'93 25hp 2 stroke Spark Plug Issue??

[TownsendsFJR1300]

RPM's sound good.

Trimming the engine up should bring the bow up.

Have you checked the relationship of the engines cavitation plate in ref to the hull itself?

From a Yamaha shop manual for correct engine to transom height;

[Jason2tpa]

Ooh ya, done all of that. Tried measurements with cav plate flush with bottom of boat, 1, 2, and 3 inches above. Of course it runs better with the lower unit lower in the water. However, this is a slippery slope. The lower the engine, the more bow drop during acceleration. The higher the engine mount the more likely to ventilate. Plus if I raise it too much (and I eventually get it on plain), then I've got a little rooster. And as you know this is a waste of propulsion. By the way, if you missed my earlier thread, I have a manual jack plate. This shifts the engine about 4" behind transom.

But you're correct. Trimming the engine up does bring the bow up. With power trim. Remember this is manual trim. I don't have the ability to flick the trim button up or down. I've got to raise or lower the trim rod, which i believe amounts to about a 1' up or down for each of the 5 settings.

RPM's sound good.

Trimming the engine up should bring the bow up.

Have you checked the relationship of the engines cavitation plate in ref to the hull itself?

From a Yamaha shop manual for correct engine to transom height;

[eight_weight]

If I am remembering correctly each hole = 4 degrees of trim and the two shallow water drive positions are 5 degrees each of positive trim.

[Jason2tpa]

Sounds about right. I dropped the height of engine on the jack plate. I got a little more bite in the water, still not much of a rise in bow. Took my prop to a shop that specializes in props. He said there are no rake/cup options on the market to purchase. I could get a prop with more pitch but that wont help to keep bow up. He said all small props normally have 0 degrees of rake. He did say he can adjust the prop for a medium cup (its aluminum) and recondition, which it needed anyway. So for $40 ill have a like new prop w about 30 degrees of cup. He couldn't guarantee id notice a difference, but what the hell. Its worth a shot. Let yall know how it turns out.

[eight_weight]

He said there are no rake/cup options on the market to purchase.

???

google powertech props.

I just put an SRA4 on mine.

have a look at that one and the 3 blades for 25 yamaha's

SRA3 and SRA4 have cup and 15 degree rake

ETA: oops. these props have 20 degree aft rake...

[Jason2tpa]

Maybe he was referring to aluminum. I dont know. Ironically this store is a dealer for powertech prop. I looked at the 3 blade props on their website but it doesnt list rake, only pitch and diameter. Oh well. Worst case is no effect once i trial my prop. If that occurs ill look into buying a new one and have my old one as a spare. Thanks for the heads up.

???

google powertech props.

I just put an SRA4 on mine.

have a look at that one and the 3 blades for 25 yamaha's

SRA3 and SRA4 have cup and 15 degree rake

[TownsendsFJR1300]

Jason, since you've owned the boat, has it ever planed (SP?) out correctly?

What I'm getting at, is the engine big enough for normal performance for the size boat?


Click on this link and put in your information as best as possible, just for S&G's;

Outboard Performance, Performance Bulletins | Yamaha Outboards

[Jason2tpa]

Hey Townsend, thsnks for the question buddy. This boat has never had issues getting on plane. Only time it does is when Ive had the trim rod too high, thus causing ventilation. The boat, 13' Stumpknocker, is rated up to a 25hp. And thats what i have. Plenty of power. I'll check out the link and let you know.

Jason, since you've owned the boat, has it ever planed (SP?) out correctly?

What I'm getting at, is the engine big enough for normal performance for the size boat?


Click on this link and put in your information as best as possible, just for S&G's;

Outboard Performance, Performance Bulletins | Yamaha Outboards

[Jason2tpa]

Cool website. The significant difference between the performance of their test model, '15 carribean skiff, and my boat is mine gets on plane in roughly 2secs or less and reaches top speed (30mph) in 5secs or less. Assuming perfect conditions. By the way, the size of the aluminum prop they tested is same as mine, 9-7/8 x 11-1/4. And Id say the vent plate on mine is about 1/2-1" above bottom of boat. But this is what ive been experimenting with.

Hey Townsend, thsnks for the question buddy. This boat has never had issues getting on plane. Only time it does is when Ive had the trim rod too high, thus causing ventilation. The boat, 13' Stumpknocker, is rated up to a 25hp. And thats what i have. Plenty of power. I'll check out the link and let you know.

[eight_weight]

you may want to call powertech and talk to them after you get your aluminium prop re-done if that does not solve your problems.

if you let them know how it ran before and after, and tell them what you are looking to get out of your prop performance wise, they are very good about getting you the right prop for your needs...

[99yam40]

Seems like I remember seeing manual operated hydrolic T&T adtermarket units in the past somewhere.
It had a lever that you moved back and forth to pump it up and had a release valve you turned to lower it

Something to look into if all else fails

[eight_weight]

Seems like I remember seeing manual operated hydrolic T&T adtermarket units in the past somewhere.
It had a lever that you moved back and forth to pump it up and had a release valve you turned to lower it

Something to look into if all else fails

another alternative

CMC tilt and trim

CMC PT-35 Tilt and Trim for up to 35 HP | CMC Marine

OP you should head over to Microskiff

they would be a much better resource to help you with props for that boat. I have seen several discussions about stumknocker boats there.

[Jason2tpa]

Interesting. Yah I'll definitely check it out thanks!

another alternative

CMC tilt and trim

CMC PT-35 Tilt and Trim for up to 35 HP | CMC Marine

OP you should head over to Microskiff

they would be a much better resource to help you with props for that boat. I have seen several discussions about stumknocker boats there.

[zenoahphobic]

Seems like I remember seeing manual operated hydrolic T&T adtermarket units in the past somewhere.
It had a lever that you moved back and forth to pump it up and had a release valve you turned to lower it

Something to look into if all else fails

Yes I have one setup with mercury rams on a 50hp.
Worked well under thrust, mounted next to engine remote control.
Just a bit strange old school pumping by hand. Release worked a treat though!

[Jason2tpa]

$600 for the hydro tilt trim, ugh. I'll just stick with what I have and hope the reconditioned prop makes the difference. Appreciate the suggestion though.

Microskiff is a fantastic website. I've been on there a number of times but never looking through their forums. I'll search for stumpnocker and see what turns up.

another alternative

CMC tilt and trim

CMC PT-35 Tilt and Trim for up to 35 HP | CMC Marine

OP you should head over to Microskiff

they would be a much better resource to help you with props for that boat. I have seen several discussions about stumknocker boats there.