Par62003 Posted November 8, 2013 Posted November 8, 2013 Hi all, I bought a 1979 DT 175 back in the summer, was told it had had a rebore and new piston, first ride and piston holed ! Damn. Anyway, took it apart, and replaced the piston and rings with new, back together and nothing, well not quite. When I first tried to start it it fired and ran for about 10 secs, since then zilch ? All it does is the occasional backfire ? There is fuel in the bowl. The piston is in the right way. The carb has been cleaned both manually with a guitar string pushed through all the holes then ultrasonically. I did a compression test the result being 100 psi cold which I don't think is too bad considering the rings are new and haven't had the chance to heat up yet. There is spark at the plug but on removing, it is bone dry. I'm stumped, I've had dozens of bikes over the years, worked on them all myself but this little "simple" DT has me flummoxed ??? Any help would be most appreciated, cheers, Wayne.
slice Posted November 8, 2013 Posted November 8, 2013 HI Wayne, if the plug is dry then there is no fuel getting through, don't matter how much you clean it if it's blocked you have to do it again. Pour some fuel down the inlet and see if it runs if it does there's your problem solved. Use some EASY START and squirt it under the throttle slide, just a quick squirt will be all you need to see if the problem is the carb.
Par62003 Posted November 8, 2013 Author Posted November 8, 2013 Thanks for the reply Slice I'll give that a go.
earthmover Posted November 8, 2013 Posted November 8, 2013 Might have a spare carb for that, with all new jets in it if you're stuck. Mark
Moderator DirtyDT Posted November 8, 2013 Moderator Posted November 8, 2013 As slices answer really.Plug out. A little 2 stroke in the plug hole. With the plug still out kick it over a couple of times. Pour some fuel down the plug hole, plug back in and try again. If you have compression and a spark the only other thing you need is fuel, delivered at the right time. If the plug is dry I would investigate fuel first. If the plug was wet then I would also look at timing.
Par62003 Posted November 8, 2013 Author Posted November 8, 2013 Cheers guys I'll try when I get home in a couple of hours, thanks for the help.
Moderator DirtyDT Posted November 8, 2013 Moderator Posted November 8, 2013 Another thing is to try the above with the fuel cap off. Sometimes the fuel cap gets a blocked vent which can make it difficult for the fuel to be sucked into the carb. Once running, the vacuum caused by the piston does the job and sucks the fuel and the symptoms are more prevalent during a cold start.
Par62003 Posted November 8, 2013 Author Posted November 8, 2013 The plot thickens ! I did as advised I poured a little petrol down the carb and a little 2 stroke oil down the plug hole, still nothing. Two other problems have appeared since yesterday, the idiot lights in the clocks have stopped working ? No neutral light, no oil light, the horn, brake light and main lights still work though ? Also when turning the engine over it sounds a bit grindy, for want of a better word. When I put the new piston in it was a silky smooth movement, now not so ? Obviously when the previous piston was holed there was the alloy debris everywhere and I cleaned it all up except any that had made its way down into the depths, is that now what could be causing the grinding ? One more thing, the pipe from the tank to the carb has an inline filter, when it's connected to the carb no petrol flows down however when I pull it off the petrol pours out ? Strange indeed. Thanks in advance for any help, this bike is proving a real battle !
Moderator DirtyDT Posted November 8, 2013 Moderator Posted November 8, 2013 The fuel sounds like the jet isn't opening or the floats are stuck and not allowing fuel into the carb. have you a bowl plug or screw you can undo to see if the fuel is filling the bowl? That said, that sounds like the least of your troubles, Grinding!!! barrel off time I think or you will knacker the rebore. You need to get into the top end to sort that out.
Moderator Airhead Posted November 8, 2013 Moderator Posted November 8, 2013 you should have stripped the engine, all that molten piston is in the bottom end and the crank bearing races are open inside the crankcase, of course you'll have grinding noises!
earthmover Posted November 8, 2013 Posted November 8, 2013 Oops! That really doesn't sound good, but at least it didn't start! Mark
slice Posted November 8, 2013 Posted November 8, 2013 The fuel filter is usually a one way thingy, it might be the wrong way round, take it off and turn it round see if that makes a difference.
Par62003 Posted November 8, 2013 Author Posted November 8, 2013 Fuel filter is definately on the right way. I didn't realise that a holed piston meant a complete engine out and full strip down, oops, probably beyond my mechanical capabilities and there are no shops around here that would take it on Anybody want to buy a poorly DT ? Taxed and mot'd one careful owner
Moderator Airhead Posted November 8, 2013 Moderator Posted November 8, 2013 Fuel filter is definately on the right way. I didn't realise that a holed piston meant a complete engine out and full strip down, oops, probably beyond my mechanical capabilities and there are no shops around here that would take it on Anybody want to buy a poorly DT ? Taxed and mot'd one careful owner to save work you could be forgiven for taking the motor out, removing the barrel/piston and pouring diesel/gas oil into the casing and swishing it all about and emptying quickly...a couple of times until no more debris is evident, some may frown upon this but not everyone is able to strip and build engines. This would be best done though before any further running and you've already done that. you would get a feel for roughness in the bearings by turning the magneto rotor by hand and supporting the con-rod with your other hand? 1
nayruf Posted November 8, 2013 Posted November 8, 2013 to save work you could be forgiven for taking the motor out, removing the barrel/piston and pouring diesel/gas oil into the casing and swishing it all about and emptying quickly...a couple of times until no more debris is evident, some may frown upon this but not everyone is able to strip and build engines. This would be best done though before any further running and you've already done that. you would get a feel for roughness in the bearings by turning the magneto rotor by hand and supporting the con-rod with your other hand? If there are no reasonable bike shops who can carry out the work in your area and you do not feel confident in splitting the casings. Are there any karting clubs in your area? (maybe 'Hooten Park' Kart club, The 175 engine is a favourite for kartists, I bet there will be a kart club member who would split your casings if you were to take the engine to them. my DT holed a piston year before last and the main brings got clogges up with debris from the melted piston, once the crank assy was removed I cleaned the debris from the big end brg and reassembled the motor with new main brgs and new crank seals, the motor has now covered a fare few miles since so all is not lost for your motor,
earthmover Posted November 9, 2013 Posted November 9, 2013 Hi Wayne, Sent you a message yesterday, did you see it? Mark
Par62003 Posted November 9, 2013 Author Posted November 9, 2013 Just seen your message Mark and replied, cheers.
Recommended Posts