Thornhorn Posted May 3, 2013 Posted May 3, 2013 1st of all I would like to Thank the forum for all the great info and experience shared. 5 months ago I bought myself a beautiful litle beast. But from the first day I felt that it lacked of power and subsequently top speed. Driving it home it strugled to reach 50 and I blamed the wind. With the with the wind on the back it would reach 60 but it would scream like a 12yo on a JB concert. Following some Mods that I read here on the forum I decided to increase the front sprocket to find that it had a 13 teeth sprocket installed ( explains the high revs) so I decided to install a 14 teeth one but no power to pull the bike. Screaming at 50 in 4th gear and dying in 5th. To try to fight this I have installed a 97.5 jet, regulated the income valves to .09, cleaned the air filter, replaced the oil with castrol racing 10.40, replaced the clutch discs, battery, spark plugs (litium or whatever they are called ) and the carburator manifold..... no change I'm now as when I started but with less 400 quid in my pocket..... I'm sorry for the essay but it went from a dream to a nightmare if someone can share a light it would be well appreciated.
EazyDuz Posted May 3, 2013 Posted May 3, 2013 My GZ125 had the same level of performance, its a heavy 125 cruiser, don't expect any more from it. Treat 5th as an overdrive gear, used only on flat or downhill roads with little if any wind.
Iceni Posted May 3, 2013 Posted May 3, 2013 I've just been given an XV 125 and am pretty up to date on the forums for these bikes atm. Firstly I have no idea about the Irish XV restrictions. The UK model has none, But the Irish one may still have restriction in place set by Yamaha. Check your exhausts. There is a restrictor ring that may be in place. Check your Inlet splitter (rubber part under tha carb) the 125 has a rescticted inner. And check the seal on that part. A leaking manifold will cause you to run increasingly lean as the bike gains revs and pull more air. I take it you have picked up the power up guide available on another forum. It goes into detail about jetting, Carb settings and generally getting more from these engines. I suspect you have a problem with the engine if it revs freely but gives no power. I would sugest looking at your valves first. They may have weak springs, poor tappet adjustment, or have a seating issue. Your valves may not present themselves as a problem because the engine seems to be running well. But even a slight leak will cause the engine to loose a lot of the top end, whilst seeming good at the bottom end of the revs. You can test the valves using a cheap compression testing tool. http://www.amazon.co.uk/dp/B0001K9TV0/ref=asc_df_B0001K9TV013080721?smid=A3P5ROKL5A1OLE&tag=googlecouk06-21&linkCode=asn&creative=22206&creativeASIN=B0001K9TV0 I've already had my xv125 over 55MPH with a failure on the manifold. I'm a reasonably normal build 12 stone. Also how much added weight does the bike have. Boxes, sissy bars, chrome addons all slow the machine. The best after market addon is probably a fly screen. It'll keep the wind off your chest and reduce the wind resistance your own body gives I plan to add one to mine. Have you checked your rear sprocket? If for some reason that has been made larger it will reduce your top speed and give more acceleration. The previous owner already made adjustments to the front sprocket so checking the rear is a good plan. I think the standard rear is 47 teeth I'll count mine for you tomorrow.
Thornhorn Posted May 3, 2013 Author Posted May 3, 2013 Wow!!! Thanks for the quick replies, I've replaced the manifold and checked the exaust so no restrictions there. Also the high rev and low top speed was with the small front sprocket. Now it doesnt achieve high revs on 5th (it can barelly keep with 5th). There was something I noticed when adjusting the valves clearance, as I didn't remove the plugs, while moving the crankshaft I could here the compressed air escaping trough the timing sprocket case. Is this normal? Should i be able to rotate a crankshaft without removing the sparkplugs?
Thornhorn Posted May 3, 2013 Author Posted May 3, 2013 Also Iceni, did you notice on your Drag that you get a lovely deep sound on your front cylinder coming out from the exaust and a not deep at all from your back cylinder? Eg that they sound very different?
Iceni Posted May 3, 2013 Posted May 3, 2013 No both of my cylinders sound the same. I think you should do a compression test for sure. Should i be able to rotate a crankshaft without removing the sparkplugs Depends on the engine, On a single cylinder engine you should be able to rotate to the compression stroke then it will be almost impossible to roll past that going by hand. On the twin you should struggle to get it past the compression stroke on either cylinder. You have to remember that you have 2 compression strokes to deal with and you may get a false feeling if your on the wrong stroke. As for the air escaping from the timing cover, If the cover was open then you should be able to feel air escaping. This is normal as the pistons have an effect on the bottom of the engine as well as the top where combustion happens. That internal pressure should not be escaping Via the timing cover tho. It should be going out of the crank breather located at the back of cylinder 2. That noise should also not sound like compressed air. It should be more like a subwoofer pounding. If you can hear a hiss it is probably a faulty head gasket and the leak is not comming from the timing cover. You can test this with some soapy water, Put a good squirt of washing liquid in a bucket then brush the mixture on the engine with it running.... Bubbles are bad.
