Larson 174 SEI w/ Volvo 3.0 GS

[Zewbie]

Hi!

I have recently purchased a 1996 Larson, and it seems to have a small problem. I have been reading through posts and the Adults Only section, and based on what I've read I'm wondering if it might be a carb/fuel system problem.

The boat starts right up and idle sounds fine. When moving the throttle slowly through the throttle range it backfires a bit in the middle of the range, but comes right out of it; the same happens when reducing the throttle. Optimum rpm at WOT should be around 4600 RPMs, however the first time I had it out it was maxing out at 2800. There is a 14.5x19 prop currently installed and I was also given a new 15x17. I know that changing the prop would help somewhat, but not 1800 RPMs.

The second time I had it out I found that if I pulled back the throttle about an inch or so from full the RPMs increased and the engine sounded much better. Doing this allowed me to get the RPMs up to 3600 or so with some fluctuation, so maybe a carb problem or the linkage is out of adjustment??

On my third outing, I checked my speed with a GPS and at full throttle was right around 15mph and RPMs were still low. At one point I was able to get it up to 19mph and it held there until I backed off, and then I couldn't get it back. I don't know if I had it trimmed just right when I hit 19mph or if the moons were just all aligned, but I believe it should be capable of going a bit faster.

The previous owners were an elderly couple that did not want the speed and purchased a pontoon boat to replace it. They did not use the boat much last year. I'm just wondering where the speed is that they didn't want?

Looking forward to your responses!.. Thanks in advance!

 

[Bondo]

Re: Larson 174 SEI w/ Volvo 3.0 GS

Ayuh,... It could be a simple as dirty fuel Filter, or as bad as a Junk Carb....
Sure sounds like a lack of Fuel though...

 

[jerryjerry05]

Re: Larson 174 SEI w/ Volvo 3.0 GS

Check fuel filters for blockage.Does it have a water/fuel seperator?Fuel pump on that model should have a filter,check that. Check vent line for blockage(bugs get in the line and make nests).
Do a spark check.Check all the plugs for even burn.
Make sure the linkage is going full forward.J

 

[Zewbie]

Re: Larson 174 SEI w/ Volvo 3.0 GS

I cleaned out the spark arrestor last night which didn't look too bad, but it shines now. I was about to do the lower fuel filter but the manual states it'll need a new gasket, so I held off. Is that really necessary, or should I only replace if it looks bad?

And as far as the vent tube goes...I visually inspected the opening on the side of the boat which looks clear. Should I take the air compressor to it?

Thanks!

 

[Zewbie]

Re: Larson 174 SEI w/ Volvo 3.0 GS

Well... I cleaned the fuel filters and found a bunch of sediment up inside the lower one as well as sediment floating in the bottom of the bowl. I filled the tank with fresh gas and 4 oz of marine stabil. I was able to get up to 3300 RPMs with a top speed of 23mph. It's still not up to the 4600 it should be but there was definitely improvement. The sputter at mid throttle range did not seem quite as bad either.

So, where to from here?

And, does anyone know what the stock prop may have been on this boat?
Thanks!

 

[Don S]

Re: Larson 174 SEI w/ Volvo 3.0 GS

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[Zewbie]

Re: Larson 174 SEI w/ Volvo 3.0 GS

Thanks Don... I did see this in the Adults only section and I have been looking through the manuals.

The manual only appears to mention the clear vent tube from the carb, however I do know the prior owner had an issue with little bugs plugging the tank vent which caused an issue. While filling the tank plenty of fumes were coming from the tank vent...is that enough to prove that is not an issue or is there another way?

I did read in the manual that the secondary throttle plate opening when switching from primary to secondary throttle circuits can show hesitation if it's sticking or not open enough. Does this transition happen about mid throttle or primarily idle?

 

[Don S]

Re: Larson 174 SEI w/ Volvo 3.0 GS

Do the fuel system tests, there is more to it than just a clogged vent. You might want to start by replacing the fuel filter in the fuel pump.

 

[Zewbie]

Re: Larson 174 SEI w/ Volvo 3.0 GS

Well, after talking with some friends one of whom insisted it sounded like a timing issue...I checked the timing. I used the Volvo shunt and the base timing seemed to be off by several degrees BTDC. I say seemed to be because after removing the shunt it didn't "seem" to change and I thought it would move without it.

Upon testing after setting base timing to 0 there was some improvement but not fully. Do to the improvement my buddy thought tweaking it while at WOT moving across the lake might be beneficial, and it was... it took off like a shot!

After doing this we checked the timing and it is not where it should be. Does this sound like a bad icm so the advance is out of whack or other ignition components? All gauges stayed where they should during testing. The plugs look to be a good color.

Appreciate the help/insight!

 

[honeys money]

Re: Larson 174 SEI w/ Volvo 3.0 GS

I have a sei178, with the same motor, and with a 14 3/4 X 19, it will turn 5,000 at 45 MPH, so there's some numbers you can go by, yours should be close, thats by myself 3/4 tank of gas.