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Old 22 October 2008, 13:38   #1
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Country: Norway
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Boat name: Zapcat
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Zapcat slow speed?????

What kind of speed should I get from a 50hp Tohatsu and Zapcat? I'm getting 32knots and thats to slow. The engine is a 2007mod and i haven't done anything too it yet, what can i do and is that a normal speed for that boat engine combo? the prop is 11x15 steel prop. What should i do? and where can i get info on tuning the engine.. The revlimiter is not cut is that why i can't get more speed?

Hope for some help here...
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Old 22 October 2008, 15:01   #2
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Count your rpm Tacho

I have a small memory tacho on mine reocrds the highest rpm which helps see if your near max rpms.

There are other posts about these on the site.

Just wrap it on an HT lead, dead easy..........
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Old 22 October 2008, 15:03   #3
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I presume that its just you and a passenger in the boat. If you carry 3/4 people it drastically reduces the speed due to the non parallel hijackers ploughing through the water. For 2 people aboard, the biggest bearing on the speed in these boats is the trim angle/weight distribution. On your rig you need it to be on the 2nd hole out from the transom on the trim(or 3rd if you carry more weight up front) and your passenger needs to sit towards the rear for high speeds/flat water . Try that and let us know.
Its worth getting a tiny tach rev counter so you can check your revs whilst on the move.
I can gain 400 revs when my passenger moves about 3ft back which makes a hell of a difference.
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Old 22 October 2008, 15:53   #4
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New prop. I had the same prop on my 4m avon searider rib with a mariner 40 and was getting 32knots.

The RR zapcats use a stainless semi cleaver prop.

http://www.zapcat-racing.com/la/2881

I'm sure they would be happy to help.
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Old 22 October 2008, 16:27   #5
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I tried with only one person in the boat and two... I can't get the rpm up.. The engine is almost new.. I was wondering wat speed I can get aout of the box with this boat... I't sounds like i can't get high rpm.. I tested the compression and it's 120... I was hoping to get 45knots but do you have to tune the engine to get this speed... Mabye is the ignition or the carburators thats need some adjustment.... The prop i bougt from winracer in Norway and it should be the right prop.. I'm gonne mesure the rpm and get back but i'm almost sure that the rpm is to low... And how know if the carburator or ignition is wrong? i'l try to cut the revlimiter tomorow and see what hapens....
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Old 22 October 2008, 16:31   #6
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yes I know but with this prop I should get more speed than 32knots I know other peopel with the same prop that says i should get 45knots or more.. I cant get the high rpm... the engine is almost new.. Maby i have to adjust the ignition or the carburators... How du I do that? and how do I know if it's wrong?
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Old 22 October 2008, 18:13   #7
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Quote:
Originally Posted by Blind_Mel View Post
yes I know but with this prop I should get more speed than 32knots I know other peopel with the same prop that says i should get 45knots or more.. I cant get the high rpm... the engine is almost new.. Maby i have to adjust the ignition or the carburators... How du I do that? and how do I know if it's wrong?
If you don't know how to, don't. Pay an engineer or you'll face an even bigger bill to repair it.
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Old 23 October 2008, 14:35   #8
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Originally Posted by Blind_Mel View Post
yes I know but with this prop I should get more speed than 32knots I know other peopel with the same prop that says i should get 45knots or more.. I cant get the high rpm... the engine is almost new.. Maby i have to adjust the ignition or the carburators... How du I do that? and how do I know if it's wrong?
Do as Nos says , and if if the engine is new you should be takin it a bit easy on it

They say run new engine in on 25-1 , having just done that with a new tohatsu I would say its not necessary on a light boat .

have you checked and cleaned the plugs ?

If your engine has oiled a plug and is running on 2 cyls , believe it or not you may not notice untill you try and give it full throttle and then it just feels down on power as if its a 30 , it doesn't run rough at all . That caut me out first time , and having recently run my toghatsu in by the book it does oil a plug almost every time you go out for a while ,always one of the two lower cyls .

Forget the rev limiter that only stops it over revving , and you are not reaching that by the sounds of it .
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Old 23 October 2008, 17:25   #9
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If your revs are down with a light load then i'd agree with Ian- I would change the plugs for new ones. Checking the ignition is easy

Heres a pdf file on it.

