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ssmacdon

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About ssmacdon

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    Ontario
  1. ssmacdon

    Leakdown Test Question

    I've checked by putting about 20 psi into the cylinder at TDC on the compression stroke. Nothing out the exhaust, a little through the dipstick hole (but new rings not broken in) and lots of air out through the carbs. The head is coming off - there is a problem with the intake valves. Scott
  2. ssmacdon

    Leakdown Test Question

    If the compression is down and it is definitely running lean - this could both be a result of bad valves, I think. I know that the compression should be a little higher after it's broken in, but I can barely start it and it runs way hot. I'll kill it before its broken in. I've pulled the carbs and the air intake manifold, even replaced the big O ring under the intake . I'm sure there is no leaks around the carbs. I didn't use starter fluid but I did put some propane frpom a torch around there (yikes) - it is supposed to do th same thing - make the revs rise if it is sucking air. Anyway, off to the garage to try again. Thanks, Scott
  3. ssmacdon

    Leakdown Test Question

    Thanks for the replies guys. The cylinder was bored and honed for an oversized piston. It is not broken in as it is hard to start and it's running lean so I don't want to damage anything. I already had the fitting for the compression tester in the plug hole so I rigged up a fitting for my compressor - figured I'd try it to see if I can tell if the air is leaking and where. I got a piece of rubber hose and I can listen up the exhaust pipe, in through the airbox and in the dipstick hole. You can hear the air easily and tell where it is leaking, I did it last night - but as noted the piston would move and the valves would open and close. I just need to make sure the piston is at TDC on the compression stroke as noted above (thanks), I think I'll put a breaker bar and 17mm socket on the nut to rotate the crank on the alternator and brace or have someone hold it so it wont move. I haven't heard any air leaking past the rings. Maybe the 120 psi compression is OK as it is a new rebuild and the engine is cold. But I wonder about the valves, when I had the cylinder head in my hands I should have checked to see if any solvent would leak past the valves. Oh well, live and learn. Scott
  4. ssmacdon

    Leakdown Test Question

    Hi, I've pulled the carbs twice and double checked everything is clean and seems OK. I think the compression test shows the compression is low - that's why I think it is the valves. I've been thinking an I think I need to check the pressure in the cylinder with the piston at TDC on the compression stroke - then I can be sure the valves should be closed. I just need to keep the pressure from moving the piston. Scott
  5. ssmacdon

    Leakdown Test Question

    Greetings, first post. I recently bought an 85 XL350R. The bike is hard to start, pops when I shut the throttle, won't rev out and feels down on power, the plug is kind of white and runs better with the choke on, sometime the revs will race on their own - seems to be lean - and maybe has an air leak. I've double checked the valve clearance, decompression cable, carbs, floats, etc. No air leaks around carbs or exhaust that I can tell. The compression is 120 psi - tha manual says it should be 199 (but I checked it cold). I didn't put any oil in the cylinder because I want to do a leakdown test anyway, and I just replaced the piston and rings (guess I should have done the valves). I bought the bike in pieces. I made a fitting to attach my compressor to the fitting for the compression tester. I'm not sure where the piston should be for the test. I had it at TDC on the compression stroke because that is where you check the vavles and they should be closed with slack in the rockers. Problem is that the pressure moves the piston and then the valves open, same seems to happen around BDC. Where do you have the piston for this test to make sure the valves are closed and how do you keep the piston from moving? Thanks, Scott
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