K&B .67 Marine question

[rigged]

hi, im running a older disk rotor 67 in my boat (36" cat) and it runs fine at 1/2 throttle and tries starts to get on the pipe, but as soon as i give it full throttle, it bogs down and tries to die. Any idea to the cause of this? Did this with the needle 3-1/2 turns out and 3-3/4 turns out.

Is it still too lean? too rich? All i know is its driving me crazy :roll:

thanks.

[MECOA]

Probably still too lean. Open up the needle 2 more turns.

[rigged]

Probably still too lean. Open up the needle 2 more turns.

still did the same thing 5 turns out.... after talking to someone else, i believe ive found that the low speed was too lean (was only 1 turn out from closed). Ive moved it out 2-1/2 and will hopefully get to see if it helps this weekend.


another note... how much head clearance should i use for running 30% fuel?

[MECOA]

Probably about .020 on the head.

As for the carb look here...

http://www.mecoa.com/faq/carb/kbsq/kbsq.htm

[rigged]

Probably about .020 on the head

i only have .010.... is this safe to run with 30-40% :?:

[freddyst]

If you are still having a problem, check you plug coil. Put a new one in and run it, then bring it back. If it looks bent, but not burnt, your head clearance could be the cause. If it looks good, I'd check the bearings and looks for leaks in the fuel system. Are you running 2 tanks? If so, try one tank at a time to see if it might be a tank or a fuel line. Another thing to check is your drive-line. If it binds or your shaft is mis-aligned, this can cause the engine to have problem. Does the engine seem hot when it returns? if so binding of the shaft or low cooling water can be the cause. The last thing I can think of (off hand) is your tune pipe length. If you are running a tune pipe, it may need to be lengthened. In fact, I'd check this first (got my response a little out of order). I race 1/8 scale hydroplanes, with 67 motors, and these are issues that have caused me problems when trying to get a boat 'on the pipe' (full speed). :)

[freddyst]

Oh, one more thing, check your needle valve assembly. If there is junk caught in it, you will never get a good tune. 8)

[MECOA]

No don't run that much nitro --- please read...

http://www.mecoa.com/faq/compression/compression.htm

[rigged]

If you are still having a problem, check you plug coil. Put a new one in and run it, then bring it back. If it looks bent, but not burnt, your head clearance could be the cause. If it looks good, I'd check the bearings and looks for leaks in the fuel system. Are you running 2 tanks? If so, try one tank at a time to see if it might be a tank or a fuel line. Another thing to check is your drive-line. If it binds or your shaft is mis-aligned, this can cause the engine to have problem. Does the engine seem hot when it returns? if so binding of the shaft or low cooling water can be the cause. The last thing I can think of (off hand) is your tune pipe length. If you are running a tune pipe, it may need to be lengthened. In fact, I'd check this first (got my response a little out of order). I race 1/8 scale hydroplanes, with 67 motors, and these are issues that have caused me problems when trying to get a boat 'on the pipe' (full speed). :)

thanks for the info. I actually found the issue before reading this.. ended up just being a needle setting.

I now have the LSN just under 2 turns out, and the HSN 3-1/4 and it gets up on the pipe and will run at full throttle now. Now to just get the pipe length set where it runs the best. I tried every different length with the pipe (like you said) before bringing the LSN out... 11-1/4 down to 10-1/2 and it never made a difference in not wanting to run at full throttle.

[rigged]

No don't run that much nitro --- please read...

http://www.mecoa.com/faq/compression/compression.htm

dont really explain why i cant run that % of nitro with the clearance under the head (which isnt .010 total, just .010 under the button). Ill be testing out some 10% to see what kind of difference it makes anyhow.