good compression?

ran the compression while ago. tell me what ya'll think.
Cylinder
#1 120 psi
#2 120 psi
#3 107 psi
#4 130 psi
The number 3 cylinder is what scares me with all the other cylinders being so high why is number 3 so much different.

Lazyman06 wrote:

ran the compression while ago. tell me what ya'll think.
Cylinder
#1 120 psi
#2 120 psi
#3 107 psi
#4 130 psi
The number 3 cylinder is what scares me with all the other cylinders being so high why is number 3 so much different.

Specs:
Standard 128~156 psi
Service limit 100 psi w/ <14 psi dif b/w cyl

Could do leak-down test to determine where compression is escaping.

Good Fortune!

How do the plugs look? Does it smoke? It's pretty close to the 10% rule, have you looked through the spark plug holes for carbon build-up on the pistons?

Several things can cause this:

1."Tight Valves", Having clearances that need a thinner shim between the cam(s) and valve bucket.

2.Carbon build up on #3 valves holding them partially open.

3.Stuck piston rings, letting compression go by the piston.

Engine Chemicals:

Mopar Combustion Chamber Cleaner # 04318001. Designed to remove carbon from combustion chambers & valves.

www.amazon.com/Yamaha-Ring-Additive-32oz...-32-00/dp/B002GUCLH2 (Yamaha Ring Free)

there is carbon on the piston so logic can deduct that there is carbon on the valves as well. it setting up as long as it has the rings might need to be set in again. it probably just needs to be ran to work the crap out of it's system

Lazyman06 wrote:

there is carbon on the piston so logic can deduct that there is carbon on the valves as well. it setting up as long as it has the rings might need to be set in again. it probably just needs to be ran to work the crap out of it's system

Take her out for an hour or so, then do the compression test. Hot numbers are what matter on the old air cooled stuff, unless the bike is particularily hard to start, and has horrible low numbers cold.

Coul just need a valve lap job. Won't know without further diagnosis.

Good luck.

yea is definitely cold lol so when I get it out next week i'll run it again