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Author Topic: Help bike won't run clean  (Read 4391 times)

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Offline steve7406

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Help bike won't run clean
« on: March 03, 2012, 08:14:55 pm »
I've just completed a rebuild on a rm125b problem is now it's hard to start and when i get it to run it's shit down low but sounds good up top. To get it started i have to use rp7.
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2000 Yamaha WR400f
1980 Suzuki RM250t
1977 Suzuki RM125b                                         
1975 Yamaha MX250b
1973 Yamaha mx360 (on the rebuild table)                                                               
1972 Yamaha dt1 250
1976 Suzuki ts 185

Offline smed

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Re: Help bike won't run clean
« Reply #1 on: March 03, 2012, 08:40:16 pm »
Was it running good before you rebuilt it or have you never had it running before? It may have been a pre existing problem with the carb or ignition :)
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Offline steve7406

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Re: Help bike won't run clean
« Reply #2 on: March 03, 2012, 08:58:33 pm »
Had it running prior and all seemed ok
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2000 Yamaha WR400f
1980 Suzuki RM250t
1977 Suzuki RM125b                                         
1975 Yamaha MX250b
1973 Yamaha mx360 (on the rebuild table)                                                               
1972 Yamaha dt1 250
1976 Suzuki ts 185

Offline smed

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Re: Help bike won't run clean
« Reply #3 on: March 03, 2012, 09:06:36 pm »
Top end rebuild or full motor,rebore, crank,mains etc,more details will help ,If you had not said it was rebuilt i would have said low compression needing a spray to get to run :)
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Offline steve7406

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Re: Help bike won't run clean
« Reply #4 on: March 03, 2012, 09:16:52 pm »
Sorry top end only seems to have plenty of comp had the carby apart aswell
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2000 Yamaha WR400f
1980 Suzuki RM250t
1977 Suzuki RM125b                                         
1975 Yamaha MX250b
1973 Yamaha mx360 (on the rebuild table)                                                               
1972 Yamaha dt1 250
1976 Suzuki ts 185

Simo63

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Re: Help bike won't run clean
« Reply #5 on: March 03, 2012, 09:17:27 pm »
God it could be a range of things particularly after you've rebuilt the motor.  Back to basics first though, spark, fuel and air .. got all those three absolutely sorted??  You're sure?

Other simple things such as carby adjustment, kill switch shorting out, blocked intake or exhaust system .... got all those right?  Again, are you sure?

If so then move onto more complex things that might be associated with the rebuild or maybe something to do with the removal/installation process (eg ignition wiring)

Can you phone a friend?
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Simo63

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Re: Help bike won't run clean
« Reply #6 on: March 03, 2012, 09:18:23 pm »
Quote from: steve7406 on March 03, 2012, 09:16:52 pm
Sorry top end only seems to have plenty of comp had the carby apart aswell

I could edit my other post but you've had the carby apart as well?  What did you do to it?  Exactly?
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Offline smed

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Re: Help bike won't run clean
« Reply #7 on: March 03, 2012, 09:26:44 pm »
Yeah all what Simo63 said plus reed valve,if they have one I am not familiar with that model :)
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Offline steve7406

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Re: Help bike won't run clean
« Reply #8 on: March 03, 2012, 09:32:14 pm »
Checked all those things all i did with the carby was dismantell clean and put back together.
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2000 Yamaha WR400f
1980 Suzuki RM250t
1977 Suzuki RM125b                                         
1975 Yamaha MX250b
1973 Yamaha mx360 (on the rebuild table)                                                               
1972 Yamaha dt1 250
1976 Suzuki ts 185

Simo63

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Re: Help bike won't run clean
« Reply #9 on: March 03, 2012, 09:38:13 pm »
Quote from: steve7406 on March 03, 2012, 08:14:55 pm
I've just completed a rebuild on a rm125b problem is now it's hard to start and when i get it to run it's shit down low but sounds good up top. To get it started i have to use rp7.

Okay so to go back to your original post, it runs well up top but just not down low ... so I would be looking at the carby and or the case reed that motor has ....

Carby - remove and dismantle again to see id you've left out the low speed jet .. or did you move the needle, or adjust the float level to high ... or play with the air screw (should be around 1.5 turns out as a start point)?

Reed valve - did you do anything to the reed valve screwed into the bottom of the cylinder? 

Maybe the spark plug is fouling down low .. try a new plug .. sometime (if you are lucky) it's the simplest things.

I'll check back in 20 minutes .. that should be the time it takes to remove and check the carby.

Or is it too late to be starting it where you are?
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Offline steve7406

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Re: Help bike won't run clean
« Reply #10 on: March 03, 2012, 09:42:48 pm »
Thanks getting late i think i will start back at square one tomorrow.
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2000 Yamaha WR400f
1980 Suzuki RM250t
1977 Suzuki RM125b                                         
1975 Yamaha MX250b
1973 Yamaha mx360 (on the rebuild table)                                                               
1972 Yamaha dt1 250
1976 Suzuki ts 185

Simo63

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Re: Help bike won't run clean
« Reply #11 on: March 03, 2012, 10:02:17 pm »
Quote from: steve7406 on March 03, 2012, 09:42:48 pm
Thanks getting late i think i will start back at square one tomorrow.

No worries, I'm packing for our 4 day conference so will stop checking back and get on with the job  ;)  The wifes' just stressing me out .. should Ipack this or should I pack that .... standard answer from me "you look great in anything you wear (and she does)" but she doesn't listen I think  ;D

Good luck with it .. likely to be something simple so don't sweat it.
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Offline PRITCH39

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Re: Help bike won't run clean
« Reply #12 on: March 03, 2012, 11:05:51 pm »
I bet it is the stator, I had the same problem with my RM250A. The bike was running fine, pulled it down for a freshen up, new piston/rings clean carb fit new boyesen reeds etc. put it back together and the bike was hard to start, pulled the barrel off pulled the carb appart put different piston in put standard reeds back in, still no good wont run cleanly has no power. At this stage I am about to set fire to the peice of shit. I decided to have the stator rewound and tested and hey presto the bike starts first kick now and has shitloads more power than ever before. The bloke that rebuilt the stator reckons he hears this story all the time, apparently the new compression put the flame out if the stator is a bit tired.

If you are in brisbane you can borrow my stator to test if you like, they might be the same.

Brian
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Offline lukeb1961

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Re: Help bike won't run clean
« Reply #13 on: March 03, 2012, 11:29:53 pm »
yeah, I'm betting on stator coils too. They are 35 years old, remember...
A mate in the UK went round the twist testing/replacing everything until.. the pulsar coils. Now has huge fat spark, instant starting and roaring performance.

try someone like Small Coil Rewinds http://www.smallcoilrewinds.com.au/

Luke
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Offline holeshot buddy

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Re: Help bike won't run clean
« Reply #14 on: March 03, 2012, 11:40:48 pm »
 is piston in right way around ???
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