Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: Steve Lake on March 02, 2009, 10:30:49 PM
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Well, just when you think there is nothing about a bike that you have owned/built/used for a decade that you can't fix.....John the plumber who i sold number 3 (srx6) to 2 years ago bought the bike round to mine this weekend with a non starting problem.
Since i sold it to him, he has had the engine rebuilt by Denver Motorcycles, with a pair of mikuni 34mm carbs and various other nice mods, and it has been an excellent bike, John adding over 20k trouble free miles since he bought it.
November 2008 saw the bike starting to have problems starting, though once running, was fine.
this got worse, until 3 weeks ago the thing just refused to start.
On saturday I removed and drained the tank, buying a gallon of fresh petrol, i checked the spark, and it was a bit weak, on testing the wiring the cable from the CDi unit to the coil was a touch intermittent so bypassed that, bypassed the side stand switch and the kill switch, with a new plug the spark seemed healthier, i checked and adjusted the valve clearances, and the exhaust valve lifter free play. Once this was all done, the engine still refused to fire, although there was an occasional bluddy great backfire!
So, thinking it seemed like spark timing I fitted a known working CDi unit.....still the same
and it was also the same with a different coil.
I checked the stator winding resistances and they are within tolerance...
As i had a spare good carb setup, i replaced those, still no signs of life...
That is where I am today....and now i must start to look elsewhere...
possibilities, as far as i can see are...
stator has moved or is damaged
cam timing chain has slipped
sticking valve (though compression seems fine)
rotor has slipped (unlikely, as it is keyed)
burnt valve
any other ideas will be most welcome.....
cheers
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this'll be an interesting one steve!
bent valve? tho noted about compression..
plug gap?? odd i know, but I once fitted a new plug to the skorp, only to find that the gap had been closed up to nearly nuthin!
a
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thanks for the input Andy
Yes, i had considered a bent or sticking valve (or burnt).. the plug gap is fine and tried several plugs
Next job (because it's easier than head removal :-) ) is a stator and rotor check.
cheers
steve
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have you tried a known coil?
if its gradually got worse then the cam timing must be okay, or it would have happened suddenly.
also when you checked the spark, you presumably turned the motor over on the starter. did it have a plug in at the time? otherwise having no compression would give the electrics and easy time, and give you the good spark.
one last thing, see if she goes with a bump start.
bullet350
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Thanks for that bill...yes I have tried a replacement known good coil.
This is a kick start SRX....and yes, did kick it over with the plug in, and spark was good.
Pretty sure it will start on the rollers
Have now removed the stator, stator and rotor look to be in good condition, and windings check out.
so next stage is to remove the head and check valves tappets etc i think.
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I had a similar problem, which turned out to be a faulty HT lead. If you've changed the coil (and presumably the HT lead) that would rule that out though. I have a compression tester that you could borrow (mind you though, you could probably buy one up for the same amount as return postage would cost).
Good luck with fixing the problem.
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another thought, have you bypassed the fuel tank and tap usinga new fuel pipe?
i had a BSA B40 which had a fuel pipe that collapsed on the inside. pushing it onto the carb caused the inner to crumple up, but when removed was fine!
bullet350
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thanks for the input guys...
Yup, the ht lead is part of the coil, and has been swopped out.....no change...
yes Bill, took the existing carbs off, and put on my trusty 40mm dellorto + manifold, fed from a plastic bottle on top.
.....no change
so tonight i have taken the rocker cover off, that looks ok on an initial inspection...tappets are in good nick and valve tops look ok.....next the head came off....and this too, at a quick glance is ok, though i will drop the valves ot and make sure the seats and guides are good.
This just leaves the barrel and piston, and i will say, the engine turns over SO freely, almost as if the rings wern't fitted...but the bore looks perfect.....will lift the barrel off tomorrow night..... then it's back to square one and re-check everything
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Aye SteveL,
Been on the road since Monday, so missed this scenario! :( Any luck? ???
This is me pondering after driving Totnes to Perth; so have you got a corroded connection or wire which breaks down under load. Sally had the earth wire from the coil which looked fine, but there was a crack in the insulation and the wire was covered in verdigre and near to breaking. Could this be a problem in one of the connection blocks with a bit of crap causing a short or not allowing the circuit to be 'made'? For it to be a gradual intermittent failure seems to be electricery rather than mechanical. The 'backfiring' would make me think spark timing, but again electrics!
Sorry, can't be more help.
My regards, Bill.
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OK...story so far....barrel off, bore looks good, but....with the piston at the half way point has a whopping great gap of over 50thou front or back....it is a short skirt wiseco 97mm...(50 thou is whopping isn't it?)
looks like piston 'rock' wear, also the oil rings seem to have lost their springyness, that is to say, barely protrude from the piston groove.
so....it's off for a rebore to 98mm, and new piston/rings/pin, clean the head up, reseat the valves, and start building it up again....
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Steve , Deja vu here old boy . Similar to the problems that have beset the Xs .3/4 will fire . 1/2 spark but won't run though spectacular backfiring from left hand silencer. Coils feed one pot on each side so not what I expected therefore not a coil. Petrol getting through , plugs are wet and black on 1/2.On top of this if the ignition switch is on or off the bike will fire .
