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Thread: ZXR250C or CBE250RR questions

  1. #16
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    Chur, keep us updated.
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




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  2. #17
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    Quote Originally Posted by bawked View Post
    This is very true, if every part of the engine is up to spec then there is no reason why it won't run well. Just because an engine has 100,000+ km doesn't mean it's shit.
    At 100,000 km's (over or near) ... without the internals being touched ... odds are it is shit.

    ie: Compression is down ... it's using oil ... and it's getting harder to start. (Have YOU checked the compression on both bikes lately .. ??)

    Quote Originally Posted by bawked View Post
    I bought a second hand set of carbs, to quickly rule out the emulsion tubes. Also if I need to bore them out I'd rather have a spare set, to use as a control/backup. Turns out the set I bought had bigger jets, so don't have to worry about getting them either. And they were cheap as chips.
    If that model worked well with the original sized jets ... why the need to replace with a larger size now ... ??

    Quote Originally Posted by bawked View Post
    Took the cbr out for a good ride today and apart from the issue at low rpm, it pulls like a beast. Puts the zxr to shame I think.
    Don't let the revs drop below 4000 rpm. (on either bike) The result may surprise you ...
    When life throws you a curve ... Lean into it ...

  3. #18
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    Quote Originally Posted by FJRider View Post
    At 100,000 km's (over or near) ... without the internals being touched ... odds are it is shit.

    ie: Compression is down ... it's using oil ... and it's getting harder to start. (Have YOU checked the compression on both bikes lately .. ??)


    If that model worked well with the original sized jets ... why the need to replace with a larger size now ... ??


    Don't let the revs drop below 4000 rpm. (on either bike) The result may surprise you ...
    1. I didn't say this wasn't the case, you were just over generalising.

    2. Because air filter + straight thru can.... Combustion works by mixing a certain ratio of air and fuel, compressing and igniting. My bike with these will flow more air, hence I need to flow proportionately more fuel to maintain correct fueling.

    3. It won't surprise me, I've had my bikes over 4k rpm before


    So I pulled the carbs off my ZXR tonight, was going to just slap the other carbs on it and see how it goes. But decided I should check valve clearances, balance the carbs and do a compression test while I'm at it. I'm betting no one has looked at the clearances in ages and they are miles out, 250's don't seem to get much love.

    So seems the needle jets are a tad worn, the beastie below being the worst. The outter two were actually in decent nick. The needle jets in the replacement carbs I have are all in better nick than the outter ones of these so that's a good start at least.

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    So guys, this is why i'll never take my bike to cycletreads again... they machined the caps of my needles down without asking me and did a fucking rough job of it at that. Apparently since the emulsion tubes were ovalised, they over fueled so lowering the needles helps neutralise this... but still, who the hell does this sort of shit?!

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    The stock main jets on 1 & 4 are 122, 2 & 3 are 125. The below is what my bike came back with... and with the recommendation to try go down to 115s on 2 & 3 to try get rid of the hesitations.

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    In the intake box there was no filter.... just this shitty mesh looking thing. I see that people recommend unifilters for the cbrs, is this the case for the zxr? They seem to be cheap as chips.

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    Does anyone have a carb balancer I could borrow, nz being nz I assume I'd have to import one.... which i will do eventually.

  4. #19
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    That gauze looks like a backfire guard. No air cleaner? I would get a stock one to get the bike back to basics. Higher airflow ones just mean more mucking about getting the jetting right. Some motors produce less power with a high flow filter.

    Have you looked into getting some needle jets turned up? Or even for a rough fix brazing yours up and re-drilling them?

    I have a Carbtune balancer, but i come with it. I dont lend tools but happy to pop over with it when your ready with it.

  5. #20
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    Quote Originally Posted by nzspokes View Post
    That gauze looks like a backfire guard. No air cleaner? I would get a stock one to get the bike back to basics. Higher airflow ones just mean more mucking about getting the jetting right. Some motors produce less power with a high flow filter.

    Have you looked into getting some needle jets turned up? Or even for a rough fix brazing yours up and re-drilling them?

