79' XS1100S Restoration

[Quasii]

Hey Guys

First time bike owner and first time working on a bike but I have a lot of experience working on automotives in general. I just picked up a 79' XS1100S for cheap and it hasn't run in 10-15 years I've been told. The engine does turn over. I can tell I will need to take apart the carburetor and clean it out good as it is sticking and the choke does not move at all. A buddy from work who has worked on older bikes before told me to do a compression test before I start investing time and money into it. I have read on another website that the test cold and dry should be around 140. The battery was dead so I used a car battery I had laying around and used jumper cables to ground and the starter to power the starter for the test. Starting from the clutch side cylinder 1 read ~75. 2 read ~85. 3 read ~92. 4 read ~89. Is this engine toast, or does it just some work to get it healthy again? Any resources are much appreciated.

[Ranger_xs1100]

Hi Quasii, welcome to the forum.

The first thing I would ask is: "Did you hold the throttle wide open during your compression test?"
If not, I'd recommend a re-test to see what compression readings you get.

[Quasii]

Thanks for the welcome!

I did, originally I had taken out the air box and the carb to inspect the carb. I initially started the test without the carb installed. I saw the low number and I did find a video stating the throttle should be fully open when doing the test. I then re-installed the carb without the air box and re-tested The throttle seems sticky. It pulls up fine but very very slowly resets to normally closed position. Unsure if this would affect the measurement. The airbox, seat, and fuel tank are currently off the bike.

[Ranger_xs1100]

Good start. The next thing I would suggest is soaking the cylinders for a day or two. Some guys use marvel mystery oil. I use rislone engine treatment. You may find that is all that is needed to bring up those compression numbers.

If the compression increases as I expect it will, to 100 or 110 across the board, that is enough to get the engine running and they will continue to rise after that.

[Radioguylogs]

Compression test results are valid if the carbs are are removed, same as if the throttle is held wide open.

[Quasii]

@Ranger_xs1100 How much of the engine treatment should I put in the cylinders?(I am assuming it will probably say on the bottle) and after it soaks do I just turn the engine over to clear it?


@Radioguylogs That's what I had assumed but wasn't sure; thanks for the clarification!

[DiverRay]

About 3 oz. per cyl. should be all you need. let it set overnight, and then spin the engine over about ten seconds before starting the test again. As stated, compression WILL be low at first, and as the bike is used, will rise back to normal
A few years ago I had an '80 MNS that I was selling. Had a call and the guy wanted compression number. The bike had not been started in about two months and I didn't think about it. Ran a test and all 4 were about 110. Rode the bike for five minutes, did a retest and all were 140.

[DEEBS11]

None of your numbers were "0". You're good for now. Clean those carbs and RIDE. Like the guys said, your compression will likely return to normal. Make sure you change the oil and filter before you start the engine. You are gonna love this bike!

[Ranger_xs1100]

Yep, what DiverRay said.

TIP: Throw a shop rag over the cylinder spark plug holes when turning over the engine for the first time after soaking.

[Quasii]

Update: finally did the engine treatment after cleaning the carb and fixing one of the float posts. Just re-did the compression test and they are running between 120-140 on all 4. Thanks for the help all!