I've stopped for the time being ,turning my attention to the running gear of the Rs .
Rob .
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Aye Steve,
Short skirt, same as was in Sally when bought, just not enough support or badly bored, honed and run in. That was a 634cc overbore!
Sorry to read of the expense. I hope you get it set up better this time.
All the best, Bill.
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Yep I agree that's a bit worn. When I was Toolmaking I used to rebore my own barrels and the rule of thumb was 3 thou per inch of bore! ;D
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Short-skirt pistons always have short lives. For a bike that will be used on the road, the skirt should be about as deep as the bore size.
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Steve , Deja vu here old boy . Similar to the problems that have beset the Xs .3/4 will fire . 1/2 spark but won't run though spectacular backfiring from left hand silencer. Coils feed one pot on each side so not what I expected therefore not a coil. Petrol getting through , plugs are wet and black on 1/2.On top of this if the ignition switch is on or off the bike will fire .
I've stopped for the time being ,turning my attention to the running gear of the Rs .
Rob .
My GPz was plagued by intermittent misfiring,particularly at low revs.The misfiring plugs were black.Fitting D8's instead of D9's stopped the misfiring,although it was still rough at low revs.Finally tracked it down to incorrect float heights on two cylinders.Adjusting the floats restored correct firing......
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Thanks Blew . I'll add that to the list of things to check .I'm going to start at one end and work my way back .
Rob .
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It's a bu55er!....rebore, new piston, valves lapped in nicely, reassembled today with particular attention to timing and valve clearances......the tw*t still won't start on the kickstart!!
will start quite easily on the rollers....warms up....and will tick over reasonably......but left at tick over, will die after a while....then just will not start when kicked......but will on the rollers.....we are thinking it is electrical, and john (the owner) has gone away with the wiring diag, and will go through the whole lot to make sure it's all ok....but basically will disconnect everything not immediately required (sidestand sw, kill switch, ign switch, charging circuit).....we had previously substituted a CDi unit and coil from my SRX with no change.....which leaves the generator stator and pickup assy.....anyone got a spare i can borrow?
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Aye Steve,
Can't promise as I've forgotten what and where! ::) However, if I get a chance after a visit to Weegie tomorrow, I'll go and have a poke about and see what I can come up with.
Cheers, Bill.
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thanks bill....would be much appreciated
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This commuting is exhausting, fell asleep in front of the stove after Scotch eggs, cauliflower cheese and chilli pickle, with pints of tea. Tasty. ;D
Promise will look in the morning and report by "End of play"! >:( Yuppie expression! :-X
Apologise if this screws things up, Bill. :-[
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Aye Steve,
Been through all of the 'stocks' and I very sorry to report a blank on these parts. I have a spare clutch case but no alternator ones and no stator either.
Sounds as though insulation breaks down, once heat builds up, but where? ??? Exasperating! >:(
I am sorry not to be more helpful.
My regards, Bill.
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Thanks for looking Bill......I have found a rotor/flywheel in my 'stock'.....so just need a stator....however, john has the bike back now, and is thinking that the carbs might be a problem, (cos he pulled them all apart and lost a rubber washer when re-assembling.....doh......wish he'd told me that before we started this saga....he also played around with a lot of the wiring.....?? )
So...anyone got basic settings for a pair of keihins (as fitted to BMW f650)??? pretty please :-)
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Aye Steve,
I have a pair of those, but can't do much until Friday night at the earliest.
Have you tried the 'Chaingang' F650 owners site for info? Try it below:
http://faq.f650.com/FAQs/Carb_Clean.htm (http://faq.f650.com/FAQs/Carb_Clean.htm)
Everything including the kitchen sink!! ;D
How do these carbs fit and perform on the SRX? I'm curious!
It's like being given a Duke engine with the shims in a jam jar, to "Keep the washers safe!" ::)
Going up the A9 tomorrow to Inverness with blizzard conditions forecast for the afternoon and at least 15cm snow with 40mph winds! :-\ Will report in on return.
My regards, Bill.
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thanks for that bill...will check it out.....
They work very well on the srx....just need an adaptor plate making up to accept the different screw locations of their manifold.... then, ideally a pair of airfilters.
safe journey Bill
Steve
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Aye Steve,
Bit of a fraud, not as windy and only heavy sleet showers. The gritters were chucking the brine solution about, so it could get worse tonight! However, we have some real good gusts at the moment and sleet at 100' above sea level.
Any serious increase in fuel consumption? Requirement to change jetting? I assume K&N 'pod' filters are fine?
Thanks for the info Steve and I'm sure the URL I posted, will answer the questions.
My regards, Bill.
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Yes Bill, K&N conical filters are used.....or a conical 2 in 1 with 5" straight strumpets between the carbs and filter.
I think john gets about the same as me (on twin dellorto's) and my blue #4 on standard carbs dynojetted....i.e. hard riding will get you to the bottom of the tank in about 120 miles.
Yes thanks again...I printed off all the guff from that website and gave it to John lunchtime today....give him something to read in bed tonight :-)
pip pip
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Thank you kindly Steve,
Mug of 'fortified' cocoa, then off to sheet alley!
Keep boppin', Bill.