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Cant get much more than 20 with aq131a in 17 foot

J

jwest

New member
"hi, I bought a 1986 165 sunru

"hi, I bought a 1986 165 sunrunner with a aq131a/270 a couple of weeks ago. New to the boating thing but was under the impression that i'd get 30ish mph(been reading every thread on here that I can find). Everything seems to be running fine but at 4500 rpm I'm only going 22.Put a doel-fin hydrofoil on and it helped to keep me on plane but just seems like I shouldnt have had to. It has 14 by 19 prop. Since reading this forum I've checked for prop slippage=none. Not sure where else to look. I did talk to the previous owner and he said that was typical for this engine and thats all he got out of it in the 5 years he had it.......any help would be great....... thanks
Joe"
 
I should add that on one of th

I should add that on one of the blades of the prop on the trailing end theres about a 1/4 inch bend at the end about 3 inches long......would this effect performance that bad?
 
"Something is wrong here.

I

"Something is wrong here.

If the RPM are 4500 and the propeller pitch is 19", to get 22 miles per hour (I assume you are talking land miles and not nautical miles) you would be having a propeller slip of around 44%, which is extremely high. The slip for a fiberglass planing boat of about 17' should be around 12-18% at the most.

Several possibilities I would look into:

1) The propeller may have a much lower pitch than 19" (around 14" perhaps). You may want to take it to a shop where they can verifiy its actual pitch.

2) The propeller may be spinning on the hub. But apparently, you have checked this and it is not the case?

3) The actual RPM could be much lower than 4500. Check the tachometer's accuracy.

4) The trim pin in the transom could be in the wrong position. Default is middle hole. If you put in the hole closest to the transom, the boat will plane faster but the bow will be too low at higer speed and that will create a lot of drag. And if the trim pin is in the hole farthest away fromt he transom, the bow may be too high and the propeller thrust will be far from parallel to the water surface, which will also rob you a lot of speed.

5) The boat may have a lot of marine growth, which will slow it down a lot.

6) The boat may be too heavy due to being waterlogged, or having too much equipment onboard. You may want to consider weighing it.

7) Where are you reading the speed? Try to use a GPS for accurate speed over ground reading.

8) I would not run a prop with a bent blade. Performace would be compromised and you will not do any favour to the prop shaft and gears.

I hope this helps."
 
"thanks for responding, I'

"thanks for responding, I'm new to this but have learned quite a bit from this forum. Since reading some of the stuff on here I've checked several of the obvious things...and yes I agree "something is wrong here"

1) pulled the prop and google'd the id number on it, thats how I got the 19" pitch

2) marked the hub and checked for slippage(none)

3) I've been thinking that the tach was off (it is on the 4 cyl setting), it says its idling at anywhere between 1200 and 2000 and it just doesnt "feel" that high. Also at about 4800 it jumps up to 5200 or so, about that time it does feel or sound like your at wot, I get scared and back off.

4)The trim pin was in the middle hole, I moved it to the closest one to the transom tonight in preparation for next time I take it out

5)Theres no growth on the bottom, its been on a trailer out of the weather for the better part of a year. could use a was though I'm sure.

6)The only weight is about 350 lbs of people (2 adults) small tool box, 16 gallons of gas, and the mandatory safety equip.

7)checked the speedo against a gps and it was dead on

8)definetly looking into a new prop, was thinking a 21" pitch for a little more top speed but not sure the props the problem (allthough I never thought about the bearings and such, seems reason enough to replace this one or have it repaired)

thanks for your time...lets me know that I'm not crazy for thinkin something is wrong"
 
"Quick note - "prop slippa

"Quick note - "prop slippage" in this conversation refers to slippage of the prop blades relative to the water flowing past the prop, once you have determined, as you have, the the prop is stable on the shaft. All propellers slip to some extent, and I second El's sentiment that the prop slippage you are seeing is very high. This prop calculator may be of some help, you can enter all known (or best estimation) values and get a return for the variable:
http://www.rbbi.com/folders/prop/propcalc.htm

El - In this post as in so many others, your guidance is invaluable. Just wanted to give you some more recognition, thanks!

Jonathan"
 
"thanks for the link, punched

"thanks for the link, punched the numbers in and it said exactly what el pescador said about slippage. Was reading some more in the forum last night and found something about clutch cone slippage possibly having effects like this. Does that seem likely? And if so is there a way I can check? Also what would be the best way to check if my tach is correct? Thanks in advance
Joe"
 
"Yes..... Ditto points 1 thru

"Yes..... Ditto points 1 thru 8, and Kudos to Eduardo. He relentlessly offers great help and advice here!
thumbs_up.gif


I'll second the tachometer idea and raise you TAT assuming that all other items are OK.
See your OEM specs, and make sure that your ignition timing is correct at the higher RPM range, known as "Total Advance Timing".
It will be right there in your OEM manual.

As for the tachometer.... get yourself a hand held lasor tach and check the instrument against this. Many of these are adjustable from behind.
http://www.google.com/search?source=ig&hl=en&rlz=1R2GGLL_en&q=laser+tachometer&a q=0&aqi=g4g-s1g4&oq=laser+tac

The idea of the sliding sleeve/cup slipage is remote, but none-the-less is a consideration. If you are in need of U-joint/bellows replacement, now is the time to look at this.
How is your gear oil?
Is it clean?
Any water present?
Have you switched to synthetic recently?

