Optimax 225 idle surging below 800 rpm.

[Venzel]

I have a 2000 optimax 225 that has 385 hrs total. it starts very weel when hot and cold with a litle trotle. It idles perfect hot or cold when its in neautral only.
when in the water and in gear, it is surging below 800 rpm, above 800 rpm, there is no problem at all. Hole shot and WOT is all perfekt to.

I have got the engine upgrade to around 250 hps, done by Lundin Marin SE. Flash of ECM and installing Boysen reeds. Also injectors have been cleaned and inproved by Lundin Marin. All 6 fuel injectors and 6 direct injectors was in wery good condition, after cleaning and testing.

Before upgrading, the engine was complete overhaul with pistons, bearing and all.

The Quicksilver DMD- tester tells no failures, and then i have replaced following components after, just to make sure:

All filters, sparkplugs and diaphragm assy 804533. All hoses for fuel is replaced, and fuel rails is cleaned.

My last Shot in the gutter, is compressor reed plate assy 835088A10, and compressor filter.

I am to be a litle frustratet, so I hope that somebody can give me some good advise here

[Savage]

I would get rid of the Boyesen Reeds and install TDR Reeds for starters.

[21xTriton05]

Do a compression check first. I never try and trouble shoot an engine without doing so first. Make the flywheel isn't rusty. Also, make sure the crank position sensor is clean. If it has air pressure at idle I wouldn't replace a compressor just to do it.
I would also be looking for reeds that don't seat all the way or may have broken off.

[Venzel]

Hi Savage,

Do you have bad experience with the boyesen reeds?

[Venzel]

Hi 21xTriton05,
the compression is perfect after the overhaul. I have replaced the reed blok valve in the compressor cylinder head, partnr. 835088A10. Reeds in engine is brand new Boyesen reeds, and all instruction has been followed installing these.
I can see that there is now rust at the flywheel, byt I will now make sure that the crank position sensor have the right values.
The funny thing is, that the engine runs fine conneckted to a waterhose, also when I put it in gear. The problem with surging idling below 800 rpm, is just when the boat is in the sea and in gear. Out of gear, it also idling fine in the sea.
My idling conneckted to a water hose is between 500 - 570 rpm. When in the sea, it drops down to 450 - 510 rpm. and some times it stops running because of the low rpm I think. But when pulling the throtle it starts surging, until I get over 800 rpm. After 800 rpm. there is no problem at all.

[Savage]

Hi Savage,

Do you have bad experience with the boyesen reeds?

I know of cases were the Boyesen reeds did NOT perform well on Optimax motors.........Dirt bikes Yes.......Optimax not so much.

[21xTriton05]

The link rod that connects the throttle body to the tps is exactly the same as when you took it off? Spin the end off just a little and it'll increase the engine rpms I believe

[Venzel]

Hi 21x..,
The link rod is not adjusteple, but the throttle plate is. I will try this.

[21xTriton05]

Hi 21x..,
The link rod is not adjusteple, but the throttle plate is. I will try this.

You may also be able to loosen the tps bolts and rotate it towards the throttle plate to get a little. It won't be a lot but you may get enough. I thought bthey we're adjustable but looking at a few this morning, none of them are. The next step would be to buy a set of pro xs factory reed blocks with carbon fiber reeds and start making it back as close to stock as possible

[EuropeanAM]

Two problems here:

1. Reeds do not match needed flow characteristics for ANY Optimax.

2. You cannot simply alter the PCM to get 250hp. The 250 uses a different throttle plate, block, porting, cylinder heads, pistons, direct injectors, fuel rails, air compressor, flywheel cover, reed blocks, and a few other things as well.

Dumping 250 fuel curve to a 200 or 225 block will result in a surging idle, as the engine is running very RICH, and the PCM is constantly trying to stabilize idle speed by raising and lowering timing.

[Venzel]

The problem is now resolved 99% by adjusting the throttle to 3.8 mm and replacing the TPI sensor. Now has only a little trouble at about 600 rpm, otherwise it runs perfectly and there are few times where the engine stops. The solution is useful and I'm very pleased with the result, got about 15 km / h on the update, but a unique feature from 30 to 50 knots.