilot screw "O"ring assembled correctly as per the link from the LiteTek site... Have you bench synched the carbies?
You should probably also do a Compression Test and even a leakdown test to ensure the engine is in reasonable condition...
Yeah I tweaked them based on the service manual, rather than using paper or something they say about lining up the top of the butterflys with one of the holes in the carby. I'm pretty sure the pilot screws were setup like that but I'll double check them tonight since they're easy to get out. Also got the compression tester so I'll give that a crack too, fingers crossed it's not low
If you are going to check the compression make sure you have the throttle wide open when spinning the engine up, or even better.. do it while the carbies are off.
Hopefully your compression Tester screws into the plug holes with a short hose or metal tube so you can get an accurate reading.
It does have various adapters to suit different sized plug holes, but I'm not sure I fancy my chances given the bloody awkward angle they're at! Will post my results tonight, was really hoping this would be a cheap bike but seems like it may well not be after all!
Ok, so this is a bit academic because the engine was cold (didn't want to start it being late at night), but figured I'd see what I could learn from that at least and once I get it started again I'll do a hot test. Could screw the compression tester in, so that's good. Took a good 10-12 cranks to get the maximum reading for each cylinder, not sure if that's excessive.
Got these figures:
Cylinder 1: 135
Cylinder 2: 130
Cylinder 3: 132
Cylinder 4: 135
Now mine is the later model Across (less power, boo!) so the service manual shows these are the numbers I'm aiming for:
So it first blush I'm barely above the single cylinder limit, which isn't great. Then for cylinders 1 & 4 I gave a squirt of WD40 (it was to hand, and had a straw - seemed a lot faster and easier than finding engine oil which would obviously be thicker), and got 155 and 160 respectively. I would have tested the other two but the battery was getting a little tired by this point because I did try to start the bike this morning a couple of times using the "backed off" mix settings from when it was hot yesterday.
Given these are basically on the lower limit for a cold engine, and all the cylinders are pretty consistent, I feel confident that the compression is ok overall, but I'll do a hot test sometime to be sure.
One head banger of a moment came right at the start, I was trying to screw the hose for the tester into the second cylinder and it just wouldn't get a purchase on the threads in the head. I pulled it up to look at it, and realised the adapter to fit the head wasn't attached... the mofo was still stuck in the first cylinder! Clearly hadn't done it up tight enough. Tried to screw the hose back into it and remove it that way, which I knew was a long shot, but failed. Cursed a fair bit, and then grabbed the extension bar from my socket set, wrapped the end in a bunch of layers of double-sided tape and pushed it down into the adapter. With a bit of pressure to help stop it slipping it actually worked. Needless to say that was a big relief!
Gut feel is that the idle circuit on the carby still isn't clean. I'm either going to boil the whole thing (sans rubber parts) in lemon juice, or see if it'll fit in a cheap ultrasonic cleaner on eBay. Hit up a local company for a quote on getting it run through their cleaner and they came back saying 165-185 + GST, so that's out.
Depending where you are in vic, you can use my ultrasonic if you like. Just hit me up in a pm.
Also that compression is nothing to worry about. Being cold it sounds about right.
90% of problems is carbs which are a pain in the ass and the other 10% is things like carbon buildup on the valve seat areas and clearances etc...
If it was running rich before, then there could be carbon build up, but given the super low mileage on the thing I'd be surprised if much was genuinely out of spec (like clearances). Will pm!
When you do a comp test it is best to have all the plugs out.
Throttle has to be wide open and slides manually lifted.
Easiest way is to take the carbs off.
I didn't lift the slides, but did have the throttle all the way open. I guess that's why it took 10 cranks or so to get it up there? I'll remove the carbys when I do a warm test.
easy way instead of lifting slides is just unbolts the top caps, remove the slides and leave the top cap open
Took the intake boots off to inspect them, no signs of cracks but they're pretty damned hard so going to get some silicone spray and get them softened up, might help with sealing and should definitely help with installation! I've completely dismantled the carbys and gone over everything again, I'm confident every passage way and jet is clear. Once the boots are soft I'll reinstall and see what happens. Hopefully work this out soon.
You can use wintergreen oil and soaking the boots in that solution to soften them up.
But do take note, if they do go soft they can expose more cracks and such to leak.
Even if the boots are on the hard side, once clamped up to the carbs if you spray start ya bastard and the engine doesn't respond to the spray then they aint sucking air.
you can buy new ones, just like the slides, but ends up very costly. you wanna be sure they are the problem
Yeah, I already enquired as to the price of new ones... $29 a piece. Given I only paid $500 for the bike I'd rather not have to go down that route. I just want to soften them a little to aid with installation, they do bend a bit but it's clear they've hardened a lot.
Use some rubber grease on the insides where the carby sits/slides in them
Silicon spray wont soften them... the Wintergreen method appears to give some temp softening but being hard isnt going to cause your lean running unless they dont clamp down properly... and the WD40 spray didnt change the running of the bike so it is unlikely that is the cause...
If you are concerned that they dont clamp down correctly.. use heat, that will get them reasonably flexible. Buy yourself a good heatgun as they are a very handy tool to have around.