Iceni Posted May 3, 2013 Posted May 3, 2013 On your compression test both cyliners should show about the same level of compression. A slight difference is common. You should see between 130 and 150 PSI on the meter depending on the engine. If the compression is lower than 125PSI then you need to look into the problem. A cold engine will also show more air leak than a hot one in most situations... Metal expands and closes the cylinder head gap a little.
neversaydie Posted May 4, 2013 Posted May 4, 2013 Id be tempted to fit standard sized sprockets, get the bike back to original and check performance. Same with the jets.
Thornhorn Posted May 4, 2013 Author Posted May 4, 2013 Done that neversaydie, 14 on front and 47 on back. Still no strength to use 5th. Just went to a local garage today to make a pressure test 5bar on front and back cylinder when it should be 11. Makes no sence will go to a different one on Tuesday.
Iceni Posted May 4, 2013 Posted May 4, 2013 If the static compression test was as low as that I would ask them to do a Leakdown test. It's similar to the compression test. They put each cylinder at TDC then pressure the cylinder to a set value and see how long it takes to drop. I'll see if I can find my compression tester and do the test on my own engine. It's only done 2K miles so it should give you a decent comparison. The lower value of the compression test may be because the engine has valve overlap. Where valves are still open at the start of the compression stroke. I don't have the information about this engine to know if it runs with an overlap I would suspect it shouldn't. 5 bar is very low. Thats similar to the compression I would expect to see from a lawn mower engine. It's enough to run, But it's not optimising the thrust of the engine to get more pop out of the fuel. I also want to hear the results of the soapy water test. It's a very direct test and will give you a 100% problem to fix rather than the compression test that tell you that there is a problem somewhere in that region! Edit found my tester but it needs an adapter for the bike. It only has 18mm and 14mm fittings. As soon as i get the adapter I'll give you the readings.
neversaydie Posted May 4, 2013 Posted May 4, 2013 Done that neversaydie, 14 on front and 47 on back. Still no strength to use 5th. Just went to a local garage today to make a pressure test 5bar on front and back cylinder when it should be 11. Makes no sence will go to a different one on Tuesday. Standard front sprocket is 16 teeth, cant remember the rear, Id double check that 47 too
Thornhorn Posted May 5, 2013 Author Posted May 5, 2013 Your right 16 /59 and I was sold the bike with 13/47..... wich makes me believe that I was sold a almost dead bike....
neversaydie Posted May 5, 2013 Posted May 5, 2013 Your right 16 /59 and I was sold the bike with 13/47..... wich makes me believe that I was sold a almost dead bike.... No wonder it was revving its nuts off Id be tempted to try to get it back to standard then assess better whats reqd. Still got the stock exhausts on?
Thornhorn Posted May 5, 2013 Author Posted May 5, 2013 No wonder it was revving its nuts off Id be tempted to try to get it back to standard then assess better whats reqd. Still got the stock exhausts on? Yep.
neversaydie Posted May 6, 2013 Posted May 6, 2013 then Id be inclined to put standard sprockets/jets back in/on, and then youve a base from which to go forward, as we know what a standard bike should go likeProblem is, is its been thrased, it may have suffered engine damage
Thornhorn Posted May 6, 2013 Author Posted May 6, 2013 Cool, I'll be doing that and will be also visiting the garage tomorow to do a second compression test.
Iceni Posted May 6, 2013 Posted May 6, 2013 Cool, I've orderd a convertor for the compression tester I have should be here by friday. I'll make sure you get that information Oddly I was chatting to a friend today about his bike, and he was having a similar problem. Turns out when he rebuilt it he didn't know the pistons were supposed to be reasonably tight and thought that when they went in easy it was a good sign lol.
Thornhorn Posted May 7, 2013 Author Posted May 7, 2013 Nothing is going my way.... only garage that I manage to get in had a broken compression tester. Buy the good news is that for the first time i seen that the bike is now running too rich as the sparks were black so I'm ordering a new filter along with the original sprockets.
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