78 85 hp cuts out briefly under 1/2 to full throttle?

[treebeard]

Hi,

Had my new to me boat out today for the first time. Motor ran like a charm with a nearly full tank of premium with 50:1 mix. Ran boat for probably 2 hours full throttle and pulling the kids on the tube and wakeboarding. Problem developed after a few hours when the motor would cut out briefly. If I brought the throttle all the way down it seems like it was running fine at low speed (no issues docking and loading the boat), only started having issues when I tried to speed up. The problem was intermittent but seems to become progressively worse. As mentioned, the motor great for the first few hours. Priming bulb still feels stiff like it is full.

Suggestions are very much appreciated.

 

[Blue Bomb]

Re: 78 85 hp cuts out briefly under 1/2 to full throttle?

Are you sure it's a miss. It might be clutch dogs in the lower unit. I thought mine had a miss, but it was lower unit. adjusted it and got one more year out of it. do a search on clutch dogs and adjust your shifter toward forward such that reverse just egages, or doesn't egage and see if it goes away.

 

[treebeard]

Re: 78 85 hp cuts out briefly under 1/2 to full throttle?

Thank you very much for the reply Blue Bomb. I will research based on your recommendation, wouldn't the engine still rev high with the condition you describe. As I said the motor was running great, then after a few hours at 1/2 to full it behaved like motors do when you start to run out of gas. I'll check all the lines, maybe something came lose in the tank and affected the filter? not sure why it would run well though at low speed if it was a fuel supply issue.

 

[emdsapmgr]

Re: 78 85 hp cuts out briefly under 1/2 to full throttle?

Probably easiest to check for spark first. Weak ignition compoents start to cause problems when the engine reaches normal operating temps. You can check the spark quality with an inductive timing light. Put it on each plugwire when the engine is under load-like idling in gear at the dock. The flashes in the gun will show you intermittents and no fires. If the spark checks out, the fuel is likely the culprit. When it starts the intermittent problem, constantly prime the fuel hose bulb. This will force extra fuel into the carb bowls. If it runs fine while you prime the bulb, you may have a weak fuel pump. (won't supply enough fuel to run the engine at WOT.) If the pump is somehow original, it may be deteriorating due to the ethanol in today's fuels. Ethanol fuel will attack the bladder in the fuel pump and any original fuel hoses in that engine which may also be original.