slight miss at 4200 rpm 1986 140hp looper

[dcolpitts]

between 4200 and 5000 rpm engine runs strong but when trimmed out will drop 200 rpm and within 1 minute will pick back up. If I lower the motor and put more of a load on the motor the rpms smooth out no problems. Thinking possibly a poor connection stator/power pack. Anybody have some insight here? Thanks

 

[rabidfish]

Re: slight miss at 4200 rpm 1986 140hp looper

Could be almost anything... <br /><br />Have you checked the spark plugs? Does one look different from the rest?<br /><br />Is it losing just one cylinder, or more than one?<br /><br />If just more than one, what is the common system between the missing cylinders? ( fuel/ignition/etc...)<br />how about fuel recirculation? Does it miss at lower speeds if you tilt it up/down ?

 

[Walker]

Re: slight miss at 4200 rpm 1986 140hp looper

First thing that comes to mind is a carb float not set right since your problem seems to be related to engine trim attitude, but as Rabidfish stated, it could be any of a number of things.

 

[dcolpitts]

Re: slight miss at 4200 rpm 1986 140hp looper

thanks for the respones, Plugs are ql77jc4 gapped at .040. motor has 50 hrs on new power head carbs rebuilt with new power head, new vro, carbs double checked. plugs are dark brown, recirc valves and nipples changed on rebuild. This problem was before new power head so I,m thinking electric. The motor idles as well as a 140 looper can but trim has nothing to with it. I'm leaning towards bad elec connaection. Besides the tests min the manual for the coils is ther any other check, It almost seems that temp and or voltage charging has something to do with this.

 

[rabidfish]

Re: slight miss at 4200 rpm 1986 140hp looper

How about a misfiring power pack?<br />How about a double firing power pack?<br /><br />What was the reason for the new powerhead?

 

[dcolpitts]

Re: slight miss at 4200 rpm 1986 140hp looper

rebuild was due to time, up to bebuild it was all original, just 20 over on the rebuild due to time and a stuck ring due to carbon. The moter for the laast 5 years runs about 20-30 gallons a week, plenty of use. power pack and stator replaced about a year ago. It sounds like 1 cyl will go out for 10-20 seconds at that rpm then kick back in. Stator, power pack check out. Thats for replies

 

[ob]

Re: slight miss at 4200 rpm 1986 140hp looper

I mirror the comments above.Not sure whether your issue is engine angle or rpm related.One other longshot is a connection problem in the wire harness leading to the engine when trimmed at a higher angle as a result of brittle or chaffed wires.

 

[dcolpitts]

Re: slight miss at 4200 rpm 1986 140hp looper

thanks for the comments I'm heading to the lake ank recheck connections will post back tommorrow