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Did a compression test....not great
- Thread starter Knight
- Start date
Yep. Gonna take more than a few rolls.
OP may want to try with the engine warm as well. Especially if working in unheated shop - oil is thick and hard to pump cold this time of year.
J_F
Guest
I just did a compression test after it was all warmed up after a ride and my results were disappointing.
Cyl1 80psi spark plug was normal
Cyl2 80psi plug real lean
Cyl3 70psi plug real rich
Cyl4 85psi plug a bit lean
And yes it does burn some oil I can see a faint blue at idle at a stop light when it's hot
Now in the Clymer manual it says the pressure range should be 156-184 psi. Is it time for a rebuild.
I tried to attach a picture of the plugs but this site is not letting me attach a picture from Imgur.
throttle open test again OP
then some oil in each cyl, test again
if all 4 go up in PSI considerably after the oil, your rings/cyl walls are done
the oil trick eliminates valves or other issues as a root cause
Mad Mike
Well-known member
The sliders would be right down which restricts airflow. A bike cranks at about 200RPM, a 650 needs to inhale 2l of air per second thich would be hard with throttle plates closed (like taking a deep breath through a straw). The numbers shown in a Clymer manual show the max the engine can breathe, so to get close to that you have to unrestrict the intake airway to minimize vacuum at the start of compression stroke. Choke OFF and WOT will open up the aurway alot, I usually jam up the sliders to get the best reading.
So I re did the compression test today at wot. And it made much more of a difference then even some have said maybe a F.I. Engine it won't make as much of a difference but I was really surprised and happy the numbers came way up. tested it's between 120-130psi between all cylinders and with some oil in the cylinder it was 180 for them all. so with such a difference between dry and wet with oil does that mean the rings are still sorta worn but the valves are perfect.
J_F
Guest
120-130 is okay for an engine that old. Pic of the plugs looks like the carbs need done. Especially the lean ones. Lack of compression will give you the opposite.
Sent from my ASUS_Z01BDC using GTAMotorcycle.com mobile app
Sent from my ASUS_Z01BDC using GTAMotorcycle.com mobile app
Mad Mike
Well-known member
I'd say that's about exactly what it should be for a mid-life cold engine (you did this cold -- right?). If you got 180 oiled, you're good and I'd keep the wrenches in your box. The cylinders with sooty black plugs are running a rich - maybe cleaning is necessary, maybe just setup is off.
That means the ring seal is sacked and the valves seem OK.
You want 125PSI MINIMUM to run modern pump gas.
No i did it when the engine was hot. this bike pulls pretty good I can still pull the front wheel in 2ed gear if I try which I'm told is harder for a shaft drive.
boyoboy
Well-known member
What are your intentions for the bike? Are you attached to your bike and plan to keep it for another 5+ years.....or is it just inexpensive fun transportation?
this should help you decide if you want to do any major engine work.
As for the carbs, if they haven't had any attention in years I would clean, inspect, and set up the carbs. As you mentioned the 80's a/c inline fours came from the factory jetted lean to pass emissions. one step larger on the pilot jets will wake up these engines in the lower rev range along with better drivability. This could be done when servicing the carbs for little $.
this should help you decide if you want to do any major engine work.
As for the carbs, if they haven't had any attention in years I would clean, inspect, and set up the carbs. As you mentioned the 80's a/c inline fours came from the factory jetted lean to pass emissions. one step larger on the pilot jets will wake up these engines in the lower rev range along with better drivability. This could be done when servicing the carbs for little $.
boyoboy
Well-known member
clutch up? says zx600 lol
I do like the bike and it has different style. I want to do the exhaust and get rid of the stock airbox since its rubber plenum has shrunk and does not sit in the box fully and someone has glued it in the past. so with these mod I'm guessing two sizes up on mains?
I guess on hard shift to second after maxing first gear.
boyoboy
Well-known member
I would fix the leaking airbox rubber (what cyl is this on? - air leak may be leaning out the fuel mixture). Clean inspect set up carbs with the stock airbox will be easier to tune than pod filters.
Two sizes up may still be lean on the mains with pods. Will need testing to know for sure. The pilots will also need to be two or more steps larger, like wise raised needles. A jet kit with your pipe and pods would be best.
EDIT
I would concentrate on the needed maintenance your bike requires first. Get all four (new) plugs showing a nice tan colour with the carbs done. If the carbs rebuild doesn't have that black plug looking a nice tan colour you will have to investigate further.
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Ok I'm still learning the whole carb thing my last bike a 90 VTR 250 had a big modified rinehart pipe (it came with it) all I did was up the main 2 sizes and it ran perfect, but that is a whole different beast.
I was looking at pods because I've been told it can help add abit of power with a exhaust.
Trials
Well-known member
Do you want to just make it louder, perform better on the street or are you preparing it for track racing?
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