Ebay purchaced K&B 7.5 OB won't start

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Ebay purchaced K&B 7.5 OB won't start

Postby Acidrain » Mon Feb 06, 2012 11:54 am

Hello all... long time lurker, first time poster.
I'm not new to glow engines, but I just can't seem to get this one going.
I bought a K&B 7.5 OB off Ebay. Seller says it worked fine last time it was run.
Took it apart and cleaned it up. Looked pretty good inside, but the carb does have a broken off idle fuel needle. It's set at it's last known running position, but the outside part is broken off, so you can't adjust it.
Anyway, using 20% nitro and a pressure tank, I can see that fuel is being pumped/sucked into the carb, and the glow plug gets wet.
The glow plug seems to be working well, and have tried swapping with a known good one.
I'm cranking it (clockwise) with my DeWalt cordless drill and the rubber gripper off my starter (starter wouldn't work, so swapped it onto my drill motor).
The main needle has a flat end. I'm assuming the main needle is not damaged, but really don't know for sure.
I can get it to pop when cranking, and I've tried all main needle settings, but just can't get it to run on it's own. Even has an occasional puff of exhaust smoke.
It's got the Carb that says K&B on the front, with a throttle barrel and stop. The main needle is on the end with the throttle arm, and the idle needle is at the fuel inlet.
Seems to have really good compression.

Some things I haven't tried are: different fuel, replacing carb needles, moving fuel tank closer. Any other ideas?
Is it possible to get vacuum leaks at the bearing seals?
Is it possible the cordless drill doesn't crank it fast enough?
Are these things inherently hard to start?
Any help is greatly appreciated!
Acidrain
 
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Location: Seattle

Postby SteveM » Mon Feb 06, 2012 12:54 pm

I think that your electric drill just isn't spinning the motor over fast enough. Make sure the pressure fitting on the motor isn't plugged. Borrow a good 12V electric starter and try again. Fuel level should be inline with the rarb.
SteveM
 
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Joined: Mon Nov 20, 2006 10:33 am
Location: Ottawa, Ontario, CANADA

Postby Acidrain » Mon Feb 06, 2012 3:59 pm

Thanks for the ideas. I'll try those.
I was looking at the part numbers, etc. to order the new carb needles and discovered I had it backwards... the main needle is broken (not the idle needle, which I assumed didn't affect the not starting). I've got both needles and a new prop ordered.
I also saw that the recommended fuel is 25%. Do you think there is enough difference between 20% and 25% to justify buying a new jug of fuel?
Acidrain
 
Posts: 4
Joined: Sun Jan 22, 2012 4:13 pm
Location: Seattle

Postby SteveM » Mon Feb 06, 2012 4:12 pm

Acidrain wrote:Thanks for the ideas. I'll try those.
I was looking at the part numbers, etc. to order the new carb needles and discovered I had it backwards... the main needle is broken (not the idle needle, which I assumed didn't affect the not starting). I've got both needles and a new prop ordered.
I also saw that the recommended fuel is 25%. Do you think there is enough difference between 20% and 25% to justify buying a new jug of fuel?


If you're just planning to run the boat for fun, then use the fuel you already have. Once gone, try the 25% blend.
SteveM
 
Posts: 242
Joined: Mon Nov 20, 2006 10:33 am
Location: Ottawa, Ontario, CANADA

Postby Acidrain » Mon Feb 06, 2012 4:46 pm

Yep, just for fun!
I just want to get the damn thing running before I dump too much money into it (brand new radio & servos, fuel tank, cable, etc.) I really think the needles are the problem. Guess I have to wait for those & give it another try.
Acidrain
 
Posts: 4
Joined: Sun Jan 22, 2012 4:13 pm
Location: Seattle

Postby Acidrain » Wed Feb 15, 2012 5:59 pm

Woo hoo! Got it running. It was a combination of things... needed a new high-speed needle valve, the tank raised a bit, and a faster starter motor.
Got the new needle valve from Mecoa (along with some other goodies) and set it to 4 turns out. Set the low speed needle to 3 turns out.
Raised the tank so that the fuel level was pretty close to the carb height.
Messed with my old frozen starter motor and got it turning. Right away I could see that it turned the motor faster than my drill motor.
clipped on the glow wires, cranked it up, choked it for just a second, and it fired right up. Thanks guys!

Oh, and 20% nitro.
Acidrain
 
Posts: 4
Joined: Sun Jan 22, 2012 4:13 pm
Location: Seattle

Postby SteveM » Wed Feb 15, 2012 7:21 pm

Great news....have fun.
SteveM
 
Posts: 242
Joined: Mon Nov 20, 2006 10:33 am
Location: Ottawa, Ontario, CANADA


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