I have been tuning my bike trying to get rid of a slight hesitation down low and noticed the the outer 2x cylinder's have alway's seemed to be running hotter than the inner 2. I think i may have found a problem with the Keyster Major rebuild carby kits for the 3LN3 and 3LN5's. Or at least a problem with the Keyster part numbers for the carb's on the motorcycle spares warehouse site? ( can't find another seller with them listed) The Yamaha parts list for the 3LN's has the main jet's listed as #100's in the outer 2x carby's (1 and 4), and #97.5's for the 2x inner carby's (2 and 3) I recently noticed that the Keyster kits have them listed as the other way around for the 3LN3 kit's , their listing for the 3LN1 kit's is right though Keyster Outer kit's Keyster inner kit's This has got me thinking that i may have fitted the new jet's from my Keyster kit's as listed on the box's they came in, so the inner's would be richer than the outer's. When i have the fuel bowls off next i will be checking what jets are in which carby's and will be swapping them around if the richer jets (#100) are in the 2x middle carby's. And i will check to see if there is any difference with the inner and outer needle's too
Were they much hotter?? trying to tune mine at the mo and cylinder 1 seems to be cooler than the other three by about 20 degrees C, the other three are within about 7-10 degrees of each other most of the time.
Yeah 216° and 222°C on the outer's and 174°C and 178°C on the inner's, now with the jet's the right carby's they are all pretty close to 200°C give or take 7°
I got a reply back for MotorcycleSpareWarehouse on the 3LN3 Keyster kit's question's Peter Lynch <sales@motorcyclespareswarehouse.com.au> Hi I have been advised by Keyster in Japan you have a problem with the Kits K-1203YKS and K-1203YKU The kits are identical except for the main jet sizes. Just fit or swap the supplied jets as you require If I can find a genuine parts manual to confirm what you say, i will swap the description around. The printing on the packages will remain the same They do not have a stronger spring. The supplied spring is as per the OEM part number For you own information, most Asian companies don't deal with individual customers. All correspondence should be addressed in the 1st instance, to the distributors around the world. We are the Asia Pacific distributor for Keyster Regards, Peter Motorcycle Spares Warehouse http://www.mcsw.com.au http://www.motorcyclespareswarehouse.com.au Japanese Motorcycle Restoration and Rebuild carburettor parts, jets, pistons and more. I have replied to him and sent a copy of the Yamaha 3LN Spare Part's Manual inc the diagram showing that the main jet's are the other way around to what the Keyster pack's say. I also let them know that the Keyster Slide Needle's are all the same but the original's are different, And i sent him the link to my Youtube video showing how the needle's for the needle's and seat have stronger spring's too. Waiting for his reply now
Funny that ended up being your issue because I thought that might be the cause - but on the page of your post I was reading when considering making the suggestion you had already posted the manual specs showing larger outer and smaller inner main jets I've read elsewhere people making the error of thinking the inners need more fuel to cool the pistons more/lower combustion temps, when in fact the higher temperature affects air density thus requiring less fuel
Has anyone brought a keyster kit recently ? Got one for my 3LN5. My outer exhaust pipes seem to be running hotter than the middle ones when using an IR thermometer. I'm assuming they have fixed the inner / outer jets being in the wrong box ? As my inners are stamped #97.5 and outers stamped #100 All needle circlips are in the centre position (3rd from top) and mixture screws are 3 turns out. I've also had to set the float height lower than 16mm as it was far too lean. Any ideas, suggestions with what to try / do ?
Welcome to the forum If you have the float height's set at 16mm then you have it set leaner than the original setting 3LN3 and 3LN5 the float's should be set at 14.7mm off the fuel bowl mounting face on each carby. This give's it a fuel heaght of 10.5mm above each line on outside of the fuel bowl's
Set the floats to 14 7mm. Got me a fuel height of 10.5mm. Outers are still about 20°c hotter than the inners. How even are they supposed to be on average if all the carbs are set to 3 turns out ? Quite a bog when down low though.
