motor problem 21 k&b

[petdos]

Hi to all and all the best to everyone for this new year,anyway my k&b 21, idles fine ,1/2 trottle fine,3/4 fine,but as soon as i put to full throtle goes for couple sec and stops,any ideas thanks,peter.

 

[Bill Gibson]

Hi to all and all the best to everyone for this new year,anyway my k&b 21, idles fine ,1/2 trottle fine,3/4 fine,but as soon as i put to full throtle goes for couple sec and stops,any ideas thanks,peter.

Can be a few things, but try one thing at a time....too lean,fatten it up.....over propped, try a smaller prop......fuel issues....are the lines good? tank sealed for pressure? no trash in the needle? Always check for the simplist stuff first to avoid aggravation!!

 

[FloridaScaleBoater]

Hi to all and all the best to everyone for this new year,anyway my k&b 21, idles fine ,1/2 trottle fine,3/4 fine,but as soon as i put to full throtle goes for couple sec and stops,any ideas thanks,peter.

Can be a few things, but try one thing at a time....too lean,fatten it up.....over propped, try a smaller prop......fuel issues....are the lines good? tank sealed for pressure? no trash in the needle? Always check for the simplist stuff first to avoid aggravation!!

All good suggestions, only one to add,

If the carb has a low speed needle that uses the "tear drop" shaped (old Picco style carbs) cut in the spray bar, make sure the tear drop is actually opening instead of closing at W.O.T.

Been there, done that!!!!

 

[NAMBA860]

its to lean!

 

[petdos]

thanks to all ,will have a play.

its to lean!

 

[Ron Olson]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.

There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

 

[Bill Gibson]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

Good point! Im one of the few that still run K&B 3.5 inboards...seems that ive had the best luck with the gold carb..dont really know why, its just seems more consistent.. not sure if Peter is using an inboard or outboard on his boat.

 

[NAMBA860]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

Good point! Im one of the few that still run K&B 3.5 inboards...seems that ive had the best luck with the gold carb..dont really know why, its just seems more consistent.. not sure if Peter is using an inboard or outboard on his boat.

i still run the k/b 3.5 inboard drum rotor version i use the prather exhaust throttle and venturi but if you run just carb the gold is best!

 

[Bill Gibson]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

Good point! Im one of the few that still run K&B 3.5 inboards...seems that ive had the best luck with the gold carb..dont really know why, its just seems more consistent.. not sure if Peter is using an inboard or outboard on his boat.

i still run the k/b 3.5 inboard drum rotor version i use the prather exhaust throttle and venturi but if you run just carb the gold is best!

what kind of a boat are you running your K&B in? Im running mine in a sport 20 hydro....how do you like your exhaust throttle set up compared to a carb? The reason why im asking is i have a brand new exhaust throttle that ive never tried, but might try if you have had good results with yours.

 

[NAMBA860]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

Good point! Im one of the few that still run K&B 3.5 inboards...seems that ive had the best luck with the gold carb..dont really know why, its just seems more consistent.. not sure if Peter is using an inboard or outboard on his boat.

i still run the k/b 3.5 inboard drum rotor version i use the prather exhaust throttle and venturi but if you run just carb the gold is best!

what kind of a boat are you running your K&B in? Im running mine in a sport 20 hydro....how do you like your exhaust throttle set up compared to a carb? The reason why im asking is i have a brand new exhaust throttle that ive never tried, but might try if you have had good results with yours.

i run mine in a 33 inch calcraft mono. i run exhaust throttles on everything i own including outboards and im developing an exhaust throttle for a zenoah 26 also. i like them due to their great idle and response charictaristics. the only draw back is they do leave a little mess in the boat. is you k/b the drum rotor version? do you also have a venturi to go with the exhaust throttle?

 

[Bill Gibson]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

Good point! Im one of the few that still run K&B 3.5 inboards...seems that ive had the best luck with the gold carb..dont really know why, its just seems more consistent.. not sure if Peter is using an inboard or outboard on his boat.

i still run the k/b 3.5 inboard drum rotor version i use the prather exhaust throttle and venturi but if you run just carb the gold is best!

what kind of a boat are you running your K&B in? Im running mine in a sport 20 hydro....how do you like your exhaust throttle set up compared to a carb? The reason why im asking is i have a brand new exhaust throttle that ive never tried, but might try if you have had good results with yours.

i run mine in a 33 inch calcraft mono. i run exhaust throttles on everything i own including outboards and im developing an exhaust throttle for a zenoah 26 also. i like them due to their great idle and response charictaristics. the only draw back is they do leave a little mess in the boat. is you k/b the drum rotor version? do you also have a venturi to go with the exhaust throttle?

Yep it is the drum rotor..i have the venturi's that came with the older K&B 3.5 inboards as i have a few of them also, but i dont know if they would work or not. ill have to see who made the exhaust throttles as i dont think that what i have is made by Prather.

 

[NAMBA860]

Try the high-speed needle at around 3-1/2 turns out from the bottom, that should keep it running and put it very close to where it needs to be. If the motor is still acting up then look for the other problems.There are several K&B carbs for that engine, the black, gold, red and the rare purple. Which carb if it's the original can help tell us which engine that you have.

