K&b 3.5 ss needle adjustment

[Mike lasorsa]

I got 2 k&b 3.5ss having the same issue. They run great for about 3 for laps then lean out and die. What is a good starting point for the needle? They are 4 turns out now only way to get them not to die is to have it 4 3/4 turns out but they run so slow then. Fuel is a year old and is 50% nitro.

 

[Grimracer]

They sound like they need the bearings replaced!

Grim

 

[Mike lasorsa]

They sound like they need the bearings replaced!

Grim

Bearings are new in one of the 2 and they’d both do they same exact thing. Zero play in any of them here is a video
View attachment IMG_3929.MOV

 

[Grimracer]

how is the fuel line routed in the bottom of the tank?

 

[Grimracer]

Did you change the PTO Bearings too?

 

[Mike lasorsa]

Did you change the PTO Bearings too?

Pto was changed as well. Maybe a bad new one? Not sure how to tell it turns over fine when it shuts off. Clunk on tank is on bottom left back side of tank. If the needle is is almost 5 turns out it will not stall but it’s slow.

 

[Grimracer]

OK.. then I would make sure to turn the boat right in your testing.. the video showed left hand turns.

The next test will be piston to liner fit...

at the end of the day run the fuel out of the motor.. with the plug in turn the flywheel all the way around... BUT.. when going over the top rock the flywheel back and forth over the top not grabbing a new breath of air. You should compress the same air AT LEAST 10 TIMES! If not you are loosing the fit. (Having said this I have had a 8 bump motor fast as lighting BUT.. it did not make it though the summer!

I typically check that with the motor both hot and cold.

Grim

 

[Mike lasorsa]

OK.. then I would make sure to turn the boat right in your testing.. the video showed left hand turns.

The next test will be piston to liner fit...

at the end of the day run the fuel out of the motor.. with the plug in turn the flywheel all the way around... BUT.. when going over the top rock the flywheel back and forth over the top not grabbing a new breath of air. You should compress the same air AT LEAST 10 TIMES! If not you are loosing the fit. (Having said this I have had a 8 bump motor fast as lighting BUT.. it did not make it though the summer!

I typically check that with the motor both hot and cold.

Grim

Gotcha I’ll check that thanks for you help

 

[Derret]

The K&B needle valves leak air by the black sinch nut thru the threads on the needle- take the nut off & put a small dab of RTV/silicone seal on end on the brass part that the needle screws into....the plan here is to seal up the threaded area of the needle valve & not leak air into the fuel stream upsetting the mixture. Usually, the threads of the small fuel fitting threads leaked also needing sealing also.
Water Bench test: take carb off the motor;
put a length of fuel line on the carb;
put the carb under water (in a bucket);
pressure in the fuel tube (breath) will show air leaks in fittings, needle valve threads etc...
pinch seal both inlet/outlet sides of carb-

Back in the day when running my OB3.5 KBs, I would carry some prepped needle valves in my tools to give to guys having your problems & that cured things up usually... MAGIC!!!!
Also, after some problems running 50% nitro fuel, I went to 40% nitro & the motor ran very well with little noticeable difference in performance ....motor/boat was happier & I was too...

Nice boat/motor - one of my 'Keepers' from those days...I still have it... hope this helps...
Thanks-
Dave Richardson
RPMInc (ret)

 

[Mike lasorsa]

The K&B needle valves leak air by the black sinch nut thru the threads on the needle- take the nut off & put a small dab of RTV/silicone seal on end on the brass part that the needle screws into....the plan here is to seal up the threaded area of the needle valve & not leak air into the fuel stream upsetting the mixture. Usually, the threads of the small fuel fitting threads leaked also needing sealing also.
Water Bench test: take carb off the motor;
put a length of fuel line on the carb;
put the carb under water (in a bucket);
pressure in the fuel tube (breath) will show air leaks in fittings, needle valve threads etc...
pinch seal both inlet/outlet sides of carb-

Back in the day when running my OB3.5 KBs, I would carry some prepped needle valves in my tools to give to guys having your problems & that cured things up usually... MAGIC!!!!
Also, after some problems running 50% nitro fuel, I went to 40% nitro & the motor ran very well with little noticeable difference in performance ....motor/boat was happier & I was too...

Nice boat/motor - one of my 'Keepers' from those days...I still have it... hope this helps...
Thanks-
Dave Richardson
RPMInc (ret)

Thank you! I will Deff try that

 

[Mike lasorsa]

Gotcha I’ll check that thanks for you help

Did the bump test cold and hot I can do it a million times and it won’t lose any compression

OK.. then I would make sure to turn the boat right in your testing.. the video showed left hand turns.

