My thundercat

[Roflhat]

Tried a squish test today, thickest solder I had was 1.15mm, tried it but it didn't squish. So I put some plastocene over it and tried that. Not very accurate but a bit of it was flattened to just over 3mm, does that sound right?

Also took a section out of the splash plate on the transom so I can lift the engine without hitting it -

Hopefully get out on the water today it's a bit calmer.

[Roflhat]

Got out for a run today, me in the thundercat and jack in his surfcat.


I managed 51.6 knots today, still with the chopper at 40mm. Couldn't tell the RPM because my tinytach has developed a crack and has fogged up. Engine is running really well now, smooth as and loads of power, but still looking for 1000 odd RPM...

[lukewhiting]

Can't pm you a photo so I'll stick it here. I have a feeling the lighting coils may have already been removed? If not what am I looking to remove? & out of insterest how much have you raised you engine giving best result? & where have you measured it from?

[Roflhat]

Yep they're gone.
The height you want to run the engine at is based on a lot of variables. The biggest being the pitch and kind of propeller. Surface piercing props need to be run a lot higher to get the revs. With my bunny I ran it 10mm off the transom, but this won't relate to your ceasar. Check out this thread - The Setup Thread - Thundercat Inflatables Forum
There are more guys with ceasars there to help you get an idea of where you need to be.
The higher out the water your engine is the less grip you'll have but the more revs (speed) you'll get.

[Roflhat]

Was out again tonight, tried the 15p bunny prop. Dropped the engine down to 10mm and out to trim 2, which is how I had my best results with the standard engine. Trim 2 was far too much, so tried 1, still too much, tried 0 (no pin), still too much. Was revving to around 6400, which is far too low for this pitch of prop.
It feels like there's something limiting the engine going to higher RPM, but obviously it isn't the rev limiter, what else could it be?

[Peter_C]

I don't know exactly how much it would help, but you might try a little propane injection for a couple of seconds to see if the motor is lean. Otherwise it could be rich. How do the plugs look after a wide open run? They tell the story of rich or lean.

Have you checked timing at WOT? Or at least at 4500rpm?

Unless there is a mechanical issue, the problem will fuel or spark.

[Roflhat]

The plugs are still wet after each run, suggesting it's still running rich. I'm making up some velocity stacks to go on the carbs and I've got a vent for the cowling, which should get more air into the engine. If it's still rich ater that I'll try drilling the main jets down some more.

The timing is bang on - for a stock engine at least. Do I want to advance the timing for higher RPM? it's at around 20* at WOT

[Roflhat]

Vent arrived for the cowling so I cut out a bit to get it in.



Still trying to get velocity stacks for it

[Roflhat]

Had nice weather for a while there so went to Scarp.


You can see my bungee set up here, it's still a handful to hold on to!


you can see how much negative trim I need to run to make the surface piercing props work


Then this happened:

[Locozodiac]

2 strokes Tohatsu 50 HP runs on 24° advance. If you overly rev that engine passing max wot numbers for long time periods, expect to wear it faster mainly due to having more compression, even breaking anytime soon standard connecting rods that were not designed to hold that huge extra power and stress...

Happy Boating

[Roflhat]

I think 24 degrees might be for TLDI. I've been told 15 for long courses and 19 for short courses on this engine

[Locozodiac]

Thinking, wild guessing is extremely bad for engine and wallet. Put an anchor around the one who told you that tech barbarities and throw him into the deep blue...

TLD engines are electronically advanced, can't fiddle with them, unless you have a Tohatsu PC program to adjust timing. No difference if being short, long or extra long LU sizes, all 3 are factory adjusted to 24°.....

Won't give even a short life span running a highly modified engine that way....

Happy Boating

[HughN]

Originally Posted by Roflhat

Vent arrived for the cowling so I cut out a bit to get it in.

That looks suspiciously like an air vent from a car!

[lukewhiting]

See you did my vent idea! Looks good!

[Roflhat]

Originally Posted by Locozodiac

Thinking, wild guessing is extremely bad for engine and wallet. Put an anchor around the one who told you that tech barbarities and throw him into the deep blue...

TLD engines are electronically advanced, can't fiddle with them, unless you have a Tohatsu PC program to adjust timing. No difference if being short, long or extra long LU sizes, all 3 are factory adjusted to 24°.....

Won't give even a short life span running a highly modified engine that way....

Happy Boating

I think 24 is for the M50D, not the D2. I printed off a spec sheet (can't find it just now). I'm going to go closer to 18 degrees, one turn at a time and see how it goes. Don't want to go burning holes in my pistons either.

[Roflhat]

Originally Posted by HughN

That looks suspiciously like an air vent from a car!

Hahaa it is! £15 on ebay. Working well too

Originally Posted by lukewhiting

See you did my vent idea! Looks good!

Yup! Was thinking about how to get a "cold air intake" on an outboard. Reckon this is as close as I can get without soaking the engine every wave I go through.

[lukewhiting]

Looks good! Good that you can close it to keep the water out

[Roflhat]

Was out for a blast today along with my dads jetski and one of our RIBs. Stunning day, one of the calmest I've seen. Was getting a steady 51.7 knots with the 18p chopper. Just on the way home I lost drive and the engine cut out. First thing I checked was the gearbox. It had dropped about 2", no bolts holding it on, just the wee pin in the driveshaft.


So I tied the gearbox on with rope and a ratchet strap and got towed in.
Got it up to the workshop and removed it to assess the damage.
The driveshaft has snapped just inside the waterpump housing, clean off. None of the bolts are present and some of the holes are mangled.
On the bright side at least I didn't lose the prop! Need to either try and get the box fixed or find a new one.

[henryfreston]

ouch!

[Roflhat]

Originally Posted by henryfreston

ouch!

I got lucky really, that prop cost me £350!