overproped?

[demolish50]

Hey, got my first new toy, (new to me) a Larson 174. It has the Volvo 3.0. It came to me with a new 19 SS prop. I'm only getting 3700 on the tach at WOT. Think it is overproped? That would be my first guess but wanted to check. Suprisingly, even at 3700rpm I get over 40mph? Just barely but a tad bit over.

 

[Bondo]

Re: overproped?

Ayuh,...

Your either Over-propped,...
Or,...
Your motor isn't making the Power it Should be.....

 

[demolish50]

Re: overproped?

That was my question. Since i am inexperienced. I'm not sure if this is "normal" for a 3.0 and a 19 inch prop or should the 3.0 be able to handle it.

 

[Silvertip]

Re: overproped?

40 MPH measured how? Pitot speedometers are notoriously inaccurate. Next would be the tach accuracy. Then make sure the engine is tuned, compression is good and its making full power. Throttle plates open fully? Is the boat full of water soaked foam? Then worry about props.

 

[steelespike]

Re: overproped?

Hey, got my first new toy, (new to me) a Larson 174. It has the Volvo 3.0. It came to me with a new 19 SS prop. I'm only getting 3700 on the tach at WOT. Think it is overproped? That would be my first guess but wanted to check. Suprisingly, even at 3700rpm I get over 40mph? Just barely but a tad bit over.

Not an expert Can you describe the 174?What year? I assume it is a 17ft? In my opinion it should be running easily 40+ with one aboard.And reach max rpm.
The Tach may be off and pitot speedos are not very accurate GPS is the only eway to be sure of speed.You should be sure the throttle is opening all the way and running on all cylinders.What is the compression?Are you adsjusting trim for best speed?Is the bottom clean?Does it seem to get on plane easily?

 

[demolish50]

Re: overproped?

Its a 1995. Yes it is a 17ft. The tach may be off, yes. I was checking the pitot speeds. I have not checked the compression. And yes I was adjusting the trim, the bottom is clean, and it did get on plane very easily. The best I can tell it has no water soaked foam.

I want to say that I was actually impressed that the 3.0 reached over 40mph, now like I said that was pitot measured. My only concern was why the tach only showed 3700 when It supposed to be 4500 WOT(per seloc manual). I was thinking the SS 19 inch prop may have been to much. I purchased this boat used and it was on there when I purchased it.

 

[Silvertip]

Re: overproped?

The easiest way to check a tach is to go to your local auto store (one that rents tools) and rent a shop tach. Do your testing and compare RPM readings. If they agree, then there is a power or prop issue. If they don't agree, you discovered the issue.

 

[demolish50]

Re: overproped?

That makes sense. I have no idea how to install a tach but I'm sure I can figure it out. I'm not sure if any of the local shops will rent one out. Will Autozone, napa, oriely do that sort of stuff? I'll make some calls tommorrow.

Thanks

 

[demolish50]

Re: overproped?

Man, can't find anyone to rent me one.

 

[Dhadley]

Re: overproped?

Any good marine repair facility will have a shop tach. I doubt they'll rent it to you but I'm sure you can arrange to set up a test run with them. Give them a call.

 

[demolish50]

Re: overproped?

Not an expert Can you describe the 174?What year? I assume it is a 17ft? In my opinion it should be running easily 40+ with one aboard.And reach max rpm.
The Tach may be off and pitot speedos are not very accurate GPS is the only eway to be sure of speed.You should be sure the throttle is opening all the way and running on all cylinders.What is the compression?Are you adsjusting trim for best speed?Is the bottom clean?Does it seem to get on plane easily?

How can I be sure the throttle is open all the way? I checked the on the carb and the lever is pushed at its maxed when the throttle is wide open. However the butterfly in the carb was not 90 degree's, more like 60? Is this normal? I have a pic if need be.

 

[demolish50]

Re: overproped?

Pic

 

[Silvertip]

Re: overproped?

The butterflies you are looking at are the CHOKE plates, not the throttle plates. The throttle plates are deeper in the carb. The reason you are getting 3700 rpm could be because the choke is not opening fully with a warm engine.

 

[demolish50]

Re: overproped?

Duh, opps..

Thanks.

 

[demolish50]

Re: overproped?

The butterflies you are looking at are the CHOKE plates, not the throttle plates. The throttle plates are deeper in the carb. The reason you are getting 3700 rpm could be because the choke is not opening fully with a warm engine.

You know, I did not think about that. When I did my test runs the engine never did get up to normal operating temp. I had to stop before then due to a steering issue that I have since resolved. (Had to replace the steering cable).

May be a non-issue, I'll test again. I've got to replace that overflow hose from the fuel pump, the red one in the pic. Its cracked with a big hole , since its fuel overflow I'm going to fix it before I go out again. Also the exhaust bellow is leaking a bit so I'm going to replace it too. I'll update this thread once I know for sure.

 

[Silvertip]

Re: overproped?

I think Auto Zone has a rental program. With a warm engine the CHOKE plate should be standing perfectly vertical. At wide open throttle the THROTTLE plates should also be perfectly vertical. If the choke doesn't open any farther than shown in the picture, you have a gas hog.

 

[demolish50]

Re: overproped?

Autozone does have a rent a tool program but they don't have a tach for rent.

I suppose to see the throttle butterflies I have to break down the carb a bit more. I may do that. The throttle "lever" on the side of the carb reaches it max that it can with the throttle cable. I took the cable off to see if it would go any more, checking for a cable mis-adjustment, and it won't. I suppose that doesn't mean the butterflies are opening all the way?

In your opinion, that motor shouldn't have a problem getting into the WOT range with that prop? SS 14.5x19.

I did make sure the tach gauge was set correctly as well, but again I'm sure that doesn't mean it is accurate.

Thanks

 

[steelespike]

Re: overproped?

Open the choke by hand and look in with a flashlight should be able to see the butterflies.

 

[demolish50]

Re: overproped?

Gotcha, will do. I'll report back my findings.

 

[bigtwin]

Re: overproped?

Most high quality timing lights have a tach. function. You should be able to rent one through your auto parts store. (or buy one I think they can be had for under $50)
All you have to do is, clamp the inductive pick-up to any plug wire, make sure that in is in 4 stroke mode, and if it has a timing advance feature set it to zero.
I use a tiny-tach with an hour meter function, it's cheap, easy, accurate and reliable.

BTW some DVOM (digital volt ohm meter) have a tach. function also.

Good luck