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Old 08-09-2014, 04:01 PM   #21
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
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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.
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Old 08-09-2014, 04:02 PM   #22
Thundercat guy
 
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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...
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Old 08-09-2014, 04:02 PM   #23
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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?
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Old 08-09-2014, 04:03 PM   #24
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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
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Old 08-09-2014, 04:04 PM   #25
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Vent arrived for the cowling so I cut out a bit to get it in.




Still trying to get velocity stacks for it
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Old 08-09-2014, 04:05 PM   #26
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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:


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Old 08-09-2014, 04:07 PM   #27
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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.
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Old 08-09-2014, 04:09 PM   #28
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That brings us up to yesterday afternoon:

Got the new gearbox on
Took her out for a run, all seems well. It's weird driving it with a complete skeg, never had one before! Much easier to turn, still need to sort out the torque steer though, unbelievably sore in the choppy stuff we've got just now. Was blowy out and as said quite choppy, still I managed 51.5 knots, I couldn't hold her flat for more than a couple of seconds without starting to lift so I reckon there's still more. We cut down the timing link a wee bit so I run more advance, closer to 24 degrees.

Also the new gearbox obviously doesn't have the exhaust mod yet, so acceleration was pretty poor with the overhub chopper. Going to drill it out, open to interesting ideas for the exhaust mod. Was thinking maybe 2x 1" holes on either side, so 4 holes instead of 2. Not sure if it's strong enough then though.
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Old 08-09-2014, 04:10 PM   #29
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Exhaust mod done
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Old 08-09-2014, 08:23 PM   #30
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Looks like i didn't gain any RPM with the exhaust mod. Sounds better and acceleration is considerably better but the top speed remained the same.
I had a fiddle with the timing while I was out today but advancing or retarding it from standard both seemed to make it slower. What I can say is that putting the ignition closer to 24* made the acceleration even better, and that the other way made it worse. Makes me wonder why it didn't help the top end though..
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Old 08-09-2014, 09:15 PM   #31
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Unless your engine has had a lot of work I would of thought 6400 with a 18p prop is good going
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Old 08-09-2014, 09:45 PM   #32
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engine has had quite a bit of work done on it I'd say, I'd like more RPM though...
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Old 16-09-2014, 12:43 PM   #33
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Couple pics of my new engine:



Just bought it yesterday and not yet arrived at the house. Unfortunately I'm off to uni for 3 months so won't be able to try it out for a while!
It's a Yamaha 70 which has been shortened and with a CES 'box on it. Just been rebuilt by a marine engineer, should be good to go. Came with an 11x21g yamaha cleaver. Need to get a tiller for it, going to try and adapt one of our old hydraulic steering systems to go on as a damper. Will be staying electric start for now until I can source parts to convert to pull start.
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Old 22-09-2014, 05:00 PM   #34
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
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Engines: Yamaha 70ces

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engine arrived today:






prop is absolutely mint as well


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Old 24-09-2014, 02:58 PM   #35
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Very cool project mate, read through it and Im very much looking forward to the continuation!
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Old 30-10-2014, 04:55 PM   #36
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
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Boat make: Thundercat
Engines: Yamaha 70ces

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Quote:
Originally Posted by NorwegianBoater View Post
Very cool project mate, read through it and Im very much looking forward to the continuation!
Cheers,
away at uni just now, trying to source some parts for it.

Need:
yamaha 60 enduro cowling and pull start assembly
yamaha tiller with gear shifter etc
hydraulic steering damper (might try making my own)
fuel tank

Want:
yamaha 90 carbs
boyesen reeds
1mm off cylinder head (or more? anyone know about this?)
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Old 07-11-2014, 09:23 AM   #37
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hey that are some nice jobs you did
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Old 09-11-2014, 01:04 AM   #38
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Enjoy reading your updates, mr friend made his own steering damper, used a damper of a sports bike to stop tank slappers, think it was a ohlins damper quite big and powerful he said it worked a treat, could always use 2 as there cheap enough used on ebay, look forward to your next update, should run very well with that yammy
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Old 09-11-2014, 11:46 AM   #39
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Country: Scotland
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Cheers guys,

yeh a lot of guys use car steering dampers, usually from a mercedes (don't know why!)
When running big props on these I find that I need an outboard hydraulic/friction damper, a bungee setup to counter torque steer and a car damper, still not easy to hang on to!
There's an old merc 150 sitting up the back of our shed with a hydraulic damper on it, going to see if I can adapt it for the yammy.
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Old 22-12-2014, 08:54 AM   #40
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Country: Scotland
Location: Isle of Lewis
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Engines: Yamaha 70ces

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Posts: 554
Anyone know how much I can remove from the 70 head? I'm thinking 1.2mm?
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