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Compression test question

  • Thread starter Thread starter NitroGS
  • Start date Start date
N

NitroGS

Guest
Hi Guys, Suzuki GS1000 1979 model

At present I have got my carbs in pieces doing a thorough clean and awaiting my new Vance Hines 4 into 1 from the States. I have read alot of the threads which confirm you need to make sure the engine is in good tune prior to vacuum syncing the carbs i.e ignition timing, ignition coils, spark plugs, valve clearances etc and finally compression. All the rest I have done apart from compression test and here is where my question comes. Can I do a compression test with the carbs and exhaust off the bike any help would be appreciated. Has an aside, I see quite alot of our memebers have V&H exhausts do they come with connecting flanges to attach to the cylinder head
 
Yes, you can do a compression test with the carbs off the bike, but the most reliable way to get accurate numbers is with the engine at operating temperature.

Whenever you get around to checking compression, be sure to hold the throttle fully open so the cylinders can fill as much as possible. A closed throttle will restrict air flow and affect the compression numbers.

Go ahead and check it now, with the carbs off. First, connect your gauge, use the starter to rotate the engine through several compression cycles, note the reading. Remove the gauge, squirt a bit of oil through the plug hole, re-insert the gauge and get another reading. Compare the two readings. If the first one was a bit low and the second was better, it shows that the oil is sealing your rings better. If they are both low, you have valve problems. If they are both good, you probably don't need to worry about it. Of course, you will want to do all four cylinders.


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Your sure can do a compression test with carbs and exhaust off. Remember that it's the piston, valves and their ability to compress basically an air mixture that you're testing here - anything outside of the valves will only affect your results if VERY restrictive. Of course it's not just compression you're looking for but also consistency to other cylinders. It's for this reason that I always remove all spark plugs as well.......this does 2 things - first it allows the engine to roll easier without heating the starter and adversly draining the battery........secondly it may show up cross communication between cylinders if you should have a blown headgasket between cylinders.

Hope that answers your question ;)
 
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