Need Help

[aussieboater]

Hi

Am having a bit of trouble with my K&B 7.5 im running 50% with a garcia pipe set at 7 1/2 inchs to the cone a x447 prop 2 blade

The problem is when i back off the throttle it just quits , could this be to lean or to rich on the carb disk or maybe lenthen the pipe , Have all new fuel lines it seems rich cause when i start it and rev it before it goes in the water it spits fuel out the pipe and hesitates with the revs coming up then when it goes in the water full throttle sounds and runs awesome but soon as i back of the throttle it dies or if it doesnt seems like its trying to get back on the pipe

Any help would be great

Thanks

Brad

 

[Valet]

I would try another Carb to start. Also look at your fuel pick up in the tank and make sure it is where you put it.

Hi

Am having a bit of trouble with my K&B 7.5 im running 50% with a garcia pipe set at 7 1/2 inchs to the cone a x447 prop 2 blade

The problem is when i back off the throttle it just quits , could this be to lean or to rich on the carb disk or maybe lenthen the pipe , Have all new fuel lines it seems rich cause when i start it and rev it before it goes in the water it spits fuel out the pipe and hesitates with the revs coming up then when it goes in the water full throttle sounds and runs awesome but soon as i back of the throttle it dies or if it doesnt seems like its trying to get back on the pipe

Any help would be great

Thanks

Brad

 

[aussieboater]

I would try another Carb to start. Also look at your fuel pick up in the tank and make sure it is where you put it.

Hi

Am having a bit of trouble with my K&B 7.5 im running 50% with a garcia pipe set at 7 1/2 inchs to the cone a x447 prop 2 blade

The problem is when i back off the throttle it just quits , could this be to lean or to rich on the carb disk or maybe lenthen the pipe , Have all new fuel lines it seems rich cause when i start it and rev it before it goes in the water it spits fuel out the pipe and hesitates with the revs coming up then when it goes in the water full throttle sounds and runs awesome but soon as i back of the throttle it dies or if it doesnt seems like its trying to get back on the pipe

Any help would be great

Thanks

Brad

What sort of carb

 

[Jerry Wyss]

7 1/2 inches from where to where? You say 7 1/2" for a 7.5 o/b on here and I'm surprised Everybody

Didn't Scream "That's Too Short!". Engines in the .12 size run them that short Brad,, mine is 10 inches from

the side of the cyliner head to the beginning of the reverse cone, baffle cone, converging cone, convergence cone,,that cone has more friggin' names than I can count :blink:

I doubt very much that your measureing "from and to" where I am,, it's not possible to get the pipe that short unless your using the wrong pipe for that motor. Most people on here have starting measurements

or set measurements from the glow plug center to the "start" of the "cone that tapers down toward the stinger. I don't do it quite that way but still the diff between theirs and mine doesn't amount to much, 3/8"max.

On an inboard 7.5 cc engine that use to run (Picco) the pipe was set 10 1/2 to 10 3/8", people

have run this same type of combo with a length of 9 1/2" on some of the more radically timed engines (Mac & CMB) But 7 1/2" on a 7.5 O/B! Sumthin' ain't right,,you must be talking about

the "beginning" of the straight section on the Garcia. That section is about 2 1/4" on the one I have,,, you must be measuring from the header flange around to the end of the "diffuser", divergent cone (here we go again). If that's the case your perdy close on the pipe.

How long has it been since you changed your bearings? Worn front bearing can make the K&B's

run weird. If thats ok, sounds like a "fuel draw problem",, if your tank is low in the boat it can

cause a problem like your talking about. The 7.5 K&B sits perdy high on most boats and the fuel

draw suffers because of that. Hopper tanks help but I just plain cured it with mine by putting a "one way" check valve in the tank pressure tube. The check is made by "YS", the airplane

engine manufacturer,, there are others but I don't use them, they just don't hold up.

The "check" holds on to every "pulse" the the pipe creates and saves the tank pressure just

for the carb,,, they work best with "spraybar" type carbs, just like the one you have on there.

When you start the engine (if you have "see thru" silicone tubing) you might see the fuel going

back and forth in the tubing,,it pumps up to the carb and when you let-up on the starter, it drops back toward the tank. If thats the case, your a prime subject for the check or a hopper

tank. Loose carb fuel nipple, loose carb and worn front bearing can cause similar problems.

