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ViragoTechForum.com Tech Help Really Strange Problem With 2005 Virago 250 [SOLVED]

#1:  Really Strange Problem With 2005 Virago 250 [SOLVED] Author: lub997 Post Posted: Fri Apr 09, 2010 3:36 am

I am having a really strange problem with my 2005 Virago 250. I started it up last winter on an extremely cold day and it didn't seem to be running quite right and I figured it was just because of the cold as it usually takes a long time to warm up unless it is 90 degrees outside, which it of course wasn't, so I rode it anyway and it did not get better as it warmed up and I ended up completely losing all power about 20 miles from home and had to ride it home going 10 miles per hour on the side of the highway because that was all the power it had. It was still running though. Upon getting it home and inspecting it I noticed that I could hear a strange noise as if the cylinder were opened up and I could hear the inside of the engine. It was a sound a lot like the sound that happens if a spark plug comes out on a car engine while it's being driven if anyone has ever heard that noise. I also noticed that the plastic intake manifold was getting some pretty bad cracks in it, so I figured that was likely the problem as that explains both power loss and being able to hear the inside of the motor. So, I ordered a new intake and put it on, only to find that now it would not run at all, so I checked the compression and the rear cylinder had wonderful compression, but the front cylinder had very low compression, so I took it apart and figured out that the exhaust valve was bent, so I got that replaced and got the valve seat machined and it was still low on compression, but was able to run now. It would only run on the rear cylinder though. The front was still not working. I could tell this because if I removed the spark plug wire on the front cylinder it made absolutely no difference in how the engine ran. It was clear that it was only running on the rear cylinder. The rear cylinder appeared to be running quite well though. So, I took apart the front cylinder again and found that the intake valve was also ever so slightly damaged, and it was enough that it was affecting the compression, so I replaced the intake valve too, and put it all back together, and even cleaned the carb and replaced the air filter and the spark plugs just for good measure, and now the front cylinder runs wonderfully, but the rear cylinder appears not to be running. The front cylinder warms up, but the rear cylinder feels cold to the touch and if you remove the spark plug wire on the rear cylinder now, it seems to make no difference in the way the engine runs, as if it is running only on the front cylinder now. This makes completely no sense since I changed nothing about the rear cylinder which was originally running great. I have checked the spark on both cylinders, the timing on both cylinders (both the marks on the cam gears and at the viewing hole on the magneto), adjusted the valves on both cylinders, it has to be getting air and fuel or the front cylinder wouldn't be running. I have even tried removing the fuel tank and seat to inspect all the wires to make sure none have any bare spots grounding out on anything, and none were. It has all of the elements that are supposed to make an engine run, spark, timing, compression, fuel, and air, and yet it is only running on one cylinder which makes no sense as the one that appears not to be working is the one that was running perfectly and I changed nothing about it. Currently the compression is wonderful in both cylinders, it still appears to be running on the front cylinder only, idles wonderfully, and dies if you give it any gas, even if you adjust the choke. I wouldn't think it could be a carburetion issue as it has one shared carb that is split off to both cylinders by the intake manifold, so if the carb is working well enough to run one cylinder logically it ought to be working well enough to run the other cylinder as well. I am out of ideas, and would like to hear any ideas anyone else might have.

Last edited by lub997 on Sat Apr 10, 2010 8:47 am; edited 1 time in total

#2:   Author: grazingazer Post Posted: Fri Apr 09, 2010 7:40 am

something caused that exhaust valve to bend...have you checked your cam timing?

#3:   Author: totallyredvirago Post Posted: Fri Apr 09, 2010 7:56 am

both valves bent! wow. did you look at the piston to see if the valves kissed it?
you replaced the front intake. did you replace the rear also?
check 12v power to the coil.. maybe just maybe the rear coil may not be plugged in.. it is something you did on the second time you removed the head.. go over all. even the stuff you did not touch..
i know when i do 1 thing to the front or rear. i remove or unplug something that has nothing to do with what i am working on. (to make room to remove something).
....dan

#4:  Re: Really Strange Problem With 2005 Virago 250 Author: lub997 Post Posted: Fri Apr 09, 2010 6:23 pm

Quote: something caused that exhaust valve to bend...have you checked your cam timing?


Yes, the cam timing is perfect on both cylinders at this point. You actually can't remove the head to replace the valves without having to readjust the cam timing when you put it back together, so that was adjusted on the front cylinder when the head was repaired and put back on. I also checked the cam gear on the rear cylinder to make sure it was timed right too, and it is, but I did not make any changes to it.