Sliding sleeve/cup slipage can be contributed to by one of the above. Again, rare, IMO!


P of E (process of elimination) will get you there. One item, and one item only at a time!
You will find the cause if you do this!
."
 
"Ricardo wrote:

<font colo

"Ricardo wrote:

<font color=""0000ff"">As for the tachometer.... get yourself a hand held lasor tach and check the instrument against this. Many of these are adjustable from behind.</font>

Ricardo, I was not aware of the laser tachs until now. They seem to work by attaching a piece of reflective tape on what you wish to measure. In the case of a marine engine (specifically an AQ130C), would you attach the tape to the pulley on the front of the engine? Thanks for enlightening me!"
 
"I checked the tach last night

"I checked the tach last night with a digital tach on a timing light and it said the boat tachometer was off. At 850 and 2100 on the digital the boat tach said 1200 and 3000 respectively, I cleaned all connections and recieved the same results, so it seems theres my problem. Ordered a new one last night along with the pertronix ignition and coil everyone on here raves about (hope that helps the hard starting). As far as the gear oil I changed that the same day I checked the prop for slippage..looked fine, just thought it was a good idea. So with anyluck a the new tachometer and a tune-up and I'll have'er running right, find out in a week or so.
I really appreciate the input
thanks
joe"
 
"I know you said that the sele

"I know you said that the selector switch is set to "4", however before springing for a new tach try it on the other positions, or switch it back and forth between the other settings a few times before returning it to "4" as there may be some junk on the contacts. This is best done with the engine off."
 
"Well, it all seems clearer no

"Well, it all seems clearer now. It would appear that your tach reads 50% higher; which means your WOT RPM are about 3000 instead of 4500, and that means:

1) You are overloading the engine at wot; and

2) If you do 22 miles per hour at 3000 RPM, your propeller slip is about 12%, which is pretty normal for your boat type and size.

What I would do is

1) check the tachometer setting. Since it reads 50% higher, it seems to read 3 pulses per RPM instead of 2. It would appear it is set for a 3-cylinder, 2-stroke engine instead of a 4-cylinder, 4 stroke.

2) Get a prop with a lower pitch. I would try something in the range of 14x17, which would give you around 28 miles per hour. And if you can go higher in RPM with that prop at WOT, then I try a 14x19."
 
"I am assuming that the engine

"I am assuming that the engine will not run above the 4500 RPM reading in the boat tachometer even if you try to give more throttle, correct?"
 
"no, it will keep goin up past

"no, it will keep goin up past 5000 pretty easy, after about 4800 the rpms seem to climb pretty fast. I read your post last night and couldnt wrap my brain around it.
It would seem to me that if the boats rpms are actually slower than what the tach says, in theory (which i'm not gonna do) I could run the rpms up past 5000 with little risk, maybe I misunderstood what you meant by "overload". I assumed that you meant I was pushing the rpms to fast. I would really like to think that I'm doin 22 at 3000.
I did fiddle with the switch on the back of the tach like robert said but didnt change anything, also no settings for 2 stroke, just the 4,6,8 cylinder settings.
I could be wrong (happens all the time),but I would think I need to get the tachometer replaced and dialed in before I did anything else, or possibly check the timing as was mentioned to try and isolate the problem."
 
"Yep, time for a new tach... h

"Yep, time for a new tach... however, just for kicks, where is the tach connected to on the ignition system?"
 
"Joe - I believe the max RPM f

"Joe - I believe the max RPM for that engine should be 4800rpm, max cruise should be about 4500rpm (others please confirm). That doesn't mean you can't wind it out a lot higher when revving it with no load (i.e. prop not engaged), it's just not designed to do that and will fail at higher rpm fairly quickly. (I assume you know all this, but thought I'd chip in for others reading this thread who are not sure.)

I found a tachometer for my 82 Bayliner that is the right diameter to slide in the stock opening for about $30 at Checker Auto (Northern Automotive in other states I believe). It does not look identical to the stock equipment, but works fine and looks sharp. As I recall, the opening size was 3-1/4" diameter. When I first switched them out, to test the old vs new tach I left the new old one connected, and temporarily connected the wires to the new one. Once I started the engine, I could see the old one was clearly not working correctly, and the new one was accurately reflecting engine rpm.

If I understand what El is saying, you and the previous owner have been running the engine at what you thought was WOT at about 4500rpm, and only getting 22mph when in fact it was running at 3000rpm, which as you said would be good news. With a new tach showing correct rpm, same boat, prop, and 4500rpm should be getting you closer to expected speed performance. With my AQ125a in a 19' Bayliner, I get 32mph (gps measured) WOT at 4400rpm. I think my prop is 14x17.

Jonathan"
 
""If I understand what El

""If I understand what El is saying, you and the previous owner have been running the engine at what you thought was WOT at about 4500rpm, and only getting 22mph when in fact it was running at 3000rpm, which as you said would be good news. With a new tach showing correct rpm, same boat, prop, and 4500rpm should be getting you closer to expected speed performance."

I hope so, looks likely.

I found a replacement tachometer on ebay that looks as close to a direct replacement as i'm gonna find with an adjustment on the back to tune it.

Robert, I read on a post somewhere on here that that its the gray wire on (if I remember right) the negative side of the coil. Thats what I went off of as I dont have a shop manual for it yet (in the mail)"
 
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