Bike stuttering at mid revs

[clabedan]

i initially thought it was something to do with carbs... So had a thorough clean, changed gaskets, checked the main jet size (140... I use pods and short megaton exhausts and the bike used to run well with this jet before)... Noticed the diaphragms were old and had small holes so ordered a brand new pair from jbm industries, convinced that I had finally solved a vacuum problem with the diaphragms...

Nope, the probleme remains

The bike starts on the first kick and idles very well... The problem comes at mid revs or a bit earlier. It stutters badly and won't go any faster as if starving gas.

I have noticed that the right hand spark plug is very wet and that the right exhaust is only warm when the left one is boiling hot... So there is definitely a probleme on the right side. Changed the spark plugs too but again, no difference.

Could it be the coil, the condensor, anything else ?
This is a very sudden problem, and I think I have checked eveything that could be checked with the carbs... So some part must have gone wrong all of a sudden...

Many thanks for your help if any of you has an idea...

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[TwoManyXS1Bs]

A bad condenser can do that. Two tests you could try are:

In a dark area, observe the ignition points.
Sparking and arcing in the points usually indicates a bad condenser.

Use a good timing light, as though you were timing the engine.
Uneven timing light flashes, skipped flashes, scatter (position of timing mark jumps about), can indicate bad condenset and/or failing ignition coil...

 

[clabedan]

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[clabedan]

Many thanks... Sounds like a good advice
Need to get myself a timing light first though



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[chizler62]

Quick thought comes to mind. Did you put a dab of bearing grease on the needle before installing and checking float height?

Lightly tap the sides of the bowls while its idling. If it doesn't change. Remove carbs. Dab grease on needles. Double check float height.

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[clabedan]

Quick thought comes to mind. Did you put a dab of bearing grease on the needle before installing and checking float height?

Lightly tap the sides of the bowls while its idling. If it doesn't change. Remove carbs. Dab grease on needles. Double check float height.

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Nope... i didn't know about this... You mean the fload needle (not the large slide needle)... Is there any reason for this? And does it have to be bearings grease (not sure where to get this from)

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[5twins]

Honestly, I've never heard of greasing the float needle. Fuel flows through the float needle and seat assembly so I don't see grease staying in there very long.

 

[chizler62]

Often times when reinstalling the fuel needle it has been cleaned and so has the seat and will get stuck or act sticky. Unseen to the eye, sometimes if wtore enough seen, there will be a ridge or groove on the needle and edge on the seat. All dry?
This system works well with the idea that fuel itself will lube the moving needle. So, until fuel is consistently running through assembly to lube it the grease helps.
Doesn't need to be a particular grease. I like the clear yellowish Yamaha grease that comes in a tube for the grease gun. Mobil makes it.

This is taught at every school I've been to. MMI,old AMI, FAST factory authorized Suzuki training. Hontec, Yamaha etc.



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[G_YamTech_314]

i initially thought it was something to do with carbs... So had a thorough clean, changed gaskets, checked the main jet size (140... I use pods and short megaton exhausts and the bike used to run well with this jet before)... Noticed the diaphragms were old and had small holes so ordered a brand new pair from jbm industries, convinced that I had finally solved a vacuum problem with the diaphragms...

Nope, the probleme remains

The bike starts on the first kick and idles very well... The problem comes at mid revs or a bit earlier. It stutters badly and won't go any faster as if starving gas.

I have noticed that the right hand spark plug is very wet and that the right exhaust is only warm when the left one is boiling hot... So there is definitely a probleme on the right side. Changed the spark plugs too but again, no difference.

Could it be the coil, the condensor, anything else ?
This is a very sudden problem, and I think I have checked eveything that could be checked with the carbs... So some part must have gone wrong all of a sudden...

Many thanks for your help if any of you has an idea...

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Did you check the spark wire itself? On my XS, the coils are right in front on either side, you can test amplified voltage to the wire by removing the spark plug cap on the plug side, leave the wire connected to the coil and back probe the wire, negative probe to negative battery post, positive probe to wire. Be sure to check it in DC volts, you need to do it with an amplified voltage meter, and a multimeter, or else you risk damaging yourself, and your tools.i but the bike (if it’s anything like a standard 650 of today’s caliber) should get a reading of at least 10k volts from the coil. You can test the coil this way too, if the pipe gets warm there’s probably at least a little bit of spark, so your wire could just be shot. I’m no expert, a diploma only makes me LOOK like a know it all.

I can share any classroom notes you want me to share with you on voltage dropping an ignition system. It wouldn’t hurt to refresh myself on it as well.

The only thing else it might be if spark isn’t an issue would maybe be if it’s recieveing too MUCH fuel, but given all the work you said you put into the carbs, I’d say fight it like a fire. Think of the problem, what’s connected to the problem, start at the tip of the flames and work your way to the root of it. If you’re not getting spark, check the plugs, unscrew them and leave them connected to the wire, ground the plug to the frame and crank the starter. Is there spark? If not, pull the plug, and screw it back in the cylinder head, next step is checking the wire, if that’s bad, the coil is either not connected, not grounded, or may be shot. Hope this helps.

 

[G_YamTech_314]

Probably not the most helpful, because I can’t remember what kind of bike this was for. If I had to guess, probably a gs500. But still, there are usually instructions in a manual as far as specs go for output voltage. EDIT... It was an ex500... close enough.

I’m also attaching a generic electrical spec document that I got while I was in school. It helps me a lot.

 

[650Skull]

OP hasn't been on the site since 19 march 2015............

 

[G_YamTech_314]

OP hasn't been on the site since 19 march 2015............

I know, I was sent here because someone wanted my opinion on it, I’m still trying to learn the best way to share info without posting directly to the thread. Oops... lol

 

[TwoManyXS1Bs]

That last pic, "general electrical specs", could be handy for others if the values were edited specifically for XS650s...