7.5 kb garbage????

[daryl2cb]

well, I joined this forum awhile back, background

I bought a boat used for 100 bucks

boat tunnel hull and 7.5 outboard.

the motor never ran, well consistent I changed the bearings, glow plug head gasket carb oring, sreaws, pto bearings and flex shaft, still runs horrible

I have taken it to the water several times and look like the village idiot consistly swimming to it. I have even gone as far as rigging up a pump system blowing water constantly to try to tune this thing, I guess I am used to os and traxxas motors that actually run.

this is the old 3 piece block, with the square carb, and the right angle needle valve, which barely, ha never stays where it is set, I had to put a piece of fuel tube on it.

so I am basically chocking this thing up to either a carb change, or a new bolt on, non kb that will work on the out drive.

when it runs, it spits fuel out the carb, and falls on its face at WOT. when I lean it out, it breaks up through 1/4 to full throttle.

if I feather the throttle it runs ok, but still breaks up at wot. I have changed everything from the linkages to the fuel tank, and new 3 ch mixing set up for better steering. needless to say my $100 good deal is turning out to be a nightmare. any suggestions on a carb or new motor? definatley not a tuning newbe, so I must have missed something here. Any ideas???

 

[Jerry Wyss]

Thats a shame daryl but I think that is an old motor. Allot of those $100 deals are like this,,

you could go thru responses of 15 boaters here and probably still not get to the fix.

I would try to get it to someone that knows these motors and get an estimate

of repair or diagnosis of it's condition.

Just a note , needle adjustments are for how the engine responds in the water,,

tuning on the stand can be misleading. Normaly, if you get it to run (what you think

is great), on the stand,, in the water it will be too lean about every time and usually

die quickly.

Jerry

 

[John Capps]

I have the same motor you are talking about. Its an old K & B 7.5 with the square carb. Mine actually runs very good considering its 15 years old or better. I had Rod Geraghty replace the bearings and inspect the rest of the motor. He did a great job at a very reasonable price. He also worked on a motor for a friend of mine. Im sure he wouldnt mind if you called him to talk about it or even look at if for you. His number is 715-926-6096. Good luck.

John

 

[Thomas Hulbert]

Check to make sure you are starting it the right way ( rotation of the starter) as they will run backwards.

Low needle seals might be gone if you can't get it to idle and transition to high speed.

3-4 1/2 h and 1-1 3/4 L if memory serves me correctly. What nitro content are you running as it will afect the needle settings.

Also what prop are you running on the hull as well as to prop depth in the water.

The more info you provide the better it is for others to help you out.

 

[jaxracer]

Sounds like a needle valve problem. I've never had much luck with the K&B needles in the carb. Try turning the needle all the way out and lock tite it. Then hook up an in line needle valve and try that.

~Mitch

 

[daryl2cb]

thanks for the advise, I found out two things one the low speed needle was jammed it was almost like someone (old owner) hot glued over it, hence leading me to think this motor dis not even have one. so I took an xecto knife and got all the compound what ever it was off. There is no way the thing was any where near 1-1 3/4 turns out, it was like all the way out. So I think this might be causing the fuel spitting out of the carb at idle, to 1/4 thrrottle. I also was able to get the needle set to 3 turns out and used a little lock tight to hold it. I am at work now, and I leave for the weekend from here, so I will not be able to test till monday, I agree there is no better way to test than in the water, but this thing is not even close to running properly if I can get it close and hit the water and add a 1/2 to richen it, no big deal. I will try to meausre the prop depth and post it, but as far as the prop, I have no idea what is on it, any markings? Any way to tell, angle finder or a pitch guage? Or just buy a new one?

I am also considering buying an after market carb off another member here and going with a remote needle setup, any thoughts on whether this might be a little more reliable setup?

 

[Ed.R]

Check to make sure you are starting it the right way ( rotation of the starter) as they will run backwards.

Almost sounds it is getting started backwards.

I have an older K&B 7.5 , and it runs great, need to work on idle setting. I'm not shore how old it is though.

My 2 cents

Ed.R

 

[Dan Hydro]

Presently using a K&B 7.5, old model with square carb on a Hot Shot 45. It took me a while to get it going right but its doing great. I have the idle needle almost flush (slightly out) with its receptacle and I have the High speed needle set at 2 and 1/8 turns (this will vary with your location, Alt, Temp).

I started out at 4 turns like the MECOA web site suggested and worked my way back until it ran perfect.

Ensure your throttle barrel does not move from side to side, if it does you will never be able to get a proper setting. Just tighten your barrel stop screw until you get rid of the side movement and that it can still rotate freely.

 

[ryan_t888]

As for the prop, look for markings on the trailing edge where the prop nut would press up to. (center of hub)

Ryan