1978 Honda CD185
Discussion
From another forum-this guy seems to be struggling can anyone help??
I recently bought a 1978 Honda CD185 Benly from ebay for a good price. The bike has only covered 18,000 miles from new and came fully MOT’d and roadworthy. I even managed to insure the bike fully comprehensive for £58 
Howether I have noticed a problem with the engine. I had this same problem with the last CD185 I owned a year ago but sold it before I fixed it.
Basically the bike will feel really nice and smooth and powerful to ride for 10 minuets. Then suddenly the bike will loose most of its power and it will feel really lumpy to ride. I think its spark plug related as per my following diagnostics…
I checked the oil level – all ok
I checked the air filter – brand new
I removed one of the cap leads from one sparkplug… engine carried on turning….
Then reconnected it and then removed the other lead from the second cylinder… engine stopped. That tells me that the bike is only running on one cylinder after 10 minuets of riding.
What is strange is I can hold the cap 1 cm away from the spark plug and it will fire more than it would when fully connected!
I then decided to remove the offending spark plug and found it to be heavily coked with black soot. I then removed the running sparkplug and this didn’t look as bad.
Out of curiosity I then swapped the plugs around and started the bike and removed the lead cap from the original offending cylinder… guess what… it carried on running. I then refitted it and did the same from the original working cylinder with the offending plug fitted…. Guess what… the engine stopped.
By the looks of things one sparkplug is getting heavily coked to the point where it no longer wants to run effectively.
Now even though the bike is 2 cylinders it only has one carburettor.
Now when the engine is running ok before the 10 minuets are over it runs really smooth with no smoke at all and nice and quiet tappets. The bike starts on the first kick with no choke.
I don’t understand why one plug is becoming badly fouled and the other isn’t. I’m getting really confused.
Could it be the carb mixture?
Has anybody on here owned one of these bikes and had a similar problem?
Advice is gratefully received.
I recently bought a 1978 Honda CD185 Benly from ebay for a good price. The bike has only covered 18,000 miles from new and came fully MOT’d and roadworthy. I even managed to insure the bike fully comprehensive for £58 
Howether I have noticed a problem with the engine. I had this same problem with the last CD185 I owned a year ago but sold it before I fixed it.
Basically the bike will feel really nice and smooth and powerful to ride for 10 minuets. Then suddenly the bike will loose most of its power and it will feel really lumpy to ride. I think its spark plug related as per my following diagnostics…
I checked the oil level – all ok
I checked the air filter – brand new
I removed one of the cap leads from one sparkplug… engine carried on turning….
Then reconnected it and then removed the other lead from the second cylinder… engine stopped. That tells me that the bike is only running on one cylinder after 10 minuets of riding.
What is strange is I can hold the cap 1 cm away from the spark plug and it will fire more than it would when fully connected!
I then decided to remove the offending spark plug and found it to be heavily coked with black soot. I then removed the running sparkplug and this didn’t look as bad.
Out of curiosity I then swapped the plugs around and started the bike and removed the lead cap from the original offending cylinder… guess what… it carried on running. I then refitted it and did the same from the original working cylinder with the offending plug fitted…. Guess what… the engine stopped.
By the looks of things one sparkplug is getting heavily coked to the point where it no longer wants to run effectively.
Now even though the bike is 2 cylinders it only has one carburettor.
Now when the engine is running ok before the 10 minuets are over it runs really smooth with no smoke at all and nice and quiet tappets. The bike starts on the first kick with no choke.
I don’t understand why one plug is becoming badly fouled and the other isn’t. I’m getting really confused.
Could it be the carb mixture?
Has anybody on here owned one of these bikes and had a similar problem?
Advice is gratefully received.
Funny how he solved similar problem on a previous 185 but is stuck with this. Must be different cause.
Sounds like might be engine problems-rings/valves causing oiling etc of plug or similar not carb related. Either that or some electric breaking down under load if there's a good spark with plug out.
Sounds like might be engine problems-rings/valves causing oiling etc of plug or similar not carb related. Either that or some electric breaking down under load if there's a good spark with plug out.
Edited by sprinter1050 on Thursday 27th May 12:44
sprinter1050 said:
Funny how he solved similar problem on a previous 185 but is stuck with this. Must be different cause.
Sounds like might be engine problems-rings/valves causing oiling etc of plug or similar not carb related. Either that or some electric breaking down under load if there's a good spark with plug out.
I don't think he did solve it if you re-read the thread.Sounds like might be engine problems-rings/valves causing oiling etc of plug or similar not carb related. Either that or some electric breaking down under load if there's a good spark with plug out.
Edited by sprinter1050 on Thursday 27th May 12:44
In my youth, I had a Honda 125 which sometimes displayed similar problems, except it was total loss of power since it only had 1 cylinder.
I tracked it down to the valve clearances being set too tight and when the engine got hot, the clearance closed up so much that the valves were not closing completely. Of course once you got around to doing a compression check, the engine had cooled enough for it to be apparently OK, so it took a while to figure out.
I tracked it down to the valve clearances being set too tight and when the engine got hot, the clearance closed up so much that the valves were not closing completely. Of course once you got around to doing a compression check, the engine had cooled enough for it to be apparently OK, so it took a while to figure out.
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