I think, just maybe, compression is a bit low.....65psi

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

I just tested the compression on my 71 xs1. It always was hard to start and finally took the advice of this forum to test compression. Highest reading perhaps once was 70. usually 30, 30, 60, 70 then 30. I tried the trick of a bot of oil in the chamber to test if valves but basically....engine rebuild right?

thank you. I know I am a numptey for even getting to this point. Do your worst. I can feel no more guilty than I already do.

nudude53

Yep, time for an overhaul. Go all the way and get the heads done too, if you don't you'll wish you had later. MikesXS has everything you'll need except the camshaft.

xsjohn

Did you hold the throttle open for the compression test...........

xsjohn

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

Thanks Nudude> when ou say the heads, replace the valves et al too?

xsjohn - Thnk you. I did not hold open the throttle. SHould I retest it with them open? I tested the bike cold...basically because I could not start it

yamaman

Yes test open throttle & as MikesXS pointed out in a similar thread, make sure you prop open the vacuum slides as well!

The engine is a compressor, turning the engine over compresses the air in the cylinder, thus giving you a reading in your pressure gauge. If you shut off the air supply (closed throttle) and its got no (minimul) air to compress, then your going to get a low reading!

Though, I think even with throttle closed it does seem low, hope it picks up for you!

xsjohn

My son just acquired a XS650 that had been setting since 1994........the compression was 30 psi the first time we tried it.....sprayed some oil in the carbs and cranked it over (after cleaning carbs) and managed to get it runnig........turns out the compression is now 150 on all 4 cylinders and it runs perfect..............

bottom line is you just never know........

xsjohn

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

Thank you guys. I appreciate it. I will test again with the throttle and will check the manual for the vacuum slide.

The oil test: i dropped a tea spoon of motoroil in there...I will be able to test it agin for a week [parents in town]. should I put some more in it when I retest or risk flooding it?

xsjohn

Clean the carbs "well" including the pilot circuit..........sounds like you have plenty of oil in there..........spray with (a bit) of starting fluid and see if you can get it to run (after carbs are cleaned)........as it runs if so spray some WD40 or something in the carbs.......then see what you have..........maybe a rebuild maybe it runs.......

points and ATU should be checked and cleaned..........and wires everywhere whould be cleaned and use dielectric grease.......(before starting)

xsjohn

yamaman

To get to the vacuum slide, you need to remove the air filter. Then the first thing you see when you look down the carb throat will be the vacuum slide! Just lift it up all the way and prop it up with something (whatever you use, make sure it can't get sucked in the motor). Then also hold the throttle open so the butterfly valve further down the throat of the carb is fully open!

Yep, I'd freshen up the oil, wont hurt. You can't sneak out there now & put a bit more in? The longer it's got to soak in the better, then a bit more in a couple more days!

If your worried that you've put to much oil in it, just kick it over a few times with the plugs out before you hook up the tester! Cheers

WillP · Full Member Joined: Dec 22, 2008 Posts: 46

terrific. Yamaman. Thanks so much. I really appreciate it.

If my mother gets on my nerves, I will tell her I am going to work on my bike: it always shuts her up.

dappleco

Yep I am still doing this wrong!
After I remove the air filters prop open the vacuum slide and hold the throttle fully open I will rehook up my tester and try again and try it again.
I am confused on 1 part, I think I have been reading too much and have confused myself.
Do I do the test with both plugs out, or just one at a time?
I think it is both. Please advice!!!
Thanks a million for everyone’s great advice and forums!!

dappleco

Yep I am still doing this wrong!
After I remove the air filters prop open the vacuum slide and hold the throttle fully open I will rehook up my tester and try again and try it again.
I am confused on 1 part, I think I have been reading too much and have confused myself.
Do I do the test with both plugs out, or just one at a time?
I think it is both. Please advice!!!
Thanks a million for everyone’s great advice and forums!!

xsleo

Go ahead and pull both plugs, no sense in making it any harder to turn over. If you are going to take the carbs off for cleaning, do the compression check while the carbs are off. Spraying a good penetrating oil into the spark plug holes will help unstick the rings. Do this, let soak for a day or two. Then check again.
Check to see if the valves are opening and closing by pulling the valve adjuster covers and watch as the engine turns over. Spray the penetrating oil in there too.
While the covers are off check the clearances. If the valves are sticking open or the adjustment is too tight the compression will be low.
Good luck with the checks. Hope you can get it to run.

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