250 life story... I had a nice 3LN(5?) which I binned after a dodgy replacement front sprocket came off in the middle of a corner. Only 14000 kms on it - you could cry. It was an insurance write off, and I bought it back to use as a race bike. Did 2-3 races and then ran a big end bearing. Bought an '89 3LN for cheap, not running that well but mechanically healthy, and registered on hold. Intent was to engine swap and keep racing - didn't eventuate. I am now in the process of making a decent road bike out of the two bikes. Have slapped wheels, forks, sprockets & chain (new), brakes, entire harness, tank, carbs (fully stripped/cleaned), and other bits and pieces onto the '89 frame. It's up and running and the electrics are most of the way there, just have the following bugs to sort, which is why I'm here to do some digging! 1. Single to twin headlight conversion - got it all wired up and working nicely but after I started the bike, she no go. Todays job to check fuses and bulbs (I dropped the headlight after initial tests, possibly that's the problem). 2. Idling like a **** - at this stage I think it's a vacuum leak because these carbs I know were very good on the other bike. Will diagnose with some engine start around the boots, maybe pull them off today if confirmed. Symptoms: bogs and needs a blip to stop conking out, after adjusting idle up to keep it alive I restarted the bike and it idled at 6000 for a minute before bogging. 3. Need a new battery - so can't test ride at the mo. 4. Oil light remains on - the oil light was behaving before I changed the harness over so I'm happy it's not an oil problem (also good in the sight). This bike (the 89) has the level sensor in the sump. The donor bike (where the harness is from) had a different sensor, possibly pressure, mounted horizontally behind the screw-on filter. I'm trying to figure out if these two systems behave differently (grounded / not grounded), and then sort a fix. As a last resort I'll just change the sumps over, screw-on filter makes life easier, and if it is a pressure sensor, I'd be much happier with that also. So hi! Munga
3LN1 has the oil level sensor and yes an oil pressure switch on the later models The sensor in the 3LN1 can be removed and cleaned ..... I put one in a container of kero and all sorts of crap came out of it .... and they can be unreliable , whether thru design or being full of grunge. The only way to really know the exact / correct oil level is to measure it in .... sight glasses (especially 25+ yr old ones) are for blind Chinamen Oil level sensor Oil pressure switch What carbys are they? Check here ..... http://2fiftycc.com/index.php?threa...0-3ln-bodywork-frame-engine-carburetors.3469/ Earlier carbs will have worn needles and needle jets (emulsion tubes) and u will battle to get it right if they havnt been replaced. Intake boots can be cracked ..... squeeze them to see how bad ..... replacements are unobtainable and if do find some new u will have to mortgage the house to afford them anyway. Final tuning of the carbs has to include them being synced .... then each pilot/mixture screw has to be set individually with the idle reset each time (bike running) If the carbs havnt been rebuilt then I suggest this ..... http://www.litetek.co/ReplacementPartsYamaha.html New battery AGM > Motobatt or SSB Correct drive sprocket for later models http://litetek.co/Sprocket_Drive_Yamaha_FZR250_3LN3.html
Hey, thanks so much for taking the time, Grey. I saw your identification thread the other day and noticed that, oddly the later model bike had 3LN1 carbs on it (going by the jet housing). These carbs worked really well when the old (newer) bike was running so I'm not expecting major issues with them. Yes I've noticed boots are hens teeth. Hopefully can salvage off the blown engine. Thanks for confirming the oil level/pressure situation. Clearly a different circuit from loom to loom. So I will change the sump after I sort out the tuning issue. Headlight issue sorted, loose adapter. Thanks again Munga Sent from my iPhone using Tapatalk
Where from Linkin? I'm going to try to seal them, gash I know, but worth a shot. Makes you wonder if it would be more cost effective to fabricate or modify some alloy intakes (CBR I think, surely not too different?). Sent from my iPhone using Tapatalk
http://www.aliexpress.com/item/Perf...100-used-with-Caburetor-PE26/32379955689.html Reverse mount, no airbox? Amazing how cheap this Chinese stuff is.
www.jp-parts.com You will need the part numbers for each boot. $250AUD was the quote I got before the aussie dollar tanked recently.
Not much work for a few weeks. This weekend, fitted the spare intake boots I had, with a bit of gasket goo for good measure. Started her up and much better, number one slide wasn't moving though - so out came the carbs again and cleaned up the little vacuum port. Nothing at all blocking it that I could see but all was well when it went back together again(?? - not complaining). Took her for a test ride and overall pretty happy. She's got a bit of a flat spot through 14-16k which I'm keen to try to remedy. One thing I noticed was the needles on the old set of carbs were set fully short and the new ones are in the middle - I might just have a play with changing them. Otherwise the bike is very rideable. The other thing I'll have a look at is the mixtures. I have a tiny bit of experience with reading plugs on my old cars - is this how most guys tend to set their mixtures? Hopefully next week I can get her legal!
The way to start is to make sure the carbs are fully seated in the boots and that the airbox is fully seated on the carbs, and there are no air leaks. You start with the idle circuit screws at 3 turns out from fully seated but not tightened. You then go and ride to fully warm up the bike. With the bike fully warmed up and on a rear stand (ie level) we begin the adjustment process. First - set the main idle adjuster knob so that the bike idles at 1600RPM. Now you adjust No.1 carb idle screw in or out slowly and listen for any changes. If the idle starts sounding "wonky" or RPM rises and falls, too rich. Back the screw in. You will hear when the carb is rightly tuned. Smooth idle and the RPM will have risen a bit. Use the main idle adjuster to set the RPM back to 1600, and then repeat the above for carb No. 2. No.2 is the main carb so adjusting it will have profound changes. Repeat for carbs 3 and 4 and then finally set the main idle to 1600. Now, the throttle test. Blip the throttle & close it. There should be no hesitation or bogging when the revs rise, and no hanging or dropping down below 1600/stalling when the throttle is closed. If it bogs down or stalls you are too rich, adjust all the screws in a tiny bit at a time until it rests at 1600 without falling below. If the revs hang at a certain RPM or there is a delay in the revs dropping to 1600, then you are too lean or there is an air leak. Check for air leaks, if none, then adjust the pilot screws out slightly until the revs no longer hang and it cleanly falls to the idle speed.
Thanks Linkin, this is exactly what I was just searching for. Do you use an auxiliary tacho for this?
Ahh, I forgot the 3LN1-3LN5 only go down to 3000 RPM. In that case, just tune the idle speed by ear. You can hear when it's too fast or too slow