Quote: both valves bent! wow. did you look at the piston to see if the valves kissed it?
you replaced the front intake. did you replace the rear also?
check 12v power to the coil.. maybe just maybe the rear coil may not be plugged in.. it is something you did on the second time you removed the head.. go over all. even the stuff you did not touch..
i know when i do 1 thing to the front or rear. i remove or unplug something that has nothing to do with what i am working on. (to make room to remove something).
....dan


Yes, I did look at the piston to see if it had any cracks or other damage and it looked fine. The front cylinder also has wonderful compression and runs perfectly now, and that would not be possible if the piston were damaged. No, I did not replace anything on the rear cylinder since it had wonderful compression and was running wonderfully before I fixed the front cylinder. It still has good compression. I got out a multitester today and tested the voltage going to the coil for the rear cylinder and it is not 12 volts. It is 10.85 volts, but I also checked the coil for the front cylinder which I know is good, and it is getting the same voltage, 10.85 volts, so both coils are getting consistent voltage. The battery has slightly more than 12 volts. I went over all the wiring again today, too and don't see anything disconnected or bare. Am still looking though.

#5:  Re: Really Strange Problem With 2005 Virago 250 Author: bikermike Post Posted: Fri Apr 09, 2010 7:12 pm

Is it possible to set the timing for the front cylinder correctly and be 180 degree off on the other ?

#6:  Re: Really Strange Problem With 2005 Virago 250 Author: lub997 Post Posted: Fri Apr 09, 2010 7:51 pm

Quote: Is it possible to set the timing for the front cylinder correctly and be 180 degree off on the other ?


I'm not sure. I was kind of starting to wonder that myself.

I have some new information though, and it is starting to look more like possibly a carburetion issue. After inspecting all the wiring again and not finding anything wrong, I got the rear cylinder to run by itself with the spark plug wire off of the front cylinder by spraying some starting fluid in the spark plug hole on the rear cylinder. It then stayed running, but would just barely idle and adjusting the choke even the slightest bit in either direction would cause it to immediately die, and then it would restart though as long as the choke was returned to its position that it had been in, and giving it any gas killed it. Then I hooked up both spark plug wires and it ran slightly stronger, but still dies when any gas is given to it or when the choke is adjusted at all even the slightest bit. What's so odd is that the front cylinder seems to be running a lot stronger than the rear one, and I don't understand how if it's a carburetion issue they can run differently with a shared carb and intake manifold.

#7:  Re: Really Strange Problem With 2005 Virago 250 Author: lub997 Post Posted: Sat Apr 10, 2010 1:43 am

Does anybody know if a bad fuel pump could cause those symptoms? I took off the carb and intake manifold and looked over them to see if I had made any mistakes when I cleaned the carb, but everything looked fine. When I got done reading the section in the service manual about rebuilding the carburetor, though, I noticed that it also had a small section on testing the fuel pump, so I did what it said to do to test it, and it failed the test. It said to put the fuel petcock in the 'on' position and push the starter button and see if anything comes out of the hose from the fuel pump to the carb, so I did that, but almost nothing came out. That would possibly explain why it can idle, but can't do anything else. Maybe it has just enough fuel to idle, but is not getting enough fuel to accelerate. It appears to be a mechanical fuel pump, because there are no wires going to it, and I don't quite understand how it works yet, but luckily I have the service manual, so maybe that will help. Going to try rebuilding it following the instructions in the service manual and see if that makes any difference in the way it runs.

#8:  Re: Really Strange Problem With 2005 Virago 250 Author: lub997 Post Posted: Sat Apr 10, 2010 5:40 am

Re-tested the fuel pump with the carb and intake manifold and spark plugs all in place, and it passed the test. Looks like it runs off of engine compression, and that is why it failed the test with the intake and plugs off. Now I am chem-dipping the carb to see if maybe that will clean anything I couldn't get to before with the spray carb cleaner. Seems like it is getting a lean mixture because it will still only idle with the choke halfway closed. The only explanation I can think of is a blocked jet causing not enough fuel to be in the mixture and too much air. Still dies on acceleration no matter where the choke is positioned.

#9:   Author: lub997 Post Posted: Sat Apr 10, 2010 8:47 am

SOLVED :)

The chem dip did the trick. I took apart everything in the carburetor just as I did last time I cleaned it, but this time removed anything rubber or plastic (because chem dip will dissolve it) and soaked everything metal in the chem dip for about an hour and then still cleaned it with spray can carb cleaner also after it came out of the chem dip, and put it back together, and it runs perfectly now. I took it for a test ride and there was absolutely no hesitation at all, and the choke issue also seems to be completely resolved. Ran and rode beautifully, and had plenty of power. The only thing additional I cleaned this time that I didn't clean the first time was the 'pilot air jet' located on top of the carburetor where the carb hooks up to the air cleaner system. I didn't know it was removeable, but this time I noticed that the manual said to remove it, so I did, and it had a passage behind it that I sprayed compressed air through. I don't know if it was that or the chem dip, but one out of the 2 fixed the problem if anyone else has this problem in the future.

#10:   Author: lub997 Post Posted: Sat Apr 10, 2010 8:49 am

Thanks to everyone who offered suggestions and ideas!

#11:   Author: grazingazer Post Posted: Sat Apr 10, 2010 9:58 am

the cam timing has to be adjusted starting at the rear cylinder
ViragoTechForum.com Tech Help Really Strange Problem With 2005 Virago 250 [SOLVED]


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