XJ 650 problems

Hi I just bought a 1982 XJ650 Maxim that needs some work and joined the forum hoping you guys could help me out. This is also a YICS engine and from what I have read on some forums this makes a difference for this model.

The problems are:
1) Low compression on all the cylinders (100,110,100,125)
I know this can mean a whole variety of things, but I was told by a friend that the spark plugs that are currently in the engine are for a car, not a motorcycle, and was wondering if this could be the cause of my low compression problem.
2) High Idle (around 4,000 RPM)
I am almost positive that this is coming from an air leak from one of the carb boots (engine-to-carb).
3) Front brake doesn't work.
I think the master cylinder is shot. So I am just going to replace it with something from ebay.

I was also going to clean the carbs, check/adjust the valves, and check the brake pads.

My question is how should I diagnose the problems? Any help I could get would be appreciated.

Mike
'82 XJ650 Maxim

 

Welcome !!
1) Did you have the throttles at Wide Open while doing the test??
2) You can check that by spraying carb cleaner-starting fluid around the suspected leaks, and see if the idle changes
3) You're going to learn how to re-build your Master Cyl - with parts from XJ4EVER in the upper right corner of every page.

Get a Service Manual for your model. Get the valves in-spec first.

You should plan on a carb cleaning and adjusting session.

carb service thread

 

Compression check should be done with ALL the spark plugs removed, so spark plugs won't matter. Disconnect the coils or ignition module before testing. Throttle wide open during test.

If you tested with some of the plugs in that is likely the cause of your low number.

 

You're in Albuquerque, so adjust the values of the compression for the distance above sea level where you live. Multiply the listed compression by the factor from the table below for your altitude

Compression Test Altitude Compensation Factors
Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773

 

Make that "rebuild the brakes." New lines, new pads and shoes, new seals in the caliper and master cylinder (even if you buy a used one off eBay.) Gotta do it; everything is 30 years old.

 

on the master cylinder
I found a new one off ebay for 2 dollars more than
a rebuild, and it came with a spare rebuild kit with it
seems silly to go any other way

 

blackbelt,

In addition to the advice given remove the air box lid and filter when you re-do the compression test.

Gary