Ok in a post below I was mentioning my compression test results. Warm bike, rear cal 180 psi, front 120. Bike has 6800km on it. I just did a cal leak test. Well I am pretty sure I did it right. Took of the cover and plugs on the right, turned the shaft counterclockwise until I got R/T. Then continued to turn it 1-1/3 times to F/T to get front TDC. Hooked up the leak tester and was next to zero leakage. Mind you the bike was cold (already had bike apart so thought I would just do a cold check) but you would think if its warm I would even get a better seal in the cylinder. So my question is WTF? How can I be getting 120 on the front, and yes I checked it around 5-7 times taking out the compression tester each time and lubing the O-ring on the tester. Can someone please help me out before I take it into the shop? Thanks all. I appreciate your help
The decompression systems on these bikes are pretty crude. Maybe one is just a bit more 'sticky' then the other one and so is not releasing at the rpm the starter motor can generate.
I have actually run an engine with more then one cylinder while I checked the compression on another. I'd be a bit hesitant on the 9 though as you don't want the second plug firing the mixture while your trying to test it. Can you get an engine to run with one injector unplugged?
Doesn't sound like you have a problem if the leak down test is good. What makes you suspect you have an issue (apart from the obvious readings), is the engine not performing well?
Yeah just the compression test had me worried. Some friends and I traded bikes the other day and both of them said there is some shudder when accelerating and happens about 3500 rpm. I think I remember reading that is common on the 109. I guess I can just disconnect the coil on the second spark plug and that should keep the cylinder from firing.
What speed and what gear are you in when you did this? And how hard did you hit the throttle? Remember this bike likes the higher rpms when getting on the power. Those are some HUGE pistons! And when you crank on the power at just 3500 rpm, it will shake the bike! If the guy was use to the inline 4, then he will not understand a v-twin. And if he is a harley rider, he will not understand the amount of power each piston is pumping out each time it fires! If you are getting near zero leakdown on a cold engine, you are doing good.
That shudder is normal on this bike. If you aren't having performance problems you may be barking up the wrong tree. If you accelerate in high gear on any 109 it will vibrate at around 3500 rpm. If the bike runs strong, ride it.
That vibration is normal. You could have worn front mounts as well, they go pretty quick. Many, including myself, have changed them for the harder rear mounts. Call Matt (FuturR) if you want the technical explanation, and stop worrying.
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