 

[aussieboater]

7 1/2 inches from where to where? You say 7 1/2" for a 7.5 o/b on here and I'm surprised Everybody

Didn't Scream "That's Too Short!". Engines in the .12 size run them that short Brad,, mine is 10 inches from

the side of the cyliner head to the beginning of the reverse cone, baffle cone, converging cone, convergence cone,,that cone has more friggin' names than I can count :blink:

I doubt very much that your measureing "from and to" where I am,, it's not possible to get the pipe that short unless your using the wrong pipe for that motor. Most people on here have starting measurements

or set measurements from the glow plug center to the "start" of the "cone that tapers down toward the stinger. I don't do it quite that way but still the diff between theirs and mine doesn't amount to much, 3/8"max.

On an inboard 7.5 cc engine that use to run (Picco) the pipe was set 10 1/2 to 10 3/8", people

have run this same type of combo with a length of 9 1/2" on some of the more radically timed engines (Mac & CMB) But 7 1/2" on a 7.5 O/B! Sumthin' ain't right,,you must be talking about

the "beginning" of the straight section on the Garcia. That section is about 2 1/4" on the one I have,,, you must be measuring from the header flange around to the end of the "diffuser", divergent cone (here we go again). If that's the case your perdy close on the pipe.

How long has it been since you changed your bearings? Worn front bearing can make the K&B's

run weird. If thats ok, sounds like a "fuel draw problem",, if your tank is low in the boat it can

cause a problem like your talking about. The 7.5 K&B sits perdy high on most boats and the fuel

draw suffers because of that. Hopper tanks help but I just plain cured it with mine by putting a "one way" check valve in the tank pressure tube. The check is made by "YS", the airplane

engine manufacturer,, there are others but I don't use them, they just don't hold up.

The "check" holds on to every "pulse" the the pipe creates and saves the tank pressure just

for the carb,,, they work best with "spraybar" type carbs, just like the one you have on there.

When you start the engine (if you have "see thru" silicone tubing) you might see the fuel going

back and forth in the tubing,,it pumps up to the carb and when you let-up on the starter, it drops back toward the tank. If thats the case, your a prime subject for the check or a hopper

tank. Loose carb fuel nipple, loose carb and worn front bearing can cause similar problems.

Hi Jerry

Thanks for your info as with the pipe im measuring from the middle of the header just below it where i cut the leg out for the pipe so centre of that (header) around the outside to the first weld does that sound right if i measure from the same spot header flange around the outside to the start of the cone that runs down to the stinger its 10 3/4" hope this helps

As for a hopper tank i do run one which is level with the carb as for the front bearing they have never been changed and the motor has had about 2-3 litres through it but its 10 yr old been in the garage for a long time

Thanks for your help

Brad

 

[Lorenzo Martinez]

Brad,

I had somewhat of same problem... Check your fuel tanks, they could have a leak. Take them out,place them under water, with one hole pluged up and with a fuel tubing to the other end, flow low pressure air into them. Good luck...

Lorenzo

 

[aussieboater]

Brad,

I had somewhat of same problem... Check your fuel tanks, they could have a leak. Take them out,place them under water, with one hole pluged up and with a fuel tubing to the other end, flow low pressure air into them. Good luck...

Lorenzo

Thanks Lorenzo i will check them

 

[MarkScott]

Brad,

Think I may have posted about the 7 1/2 length(?) From the paper - " We recemommend a length of 7 3/4 inches around the OUTSIDE of the bend to the weld at the back cone shoulder. This is with the stock GARCIA header of 2 1/2 inches". Goes on to take it down to 7 1/4 for more speed. Figure the over all length would be the pipe plus the header. This would be from 10 1/4 down to 9 3/4. This would not include the length from the plug down to the header I'd think. With all this, it would be in the ball park of what has been suggested above. Hope this helps.

 

[Jerry Wyss]

"How long has it been since you changed your bearings? Worn front bearing can make the K&B's

run weird. "

Hi Jerry

" as for the front bearing they have never been changed and the motor has had about 2-3 litres through it but its 10 yr old been in the garage for a long time"

Thanks for your help

Brad

Brad

Well there ya go, You can have a new bearings in the engine and "10" years later they won't

be worth a hoot 99.9% of the time.

