OzVMX Forum
Clubroom => Tech Talk => Topic started by: Gippslander on May 21, 2011, 09:56:11 pm
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My 73 Husky CR250 starts first kick cold and runs for as long as you want -- say 30 minutes -- then pull up and stop and it will not restart -- no spark -- dead.
Questions:
Is this a common fault with Motoplat red wire coils?
Is there another coil that can be used or is it the original or nothing?
Thanks
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Tried another coil -- thanks Bendigo Dirt Bikes -- now has good spark when hot.
But still hard to start hot -- leave it stand 10 minutes after a hard 20 min run and it refuses to start -- the following are what I see:
1 - fuel in the carb -- pulled the 17 mm main bung and fuel in there
2 - timing correct -- marks line up -- drill bit goes into the "motoplat holes" at the correct place
3 - good spark at the plug
4 - good compression
5 - has new crank seals and has been running ok except for this hot start problem
BUT -- after a dozen kicks plug is bone dry -- so looks like a problem in the carby -- 38 mm Mikuni
try kicking with the choke on -- plug gets a little wet -- but still no "sign of life" :-\
Any suggestions?
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Have you tried a nother plug?
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Yep -- should have mentioned that -- tried a new plug -- sparked ok but no start.
I just think its the carby -- it's new and it has never been a good hot stater -- as said had spark prob's but those are fixed now so there could have been a carby prob' all along.
And I think the spark problem was a recent problem -- because about 6 weeks ago the bike decided to rev it's head off -- no idea why -- and I foolishly pulled the plug lead off but it dieseled and blew it's brains out -- new rod required -- and after doing a bit of reading I think the ignition system was damaged by 60 secs of flat out running with the plug lead disconnected.
The real problem is that I'm just blundering along -- I was a motor car mech' 32 years ago and have forgotten what I knew and never really knew anything about 2 strokes -- the Bultaco I had as a junior always went and I did nothing to it -- just reliable -- so this is all new.
I have a new 36mm Mikuni -- and "just for fun" I'm going to try that.
I'm wondering what the jetting will be compared to the 38mm -- presently the 38 mm carby has a 270 main and runs well -- chocolate coloured plug when I do a full throttle "plug chop" and with a 280 main it just "fluffs" a little at full throttle.
(I purchased every size main 200 to 430 and started at 430 and did 15 changes down to 270 before it ran right -- that took 2 Saturdays -- up around 400 it was so flooded I had to lie it almost upside down and kick it dry and there was a few times where I pushed it up the top of a 400m hill and roll started it down -- all part of the fitness training!!!)
I'll start with the same 270 but I cannot get my head around which way the main jet size will go when I go from a 38mm to 36mm carb -- ANY SUGGESTIONS on this?
Anyway I know "it's only" a hobby but startin' to get cheesed off -- have only got so much time to work on the bike and it's been 10 weeks now and I still can't get it right -- missed the first 2 rounds of Viper and if I cannot get it going will miss first round of Vic Classic Motocross next week :-\ anyway the wife "understands" -- today she said "wouldn't you be better just buying a new one" ;D and when I explained that they don't come new she said -- "Oh well your delayed comeback will give the other fellows a little more time in the sun" ::)
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Try running a earth wire direct to the coil from the ignition helps. I had this problem before and it turned out to be the motoplate.
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Try going larger on the pilot jet. May be a little lean when hot. This cured my hot starting problem on my 38mm Mikuni on the 500AE.
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OK -- the direct earth is a good idea -- an easy thing to try -- will do that tomorrow.
The pilot is already a 45 so that should be big enough -- but it's worth a try -- I have two spare 35 pilots so I will get the number drills out and work out what is a bit bigger than a 45 and drill out one of the 35s -- to try that -- will do that tomorrow.
(And I assume the size of the pilot jet is more the centre hole than the side holes)
Just tried the new 36mm Mikuni -- would not start -- gave a couple of bangs on one try -- and then kicked back once so I'm thinkin' timing etc' but that does not make sense because I've double checked that -- all ok -- only thing I cannot be sure of is that the flywheel I'm using is not the one that was "matched" to the stator I'm using -- but as said it started straight up this morning and ran really well and then when I was knackered I pulled in and after 10 mins it would not start again ???
Will try the earth first -- then the bigger jet -- fingers crossed ::)
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-- only thing I cannot be sure of is that the flywheel I'm using is not the one that was "matched" to the stator I'm using --
That matched to the stator thing caught my eye a while back when I was reading something.
I,ve got a couple of SEM,s here and while I was working on one I tried a different flywheel.
It did NOT fit, so I started measuring and sure enough the stators are all different sizes [ outside].
If the flywheel does not drag on the stator and the timing is right with a timing light then matching won,t come into it .
Just my view
Cheers Mike.
Ps . You havn,t got a leaky crankshaft seal or base/crankcase gasket because they will give you those symptoms.
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Another thing that's worth a try is, when it won't start hot or whatever, give it a shot of 'start ya bastard' up the carby.
If it starts with that it proves that you have spark.
It does not necessarily prove its the carby however, could be crankcase airleak or some other weired thing that happens to 2 strokes.
[Most people that can de-mistify 2 strokes are a bit odd]
cheers pancho
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Gipps,
A good way to check if pilot is to lean is to leave bike running when hot, click into neutral and allow to idle down for about 30 sec's then give the throttle a quick blip, if it bogs or hesitates right off the bottom before picking up revs again, your pilot is too lean. Although this is only accurate if your air screw is set right.
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Pancho -- I did give it a shot of start ya bastard -- no go -- so that's an indicator of no spark -- but it has spark when you pull the plug and hold it on the head and kick it over -- will try the earth wire tonight -- and it could be the seals and gasket -- have had it apart three times? in 8 weeks since they were new... ::)
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Pulled my 400 apart and it had been rebuilt but they had rolled the lip on the new inner seal [ behind the drivegear] .
That would have caused the problems you are talking about.
Very lucky I found it. :)
Another thought is the Make of spark plug.
I once put a Champion in a KTM to save money and it did that.
Would not fire when hot then was ok when cooled down.
Repco have Bosch plugs for $4.50 .
Just bought a bunch.
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using NGK plug? Tried a hotter new plug after 20min wait?
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Have just been able to get some time to look at the Husky.
Ran an "outside" wire from the coil to the engine -- bolted up tight each end -- started first kick ;D
So, I will run a proper wire from the motoplat backing plate to the coil -- a permanent one -- and will try again this Saturday.
Thanks for the suggestions/help -- much appreciated especially because I would not have thought of the wire.
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First thing this morning I had some time so I installed the permanent earth wire -- and the bike started first kick and run for a few minutes and then shut off and started again etc etc -- so it will be interesting to see what it does when it gets stinking hot when I try it out this Saturday morning but as said so far so good ;D
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And then it would not start hot today -- very weak spark -- so motoplat will go asap
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Penton Owners group EBay shop PVL landed in Aus is about $450.00, I like my bikes to start with a few kicks and this is the best fix I've found.