The next test will be piston to liner fit...

at the end of the day run the fuel out of the motor.. with the plug in turn the flywheel all the way around... BUT.. when going over the top rock the flywheel back and forth over the top not grabbing a new breath of air. You should compress the same air AT LEAST 10 TIMES! If not you are loosing the fit. (Having said this I have had a 8 bump motor fast as lighting BUT.. it did not make it though the summer!

I typically check that with the motor both hot and cold.

Grim

did the bump test. Cold and hot I can compress the same air over 30 times. They both have a small head shim do you think timing could be a issue here?

 

[Mike lasorsa]

The K&B needle valves leak air by the black sinch nut thru the threads on the needle- take the nut off & put a small dab of RTV/silicone seal on end on the brass part that the needle screws into....the plan here is to seal up the threaded area of the needle valve & not leak air into the fuel stream upsetting the mixture. Usually, the threads of the small fuel fitting threads leaked also needing sealing also.
Water Bench test: take carb off the motor;
put a length of fuel line on the carb;
put the carb under water (in a bucket);
pressure in the fuel tube (breath) will show air leaks in fittings, needle valve threads etc...
pinch seal both inlet/outlet sides of carb-

Back in the day when running my OB3.5 KBs, I would carry some prepped needle valves in my tools to give to guys having your problems & that cured things up usually... MAGIC!!!!
Also, after some problems running 50% nitro fuel, I went to 40% nitro & the motor ran very well with little noticeable difference in performance ....motor/boat was happier & I was too...

Nice boat/motor - one of my 'Keepers' from those days...I still have it... hope this helps...
Thanks-
Dave Richardson
RPMInc (ret)

Ok so the only air leak is from the small hole on the body which id assume acts like a idle bleed off?

 

[Grimracer]

Did the bump test cold and hot I can do it a million times and it won’t lose any compression

did the bump test. Cold and hot I can compress the same air over 30 times. They both have a small head shim do you think timing could be a issue here?

MONEY!

 

[Grimracer]

Ok so the only air leak is from the small hole on the body which id assume acts like a idle bleed off?

Nope.. thats the idle air bleed.. for now set that so you can see 1/2 the screw in the hole.

 

[Mike lasorsa]

The idle screw? I do notice if these things sit a day they almost have to be forced to turn over. As soon as it turns over it’s fine though. Wonder if I got a bad new bearing. I know the one engine has the original bearings.

Nope.. thats the idle air bleed.. for now set that so you can see 1/2 the screw in the hole

 

[Grimracer]

then.. the bearings could be bad.. you need to pickle the motor after each day.. I use CorrosionX but others will chime in too.

If you have not been pickling the motor after each day.. your bearings "could" be bad.

After your done for the day.

Pull off the fuel line
Run the motor to remove any fuel in the motor
Remove the plug and open the carb
apply your oil into the carb at first and rotate the motor by hand to work oil EVERYWARE!
Place a rag (not paper towel) over the plug and carb and hit turn the motor over with the starter.

Me.. I would remove the power head and add more oil to make sure I get the PTO bearings too!

Grim

 

[Mike lasorsa]

then.. the bearings could be bad.. you need to pickle the motor after each day.. I use CorrosionX but others will chime in too.

If you have not been pickling the motor after each day.. your bearings "could" be bad.

After your done for the day.

Pull off the fuel line
Run the motor to remove any fuel in the motor
Remove the plug and open the carb
apply your oil into the carb at first and rotate the motor by hand to work oil EVERYWARE!
Place a rag (not paper towel) over the plug and carb and hit turn the motor over with the starter.

Me.. I would remove the power head and add more oil to make sure I get the PTO bearings too!

Grim

That’s what I do for the most part. Sometimes I won’t take power head off. I just don’t see how a bad bearing would make it lean out and die. If it stays very rich it will run the entire tank. I’ve never had bearing issues so it’s new to me

 

[Grimracer]

Its all about the seal.. if the oil has to seal up a bad bearing then you have this very issue.

then.. tank location.. is it lower in the boat?

Grim

 

[Grimracer]

I should add.. the K+B PTO has the bearing on each side of the PTO housing.. if it has seen a bad bearing it CAN damage the center passage between the bearings.. ALSO.. if you ever get your crank shaft out of the motor.. if you see grey "Spots" in the area the crank is running in the case you need to VERY carefully polish those away.

Keep up the good work!

Grim

 

[Wasted wages]

I was just typing this out grim...great minds..

Pull the crank out and inspect the area in the case that the crank passes thru. If it is scored or worn ( which can happen when run with a bad bearing ) then you lose the labyrinth seal and it will cause the motor to go lean..