Do Not run it until the bearings get replaced,, the main reason is that the "crank induction window"

is close to the "front housing bore", if paticles of bearing have gotten between those two parts

it will "gall" the crank and the front housing bore leaving you with two useless parts. Thats a bad deal

in todays parts availibillty for that motor.

For the novice changing them two bearings can be "fatal" to the parts alone. Get help in this area before

you try to change them, the use of a small (cheap propane torch) in experienced hands can do the job

easily and quickly without killin' anything. Alot of boaters use the oven to heat things up but my contention

with that is that it heats-up all the parts, swelling them all still keeps things too tight for my liking.

First, I like to (after the front section is removed) see if I can move the crank "back" by tapping with a hard

plastic hammer, I don't want too move it very far, just enough to "create some space" between the rear bearing and the buisiness end of the crank. No heat has been applied yet,,the reason I do it this way is that

sometimes the rear bearing can be harder to get off the crank than anything else and "you don't" want to

knock the rear bearing out "with the crank" when things are cold, that can hurt the abillity of the aluminum

housing to hold a new bearing. If the rear bearing moves with the crank in this proceedure,STOP, heat it up

and remove them together,,the front is a piece-a-cake, little torch and tap it out from the back side. I use an appropriate size nut driver without any sharp edges on it and another nut driver handle and tap it out

while its hot.

The K&B aluminum case parts are lighter in weight and wall thickness than most other motors, so they don't

require as much heat to swell them up, but it's a "learned" technique,, I learned when you could still get new

parts easy, now-a-days, that's a problem.

Let me know how it goes

JW

 

[Greg Johnson]

Hi

Am having a bit of trouble with my K&B 7.5 im running 50% with a garcia pipe set at 7 1/2 inchs to the cone a x447 prop 2 blade

The problem is when i back off the throttle it just quits , could this be to lean or to rich on the carb disk or maybe lenthen the pipe , Have all new fuel lines it seems rich cause when i start it and rev it before it goes in the water it spits fuel out the pipe and hesitates with the revs coming up then when it goes in the water full throttle sounds and runs awesome but soon as i back of the throttle it dies or if it doesnt seems like its trying to get back on the pipe

Any help would be great

Thanks

Brad

FWIW, Where is your low speed needle set? I've found that you can go nuts looking for fuel related issues and it comes down to the low spped needle setting is too lean. As soon as you back off the throttle the engine leans out and dies.

Greg

 

[lohring]

From the mention of carb disk, I assume you are running the newer K&B carb. This should be set so the disk is turned counterclockwise (richer) until the edge of the slot is at the center of the hole. I would run the smaller (7.5 size) carb, not the 11cc carb that once came with the K&B Pro. Then set the needle as rich as the engine will run. If the engine runs but starts quitting as you lean it down, I would suspect an air leak. Usually this will be at the crankshaft seal area. Probably you are just too lean on the low end setting.

Lohring Miller

 

[aussieboater]

Mark (OB NUT) what is your email addy and ill send it to you

Thanks

Brad

Hi

Also what type of glow plugs are you guys running and the % of nitro with that

Thanks

Brad

Hi

Am having a bit of trouble with my K&B 7.5 im running 50% with a garcia pipe set at 7 1/2 inchs to the cone a x447 prop 2 blade

The problem is when i back off the throttle it just quits , could this be to lean or to rich on the carb disk or maybe lenthen the pipe , Have all new fuel lines it seems rich cause when i start it and rev it before it goes in the water it spits fuel out the pipe and hesitates with the revs coming up then when it goes in the water full throttle sounds and runs awesome but soon as i back of the throttle it dies or if it doesnt seems like its trying to get back on the pipe

Any help would be great

Thanks

Brad

FWIW, Where is your low speed needle set? I've found that you can go nuts looking for fuel related issues and it comes down to the low spped needle setting is too lean. As soon as you back off the throttle the engine leans out and dies.

Greg

Hi Greg

I have it set at about half way

Thanks

Brad

 

[MarkScott]

Mark (OB NUT) what is your email addy and ill send it to you

[email protected]

 

[Jerry Wyss]

3 or 4 liters of fuel thru it and put it in the garage 10 years ago! The Red Lights Blinking h34r:

 

[aussieboater]

problem solved (glow plug)

 

[aussieboater]

Also jerry i will do the bearings just for you mate thanks for the info