K&B 3.5 woes

[mathis]

My K&B 3.5 outboard is driving me to madness! (I may have had a head start) Here is the scenario: 1) Finished last season with the OB on a tunnel, and installed it in a Spitfire 1.

Day 1: Could not run at all with the hopper tank w/o pressuring it with fuel bulb. Removed hopper. Still did not run very well (not sure it was doing well at the end of last season) Compression on last years new ss piston and sleeve was minimal. Removed that and installed powerhead from ebay (“racing engine, do not bid if you don’t know how to break it in…”) Its pinch was so tight, it could bairly be turned over. If it flooded, I had to remove the glo plug completely. It would run on the beach, run with it in the water holding it, but let it go and it would go 50 feet and quit. Every time. Needle out past 8 turns, same thing. Thinking I did not have enough pressure to the fuel tank, possible leak at header, due to press fit where header meets engine. (below header brass pipe, copper elbow and Equalizer pipe) . SS air head.

Day 2 I silver soldered a brass and copper bolt up header. No leaks blowing in the pipe.

Went back to water cooled head. Same problem. Will not run in the water. Put tubing on the carb in case water spraying in. No fix. Front bearings are good, no leaks there. Pinch still impossibly tight. Locks up sometime w/o glo plug.

Day 3 Removed ebay racing power head. Put in an old piston and sleeve with decent compression. Removed tank and re bent the tubing to make sure no kinks. This day it would go half way around the course , but that’s about it. Again, the needle did not seem to matter much. 5 turns out, 8 turns out, either rich on the shore but quits under load.

When this engine was on the tunnel, the tank was pretty high. Now the fuel has to rise about 2.5+ inches to the carb nipple. I’m wondering if the equalizer pipe pressure and the carb suction are insufficient to provide fuel. That might explain why the needle is so insensitive, ie it’s all it can do to get the fuel up, so one needle setting is about the same as another.

Its not fuel, running 50% and 60 % Redmax.

Am I missing something? Do I need engine guru, exorcist or new engine?

Thanks fellows!

 

[Brian_Nelsen]

This may be a silly question but I gotta ask. Did you try cleaning out the needle? Dirty needle can act like low fuel pressure. Other than have you checked for a good seal around the carb?

Brian

 

[Jerry Dunlap]

This may be a silly question but I gotta ask. Did you try cleaning out the needle? Dirty needle can act like low fuel pressure. Other than have you checked for a good seal around the carb?
Brian

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Bad bearings in the engine will also cause problems similar to what you are describing.

JD

 

[MarkScott]

I've never had a K&B 3.5 OB needle out more than 4 turns and that was to break in the motor. 3 1/2 half turns out is norm.. Motor depth could be another issue. How old is the fuel lines?

 

[mathis]

I pulled the carb off, pulled the needle out (clean, no galling) pressured fuel through to see how it came out, pulled the barrel, re installed compressing the O ring as best I could, then blew thru the venturi stopping the fuel port and checking for leaks.

All that seems fine. Good question, thanks

Mark

 

[Grimracer]

Mathis,

Hum.. looks like you are loosing it.. i see nothing wrong with your engine and its running just fine.. Mathis.. your shoes untied... look down... (come on I waters guys, play along).. Mathis, did you not know that the boat is only to go 50 feet.. TRUE... its a race to see who can go the furthest on a 1 sec burst of power ... ahhhhh mathis.. there a knock on your door.... knock! knock! Knock.. hear it?....(keep playing along and Mathis will never catch on) ...

Aha...ah ah ah... Did you say you blowed the pipe...ah ah ah...thats cool...

OK.. Im done...

If the lip liner is being pinched by the case its going to be tight at the top... I have seen this on K+Bs in the past.. You should take and lap the liner to the case.. Also use a tork wrench to tighten the head bolts.

Your K+B can be snug at the top but it sounds to tight.. If you can not turn it over by hand after the first 4 tanks or so you have a problem with the engine.

Good luck..

O yea if you are still having problems send the motor to Rod Greaghty.. he has years of setting up K+Bs and can get the thing straight for you.

Grim

 

[snowdog-2112]

All ideas so far are good but I would look at the propellor depth to start. That will be the easiest. Unless you're running a submerged propeller, you want the prop running 1/2 in and 1/2 out of the water line.

 

[mathis]

Letsee, I think the bearings are good. I have had bad bearings before, and the ebay engine bearings are the best I have and seem new. No fuel spitting around flywheel. My fuel lines are mixed, old from the pipe to the vent, new from the tank to the engine. Think they are OK, but easy to change. The crank is old, with some wear on the crank pin, but not bad, I think. Rod is new. The motor depth is just a bit high; bow goes up, accelerates, bow drops, cavitates, but will get up to speed. Prop center depth about 1/8 below rear sponson. The boat is heavier than my old tunnel, about 5 pounds.

