2.5 merccruiser low rpms

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  #1  
Old 07-05-04, 07:17 PM
keltie
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Exclamation newbie girl! merc 2.5-no power/torque @ 3500 rpm

just bought a renkin elite 1988 with mercruiser 2.5 and alpha leg ( what's the hp on that by the way)...starts fine with 2 pumps of the throddle. no trouble getting up to 3500 rpm but really sluggish speed...no torque. has a long time getting on step. also hear some ticking sounds at low rpms. HELP...i'm a female that has some mechanical education and understand the jargon. could it be carb, vapor lock, loose hubs on prop. HELP...feel like we put $ in the toilette!!HELP HELP! 1st inboard..jut sold our 90 merc outboard and now regretting it...hope there are answers out there!!!!
 
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  #2  
Old 07-13-04, 05:56 PM
keltie
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2.5 merccruiser with 3.0 carb???low rpms?

just bought a 88 renkin elite open bow with motor as above. had sparks changed and tune up as had problem getting up on step. was really sluggish with rpms of 3200-3500 and since the work now rpms of 3800. took a while to get up to speed with 3800 and 2 adults/2 kids but with 6 adults barely got to 3000 rpms and hardly moving. any simple things we could check...hoping it's not the compression!!! or timing!!! shouldn't a boat like this W)T rpms be about 4500. this is a ski boat
 
  #3  
Old 07-13-04, 05:59 PM
keltie
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inboard vs outboard for skiing

we had a 70's starcraft closed bow with 90 merc outboard and now a 88 renkin with 2.5 merc and apparently 3.0 carb?!? no problem with skiing with our outboard but theis one is sluggish and takes a long time to get on step (see thread of merc 2.5 with 3 carb..low rpms) what should we expect for differences in an in/outboard when it comes to torque, time it takes to reach top speed etc
 
  #4  
Old 07-13-04, 07:47 PM
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with 6 adults on board, that's a lot of weight for a 2.5 to handle. frankly, it's underpowered.
 
  #5  
Old 07-14-04, 05:58 AM
pete43
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all I know is that outboards more $$$.....Inboards (which I have) have the advantage of "line of site" view from spotter to skier (no outboard engine cowl in the way) I have a 130HP inline 4 cyl and I have pulled tubes (2 man) and kneeboard with no problem..Have not tried skis yet..but it should not be a problem...This is not a "fast boat" (top speed wot range 40 to 42 mph)but it has enough power to pull 25mph + which is fast enough for most skiing anyway.... It is OK on gas being a 4cyl..you can have a good day (4 to 6 hours) on a little more than a half of tank of gas (10 gallons)..Another plus (even though still loud) is that I/O is "quieter" than an outboard.The disadvantage if I/O like I have is worries of fuel, oil, etc in bildge (it is an old boat-'87)..Its just a matter of staying on top of it in maintenance..Another is the stern drive coming up (draft) limitation..An outboard can be taken totally out of water..I ran into some "lakeweed" the other day and had to oar out of it...drive would not raise up enough to get me out of it...anyhow,hope this helps..Oh, and the last thing about an outboard, if you have a rotted-weak transom you have to replace transom (it totally hold outboard in place)on a I/O there is "less stress" on transom since only drive is attached to it...more stress on motor mounts in bilge than anything else.....hope this helps out and sorry so long...... ...pete43
 
  #6  
Old 07-14-04, 07:53 AM
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Id say its all in what you want to do with the boat or use it for. On any boat I have had it takes about a year to find out just what "wheel" or prop I want on the boat For one thing so the kids cant go over the RPM red line. Some shops will rent you props to try them out and see what you need in pitch and Di there. You can find one that will get you up and out of the hole.


ED
 
  #7  
Old 07-14-04, 07:53 AM
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Hello: keltie

I combined (merged) your two questions into one thread. Doing so allows it to be more easy to follow along than jumping from one thread to another. Kindly use the reply button to continue this post as long as it pertains to the same boat(s). Doing so will help us all. Much appreciated & Thanks.

I agree. The current boat is underpowered for the load. Changing props may help some but you will lose some power and thrust in exchange for the low end power to pull skiers.

Always a compromise when changing props and more so of a compromise when the existing engine is underpowered for the intended usage. Lighten the load with less weight of passengers when sking will be done.

Regards, Good Luck & Safe Boating.
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  #8  
Old 07-15-04, 12:25 PM
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Wink

I say play with the prop . Rent one and see what it will do on the pitch and D of it. Also check the carb out to see if its clean.


ED
 
  #9  
Old 07-16-04, 05:36 AM
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Hello; keltie

If the engine runs well, chances are the prop is the cause. May not be all of the problem but part of it. May be best to check with the local boat repair shops or dealer and verify, if the current prop is the correct one for that engine.

May not be a prop problem. Coming up on plane can be caused by several other conditions or problems. Prop may be the easiest and least expensive to correct.

Prior owner may have exchanged props prior to the sale or had the same problem and did not have it ckecked out or did not not know what to do either.

Always some risk buying used from a private unknown owner. If the prior owner is not known and that is the case. If purchased from a used boat dealer, return the boat and state the problem encountered.

Not all boat dealers or mechanics are equal. Some are better than others, while some are exceptionaly far better than all the rest.....

Kindly use the reply button to add any additional information or questions, etc. to this thread. Using this method also moves the topic back up to the top of the daily list automatically.

Regards, Good Luck & Safe Boating.
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  #10  
Old 07-19-04, 05:54 PM
keltie
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just had compression test done...i have cut and pasted the results of our mechanic

end cylinders are at 150
2 center cylinders are at 120-125
He also said that there is lots of blow by, and the problem could be a head
gasket...however, you dont know until it is taken apart. The problem could
be more serious, such as a complete rebuild...again??? already been rebuilt!!

He wasnt sure on the condensor in the dist and he did not do a recheck once
he reset the timing so im not sure. He did suggest to switch to electronic
ignition distributor....check the cost

He recommended for the drop in compression to use 4 cylinder engine restore.
it goes with the oil and is supposed to seal any gouges in the cylinder
wall

We will probable try the seal 1st unless any other advice. should we get better rpms at that compression?? 3800 with 2 adults at WOT and 3500 with 6 adults WOT (17 ft rendin with 2.5 merc)...could it be just a distributer cap??? need to ski...summers are short in canada!!
 
  #11  
Old 07-19-04, 06:01 PM
keltie
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here's what we found out so far. are those compressions all that bad?!?! we thought we'd try the sealant 1st. shouldn;t we get better rpms than 3500-3800 with 2 - 6 people on board???
it's a 17 fter with 2.5 merc. do you really think underpowered??

Compression
2 end cylinders are at 150
2 center cylinders are at 120-125
He also said that there is lots of blow by, and the problem could be a head
gasket...however, you dont know until it is taken apart. The problem could
be more serious, such as a complete rebuild.

Timing
Mark reset 8 degrees

He wasnt sure on the condensor in the dist and he did not do a recheck once
he reset the timing so im not sure. He did suggest to switch to electronic
ignition distributor....check the cost

He recommended for the drop in compression to use 4 cylinder engine restore.
it goes with the oil and is supposed to seal any gouges in the cylinder
wall

I am hoping to get a 15deg prop to check it out as well to get some more
performance/torque
 
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