    I have a Carbtune balancer, but i come with it. I dont lend tools but happy to pop over with it when your ready with it.
    I'm sure I had a filter in there from when I replaced my throttle cable, maybe cycletreads took it out and forgot to put it back in... I got a second hand set of carbs which have much better looking needle jets, so i'll use those as my base.
    Sounds fair enough, i'll let you know when I'm good to go.

  6. #21
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    If the spare emulsion tubes are betterer use 'em with the corresponding needles, go with stock jet sizes, make a uni-foam filter of buy one, don't go pods. Then re-jet to suit.
    The smaller jets installed with decent emulsion tubes and needles will be insanely lean
    Lowering the needle won't fix an out round hole, this makes me LOL. Only way to fix is replace, or solder and re-dril. But to drill and ream one to the right specs is another story all together

    One hori as fuck thing you can do is lap the old needle and seat in. But with your spares, there's no need. The other is to drill out the ovalisation (is that even a word) and use the lowered needles
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




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  7. #22
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    Oh and build a manometer, best carb sync tool you can buy and it costs bugger all to make
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
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  8. #23
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    Ok will get a filter, and some 122 jets so I can start with everything stock and go from there.

    Finished work late today, so only managed to take the radiator off and barely started checking the valve clearances before it got too dark. It seems that the clearances are really really tight though, its hard to judge how tight though.. as the super thin feelers are not stiff enough to slide between the cam and seat easily. But I couldn't even slide .063 under them so which means they are at least .10 mm tight. Some I could slide a .406 under, so they are massively off as well

    I'm guessing that if I did a compression test 2 & 3 will be low as the valves aren't fully closing, so that's on tomorrows agenda. Then i'll finish measuring up the clearances and get some new shims... might take a couple iterations if I can't measure the gap under some of them. Hopefully it was just due to the dark and not being able to see what i was doing though

    Also saw some cam rub marks on the valve cover, looks like it has good tension now... so must've had the chain and/or tensioner replaced at some point.

  9. #24
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    Yeah they tend to get tight in the valves as the seats recess, not uncommon at all and they do it faster when you run them lean
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
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  10. #25
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    Ah that makes sense, lucky I haven't burnt a valve I think.

    Looking at the plugs only one cylinder was rich, the one with the very worn emulsion tube. For shits and gigs I might put a 115 jet only in that carb to see how it runs.

  11. #26
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    Personally I wouldn't do that
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
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  12. #27
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    Quote Originally Posted by bawked View Post
    Ah that makes sense, lucky I haven't burnt a valve I think.

    Looking at the plugs only one cylinder was rich, the one with the very worn emulsion tube. For shits and gigs I might put a 115 jet only in that carb to see how it runs.
    Problem is at WOT the motor is still very lean if you do that. Things can melt.

  13. #28
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    Quote Originally Posted by ducatilover View Post
    Personally I wouldn't do that
    Haha fair enough, I probably won't either since I want to get this running nicely quickly, so I can give my cbr some love before summer.

    Seems the clearances weren't as bad as thought, well only 2/16 were in spec. But they aren't as far out as suspected, seems seeing what you are doing is a big help

    Calculated what shims I need so hopefully I can pick them up tomorrow, slap em in on sat, and bolt the beast up ready for syncing and a test ride.

  14. #29
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    Quote Originally Posted by bawked View Post
    Looking at the plugs only one cylinder was rich, the one with the very worn emulsion tube.
    For one with so much knowledge ... you ask many questions ...

    With NO air filter ... they'll all be running lean ...

    Quote Originally Posted by bawked View Post
    For shits and gigs I might put a 115 jet only in that carb to see how it runs.
    Go for it ... what possible (more) harm/damage could it do ....
    When life throws you a curve ... Lean into it ...

  15. #30
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    Quote Originally Posted by FJRider View Post
    For one with so much knowledge ... you ask many questions ...

    With NO air filter ... they'll all be running lean ...



    Go for it ... what possible (more) harm/damage could it do ....
    Worn emulsion tubes will be making it pig rich in the low and mid range, and possibly a little rich right up top (if you could get the fucker to rev that high with the tubes) so going down many jet sizes may help the transition up the needle, but right up top it's probabl lean off again
    So, the plugs can read rich. But chances are the 12k+ rpm range will start getting back towards normal/lean.
    Quote Originally Posted by Paul in NZ View Post
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
    Bling your bike out!
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