Ok, i have a few question's for you, How well did you clean the carby's, there's cleaning then there's cleaning ? Did you pull the pilot merge chamber bung's out and check all the hole's are open and check the pilot hole at the bottom of the mixture screw thread's in the carby body were open by poking some fine fishing line through them Have you tuned the bike yet? 3 turn's out is a baseline setting when the bike was new eg warmed it up to normal operating temp and adjust the mixture screw's then You want the mixture screw set so you get the fastest / smoothest idle from each carby, then drop the idle speed back to 1600 rpm's and move onto the next carby. I played around with my 3LN3 carby's for a long time before i got them right, the most important thing was float level/fuel height, the other was the mixture screw's. My mixture screw's needed to be set leaner than your's. Have the carby's been synced using a sync tool ? Are your intake manifold's all still soft with no fine crack's ? Are your carby to airbox boot's all still soft and do they seal your airbox off properly ?
How well did you clean the carby's, there's cleaning then there's cleaning ? I've cleaned them using carby cleaner and compressed air. Did you pull the pilot merge chamber bung's out and check all the hole's are open and check the pilot hole at the bottom of the mixture screw thread's in the carby body were open by poking some fine fishing line through them Cleaned out the pilot merge chamber by running carby cleaner through and compressed air. Have you tuned the bike yet? 3 turn's out is a baseline setting when the bike was new eg warmed it up to normal operating temp and adjust the mixture screw's then You want the mixture screw set so you get the fastest / smoothest idle from each carby, then drop the idle speed back to 1600 rpm's and move onto the next carby. No, I have just installed the keyster kit. I am wanting to try tune. I played around with my 3LN3 carby's for a long time before i got them right, the most important thing was float level/fuel height, the other was the mixture screw's. My mixture screw's needed to be set leaner than your's. Have the carby's been synced using a sync tool ? Not by me, no. I haven't separated the carbs either. Are your intake manifold's all still soft with no fine crack's ? Got new ebay ones on. Are your carby to airbox boot's all still soft and do they seal your airbox off properly ? Yep they are soft and there siliconed to the airbox, so should be no leaks. What baseline am I going for before I start to tune ? I've assumed temperature. I've assumed that with the same float height / level, needle circlip height, and mixture settings they all should be roughly similar exhaust temperatures ? Just weird how its the two inner cylinders, might have test out the coils tomorrow as 2-3 share a coil pack.
There still a few more question's to be answered ^ If you haven't cleaned the merge chamber's and the mixture screw port's into the main bore's of the carby's, then that may be causing the temperature difference between inner and outer exhausts Bike should be at around 1/4 to just under half on the temp gauge before adjusting the mixture screw's But make sure the carby's are cleaned properly first
This is a picture of the mixture screw port's into the main bore on the carby If the 2x inner carby's have these ports blocked or partly blocked then they wont be getting as much fuel as the 2x outer carb's GIve your local Repco a call and see if they sell Threebond Super Engine conditioner (petrol version) and if they do grab a can, if they don't have it try the nearest Subaru part's department Strip your carby's down and spray them thoroughly with the Threebond, let the Threebond work it's magic for a while and then give the carb's including all port's a clean out with carby cleaner then compressed air
Did u have the bung out to clean ? And make sure the screw is setup like this https://www.litetek.co/Guide_MikuniBDST_Rebuild.html
Should I strip down the carbs again, get some of the Threebond Super Engine conditioner and make sure it has been completely "cleaned". What am I looking for once it is back together ? What have you guys experienced temp wise before you start tuning ? Are they pretty close ?
I would be cleaning it out better if you can My exhaust temp's are all around 220 C from memory, right up near the mounting flange's
I wouldn't be basing everything on your exhaust temperatures. It is just a guide and nothing more. For example, a cylinder with lower compression is never going to burn as hot as the others. Yes, your 30 year old carburettors should be overhauled. Did you fit new o-rings to the merge chamber bungs? Once it is together you use a Morgan Carbtune to synch and set the mixture screws by ear, not 'n' turns out. If you are unable to do that then you will have to do some 'set & ride' experimenting to find what works best for your engine. As for electrics: The TCI unit will fail long before the coils. Coils are the last thing on the entire motorcycle that I would expect to fail. However, leads and caps do need to be replaced or cleaned up regularly.
