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HELP ME B4 I throw my O.B. out the window!!!

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HELP ME B4 I throw my O.B. out the window!!!

Old 09-08-2003, 11:27 PM
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Default HELP ME B4 I throw my O.B. out the window!!!

I have attempted to set up and start my K&B 7.5OB according to the instructions on their web site. Every thing is the same except the part where th engine start and idles normally. Instead of idle the engine instantly revs sky high and suddenly stops. This happens in a time span of about 1-2 secconds!!! NOT GOOD! This happens even when the throttle is nearly closed!! What is happening here and how can i stop it?

P.S. - lamens terms please
Old 09-08-2003, 11:42 PM
Mr Cajun Gator
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Default RE: HELP ME B4 I throw my O.B. out the window!!!

your engine is getting too much air and not enough fuel. make sure that the carb is down and sealed, also the same with the front cover plate.
Here is some info I got from surfing the net, help me alot

Setting the Needles

If you are new to running nitro engines then the best advice is to get
some help from an experienced boater (one whose engines run consistently
well). It is well worth acquiring the expertise to set up your engine
yourself as many boaters seem to have only a rudimentary knowledge of
engine set-up.
I will be discussing the following variables on this page.
Tuned Pipe Length.Normally measured from the centre of the Plug to
the widest part of the pipe. In talking with others to get the
initial pipe length make sure you are both talking the same
Main needle valve Often a radio needle valve. Used to set the
fuelling at full throttle.
Low-mid range needleSets the fuelling at low throttle settings.
Prop sizeBy larger I mean one that gives more engine loading, this
could be a prop of greater diameter or even a prop of lower diameter
and higher pitch

Overview of the variables and their effects
Tuned Pipe Length.A shorter pipe length will give increased revs but
reduced torque. A longer pipe length will give more torque and less
revs. Higher revs will require a richer main needle setting to get
correct running.
Main needle valveToo rich and the engine will have too much fuel and
not enough oxygen to burn it, you will loose revs and power. Too
lean and the engine will loose revs and power, also the engine will
be more likely to blow plugs and suffer other damage.
Low-mid range needleToo rich and the engine will have poor pickup
from low throttle settings. Too lean and the engine will rev very
hard on the bank on any throttle setting and stop once under load
(in the water). Initially it is much better to have this needle set
Prop sizeA larger prop will require more torque to turn it. A
smaller prop will allow the engine to rev more freely.

Setting the Needles and Pipe length
The first step is to talk to the suppliers of your engine, pipe and hull
to find a reasonable starting point for needle settings, pipe length and
prop. Forming a good relationship with your suppliers is of great benefit
to all aspects of boating, if they wont or can't give you any guidance ask
other boaters running similar engine and hull set-ups and seek another
The initial needle settings should both be rich, the pipe long and the
prop small.
Setting the main needle
Run the boat with these settings to get a feel for the performance. If you
are using a radio needle valve (my preferred choice) you can now start to
lean out the main needle valve, otherwise bring the boat in and adjust the
main needle manually. As you lean out the needle the engine should start
to rev harder and give increased speed. If you get to the end of the radio
needle travel and the performance is still increasing then bring the boat
in and adjust the radio needle to operate at a leaner range and repeat.
With a radio needle valve you should aim to get the needle set up so that
the best performance is towards the middle of the radio needle valve
adjustment as this will then allow the setting to be richened of leaned as
appropriate for changing conditions.
Setting the Pipe Length
Shorten the pipe by about 1/4 of an inch (.5 cm) and re-tune the main
needle as above, remembering that a shorter pipe length will require a
richer needle setting. If the engine will rev out with the same prop
higher speeds should be reached. Carry on shortening the pipe length in
these increments until you find the engine is having difficulty revving
out, at this point lengthening the pipe by 1/4 inch should give the best
I have found that running in rougher conditions allows me to run a shorter
pipe length as the hull breaks away from the water easier.
Choosing the correct prop
Try a larger prop, you will probably find that the tuned pipe length will
need to be increased and the main needle re-set. Is the boat faster for
your uses, acceleration from the corners is important for racing but not
for straightaway speeds, if so try a bigger prop.
Getting the right prop will require lots of testing.The Octura 1455 and
x455 are both 55mm diameter props with pitch 1.4 times the diameter yet
both give different results (the 1455 generates more lift than the x455).
Low-mid range needle
I would advise you to get yourself fully used to the above settings before
starting on the Low-mid range needle.
With your best set-up of main needle, pipe length and prop lean out the
low to mid range needle slightly. If all is well you should find the
throttling of the engine is unchanged or slightly improved, improved
throttling will show in the boat getting onto the plain easier from low
revs. Continue leaning the low-mid range needle and you should find that
the engine comes up to high revs much easier, when you set this needle too
lean you will find the engine revs very high on the bank even at low
throttle and stops quite abruptly on launching. At this point richen the
needle setting slightly to give the best set-up.
You should now find the engine gets up to full revs easier, this means
it's worth trying a shorter pipe length and or a larger prop to see if
this gives a better performance.
Old 09-10-2003, 06:30 AM
Ken Hildreth
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Default RE: HELP ME B4 I throw my O.B. out the window!!!

there are a few things to check on your motor, First check all your fuel lines and tank for any leaks, you can blow into the line and pinch the pressure line and insure that it holds pressure. after that, you may have to tell me which outboard you have, If yours has a gold round plate on one side, That plate is a low end needle, if this is set too lean the motor will do just as you stated, rev up and die. and you must richen this until the motor gets better, I am not very fond of that particular carb. I may have one you can use in its place but will have to look and see if that is the case. hope I have helped some. Ke
Old 09-25-2003, 05:38 PM
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Default RE: HELP ME B4 I throw my O.B. out the window!!!

Also check for stress cracks in the motor case around the carb or the o ring that seals the carb and case together
Old 09-25-2003, 06:57 PM
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Default RE: HELP ME B4 I throw my O.B. out the window!!!

Instead of throwing it out the window you can box it up and send it to me.

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