Sudden high rpms, loss of speed, smooth engine, not the prop..

[fordplayin']

I would be extremely grateful for any thoughts on this. I have an four winns with an OMC Ford 302 engine. It normally runs 4500 rpms and close to 50mph. We recently had an alternator replaced and a sea/raw water pump rebuilt. When we put the boat back in the water it had lost 8 mph... and gained 1000 rpms. The mechanic did do a slight adjustment on the idol as it had been stalling in neutral. It runs great, very smooth, no rough ride and the engine sounds great. I believe the tach is correct, even if it wasn't we lost 8 mph. We have cleaned spark arrestor, changed distributor cap and wires, it had a compression test before the season began, so I know these are okay. We have 2 props and marked and used both and neither are spun, same results with both. We cant see any problems with gas lines and wouldn't air in lines be causing an obvious rough ride, or engine hesitation of some sort?? Could it be the anti siphon valve? Were checking that next, but any other thoughts are appreciated. Also we plan to check water separater filter but that was new as well. Gas was emptied and changed this season. Boat doesn't have any water in bilge and it is running the same same with and without the family. We are noticing if we play with the throttle we actually seem to be better not at full throttle and got 43 mph with our kids yesterday showing about 5000rpms but when went wot it went 41, 5300rpm this is completely different than we ever remember...
Thanks in advance.

 

[kenny nunez]

I would be extremely grateful for any thoughts on this. I have an four winns with an OMC Ford 302 engine. It normally runs 4500 rpms and close to 50mph. We recently had an alternator replaced and a sea/raw water pump rebuilt. When we put the boat back in the water it had lost 8 mph... and gained 1000 rpms. The mechanic did do a slight adjustment on the idol as it had been stalling in neutral. It runs great, very smooth, no rough ride and the engine sounds great. I believe the tach is correct, even if it wasn't we lost 8 mph. We have cleaned spark arrestor, changed distributor cap and wires, it had a compression test before the season began, so I know these are okay. We have 2 props and marked and used both and neither are spun, same results with both. We cant see any problems with gas lines and wouldn't air in lines be causing an obvious rough ride, or engine hesitation of some sort?? Could it be the anti siphon valve? Were checking that next, but any other thoughts are appreciated. Also we plan to check water separater filter but that was new as well. Gas was emptied and changed this season. Boat doesn't have any water in bilge and it is running the same same with and without the family. We are noticing if we play with the throttle we actually seem to be better not at full throttle and got 43 mph with our kids yesterday showing about 5000rpms but when went wot it went 41, 5300rpm this is completely different than we ever remember...
Thanks in advance.

 

[fordplayin']

So crazy thought, the anti siphon valve actually had some gunk at the bulb we cleaned it out could this really be the problem? That would be great!!

 

[kenny nunez]

Make sure that the throttle is opening the carburetor all the way and not “over stroking” which means the throttle goes all the way at one setting and if it goes further it starts to slightly to actually pull the carburetor off of WOT.
Under most situations the description points to a wrong propeller but you said that you tried others with the same result.
Haye you ever pulled the suction tube out of the tank? There is a small filter in the tube that can cause fuel delivery problems.

 

[fordplayin']

Ours doesn't have a filter or screen on the bottom of the tube. I've checked in to this and apparently its normal. Its slanted on the bottom with no place for a screen or filter ... I've seen diagrams that show filters though, which is why we looked into it. Do you think this could be the cause? I realize the only way to know is go to the river...

 

[kenny nunez]

Ours doesn't have a filter or screen on the bottom of the tube. I've checked in to this and apparently its normal. Its slanted on the bottom with no place for a screen or filter ... I've seen diagrams that show filters though, which is why we looked into it. Do you think this could be the cause? I realize the only way to know is go to the river...

 

[kenny nunez]

My favorite tried and true method is to by pass the tank with a 6 gallon outboard tank. That method usually narrows down the problem.

 

[fordplayin']

Interesting... on the throttle, if were engaging the throttle should it open to 90 ° when wot, sorry if that's a dumb question.

 

[fordplayin']

Interesting... on the throttle, if were engaging the throttle should it open to 90 ° when wot, sorry if that's a dumb question.

 

[fordplayin']

On the carb plate I mean

 

[kenny nunez]

Just have someone push the throttle wot and be sure that the carburetor butterflies goes all the way open and stays, not trying to start closing.
If you ever watch the way the control works on the back side you will see what can happen.
It just depends on who rigged the boat and set up the controls, some just go 90* or further or less.

 

[CaptnKingfisher]

My first thought is that the mechanic didn't fix the real problem when he adjusted your idle speed. Stalling in neutral could be a consequence of a problem in the ignition system or a dirty carb or a vacuum leak. If he was adjusting the idle speed and air mix to make the stalling go away you might be way out of spec and as a result getting poor performance at high speeds. I would verify your idle rpms are within spec for the engine before hunting down other solutions. I'm not sure what youre manual calls for but I would guess it should be around 600 rpms in gear in the water. Check that out before anything else

 

[fordplayin']

Thanks for this thought. We were out again yesterday. We did realize one of our 2 props(a stainless steel one) did infact show it was probably a spun prop. The other , not stainless, however it should only make us lose 2-3 mph and have no bearing on rpms is NOT showing its spin. We sent the stainless in yo be rehubed a week ago, of course we wont get it back for another week. We realized today our idol rooms should be 550-600. The carb was cleaned/taken care of I forget the exact work done in May. We originally believed the problem was it hadn't been run in a long time and even though gas was completely drained, we should have run ethanol free 89, not thinking we ran 87 with ethanol. It was seeming like we were working out kinks... I would have been curious to see it not touched. We will turn that back. I also noticed one of the blades on the aluminum prop is slightly torqued, not sure how much it has to be bent or out of alignment to make an issue?? We hadn't run this prop in many years preferring the speed of the SS. Is there anything else in the lower unit, you could think of that would mimic a spin prop IF correcting the idol and the puttung SS on fixed doesn't make a difference... I understand the carb still could be the culprit I'm just a bit suspect of that per maintenance in May with not a ton of hrs before problem occured. My apologies for long details. I'm trying to think of all bases. Thanks again everyone!!!

 

[fordplayin']

Well super encouraging... we turned idol back went out last night. The rpms didn't go above 5000. That is a huge improvement... and we got up to 44mph, so gained 5. Seems random. We fiddled with a few things, just making sure all hoses were tight, everything was ?? My husband did clean out a gas tube that's on top... bear with me this isn't going to be technically correct... maybe overflow hose, or something to do with carb... its small, I'd guess 12-18 inches long and orange. Not the actual fuel lines. It had a some gunk at one end. Maybe that helped as well. Anyway from this text to Gods ears I'm praying when we put the S.S. prop back on we get our speed back close to 50 (as this aluminum isn't perfect) and rpms back under 4800. The engine has always sounded beautiful through all of this, so it sure seems like it is all good.

 

[vgnech]

I had same problem with my engine and have a chevy 305 and rebuilt car and still. Had same problem then I found out it was the pump in the float bowl
I replaced the rubber seals and it fixed the problem and now I can get full rpms