RPM loss

[Todd Humphreys]

I have a recently reringed 1982 75hp Johnny. Approximately 20 hrs of total running time the rpm's are gradually declining. Fresh rings the motor turned 6200 rpms; 15 thru 20 hrs the rpm's are at 5800. Is this normal???

 

[DJ]

Re: RPM loss

I would be concerned.<br /><br />Any signs of metal transfer on the spark plugs?<br /><br />How is the compression?

 

[OBJ]

Re: RPM loss

Loopers hate running lean. I'm assuming that the engine was rebuilt recently. Were the carbs overhauled as part of the rebuild?<br /><br />I would take DJ's advice and get compression readings on each hole.<br /><br />Stay in touch.

 

[reeldutch]

Re: RPM loss

defenetly check compresion.<br />may be do a link and synq if comp readings are good.<br />defenetly check for running lean.Clean carbs set float etc.<br />wat brand of tcwIII are you using.<br />run it on 50:1 with champs Ql77jc4<br /><br />reeldutch

 

[Todd Humphreys]

Re: RPM loss

No metal on plugs. Carbs were rebuilt when rerings with kits. Carbs are not adjustable, they have fixed jets. I did do a quick test of compression using my finger over the plug holes and hand spin flywheel over and the bottom cylinder has no compression. Top and middle cyls pushed air passed my finger, bottom had no pressure in the up stroke. I'm going to pull the head off and have a look inside. Citgo Marine plus oil. 50:1 with QL77JC4 plugs. Thanks for all the tips.

 

[reeldutch]

Re: RPM loss

oil is good plugs are good.<br />pull the head an take a look.<br />remember that if your walls are scored or rings are broken that there must be a cause.<br />after you reringed did you check the ringgap?<br />did you hone the block and cleaned it thourough?<br />check the compression with a gauge.<br /><br />let us know what you find.