Mark

 

[Grimracer]

Letsee, I think the bearings are good.  I have had bad bearings before, and the ebay engine bearings are the best I have and seem new. No fuel spitting around flywheel.  My fuel lines are mixed, old from the pipe to the vent, new from the tank to the engine. Think they are OK, but easy to change.  The crank is old, with some wear on the crank pin, but not bad, I think. Rod is new.  The motor depth  is just a bit high; bow goes up, accelerates, bow drops, cavitates, but will get up to speed. Prop center depth about 1/8 below rear sponson.  The boat is heavier than my old tunnel, about 5 pounds.
Mark

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Mathis,

Motor sounds way to low dude..

Grim

 

[mathis]

Yes, I could be losing it! Last brain scan looked OK, but morphology is no gurantee for functionality. The sleeves are not tight in the cases. (Learned about that on Intlwaters).

How come Brian and Grim have the same picture? Think some other fellows have the same pic too. Defalt pics? Clones? What gives?

How does one contact Rod Greaghty?

I agree that the "ebay racing " sleeve and piston are in need of a good lapping. I read Izitbrokeyet's procedure but have not obtained the proper lapping compound, but in the meantime the old replacement piston and sleeve really ought to work, at least I am pining my hopes there. Still, I'm considering a new motor. Something that comes together with intention rather than happenstance, fast bidding and serendipity.

Thank you all for your help.

Mark

 

[LawlessMan]

I put a used carb on my 7.5 this spring and thought it was fine. Someone who knows whole encyclopedias more than me (which is most everybody that participates here), pointed out that there was something wrong with the way my linkage was hooked up, so the motor was fine when I started it, but it died as soon as it hit the water. I reversed the linkage setup and everything straightened out. I'm a little hazy about the technical details, but it had to do with the direction the barrel was rotating. By rotating the barrel 180 degrees the proper action was restored. (I found that the stop screw was broken off, by the way, which is how it got rotated 180 in the first place). Just one more thing you might check.

 

[Mike Larson]

Hey mark.... the motor is sucking serious air from somewhere, im still thinkin bearing, check carefully for a cracked case..... front plate? you can dump fuel ie; needle out 8 turns.... all you want, its still getting too much air from somewhere, the loss in crankcase pressure is also not allowing your pipe to pressurize the tank correctly, from the same problem, order new bearings/gaskets, after you thouroughly inspect the case/plate/pto, this is my 2 cents, good luck

 

[Lake S.P.O.R.T.]

I know you stated that you have tried different motors but there is one more thing that can run you crazy on a K&B if you have not experienced it before. The two little allen screws that hold the carb in on each side can leak air in and fuel out even though they are tight. When you fire the engine up on the stand look very closely at both of these for several seconds while giving the engine a little throttle. Now, I always apply locktite to these. Make sure you degrease the screws and the threads in the case or the locktite will not work as well. I had a brand new SX that I could not get a needle setting on, until I found that and fixed it. One more thing that can cause this problem is a tank stopper that is not sealed good. Hope this helps.

Oh, in case I missed it, what size prop are you running on the motor?

 

[Jerry Wyss]

Mathis, You said the crank was "used" but still in good shape,, "few marks on the pin",, How 'bout "marks" on the crank between the bearings? where the "induction

window" is ? :huh:

Also, sucking fuel up 2.5 inches is a bit much for many engines.

 

[mathis]

On M. Larsons suggestion, I partially dissembled the engine to check the bearings and seals once again . The front bearings are smooth and tight, the PTO bearings are not as tight, but they are still smooth, . Mind you, I cannot seem to blow by them with my aging lungpower, but they may be leaking like a sieve under operating conditions. I think I will try plumbing the glo plug port with my airbrush compressor, and (hopefully) see where air may be leaking out. Does that make sense? Had I changed the powerhead completely, I might have eliminated case and bearings and seals as a problem, but I only had one set of good front bearings, and one PTO so I just changed the crankcase, the piston and sleeve and the head, and the problem persisted. Whats worse is that the "ebay Racing" piston and sleeve had another problem as well; the "pinch" flirting with the "seize",

I did not pull the front bearings out last night to check the crank condition, but I do recall some scratches on the crank in the induction area, as Jerry Weiss suggested that I watch for. Doubtless, these occurred when the front bearings failed bigtime last year. This may be another problem.

This was my first model boat engine. I purchased it way past its prime, but after modding it with pipe, piston, sleeve, head, carb, etc, I was buoyed by the remarkable performance improvements. The current series of events demonstrate that it was more luck than understanding.

Lake S.P.O.R.T asked about the prop, its a x440 cupped and trimmed and balanced per articles on this forum. When the engine runs, this prop is way, way better than the stock one.

. I purchased a new SS yesterday from Phil's Hobby Starting new is a data point I dont have. And, I can race while I grapple with the current problems.

Again, I thank all of you who have offered suggestions and analysis. This is a terrific forum. Without your collective knowledge and generosity, this hobby would be seriously diminished.

Mark

 

[bbnate804]

could you fire up the motor on the stand and spray parts cleaner or wd-40 around the bearings with a straw? it wouldn't blow up the motor would it?

nate

 

[mathis]

OK, I see, finally. 1) Mysteriously black engine mount. (I never painted that!) 2) Lower unit internally swimming in castor. Appears that if the engine runs long enough, any crankcase leaks will be revealed. A couple new PTO bearings, and I should be back iin the fast lane.

Many Thanks to all,

--Mark