1980 DOHC CYL-1 Carb issues.

CafeDOHC

CB750 Member
Messages
11
Reaction score
0
Points
1
Location
Philadelphia PA
I'm posting here to see if anyone has tips in helping me figure out my issue.
So my Cylinder 1 plug keeps fouling after a short period of time, I can hear my motor pinging
then the plug will foul. No oil or wetness on the plug when I pull it, just a lot of black carbon
build up preventing spark. New intake boots, CBR F2 plug wires and coil packs are functioning normally.
My idle is weird and is always different from ride to ride. The bike also has NGK Iridium plugs, K&N pod filters and a 4>1 exhaust
with 53E Primary needles. I pulled my carbs off and inspected the inside and all carbs are spotless, no varnish or discoloration,
newer unstained floats. Its definitely over fueling as the tip of my exhaust is also black with carbon build up and
it has the tell tail smell of extra rich unburnt fuel. This week I plan to check carb sync with a set of gauges as
the next step, but what am I missing? Any tips are welcome.
Thank you!

**Image of a brand new plug with 10 miles**
 

Attachments

  • IMG_2396.jpeg
    IMG_2396.jpeg
    81.6 KB · Views: 100

dirtdigger

Moderator
Staff member
Messages
3,343
Reaction score
59
Points
48
Location
Black Hawk SD
Nope, Honda spec for the valve clearances is way to tight and they can burn valves very early in their life. Many times you are lucky to get 20000 miles out of them. Burned valves or low compression is common under 20k. If valves have never been adjusted then I can almost guarantee that valves are being held open.
 

CafeDOHC

CB750 Member
Messages
11
Reaction score
0
Points
1
Location
Philadelphia PA
Nope, Honda spec for the valve clearances is way to tight and they can burn valves very early in their life. Many times you are lucky to get 20000 miles out of them. Burned valves or low compression is common under 20k. If valves have never been adjusted then I can almost guarantee that valves are being held open.
good to know, great info. valves have been adjusted relatively recently actually, but I did not own this bike prior to carb rebuild and valve lash adjustments, I am just working out the kinks on this bike I purchased.
 

CafeDOHC

CB750 Member
Messages
11
Reaction score
0
Points
1
Location
Philadelphia PA
Nope, Honda spec for the valve clearances is way to tight and they can burn valves very early in their life. Many times you are lucky to get 20000 miles out of them. Burned valves or low compression is common under 20k. If valves have never been adjusted then I can almost guarantee that valves are being held open.
Update, took the bike to several shops to have them listen to the noise and issue I have. Everyone agreed its probably valves. Its in a shop now, so I'm just waiting to hear back what they find. Will update as I find out what's going on.
 

CafeDOHC

CB750 Member
Messages
11
Reaction score
0
Points
1
Location
Philadelphia PA
Another update, from this thread.
7 of 16 valves were out of spec, they have been shimmed and issue has been resolved.
Now as far as the noise I had originally mentioned that sounded like a ping or wrist pin, rod knock or out of sync carbs, I have hunted that noise source down to be the Primary Chain Tensioner. So now I have to hunt down that part which is nearly impossible to find.
 

CafeDOHC

CB750 Member
Messages
11
Reaction score
0
Points
1
Location
Philadelphia PA
Final conclusion of this saga. Pulled oil pan to check tensioner. Turns out my Cyl #3 rod bearing at the crank ( right next to that primary chain tensioner) ejected itself and the rod was moving back and forth on the crank. Time to hunt down a motor.
 
Top