October 6, 200817 yr I've got a 04 315, its a sweet bike but always been in need of a bit of work. So i thought i spend a bit of money and sort her out. She's got new wheel and supention bearings bash guard and exhaust. The problem is that after all the time and money she's running like s**t. The new exhaust sounds great at idle and low revs but knocks really badly from halfway up to full revs. I told that this is because its running lean. The tip i was given was to raise the jet needle in the carb up a notch. When i tried this i found the needle is already at it highest setting (the pin is at the slot furthest down the shaft) What else can i try to sort this out? The bike never used to have this problem, is it normal to have to reset the carb after changing the exhaust? The old exhaust had a hole in the muffler and the packing in the expansion chamber was rock solid. Any tips would be a great help as i've spent quite a bit of time working on the dam thing all ready and just want to ride it. I've never worked on a carb before so please explain so a newbie such as myself will understand Thanks a lot Matt Also i've been reading some of the posts about the Keihin and oko carbs being a good upgrade (not that i want to spend anymore money right now) what are the models that fit on a 315 in case i see an amazing deal on ebay.
October 6, 200817 yr Have you tried hi octane fule, ie superunleaded. Its common for 315's to do this.
October 6, 200817 yr If you PM me your email address (and I can work out how) I'll send you the diagram for the 02 carb which i think's the same. It's easy enough to strip and clean one, just be gentle with the brass screws and keep an eye on every thing that comes out so you can put it back in the same way. You can buy some carb cleaner to squirt through the jets and passages from Halfords or similar. Be careful doing this as I squirted the cleaner in one hole and it popped out another into my eye! Not fun! Are you in the UK? If so it should run fine on super unleaded. Check your spark plug to get an idea of how lean/rich the bike is running. If you had a hole in the exhaust before I would have thought this would effect how it runs especially if it had been set up to compensate for the hole in the first place.
October 7, 200817 yr Author Cheers for the advice so far I'm english but live in the states but the bike has always run fine on the highest octane unleaded. So after talking to a few more people i looked in the carb to see what jets i had. 33 pilot and a 110 main The carb looks clean but i'll clean it and blow it out to be sure. The only other thing i noticed was the o ring on the by starter jet (60) was damaged, would this course any problems? Looking at some of the other posts i saw people where recomending bigger jets Main 122 pilot 45 slide 3.5mm this was for a Keihin carb but would they similar or the same for the standard carb?? (also what is a slide of 3.5mm) Thanks a lot Matt
October 9, 200817 yr Always worth changing the o ring. Could be letting air or fuel flow to places its not supposed to be. Not sure on the jet sizes, the carb you have quoted from is a different type of carb, not sure how it works so i can't comment. Can't remember what my jet sizes are but I'll have a look next time it's stripped down.
October 11, 200817 yr It is not uncommon for an exhaust change to make a difference in fuel metering. What you describe though would be a slightly richer situation since you are flowing less air with the more restrictive exhaust.
October 13, 200817 yr If your super unleaded (93) is 93 octane then there lies your problem as the montesas are high compression engines designed to run on 98 RON fuel. 93 octane would be too volatile and cause pre-ignition (Knocking). This is where the fuel mixture ignites BEFORE the engine reaches TDC, pushing back against the piston as it moves up its stroke. This aint good for your engine...
November 9, 200817 yr If your super unleaded (93) is 93 octane then there lies your problem as the montesas are high compression engines designed to run on 98 RON fuel. 93 octane would be too volatile and cause pre-ignition (Knocking). This is where the fuel mixture ignites BEFORE the engine reaches TDC, pushing back against the piston as it moves up its stroke. This aint good for your engine... 315's are very sensitive to fuel and carb settings....put your circlip needle position midway...if the needles right up, that'll knock even more as you will be richening the mixture betweenn 1/4 and 3/4 throttle openings. Use an octane booster if you can't get super unleaded...STP do a good one...good synthetic pre-mix at 80:1...if you fancy sorting it for good, I was the bloke who posted about the OKO 28mm carb change...it's amazing and they are available off the 'bay for
November 11, 200817 yr So in the Uk should I run super unleaded? my 97 315 has a new 04 carb on and runs great except a little 'knocking ' at certain revs. mixture screw is 3 3/4 turns out as per manual? cheers Dom
November 24, 200817 yr OOPS just checked manual, says 1 turn out! It was the previous keeper who said 3 3/4! which is right its a 97 315 with an 04 carb?
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