Hunter 460 Throttle Question

Aug 15, 2014
12
Hunter 460 Des Moines, WA
Hello, I have a 2001 Hunter 460 with the flex-o-fold prop, previously my WOT was around 3600rpms. This put my cruising RPM's at around 2800. Over the last year i've noticed I can no longer get up to 3600rpm's. I top out around 2900. Thinking this could be because of a running gear or bottom growth issues I had the boat hauled, new bottom paint, running gear inspected (nothing looked out of the ordinary). I'm still not able to get the RPM's above 2900. I had the engine serviced, oil change, fuel filters, valve timing, belts, etc etc. After performing the engine service i'm still unable to get above 2900rpms. Does anyone have any other suggestions? Are there adjustments I can make to the throttle cable? I've heard they can stretch and or may need adjustment from time to time. Any suggestions would be greatly appreciated!
 
Feb 17, 2013
53
Hunter 380 Port Clinton, Ohio
Perhaps the problem is an incorrect reading from your tach. They sell a small tach with a sender that clamps onto one of the injector fuel supply tubes. This gives you an accurate rpm reading. Install one of these and compare the two readings. You could have a partially plugged injector also.
 
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
The above is a good suggestion. It's unlikely a cable would stretch sufficient to be noticeable.
 
Jun 2, 2011
347
Hunter H33 Port Credit Harbour, ON.
There are usually 2 stop screws on the governor lever, one for full throttle and one for Idle. Check to make sure that the screw for the full throttle has not come loose and moved to limit the governor lever movement. The governor lever is what the throttle cable connects to. What is your unloaded full throttle? If it is the full throttle stop adjustment the RPM in no load should also be low.
 

Mikem

.
Dec 20, 2009
820
Hunter 466 Bremerton
Carol, you didn't mention it but has your speed dropped as well. If not it might be the tach. If it is the tach I recently replaced my malfunctioning tach with one from SBO. It was easy to install and worked flawlessly. BTW it was identical to the original so no fit issues.
 

senang

.
Oct 21, 2009
304
hunter 38 Monaco
Can it be that the Flexofold is now limiting the rpm because of not folding completely as before?
 
Feb 14, 2014
7,400
Hunter 430 Waveland, MS
or may need adjustment from time to time
If you have a Morse Controller, then it can "creep" and need an adjustment.
I find the difference in my Cruising SOG, at 3200 rpm versus 2200 rpm is 0.5 knots. My fuel consumption goes dramatically UP for that extra speed.

Your exhaust riser or muffler can be restricted also.
Jim...
 
Aug 15, 2014
12
Hunter 460 Des Moines, WA
Can it be that the Flexofold is now limiting the rpm because of not folding completely as before?
When the the bottom paint was done, I had them check the prop. It was cleaned and they said it appeared to be functioning correctly. I replaced the tach today but in neutral I was only able to achieve slightly better WOT rpm's. I believe it was around 3100 whereas before it was 3600. I'll try on Sunday when I return from the weekend. I looked at the throttle cable (see image attached), it appears to be OK. The aft screw regulates the max throttle. Would anyone advise adjusting it? Not sure how this would have changed over the course of the years.
 

Attachments

Aug 15, 2014
12
Hunter 460 Des Moines, WA
Carol, you didn't mention it but has your speed dropped as well. If not it might be the tach. If it is the tach I recently replaced my malfunctioning tach with one from SBO. It was easy to install and worked flawlessly. BTW it was identical to the original so no fit issues.
Mike, I haven't seen my speed drop when cruising at 2700-2800 RPMs. For curiosity sake, what do you typically cruise at? Your boat is as close as it gets to mine. :) - Chris
 

Mikem

.
Dec 20, 2009
820
Hunter 466 Bremerton
Hi Chris,
I cruise around 2900 which gives me almost 8 kts. fYI, I still get 3600 rpm at WOT. With a light boat that's 8.6 kts. I have 950 engine hours. I'm sure you have more than that. Twice I had engine rpm drop. One was a malfunctioning tach (I had to keep tapping the bezel to get anywhere near a correct reading) and the other was clogged fuel filters. Have you looked at the throttle cable in operation...any apparent slippage when advancing to WOT? A big item not checked, and mentioned above, is the mixing elbow. Yanmar recommends that if the engine runs below 2000 rpm for a prolonged period the throttle should be advanced full for several minutes to clear the turbo and also cycling the throttle in neutral idle to full rapidly 5 times prior to shut down for the same purpose. Mixing elbow and turbo are the two remaining biggies as far as I know. A fellow on my dock worked at Tacoma Diesel for 31 years and just rebuilt my son's 20hp yanmar. Runs like a top. He is now an assistant Wa state ferry asst engineer. I will ask him for suggestions. Cheers, Mike. Say hi to your Mom.
 
Jan 12, 2011
930
Hunter 410 full time cruiser
It's probably the exhaust side. I would say its bottom growth, I got mine cleaned the other day and picked po 400 rpm. But you said you cleaned the bottom and prop.So that leaves and exhaust problem or a tach reading problem based on what you have had done.
 
Aug 15, 2014
12
Hunter 460 Des Moines, WA
Hello, a bit of an update. I’ve replaced the tach and can now confirm that I can achieve 3600rpm WOT in neutral but in gear and at WOT I can only achieve 3000rpms. Does this arrow it down to running gear? Again, I appreciate all of your input. - Chris
 
Jun 2, 2011
347
Hunter H33 Port Credit Harbour, ON.
Since the engine will turn at 3600 rpm in neutral it eliminates the upper stop and the cable adjustment as being an issue. It also indicates that the total volume of air that can be passed by the engine is free to flow out the exhaust, assuming the engine is naturally aspirated, (as opposed to turbo charged) and this most likely eliminates the exhaust elbow restriction. When the transmission is engaged there is a load on the engine which drags the speed down. As the speed reduces the governor opens to deliver more fuel to maintain the engine speed. If there is sufficient fuel being delivered the engine will burn the fuel and the engine speed is maintained. If there is too high a load on the engine there is not enough power in the engine to drive the speed back up, even though the extra fuel is being delivered. This results in black smoke coming from the exhaust due to the unburned fuel in the exhaust. (air to fuel ratio is wrong) The black is caused by a carbon rich exhaust. Too high a load can be caused by a miss pitched prop, fouled prop or dirty bottom. If the fuel being delivered is sufficient to keep the engine at speed with no load but only barely then there may not be enough fuel available to burn when the engine comes under load. In this scenario you would not have black smoke coming from the exhaust because the engine is able to burn all of the fuel being delivered.

If you do not have black smoke associated with the engine slow down then it is either a fuel delivery issue of a governor issue. The odds are clearly on a fuel delivery issue. If there is black smoke associated with the engine slow down then it is either the exhaust elbow clogged / restricted or an overload issue.

Best of luck.
 
Jun 2, 2011
347
Hunter H33 Port Credit Harbour, ON.
It is a turbo.
If the exhaust smoke is black during the reduced speed then exhaust restriction is a greater possibility. The turbo produces a much higher air flow than a NA engine while under power. Also check that the connection from the turbo exit to the intake manifold is not leaking. (lost boost pressure / reduced engine power)
 
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Feb 14, 2014
7,400
Hunter 430 Waveland, MS
exhaust restriction is a greater possibility.
:plus:

Normally Engine RPM is directly related to HP available. Applied HP to your gear box and propeller is what you are after. 8 knots for your hull length sounds great.

I wouldn't open my Exhaust system just to confirm loss of few hundred RPM. I would log it and monitor if you lose more over time.
Jim...