Need Some Info

I recently purchased a 1986 XJ700 Maxim. I probly paid too much for it and did not give it a good lookover when I picked it up so I'm hoping I did not get ripped off.

The bike seems to run strong. I had to replace the battery and all the spark plugs. The oil was dirty and I did not know if the kid that had it even put proper motrcycle oil in it so I changed the oil and filter with very expensive motorcycle oil.

I have conducted a few tests to check the engine condition and here is what I have found.

With the engine cold I dry compression tested each cylinder and every one of them were putting out about 130-145 psi. I do not know what they should be at but i'm hoping that is an acceptable pressure for an engine with almost 13k miles on it. If you know what the factory spec pressure is supposed to be or anyting else I would greatly appreciate the info.

I have also noticed that the new spark plugs are showing alot of dry carbon on them, but I assume that is because I have been playing around starting it up in the garage and not running it down the road to get it hot.

I noticed that the air filter was dirty and some engine oil has been being blown in the air box and on the filter so I left the filter out and ran it with my hand in the airbox and put my finger just in front of the blowby hole from the gear box and revved the engine high and hardly felt any air coming out so hopefully that is a good sign.

The only other thing I noticed is that by taking the oil fill cap off were the clutch is with the engine running there is quite a bit of air coming out of it.
I do not know if that is bad or the clutch being right there spinnngin very fast could be creating the majority of the air coming out.

I know this is a long series of questions and maybe too over elaborate but I figured I would post every concern I have at once and get it out of the way with.

Any hints tips or specification info would be greatly apprecicated. Thanks

 

The compression numbers are right up there. Excellent.

Do another plug reading. Bring a set with you. Take a ride. Warm it up good. When safe ... run it up to cruising revs - then, hit the kill switch, clutch lever and coast to a stop. Those are the plugs we want to read. Pull 'em; pop in the spare set you brought and head for home.

The crankcase is vented to the airbox from the hose connected to the top-rear of the shifter cover. Some oily slime in the airbox is Normal. Excessive slime is not normal.

Clean-out airbox. Wipe clean shelfed area behind the filter.
Observe oil level in window with bike on CENTER stand -- cold.
Add small amounts of oil to bike until "Bubble" in Oil Level View Window is gone and level of oil is just at the very top of the Viewer.
(Makes it real easy to monitor oil level.)

I have a feeling that bike is "Zero-defects" and we can just tune it to it's razors edge of performance.

Welcome aboard.

 

Andy,
First of all...130-145 lbs. preasure is way too much. Might I suggest losening the head bolts and letting some of that preasure out before she BLOWS!!!!!
LOL just kidding. I wouldn't be too concerned about the engine. Unless it burns blue smoke out of the exhaust, you should be in good shape.
I would clean/replace the air filter, change the oil (flush the engine out too) and put some good oil in it (synthetic like Amzoil is good stuff)
Take it out for a nice long ride before you do a plug check - just idoling in the shop won't give you a true reading and usually the engine is cold anyways.
I'm sure others have ideas here too. >PD<

 

I know there are some who swear by Synthetic Oil. If you run Synthetic and are trouble-free ... great!

I do not recommend Synthetic ... (at the moment)!

I recommend: Castrol 20/50

Will I ever change my mind? Maybe. On the day I joined-up, in here ... I still an Old School "Tweaker" ... who set Pilot Screw Mixtures "By ear"

Now, I have a ColorTune Plug set in a plastic case, lined with crushed velvet, and would do a TV Commmercial testimonial for the thing in a heartbeat!

 

Yamaha manual says

standard compression is 156 psi
minimum compression is 128 psi
maximum compression is 171 psi

 

Rick , honest question here . What is the idea going to cruising revs then killing for a plug read ? I was always shown to find a safe stretch , then WFO in 3rd for a few seconds , then kill . The idea being that while cruising , you are at maybe a 1/4 of your throttle , but when drving in real life , your carbs are actually living on the main jets most of the time since most of us go 1/3 to 3/4 throttle before shifting .
Your method would give you a reading of extended riding at 1/4 to 1/3 throttle , yet you may still be too lean on the mains for every day driving (upshifting and down shifting)
I was tought as I said , WFO then read . This gives you a read on the mains , then new plugs , putt around town being very carefull not to go more than 1/4 to the red line , then read . This gives you a read on intermediates . When you think about it , most people twist the throttle over 1/2 way , then shift , which puts them into the main jets .
For the record , I've always done both above tests as I describe then after driving the way I personally drive daily for about 50 miles , done another plug read .

 

You're right about that. The best way is to get high-up on the tach and kill it.
You really do need to wind-it-out and kill it to get the best read on the plugs for mixture.

Please be careful.