3500 RPM is all she wrote

[mikerider]

I have a 18 foot center console deep-v with an 80s Evinrude 140 on it. The prop is a factory 13in x 19p. The motor is tuned up, the prop is in good shape, and when in full throttle, the linkages move to their full open position. However, I can't get the RPM over 3500. It planes fine, has decent holeshot, but I think its got more top-end that I wanna try to squeeze out of it. I've heard of an incorrect prop affecting RPM, but by 1000-1500 RPM? What am I missing and if it is prop, what size would yall suggest? Thanks in advance. Mike

 

[OBJ]

Re: 3500 RPM is all she wrote

Do you have spark at all cylinders Mike? You can find out by taking a timing light with you and checking each spark plug wire at WOT. Does "sound" like you are dropping one. Any maint history will help also....compression good?

Can you give us an idea of set up? Tell us where the anit-cav plate is in regards to the keel of the boat. Are you using the TNT...trimming out as you come up on plane?

 

[emdsapmgr]

Re: 3500 RPM is all she wrote

A few more questions: Have you had this boat for a long time or is it new to you. Has it ever run faster? How did you choose the 19 pitch prop? Is the engine a looper or crossflow? Is the boat fiberglass?

 

[kenmyfam]

Re: 3500 RPM is all she wrote

They are good questions you have been asked. My 140 of a similar vintage (1985) according to the handbook came standard with a 14" x 17" pitch prop.
I can pull 6,200 rpm on my 164 Doral full of people with this prop. The hole shot is great with this one. I have a 14" x 19" cupped that I use that then gives me 5,500 rpm at WOT and hole shot is just a tad slower.
Does sound like you could be on 3 out of 4 cylinders.

 

[mikerider]

Re: 3500 RPM is all she wrote

Thanks for all the help so far. To answer a few questions: I bought the boat cheap with a bad motor. I bought this motor from a mechanic that changed the head gaskets, water pump lower unit oil, and checked it all out. Plugs are new, but I should check it at WOT with a timing light, which I will do Wednesday. He assured me that the compression was well within spec. The cavitation plate lines up perfectly with the bottom of the hull. The boat is fiberglass. Since I've put the combo together (two months ago) it has always ran the same speed, which leaves a little to be desired. I am trimming properly - no plowing or porposing during plane. I think the engine is a crossflow. Thats the one that has a large hump between the cylinder banks, right? The prop came with the motor. The boat's dry weight is approximately 1200 lbs. Thanks again. Mike

 

[tashasdaddy]

Re: 3500 RPM is all she wrote

mike, get the model number of the transom mount, or the welch plug between the heads. are you sure the boats foam is not waterlogged?

 

[steelespike]

Re: 3500 RPM is all she wrote

After you confirm spark you may want to confirm the tach is accurate and get a GPS speed.

 

[mikesea]

Re: 3500 RPM is all she wrote

do the plugs look like they are all burning equal,you can run the engine on a hose and pull each plug wire off 1 at a time,and see if your misfiring on any,if your missing on just one check all the wires that go to the coils,also check that the coils are being grounded well,older ones have a seperate wire,newer have a grounding strap that can get corrosion like a car battery,you could also have a bad plug wire

 

[emdsapmgr]

Re: 3500 RPM is all she wrote

Thanks for the extra info. A couple of simple things to verify: be sure your spark advance is going fully against the stop when at full throttle. Also, make sure your tach is set to 6 for the new engine. Your 19 pitch prop is probably pretty close for the weight of boat-a change to a 17 would probably increase rpms only by 300. FYI, both looper and crossflow 140's have the hump in the back. The crossflow is bolted, the looper is cast into the block.

 

[OBJ]

Re: 3500 RPM is all she wrote

I'm kinda' falling in line with making sure the tach is giving the correct reading.

 

[mikerider]

Re: 3500 RPM is all she wrote

Yeah, the tach switch position sounds like something I should check out. Unfortunately, I'm at work and can't get to it yet. I saw the switch the other day on the back of the tach and kinda wondered about it.......the old motor was a Force (POS) that I never attempted to fix, I just took the previous owner's word that it needed repair and I disposed of it. I'll check the position of the dial switch and repost. Thanks for all the help so far.....you guys are awesome and I feel like I should check my mailbox for a consultation bill. Mike


By the way: tashasdaddy - This boat was outside uncovered for a while and the water logged foam problem may exist. I will end up replacing a small section of floor soon. If I find wet foam, should I remove as much flooring as possible to take out the foam, then replace the flooring after allowing the inside to dry completely? Probably end up replacing stringers too..... Please tell me there is an easier way.