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RhysWithTheXVS

Xvs 125 starting problem?

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Hi all, I'm new here so apologies if I've posted this wrong, but I was wondering if anyone had any advice for me? 

My 125 dragstar has recently been playing up just after starting making it hard to get it running. it'll start okay, but then on giving it any throttle the front cylinder will bottle out and stop firing properly. this is a consistent problem and I've tried to remedy it by changing the sparks, oil, and a few other things, but none have seemed to work. 

It might be useful to say I changed the pipes to straight throughs when I got it and the mixture leaned off due to the decreased back pressure, but I rejetted the carb which fixed the problem- but now my front exhaust is blowing a little due to faulty studs of which I am waiting for new ones. could this be part of the problem?

The bike also looks like the rear cylinder had been replaced before I bought it (I've only had it 9 months); it just looks newer to me. is this something I should be worried about, like was the previous owner trying to fix a problem that has only just started to affect the front cylinder, causing me to have to replace it? 

Sorry for the lack of info on the problem itself, I'm not very experienced at mechanics yet, having only a year of riding experience, but I'd really appreciate some insight from someone more experienced than myself. thanks!

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Hi...I would say the first things to establish is whether it is losing its spark,its fuel or its compression.Put a spark tester on the front plug and check spark whilst attempting to run it,if losing spark work back through cap,lead,coil,cdi etc.If still sparking , check inlet manifold,is the rubber split and leaking?(means mixture to front is too weak)...it is a common problem...if all ok you need to do a compression test...the two cyls should be roughly equal,if the front is down put a squirt of oil in and try again..if it comes up dramatically then its a front cyl strip down to find the problem.

Good luck

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Didn't it run ok before you fitted the straight through pipes and re jetted? 

If so then this problem is something that you have given it. Most likely you have re jetted wrong and she is running too rich and is bogging it down.

the rear cylinder will look in better condition to the front as it is protected by the front pot and your legs so doesn't get nearly as much shit n crap from the road. The only way your know if it is a new pot is by taking it apart and checking the tolerances.

 

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Thanks guys! I've just checked inlet and looks fine, I doubt it is sparks because once the bike warms up the problem tends to go, but it's next on the list to check so we'll see I guess. as with compression, as I say I'm not massively mechanically minded so I'll have to look up how to do it, and possibly take her in just to make sure. my guess is that it is just mixture, but it is only a gut feeling so I'll reseal my exhaust to make sure I am getting the same back pressure as the rear cylinder and see if it the problem is still there. if not I'll keep checking! I really appreciate the help, and I'll post an update as soon as something interesting happens. :)

Okay I've looked up compression testing, looks simple enough I just need to find someone with the gauge- I'll update with results soon :)

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1 hour ago, RhysWithTheXVS said:

Thanks guys! I've just checked inlet and looks fine, I doubt it is sparks because once the bike warms up the problem tends to go, but it's next on the list to check so we'll see I guess. as with compression, as I say I'm not massively mechanically minded so I'll have to look up how to do it, and possibly take her in just to make sure. my guess is that it is just mixture, but it is only a gut feeling so I'll reseal my exhaust to make sure I am getting the same back pressure as the rear cylinder and see if it the problem is still there. if not I'll keep checking! I really appreciate the help, and I'll post an update as soon as something interesting happens. :)

Okay I've looked up compression testing, looks simple enough I just need to find someone with the gauge- I'll update with results soon :)

I had problems with compression twice, low compression doesn't go away once the engine is warn, but on my bike the low compression caused the engine to stumble a little for about 30 seconds untill it had warmed up if you tried to rev it.

I find that when problem solving the most likely and simplest thing is usually the cause of the problem, in this case you mucked about with the piped and carbs and now it doesn't run right, so it's probably that. Replace that defective stud so the pipes make a good seal, put the stock jets back in and go up in SMALL integers from there, you can usually get a kit with a selection of jets off ebay. Keep in mind:

  • With correct air/fuel it should be easy to start (rovideed there are no other issues)
  • Spark plugs should be a good colour (you can find a spark plug chart on Google or in the back of a haynes manual)
  • A lean engine tends to run rather hot and will throw much more heat onto you as you ride
  • A rich engine doesn't run as hot but will stumble, or in extreme cases even smoke a little
  • A lean engine will stumble when you try to rev it up, might stumble more when cold

How did you check the intake rubbers? The best way is to spray something like carb cleaer onto them whilst it's running and listen for changes in engine pitch that will indicate the solvent is getting in, Sometimes the intake rubber can be perfectly fine but the seal to the engine or around the carbs/filter can be bad.

And one last thing, you said you have straight pipes, and bigger jets, but what did you do to the air filter? You have more exhaust flow, and more fuel, but do you have more air? It could be an issue of restricted air flow  and it not getting enough air instead of too much.

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Again, did this problem start after you fitted the new pipes???? no point confusing yourself with compression tests and wasting money on test gear if it ran fine before you fitted the pipes as this proves that there is nothing wrong with compression to start with.

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I have a mate with a compression tester, so I might as well give it a test to make sure all's okay anyway seeing as it's pretty simple to do, but I see what you mean. I have a feeling now that it is the blowing exhaust as the other cylinder is running fine and has never really been a problem. once I get it fixed hopefully there will be a little back pressure and it might balance out. If not, I will have to go back to original jets and work my way incrementally. I have a feeling that it's rich, now you say that, as it's smelling a little and occasionally smoking. once the seal is fixed, I will let you know how she's behaving :) thanks for all the wisdom!

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Out of curiosity what was the size of the standard jet you took out and what size did you put in? 

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