A simple way is some plastic tubing that is a tight fit in the bowl drain thread.
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wont accelerate
- Thread starter azcafe
- Start date
azcafe
XS650 Addict
Thanks for the info guys. I will try that and see what happens.
Since my engine runs so rough with the choke off does that mean that one carb is being starved of fuel?
Since my engine runs so rough with the choke off does that mean that one carb is being starved of fuel?
azcafe
XS650 Addict
So I am about 90% it is a compression issue out of the left cylinder. I took the carbs off again tonight and followed the carb guide cleaning instructions very closely and got that all situated. Then I decided to retorque the head nuts since I hadn't done that yet. I torqued them to 30lbs and then readjusted the cam chain tensioner which really did need to be adjusted and reset the valves. After that I did a spark test on each side to make sure I was getting spark to both. Please note I have not put the carbs back on during any of this. When I was testing the left spark plug, meaning I had the right spark plug in the motor and was grounding out the other one on the engine to see if it sparked i still had to give it some pressure to kick the motor over. Then when I was testing the right spark plug meaning I had the left spark plug in the motor and the right one grounded out on the motor there was no back pressure and I barely had to kick to get the motor turning. So then I unplugged both spark plugs and cover took the key out of course. I plugged both spark holes with my pinky and my right (right cylinder) would get sucked in and then forced out while my left pinky (left cylinder) I felt absolutley nothing.
Am i safe to assume I have not compression on the left cylinder and that I need to tear down the top end?
Am i safe to assume I have not compression on the left cylinder and that I need to tear down the top end?
Your simple test with your finger sure points toward very low compression on that left cylinder.
Gary mentioned you should do a compression test 2 days ago. Good idea to buy a compression gauge so you can have some numbers. You ask for member's opinion as to need to re-open the engine, so its best if you can post some real numbers from a compression gauge.
Gary mentioned you should do a compression test 2 days ago. Good idea to buy a compression gauge so you can have some numbers. You ask for member's opinion as to need to re-open the engine, so its best if you can post some real numbers from a compression gauge.
plane_ben
XS650 Junkie
Put the right cylinder at TDC and look through the plug hole. See if there is a hole in the top of the piston. When you mentioned before that you rode it quite hard for a while before this problem, and then later you said you had stock jetting, you might have been to lean. I assume you are running pods and free flow exhaust? That would make you run very lean and since the right cylinder runs hotter than the left, it burned first.
azcafe
XS650 Addict
Thanks guys.
Retired gentleman. I know I really need to get a compression test done just haven't had time to go pick up a compression tool.
Plane Ben
I will check that out.
When I do a compression test should I back the valves all the way out or just leave them set where they are suppose to be.
Is there multiple test I can do to pinpoint where the compression leak is.
Retired gentleman. I know I really need to get a compression test done just haven't had time to go pick up a compression tool.
Plane Ben
I will check that out.
When I do a compression test should I back the valves all the way out or just leave them set where they are suppose to be.
Is there multiple test I can do to pinpoint where the compression leak is.
As long as the valve clearances are set at the normal specs, then the compression test will work fine.
A "leak down" test can help tell you where the compression loss is happening.
azcafe
XS650 Addict
So I did a compression test this weekend and sure enough the left cylinder has zero compression. The right cylinder was reading low too. It only read a max of 110 psi. I have enough parts to build up a 447 engine so I think I am going to do that since I don't have any spare 256 parts. Hopefully I will get better compression out of the 447 motor.
plane_ben
XS650 Junkie
If you want to drive to Tucson this weekend, I have a complete 256 motor that I stole the cam from. I have no plans for it at this time and I may have to move in a couple months. So it is yours to come and get. Also have two sets of used pistons for 256. PM me if interested.
azcafe
XS650 Addict
Alright so I got some parts from Plane Ben and replaced the cylinder jugs the whole head and all the valves. I relapped all the valves and they had no light coming through them when I installed everything. I got the biking running and did the cam chain, valves and timing adjustment and also synced the carbs as well as going one step richer on the main jet. My left cylinder is still reading about 15 psi lower than the right and is backfiring a bit out of the exhaust when I ride it. The cylinders are reading 90psi for the right and 75psi for the left. I know those are both low but when I ride it the acceleration seems about the same as my friends XS. I am going to use the same compression tool on his XS to see if it is perhaps the tool that is giving out low readings. Any other suggestions on what it might be?
azcafe
XS650 Addict
Hey All,
So I discovered it was user error on the compression test. I was not opening the throttle which wasn't allowing any air to get in.
When I did the compression test again I had 120psi in the cylinder and I took the pod off the carb on that one. When I went the test the right cylinder it would get up to about 110 115 and the pod is on the carb and the compression gauge started leaking out of the release valve so I assume it would be close to the same.
So now to address the slight back fire problem. I attempted to sync the carbs based on the dead cylinder method on the carb guide and I am not sure I did it correctly. I don't have an rpm guage so it is a little hard for me to figure out. It doesn't back fire at idle it only back fires when I start to get on the throttle a bit when I start going. I am one richer than stock on the main jet and stock on the pilot jet. Should I go one richer on the pilot or play around with the air fuel screw?
So I discovered it was user error on the compression test. I was not opening the throttle which wasn't allowing any air to get in.
When I did the compression test again I had 120psi in the cylinder and I took the pod off the carb on that one. When I went the test the right cylinder it would get up to about 110 115 and the pod is on the carb and the compression gauge started leaking out of the release valve so I assume it would be close to the same.
So now to address the slight back fire problem. I attempted to sync the carbs based on the dead cylinder method on the carb guide and I am not sure I did it correctly. I don't have an rpm guage so it is a little hard for me to figure out. It doesn't back fire at idle it only back fires when I start to get on the throttle a bit when I start going. I am one richer than stock on the main jet and stock on the pilot jet. Should I go one richer on the pilot or play around with the air fuel screw?
