Compression test

[dlbryant1]

Please tell me how bad you think this is. My bike has 43,000 mile on it and it runs almost ok. I have only had bike bike for a month and I have put about 500 miles on it. I had a pickup wire problem and now it doesn’t fell right when cruising. I was going to check timing next and then sync. carbs. I have the individual filters, and I was thinking this bike would run lean but the plug say rich. This is the reason I was going to check everything.

#1 100psi
#2 120psi
#3 120psi
#4 100psi

I added oil and got 125psi on #1 & #4.

[MartyA]

Clymers says 142 +/- 14 is normal at sea level, and more than 14psi difference between is bad. You are below the 128 suggested minimum.

The first 3 choices are head gasket, valves, or rings. Getting a boost after adding oil is indicative of rings. What did you get after adding oil to #2-3?

Head gasket 'usually' breaks down between 2 adjacent cylinders, does not appear that is the case.

That leaves valves. If you have been running rich (yeah you can run rich with indy's), excess carbon might be preventing the valves from closing completely. Or they could be bent from prior abuse and not seating correctly. Or the return springs are weak.

Other veterans should chime in here, I'm thinking it's teardown and inspection time.

[TopCatGr58]

Hey there Dlbryant,

You're a bit more than the recommended 10% variance between cylinders, but not too severe. Just have to ask a few points to ensure you performed the test accurately....such as wide open throttle, books recommend also doing with hot/warmed up engine. Your added oil test does confirm that your rings may be a bit weak, but brand new, the bike was supposed to have 142 (+/-)14 psi, so your's are a bit low with the 100 values, not too bad with the 120!

Did the bike sit for a long time before you got it? Could still have slightly stuck rings, did you do a good oil change...try adding a little IIRC Marvel Mystery Oil or Tranny fluid....do a search on techniques for awakening long sitting bikes/engines, some more knowledgable folks discussed this process recently!! Checked you cam chain slack lately, can also affect valve timing/compression if too loose.

Plugs say rich? As in black? Sooty or oily? Could be oil being burned more than excess fuel? Might try going to a slightly hotter plug. Instead of just synching the carbs, try a thorough cleaning first so you can inspect the innards, the float levels, rubber diaphragms, etc.. Vacuum advance moving freely, not stuck, vacuum line to it intact, no holes?? Lots of things to check!!! Good luck, let us know!

[fusionking]

I've seen worse

I'd probably keep on riding while I collected goodies for the winter / never-project! Does it smoke? Running it hard can improve both the ring seal and blow out the carbon especially if you take Geezer's advice and use Gas-ahol. You know I believe if you keep it full of a good grade of oil .........you can't blow one of these things up!!!!!!!! Just be careful with the trans.

[sixtysix]

Check TC post and do the test according to the book, WOT, engine hot, I even think you are suppost to remove the other plugs so the engine spins more freely. If it is still that low than you may have issues...

[Geezer]

I know this sounds crazy buy there is a good chance all you need to do is run the crap out of it. Let me explain, as engines get old the valve guide seals break down and allow oil to seep down the valves. The exhaust valves run hot enough to burn it off but it builds up as carbon deposits on the intakes. This isn’t the hard carbon like you get on the tops of pistons but rather the soft stuff like you get in the baffles of a 2-stroke baffle. Often the engine doesn’t run hot enough to burn any of it off the intakes

There are 3 ways to fix this but only one is any fun. You can tear it down, take a wire wheel to the valves and replace the seals. You can try many of the carbon removal products that don’t require a tear down.

Now for the fun way to fix it, take it out on the freeway and run it hard, not a little hard but run the crap out of it. Take all exits and WOT down the entrance ramps getting back on. Keep it at or near red line as much as possible (1st~3rd gears only) and 30 to 50 miles later drive it home at a normal pace. Let it cool enough to work on it and run another test by the book.

I’ve done this many times on large displacement bikes that have low compression and shouldn’t be needing a rebuild. It’s just that when you have a machine with this much power there’s just so much extra on tap it’s usually not ridden very hard.

Geezer

[fusionking]

Yea, thats pretty much what I was driving at. Well said.

[TopCatGr58]

Well, shoot,

Maybe that's why mine still runs so good, almost how I ride it ALL THE TIME!?!? Not really, but a good twist of the throttle often sure does feel good, and now I'm sure it's good for the engine, too!!

T.C.

[tony7914]

Re: I've seen worse

Originally posted by fusionking
I'd probably keep on riding while I collected goodies for the winter / never-project! Does it smoke? Running it hard can improve both the ring seal and blow out the carbon especially if you take Geezer's advice and use Gas-ahol. You know I believe if you keep it full of a good grade of oil .........you can't blow one of these things up!!!!!!!! Just be careful with the trans.

hey there!!
i don't know how well it would work on a bike, but you might try "gum-out high mileage" i used some of this on my car and it cleaned up the fuel and intake system very well! i would be interested to know if anyone else has tryed this or not!
hope this helps!

tony

[dlbryant1]

Thanks for everyone input. I believe I will try some Marvels mystery oil in gas and some 4 cylinder Restore in the crankcase. This bike set for 2 or 3 years and I agree that it needs to be run. I am going to check cam chain, timing, and floats, and synchronize carbs. When I got this bike it poured fuel out the overflow so I replaced the needle valve but did not check the float level. I hope the floats are the problem with running rich. The bike is not burning oil. The plugs are tan on the tips and black soot on the OD. Vacuum advance in good working order.



I am going to enjoy running the crap out of this bike.

[TopCatGr58]

Hey there DL,

I hope it's not too late, but I would be hesitant to put RESTORE in the oil. It seems to me to be a thickening agent, but might also be a more slickier lubricant type additive(like motor honey-STP), and might interfere with your clutch making it slip more???

If you've already added it, then good luck and let us know how it does, and if you notice any problems with the clutch....slipping??

Happy riding. T.C.

[floridajoe]

hi there everybody

i just got my 79 xs11 6 months ago and it ran kinda pourly got the carbs rebuilt got better did oil change and somebody told me to used lucas oil and there you have it clutch slipped a lot 2 oil changes later its getting better ,,, i will stay with straight oil only