stork955

Gday, if the manual says go with a resistor plug - do so - it limits the secondary ignition current which can take the CDI out with the wrong one. Also it will pay to clean the entire exhaust, this should be done on all 2 strokes. You will be amazed at the difference. HTH, Cheers, Stork.

Gday, all engines go over-rich on deaccelleration, this is because some fuel sticks to the inlet tract walls during normal running. When you shut the throttle you increase manifold vacuum greatly and so this fuel gets drawn into the engine (over rich!) If there is a hole in the exhaust (leaking gasket etc.) this adds a bit of air and given enough heat, combustion occurs - banging in the pipe! This is a common cause of "backfires". Also as written above the other issues can cause the same thing. If the bike idles and starts OK your jetting is correct so dont change it! Check the other stuff first. HTH, Cheers, Stork.

Gday - you need to check if your clutch is a brake fluid type or a hydraulic fluid type. The Hydraulic type has a green cap on the m/cylinder and uses a different fluid, 5 weight fork oil will do if you cant find "clutch fluid". The Black covered m/cyls use normal DOT 3 or 4 brake fluid. You will need to rebuild your cylinder if the wrong fluid has been used in it as the cups are made of incompatible materials. Kits to rebuild are cheap and it is best to replace all the parts inside with the new bits anyway. If your m/cyl is leaking (as you say) it needs rebuilding anyway, so do that and then double check that you have a small amount of clearance between the end of the piston and the lever. Your system will not work without this clearance. And for the interested folk still reading at this point, the only difference between the Ford m/cyl picture above and the m/cyls on our bikes is that we dont have the "inlet valve" which is actually a residual pressure valve in the end of the m/cyl. This is only used on Hydraulic Drum brake cars to keep the brake shoes out near the drum so you dont get a low pedal. Apart from that they work in an identical fashion, we have both ports etc and the piston/cups design is the same. HTH, Cheers, Stork.

Excellent news! Glad you got it there in the end. Stork

Hmmm, I dont think you have a bleeding issue there. If it pumps back up it sounds almost like something is retracting the caliper pistons/pads back from the disc (Much like what you get when you fit new pads and have to pump the brakes back to the disc). Weird - maybe its worth leaving the reservoir cap off overnight and see if that makes any difference. Cheers, Stork.

Excellent! The brake will probably improve further as the new pads bed in to the disc. Cheers, Stork.

Yep - better to do it right first time. Peace of mind and all that! Cheers, Stork

Is the carb a mikuni? If so its a strong possibility that the needle is generic, they use a numbering system on many of them. Keihin are similar. Try genuine first - you may be surprised at the cost and availability! HTH, Cheers, Stork

Measure the piston and take the seal into a car brake parts seller. You should be able to at least match it up there if genuine is not available. I have sourced pistons and seals for "unusual" applications this way in the past. Also it might pay to search the net for the caliper manufacturer - AJP have a comprehensive site in the states for example. HTH, Cheers, Stork

Gday Paul, maybe a silly question but you havent fitted a m/cyl seal backwards possibly? Both should point to the closed end of the cylinder. Cheers, Stork

Gday Paul, just reading back through the thread, check out Ians way of priming the system with a syringe on the m/cyl (reservoir hose - on the first post page) That would definately get things going OK. It also makes sure there is a free transfer port in the m/cyl which could be your problem. Cheers, Stork

Yep - there is still air in there. Did you prime the m/cyl first by just moving the piston and watching the reservoir? Its hard to describe but easy to do - after the bubbles stop apperaing in the reservoir then go on to the caliper. Tap fittings as you go, and take your time - slowly and gently is the answer - rushing just emulsifies the fluid and you go backwards. Another thought, You have had the m/cyl apart correct? If so were both holes from the reservoir free and clear of rubbish? Cheers, Stork.

Just a quick thought, make sure you never have the bleeder open unless there is pressure on the m/cyl - i.e. push the pedal (lever etc), then open the bleeder until the pedal reaches the end of its stroke and hold it there, close the bleeder and release the pedal. This makes sure that you dont draw air back in. See if this helps, Cheers, Stork.

Yep - stick with it. The satisfaction will be greater when you get it sorted out! Let us know how you go. Cheers, Stork

Gday, these little singles use a pressed up crankshaft and fitting a new big end is not the job for a home repairer. They are pressed together and aligned in a jig and then trued using dial gauges. Its tricky but most bike shops will do it for you for not too much money. That is if it needs replacing, check the rod side clearance as mentioned before and check for roughness. Too much side clearance means the thrust washers are wearing and this will lead to a rod failure which you dont want. If all of that is OK no need to worry! HTH, Cheers, Stork.

Stick a 20 thou feeler gauge in beside the rod. If it wont fit in you are OK. If it does keep going until you find one that wont go in. Much more than 25 thou is too much. Feel the bearing - is it rough? (wind the crank over while holding load on the rod in an up and down fashion) If not - good. See how this goes. Cheers, Stork

Gday, remove it from the bike (obviously) and remove the top cap and float bowl. Use only quality screwdrivers that fit properly! Remove the slide and put aside carefully. Remove the float noting how it all fits together (take pictures if necessary). Remove the 2 jets from under the float area and the needle from the needle valve (float). Lightly screw in the idle and mixture screws counting turns and recording them. Unscrew fully. Use throttle body or Carb cleaner and go mad making sure every little passage is free and clear. Likewise with the jets and flaot needle. Clean off the outside of the carb body and carefully do the slide also. Reassemble all as they came apart. Check the float level - search around in here Im sure it would be documented somewhere. Fit the bowl and carb top/cable etc. Do the airfilter while you are at it. Cheers, Stork.