Good point! Im one of the few that still run K&B 3.5 inboards...seems that ive had the best luck with the gold carb..dont really know why, its just seems more consistent.. not sure if Peter is using an inboard or outboard on his boat.

i still run the k/b 3.5 inboard drum rotor version i use the prather exhaust throttle and venturi but if you run just carb the gold is best!

what kind of a boat are you running your K&B in? Im running mine in a sport 20 hydro....how do you like your exhaust throttle set up compared to a carb? The reason why im asking is i have a brand new exhaust throttle that ive never tried, but might try if you have had good results with yours.

i run mine in a 33 inch calcraft mono. i run exhaust throttles on everything i own including outboards and im developing an exhaust throttle for a zenoah 26 also. i like them due to their great idle and response charictaristics. the only draw back is they do leave a little mess in the boat. is you k/b the drum rotor version? do you also have a venturi to go with the exhaust throttle?

Yep it is the drum rotor..i have the venturi's that came with the older K&B 3.5 inboards as i have a few of them also, but i dont know if they would work or not. ill have to see who made the exhaust throttles as i dont think that what i have is made by Prather.

those venturis will work. it might be a gardner or law they were making them then also besides prather.

 

[Tom Foley]

[

what kind of a boat are you running your K&B in? Im running mine in a sport 20 hydro....how do you like your exhaust throttle set up compared to a carb? The reason why im asking is i have a brand new exhaust throttle that ive never tried, but might try if you have had good results with yours.

My K - B/ Supertigre X-15 rear rotor hybrid motor from Cal Lang has the ehaust throttle and the black carb linked by a simple linkage . Those KB venturis are tiny . Anyway thats not this guys problem .

 

[petdos]

Thanks again guys for the imput,im running a gold carb in a 33" mono,peter.

 

[jetpack]

Gold carb. Everyone has trouble with those. Welcome to the gold carb club.

The gold carb is bored out to the maximum and have very little fuel draw by itself at wide open. Not much of a "venturi" effect with them. Most people have been forced to use a small 1oz hopper tank close to the carb for it to draw from.

Be sure the tank is high enough, close to the engine, and is getting ample pipe pressure. Also be sure the carb is put on the right way, not backwards - meaning the barrel is opening the right direction.

I'll see if I can find a picture to post to help make this more clear on which way it should open...

The previous replies are good too...keep trying...but from my experience and what you describe, the engine is starving for fuel as it reaches wide open. Slobber it up rich on shore, so much you have to keep blipping the throttle to keep it cleared out and running, then give it a good hand-toss launch and nail it. Gold carb instructions say 6 turns out as a starting point reference.

Edit: Can't find a pic which way the barrel should open, so I'll try and explain it. When the carb opens, be sure the bottom of the carb barrel opens nearest the cylinder, not the output side of the housing - if what you have is a front-intake engine, not the drum rotor type.

 

[petdos]

Thanks heaps will check things out ,was really suprised to see the 6 turns though,peter.

Gold carb. Everyone has trouble with those. Welcome to the gold carb club.
The gold carb is bored out to the maximum and have very little fuel draw by itself at wide open. Not much of a "venturi" effect with them. Most people have been forced to use a small 1oz hopper tank close to the carb for it to draw from.

Be sure the tank is high enough, close to the engine, and is getting ample pipe pressure. Also be sure the carb is put on the right way, not backwards - meaning the barrel is opening the right direction.

I'll see if I can find a picture to post to help make this more clear on which way it should open...

The previous replies are good too...keep trying...but from my experience and what you describe, the engine is starving for fuel as it reaches wide open. Slobber it up rich on shore, so much you have to keep blipping the throttle to keep it cleared out and running, then give it a good hand-toss launch and nail it. Gold carb instructions say 6 turns out as a starting point reference.

Edit: Can't find a pic which way the barrel should open, so I'll try and explain it. When the carb opens, be sure the bottom of the carb barrel opens nearest the cylinder, not the output side of the housing - if what you have is a front-intake engine, not the drum rotor type.

 

[jetpack]

I'll try and upload the 3.5 SS O/B instructions which uses the gold carb. It will outline the carb adjust for you. Yeah, six turns suprises me too because I don't know any other carb that opens that much on the main, but running mine it proved it too.

I tried to outguess them first time starting mine, opening it up to four turns, thinking "they have to be wrong" and keep myself from flooding it right from the get-go, then kick myself for listening to them...but they were right!

 

[petdos]

Thanks again for info ,have made ajustments ,thought the bloody needel was going to drop out,anyway we'll see how it goes now,thanks peter. B)

 

[David Homer]

Here's an old trick that works well on those gold carbs. You might not be getting enough flow through that needle no matter how far out you go. I used to take out the fuel nipple and put on a pressure fitting gasket. That raises the nipple inside the carb body and helps the flow. Another thing I've done for years on those K&B carbs was to grind a small 45 degree angle off the back side of the spray bar. The idea is to get the fuel mixture going straight back into the engine.

There's a couple other things you may need to inspect on those engines. Make sure you have good gaskets on the front/back plates. Soak 'em in oil before assembly. The bottom of the crankcase has a nasty habit of cracking as well. Hard to see unless you really look for it. Anywhere there's a crankcase air leak, that will make it go lean at full throttle as well.

The red carb is too big, the black carb (if you can find one) is actually a little more user-friendly than the gold. The "ideal" bore is somewhere between the black and gold carbs, I don't remember the exact dimension..

 

[jetpack]

here's a carb pic.

be sure carb opens up nearest the crankcase.