But it youre unsure in any way then dont do it. Theres no harm in asking for advice though
Attached Files
File Type: pdf M40 50D2 Ignition Timing.pdf (190.5 KB, 457 views)
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Old 23 October 2008, 17:40   #10
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Gray and I have a Zapcat, with an unmodified engine - and we clocked it at 43.1 knots last year when we were testing it out with two of us in it (and im not a small guy ). Definately sounds like you're not hitting revs, check the plugs, and the engine height.
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Old 23 October 2008, 17:47   #11
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Thats good Easyrider I have been promised a PDF manual from Extreme Marine but still waiting

and for sure the stealer didn't check that when he did the "first service" read tinker about and rev up a few times

Is there also a description of the carb linkage setting / balance

Iam used to timing lights and vacuum guages , this reminds me of an old fergie tractor i used to work on
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Old 24 October 2008, 13:41   #12
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Originally Posted by ian parkes View Post
Thats good Easyrider I have been promised a PDF manual from Extreme Marine but still waiting

and for sure the stealer didn't check that when he did the "first service" read tinker about and rev up a few times

Is there also a description of the carb linkage setting / balance

Iam used to timing lights and vacuum guages , this reminds me of an old fergie tractor i used to work on
I havnt found anything for the carb balancing yet-i asked the tech guy at tohatsu uk about a service manual a few weeks ago-he said they were waiting for some to come in, but you can only get them through dealers though.
I forgot to answer a quesion you asked on your other thread about mixture settings- i'll go and find the thread and tell you my latest findings
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Old 24 October 2008, 16:10   #13
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I expect the manual will just give set up measurements for the linkage rods just like it does for the timing .
It seems to me what happens is that the tickover screw gets turned up to compensate for a badly set motor .
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Old 26 October 2008, 10:00   #14
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Slow zapcat

I found with mine that the trim seriously affects the performance, to the point of having to be virtually milimetre perfect. Does it have a prop guard? Taking this off will increase speed noticeably. Sounds like running on two cylinders though. Check the bottom plug which gets wet quite easily.
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Old 26 October 2008, 13:47   #15
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I found with mine that the trim seriously affects the performance, to the point of having to be virtually milimetre perfect. Does it have a prop guard? Taking this off will increase speed noticeably. Sounds like running on two cylinders though. Check the bottom plug which gets wet quite easily.

Glad its not just me . I have a theory that the motor doesn't like being fully tilted for any length of time , which I have to do when trailering . I only seem to oil a plug just after launching now as I don't tilt the motor up fully if iam stopped at the beach . The choke working on the lower 2 carbs only is also a cause i think .

Would also be nice if someone made some sort of fine screw adjuster for the trim
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Old 11 December 2008, 01:15   #16
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Probably stating the bleedin' obvious, but are you running all tubes at correct pressures (especially hijackers)? This can have a huge affect on speed
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Old 11 December 2008, 18:47   #17
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Everyone always tend to think theirs something wrong with the motor and maybe so. First off does it sound like it's not firing properly? What are your rev's @ WOT? What height is your motor mounted at (prop shaft centerline where is it in refference to the bottom of the boat)? What prop exactly are you running because different type with different performance depending on what you want and your set up. Are the tubes properly inflated?

Need more info to get the CAT guy's to help but usually the wrong prop and engine height are your worst enemy.
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Old 18 December 2008, 16:26   #18
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Need more info to get the CAT guy's to help but usually the wrong prop and engine height are your worst enemy.
I will agree with that comment. Tohatsu engines are very prone to give you wot performance problems if engine is not adjusted/working on recommended factory height specs. Is your cat/engine combo splashing too much water on transom area ? If so, you are loosing top rpm and final speed because of water drag against tail. Your engine, anticav plate/water level should be between 10 to 30 mm according to service manual.

Correct/adjust engine height if necessary, then proceed to put a taco and test engine max revs available at wot, with current pitch size check if under or over reving untill correct max revs are obtained, repitch if needed.

Happy Boating
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Old 19 December 2008, 06:26   #19
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Stepping back slightly form the problem it sounds like it;s not making max available RPM - Zapcats were designed to runs with Tohatsu 50's? I would imagine even if you messed up the trim spectacularly, it should make a reasonable effort to ge to max RPM. As someone said earlier - a 3- cyl 2 -stroke will not sound spectacualrly rough with only 2 cyls firing, but due to the two remaining cyls having to compress the air, only to get nothing back out in the form of a "bang", it feels more like half than 2/3 throttle.

As an example when i got the Merc it ran Ok at idle, but when I first opened the throttle it did a half hearted impression of a 25. Took the plugs out, bottom one was literally dripping with oil, middle was not so bad but still manky. Changed them, puttered out the marina (even sounded better at tickover) pushed the lever forward & was nearly thrown off the back of the seat!

Moral of the story: Spark plugs are cheap, and don't like being drenched in oil! I'd buy a new set of plugs. What's the worst that can happen? - you end up with a spare set for the next service.


If you are towing, a good idea is to pull the fuel connector before you come ashore or when you are flushing & let the engine drink the contents of the carb bowls. It's not a problem with auto mixers, but also saves oil build up as the fuel evaporates if running premix.
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Old 19 April 2009, 07:10   #20
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Just a question

Hi Guys,

I'm getting into the ZapCat's as well and I have a question :

Does somebody know the exact height of the cav-plate ? To what part of the boat can I relate it to set the correct height ? I was told to go a couple of centimeters above the center line of the high-jackers, is that correct ?

Thanks guys,
Martin
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