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Old 21 March 2011, 07:36   #1
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135 power increase

for you engine moguls out there.
can you shed some light on this confiqurence I am in two minds to add this as is , or just run the std bits but with the + 30 thou pistons

135hp carb motor,
+ 30 thou pistons
clean & ported exhaust area
fitted with WMV 16 carbs from xr6
xr6 exhaust divider plate
xr6 exhaust can + top plate jetted to suit

main jet .078
idle 0.44
vent jet 0.82

will it push it up to 150 or ? or am i just creating an accident awaiting me turning the on key???
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Old 21 March 2011, 11:02   #2
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150

Hi, you have to be pretty carefull when it comes to changing exhaust plates, dividers, etc etc and especially jets in my opinion. When any outboard has the wrong jets in the carbs you are going to run LEAN or RICH. most danger is running too lean and obviously lean is HOT and this causes damage. I have seen the old style mariner 150 and 175hp carb engines with the wrong jets in and seen melted pistons from it. I wouldnt do it if it was my OB. cheers
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Old 21 March 2011, 11:05   #3
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Hi, you have to be pretty carefull when it comes to changing exhaust plates, dividers, etc etc and especially jets in my opinion. When any outboard has the wrong jets in the carbs you are going to run LEAN or RICH. most danger is running too lean and obviously lean is HOT and this causes damage. I have seen the old style mariner 150 and 175hp carb engines with the wrong jets in and seen melted pistons from it. I wouldnt do it if it was my OB. cheers
thanks for that think i will go with the std set up its been troubling me working it out, give me a quad engine any day

thanks for the input
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Old 21 March 2011, 16:17   #4
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obviously lean is HOT and this causes damage.
cough cough.... some engines run cooler lean of peak...
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Old 21 March 2011, 20:06   #5
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cough cough.... some engines run cooler lean of peak...
Cough cough...

It's probably a good idea to get at least a basic idea of performance engine tuning before you comment.

I'm with Outboardtech -I wouldn't try for a power increase. Apart from anything else, you've got a tight new engine that needs running in. If you get anything wrong, it'll be a very expensive mistake. Changing port height is going to change the torque curve of the motor too (plus the time and equipment involved in getting port height and profiles exactly the same over 6 cylinders) and you're quite likely to find you're either falling foul of the rev limiter before you hit peak power, or bogging down at low revs.


It's easier and more practical to buy a bigger engine.
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Old 21 March 2011, 20:32   #6
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Cough cough...

It's probably a good idea to get at least a basic idea of performance engine tuning before you comment.
I did not mention high performance engine tuning or even that I was relating to the marine sector, however it is a fact that certain high performance engines run cooler and more efficiently lean of peak. Or do you disagree with that?
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Old 21 March 2011, 20:59   #7
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I did not mention high performance engine tuning or even that I was relating to the marine sector, however it is a fact that certain high performance engines run cooler and more efficiently lean of peak. Or do you disagree with that?
Yes, I do disagree with that. Apart from anything else,the phrase 'performance engine' is a misnomer,your statement is showing no constants and 'lean of peak' means absolutely nothing. Lean what? Peak what? Cooler than what? Trousers? Hair growth rate? Hot air output?



If You hadn't noticed, this thread is to do with one specific outboard.If you're not referring to an outboard then your post is irrelevant to the discussion anyway.
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Old 21 March 2011, 21:56   #8
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Yes, I do disagree with that. Apart from anything else,the phrase 'performance engine' is a misnomer,your statement is showing no constants and 'lean of peak' means absolutely nothing. Lean what? Peak what? Cooler than what? Trousers? Hair growth rate? Hot air output?



If You hadn't noticed, this thread is to do with one specific outboard.If you're not referring to an outboard then your post is irrelevant to the discussion anyway.
Brilliant.
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Old 22 March 2011, 04:47   #9
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I did not mention high performance engine tuning or even that I was relating to the marine sector, however it is a fact that certain high performance engines run cooler and more efficiently lean of peak. Or do you disagree with that?
Complete Tosh!
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When a boat looks that good who needs tubes!!!
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Old 22 March 2011, 04:54   #10
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want more power, to go faster, BUY A BIGGER ENGINE
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Old 22 March 2011, 06:04   #11
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want more power, to go faster, BUY A BIGGER ENGINE
only cos i got it in bits = an xr6 sitting there with other bits

staying std now
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Old 22 March 2011, 18:06   #12
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Originally Posted by Nos4r2 View Post
Yes, I do disagree with that. Apart from anything else,the phrase 'performance engine' is a misnomer,your statement is showing no constants and 'lean of peak' means absolutely nothing. Lean what? Peak what? Cooler than what? Trousers? Hair growth rate? Hot air output?

If You hadn't noticed, this thread is to do with one specific outboard.If you're not referring to an outboard then your post is irrelevant to the discussion anyway.
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Complete Tosh!
For anyone remotely interested, I have replied to these two posts in the bilges section here in order to save Nos the trouble.
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Old 23 March 2011, 03:03   #13
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For anyone remotely interested...
After 32 years in related industry, I thought I might be. Turns out I'm not
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Old 23 March 2011, 03:50   #14
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For anyone remotely interested, I have replied to these two posts in the bilges section here in order to save Nos the trouble.
Thanks for the explanation that you weren't talking about boats but aero engines - Think about this - Just imagine someone believes that reading this helpful information on a boating forum believes it and blows their motor up? I'm not saying they would, but irrelevant and misleading information can do a lot more harm than good.
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Old 23 March 2011, 08:24   #15
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tee hee i only wanted advice

dare i ask aquestion about flexithane paint
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Old 23 March 2011, 12:58   #16
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tee hee i only wanted advice

dare i ask aquestion about flexithane paint
Do you definitely mean flexithane paint, Nugent, and not flexiplane?

I only ask to avoid confusion - I would hate to see you trying to apply the first with a long roller while on the plane instead of employing doublejointed Wingwalkers with Aerosols (the correct technique for flexiPlane)

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Old 24 March 2011, 02:49   #17
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Do you definitely mean flexithane paint, Nugent, and not flexiplane?

I only ask to avoid confusion - I would hate to see you trying to apply the first with a long roller while on the plane instead of employing doublejointed Wingwalkers with Aerosols (the correct technique for flexiPlane)

wing walking with a life jacket would disturb the ride surely not, also the paint spill will end up at the tail end for sure!!
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Old 24 March 2011, 17:05   #18
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Increasing the volumetric efficiency (porting etc) without proportionally increasing the amount of fuel going in will lead to a lean mixture which will potentially melt a hole in one or more pistons, probably the top one/s (because they are furthest from the nice cool water)
a dyno set up would be the answer.
Or in the old days a full throttle run ,cut the engine at full throttle and pull the plugs out and then increase the size of the main jets until the plugs come out the right colour ,known as a ''plug chop''
This is based on a knowledge of petrol engines generally,no matter what the engine is in, I believe that a lean mixture will make the combustion chamber run hot (not necessarily the engine run hot) and if you're lucky melt the plug and if you're not the piston crown.
But I am happy to be corrected.
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Old 24 March 2011, 19:28   #19
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Here's a reasonable way of getting a rejetting into the right ball court without melting the pistons.

A 2 stroke engine will 4 stroke when its mixture is too rich. So start testing with main jets which are rich enough to just bring on 4 stroking under load. Reduce the jet size to get the engine just 2 stroking and then a good starting point will be one jet size smaller than that.
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