Help me with my k@b,cant keep rpms up

[James montgomery]

I have a .21 k@b outboard i have a 438 prop on it and pitch is set right but cant keep my rpms up on boat, i have richend it leand it out i cant find the sweet spot , plz any ideas plz let me know or if this has ever happend to u. Willing to try new props and setup

 

[Tim_Duggan]

Some more info might help.

What type of hull - propshaft height - nitro % - plug type etc.

 

[RodneyPierce]

Tim, its an air cooled KB, not sure on plugs. 45% byrons fuel. TS3 hull.

 

[Tim_Duggan]

Tried raising the motor up? if so - what does it do?

 

[James montgomery]

It acks like it will start pulling rpms and dies back down , and even after changeing pitch in moter mount it will still i gess wht u call wet and want to pull rpms and bog out again, now i have started it in revres a few times but not sure if that is causeing the problem and need new sleavr and piston

 

[James montgomery]

Glow plug is i think, odonnell, it is the blue plug, and it is water cooled, he got every thing else right but that, sry rodney,lol. Thank u for try to help,lol

 

[jim hagan]

if you have an inline fuel filter, check it for crud. If it is partially plugged it will speed up and slow down due to restricted fuel flow. Had this happen a couple times and after trying everything I could think of checked the filter and found it plugged. Now I start there and save myself a lot frustration.

 

[James montgomery]

I dont have a fuel filter on my boat, only on my fuel pump, maybe i should cheack carb and see if it is block now that u say something about the fuel filter , thanks for the info. I really like this web site, best site gor info ever

 

[Steve P]

You might try a hotter plug, my 21s do not like the OD blues they run better on the purples

 

[James montgomery]

Thanks for info will see if that makes a dif have go to lhs to get

 

[Hayden Bright]

You could have gone to high with prop height also so the boat is reving nice then coming off it's plane loading up and killing the revs..... lower slightly and see if there is an improvment, if not then you can rule that out....

 

[shoboat]

James,

Is the X-438 stock? It has 4.29" of cup.

Too much cup for great RPM.

Send it to me if you want it re-pitched.

Thanks,

Mark Sholund

 

[David Murany]

Dont know a lot about outboards but if the engine picks up rpm in the corner then you have a little to much wheel on it. This is usually what we run into with our outriggers when we try to turn to large of prop. Have also had this scenario when the carb bore was too small. .330 to .350 is the ballpark on .21 carbs.

 

[James montgomery]

Wow, thanks guys for all the great info, this hobby and site is the greatist place to get help,i went to the pound and tryed every thing even new plug and still not geting the rpms. I got back home and tryed bench testing it and just bench testing it it didnt pick up rpms

 

[James montgomery]

My carb is set at three truns out and acks like it is to much fuel,with bench testing it out of water it still didnt want to gain rpms

 

[bob miller]

james , you might want to check your drive cable and make sure it is not binding or starting to kink , also check if your cable is the correct lengh , if too long it can cause more drag on the motor.....bob

 

[Kez]

My carb is set at three truns out and acks like it is to much fuel,with bench testing it out of water it still didnt want to gain rpms

I have had at least two K&B carbs with the needle thread bore off centered. When you have one of these carbs,the needle will not close completely. Then when you open the needle three turns, it is actually running a lot richer. Try a simple test: Close the needle completely. Then try to blow air into the fuel inlet nipple with a fuel bulb or syringe (connect with a fuel tubing). If you can blow air into the fuel nipple, the needle is not closing properly. You do not need to replace the whole carb, just the brass threaded part where the needle thread into.

Another thing to check is the liner. Does it line up with the exhaust port correctly? I have had a K&B stock from the factory with the liner rotated off by about 30 degrees.

kez

 

[James montgomery]

Cool thank u guys i will cheack thoes things, i have cheacked the lineralready it was out of wack about two weeks ago. It would run good for two laps and die even like that it would still gain rpms. I will cheack thoes other things and get back to u guys thanks again

 

[Hayden Bright]

Sounds like she is set very rich is all...easy fix for that one Im sure the K&b guys can give you a needle setting to get you making some RPMS...

 

[James montgomery]

Ok so i cheacked cable and carb, cable is not binding. I could blow very little air throw the carb al the way closed. So changed that out and will try a bench test here in a little bit. Plz keep the info comeing. If anyone has a stock k@b they want to sell plz let me know or send me a pm plz, i got a 100 buck money order i can make out and send. Thanks again guys. This hobby is like a drug once u start it is hard to get away from.lol

I love this hobby,but so **** fustrating but cant get away from it