1998 175 Rude oceanpro

[walleyehed]

This engine runs and operates great at all throttle settings except between 800 and 1000 RPM.<br />It is very simular to a lean idle condition, but AT idle it runs fine, fwd, neutral & rev.<br />I've checked idle screws and enrichening has no effect, link-N-sync per manual is good, timing is normal specified location.<br />Fuel system is clean, as well as fuel/water separator. bulb stays firm.<br />This engine will sneeze once and if you don't hit the key quickly, it will sneeze and die.<br />The key thats throwing me off is that it runs great in gear @600-750RPM, and you have to transition quickly to a setting above about 1200RPM. Ideas???

 

[Reel Appeal]

Re: 1998 175 Rude oceanpro

When you say sneeze I will assume you mean backfire?<br />Is it overheating?pumping water at ALL speeds?<br />Improper timing,incorrect firing order,bad/worn spark plug(s),battery connections,water in the gas.I would suspect debris in the carb(s) or possibly a stator/trigger problem.

 

[walleyehed]

Re: 1998 175 Rude oceanpro

Lean condition symptoms...sneeze, yes backfire.<br />Water pressure gauge shows excellent readings at all rpm and plane-speed conditions. We have the timing sync electronic testing equipment, and all signs are normal. It gets new plugs every 60 days which is also when we change fuel/water separator.

 

[walleyehed]

Re: 1998 175 Rude oceanpro

^^

 

[angus63]

Re: 1998 175 Rude oceanpro

Are the carbs opening the same time the advance begins to move? Does it happen under a load and in nuetral? Is your idle timing set 2° to 4° ATDC? When did it start happening? You may want to stick a couple of fingers in each carb one at a time while in this rpm range and see if you can isolate the carb and tear it apart.<br />Good luck

 

[Dhadley]

Re: 1998 175 Rude oceanpro

Are we looking at a lean sneeze back thru the carbs or an actual ignition backfire thru the exhaust? If its a sneeze it almost sounds like it may be picking up some throttle linkage too quickly. A little past that and then the ignition catches up. <br /><br />Look at the side plate gaskets although if one was leaking it should be sneezing below the 800 range. Ya never know!<br /><br />Is it on a jackplate or is it otherwise mounted high that reduces backpressure? What plugs and grade fuel?<br /><br />Have you tried the toothpick trick to try and isolate the cylinder?

 

[walleyehed]

Re: 1998 175 Rude oceanpro

They only have 93 oct. at our gas dock, and I'm NOT convinced that's the way to go.<br />The sync is in order acording to the manual, BUT, when advancing throttle to that 800-900 mark, it sounds as though there is a higher vacume type noise that DOES go away when I manually move the timing arm fwd (advance), or continue on with the throttle.<br />QL78YC on the plugs, .030 on gap.<br />This engine is a 25" mounted directly to the transom in the lowest position.<br />It's on a 22ft Boston Whaler we use for towing other craft with...<br />No toothpicks yet, DH....talk to me....<br />K<br />BTW, yes, a lean sneeze.

 

[Dhadley]

Re: 1998 175 Rude oceanpro

OK, put the motor in the range that it messes up in. Have some toothpicks handy and put one in any of the low speed air jets. If blocking the airjet on that carb eliminates the problem, thats the cylinder thats getting too much air. <br /><br />It may not be related to simply one carb (cylinder). If you put the toothpicks in the mid range jets it will still have some minor effect on the idle. Just like the mid jet affects the top rpms slightly. Probably more than you'd think actually.<br /><br />93 octane has more oxygen bearing compounds so the motor will run slightly leaner anyway.