low compression

i recently started having some engine issues. first started with a fuel soaked plug and backfiring in the exhaust system. first i checked the float height, then i pulled the carbs to disassemble and found a pin hole in my suspect vacuum diaphragm, other then that i bench syn'd the carbs and reinstalled, checked the air fuel screw to all be sent correctly, and put in new plugs.

since all of this the bike smokes very bad , black sutty plugs on all four plugs and smell strong of fuel. i was assuming the bike was burning off extra fuel that has made it into the cyliners and exhuast system but it just keeps smoking.

i decided to compression test the engine while it was warm and then again after I added a little oil to the cylinders to seal any leaking rings; my results were pretty shocking

cyl psi psi w/ oil
1 88psi 130psi
2 82 psi 160psi
3 98psi 125psi
4 95psi 115psi

is it normal for all the cylinders to be this low ? im not sure what to do but this all seems to point to bad rings?

and suggestions are greatly appreciated

One thing to consider when adding oil to cylinders to test compression is the fact that a little goes a long way, and that if that method for checking compression leaks is employed it's important to add the same amount of oil to each cylinder. The link below gives a description that might be helpful. Ed

www.kzrider.com/forum/2-engine/609912-19...n-head-gasket#797030

Those seem excessive low.

Just in case...in my experience such low numbers often can come from procedural errors or test-equipment failures.

Its easy to sometimes accidentally leave a choke on, or forget to hold the throttle wide open while cranking. Also, there are a lot of test gauges that are simply designed wrong. Gauges should have a check valve right in the tip of the tester that goes into the spark plug opening. If the check valve is closer to the gauge, it will cause the gauge to register much lower than it should. I just went through this on a gpz I recently purchased. The seller's gauge was built wrong and his results were 50 psi lower than the two gauges I brought.

That said, the fact that 1 and 2 increased so much with oil seems alarming.

How long since your last valve adjustment? If the valves are not adjusted regularly the clearance closes down until the valves hang open and burn, losing compression in the process.

Thanks for the advice guys. I will have to double check to make sure the choke was in the right position, that is a possibility

A valve job hasn’t been done in sometime. Also another great avenue to explore.

I added just a few squirts of oil per cylinder. I kinda rushed the full test tonight and I will have to give it a second go tomorrow. I’m will report back. Thanks

You sound like you know what you are doing so just checking you did have the throttle wide open when you did your comp test? Those initial readings without oil sound suspiciously like what I would expect with the throttle closed.
Even the oiled readings sound low hence my suspicions.

Rings at the very least.

A leak down test will help you pinpoint the problem.

If it's been sitting for a while the rings could be stuck / gummed up. They will usually free up once you get it started. If it hasn't been sitting and the problem showed up then do the regular maintenance as previously mentioned. If that doesn't work then you got ring problems.

1. Add some marvels mystery oil to the cylinders to free up possible ring sticking

2. Adjust the valves

3. Perform Italian tune up for 100 miles or so and then check compression again.

Remember to test compression on hot engine with throttle held open.

Blue or black smoke? That will tell you oil or fuel, respectively. How long did you run it? A fuel-wash sometimes requires a decent run to fully clear. And be sure the crankcase isn't full of fuel.