Gday, check out the "Rev 3 Rear Brake Problem" thread over in the Beta section. Sorry I dunno how to post thread links. There may be some stuff there to help you out. Cheers, Stork.

Gday, get it measured while its apart, as Zippy says, its easier to check that out properly now than have to do it again later on. Even if the bore looks perfect it may not be, and of course the piston can wear as well. Do it once and properly and you can sleep easy then! Cheers, Stork.

Gday, oversize pistons are usually marked so on the crown. Look for scoring/damage to the bore, deep stuff that you can feel with your fingernail will need reboring. Make sure you clean everything properly, including gasket surfaces. Check the reeds are closing properly while you are there. It would pay to get the exhaust cleaned, there are many methods all documented around in here. It would pay to have your piston and bore measured properly if there is an existing rattle, your local engine rebuilding place should be able to help here and possibly with the exhaust cleaning as well. Run it in at no more than 3/4 throttle with varied engine speeds for an hour or so. The initial ride should be easy with a burst or 4 of high gear/almost wide open throttle to load the rings up and help them seat. (Not too much of this!) Look at the aircleaner also, very cheap from Yamaha. It would be a shame to rebuild the engine and use a less then ordinary filter with that. HTH, Cheers, Stork.

Yep - almost - It can help in that you can roll the system around to work out all the air from corners in fittings and the like. Air likes to go up always so keep the m/cylinder low and the caliper and reservoir high as you want to push the air out of the caliper. You also need to prime the m/cyl first to get things started. Usually I do this on the bike by very gently just cracking the lever/pedal very slightly multiple times. After a little while you will begin to see air appearing in the reservoir, this is coming out of the m/cyl. The important thing is that the system is closed during this (bleeders done up) and the amount of movement is very small, just enough to move the piston a couple of millimeters -no more than that. Afterwards, when it seems most of the air is gone using this method and you begin to feel a "lever" coming on, I tap fittings etc with the handle of a screwdriver to help the process of removing air along and bleed in the "normal" fashion from the bleeder screw. (It might pay before you start doing anything to make sure that the bleeder screw is not blocked up - this has caught me out before...) Be very patient! Also make sure all of the other things we have talked about are OK before you start, just so you dont chase your tail around. Good Luck, Cheers, Stork.

Gday, I tried this on the CP in my Square 4, unsuccesfully. The main hope was to use just oil, but it proved too difficult in the end so I went back to grease/oil. Certainly removing the gaskets and using a good quality sealer helps, dont use common silastics, the best are either Loctite flange sealant (cant remember the number) which will remain fluid outside the joint so dont let that fool you into thinking it hasn't gone off, or even better is 3 Bond (also sold as Yama Bond from yamaha dealers), there are many grades, go with the Grey case sealant which many if not all manufacturers use on their bikes. Make sure you are not reducing any end float by removing gaskets. I cant remeber if this is the case as it has been years since I did mine, possibly the shift case gasket to the main case may help control end float on the 2 shafts. HTH, Cheers, Stork.

Gday, I agree that the seal profile is unlikely to cause problems, considering that these are a fairly common caliper design fitted to a few different bikes. ( I assume they are AJP - possibly wrongly....) It is vital that the m/cyl releases correctly and uncovers both ports inside (the pushrod thing). The caliper seals are designed to flex and pull the piston back a few thou, which is all they need. Most are fairly tight when new and it is very unlikely that genuine parts are going to be incorrect. Notice I said "unlikely" :-) I'd be having a very close look at the breather hole in the reservoir cap - this is most likely the trouble, and the the pushrod clearance next - in order of "easiness". Have you got your new pads yet Scorpa250? Cheers, Stork.

Gday, If the brakes change when they get hot it would either be that the fluid is boiling (you cannot compress a liquid but you can compress a Gas) due to the fluid being old, or that the transfer port in the master cylinder is blocked (either the old fluid again has blocked the hole with rubbish, or the pushrod from the pedal is adjusted too long and holding the piston in the m/cyl across the port). Both quite common. There must be some small amount of freeplay between the end of the pushrod and the master cylinder piston. Cheers, Stork.

Gday, Brake fluid (aprt from the silicon type) is Hygroscopic, which means that it absorbs water from the atmosphere by nature. It gets in through the hoses and is present in the reservior. If you look at any maintenance manual for any vehicle you will see that Brake fluid should be changed at least every 2 years because of this. I dont think that this is the problem we have here however although your fluid should be changed regularly! I dont have a Rev 3 but I'm beginning to suspect that the reservoir can not compensate for the pad wear by allowing the fluid inside itself to get into the master cylinder. This is caused by the rubber diagphram thing that goes under the cap - it is designed to allow atmospheric pressure to act upon the fluid but not actually allow air to directly contact the fluid for the reasons above. If the pads wear somewhat and the pedal begins to go spongy this is symptomatic of this effect - the fluid is not replacing that which has gone into moving the pads further out. Usually the cap has either a small air bleed hole or in the case of front m/cylinders a passage thet runs from the outside of the cap to above the rubber bellows. An interesting experiment would be for someone who is experiencing this to remove the rear filler cap, pump the brake back up and top the fluid off, and replace the cap again, then see if the problem is solved. I hope all this makes sense. Cheers, Stork.