K&B 3.5 Won't Go Around One Time!

[Pete Markese]

In another thread entitled "Hopper Tank" I had been talking about a problem that I am having with a K&B 3.5 outboard that just won't stay running. I had thought that maybe I was having a fuel starvation issue and that possibly a hopper tank would help. It did not! I am looking for any help that I can get as to why this engine won't stay running.

THE PROBLEM....the boat will launch like a bullet but will die in the middle of the lake after only a 100 yards or so. I know...you're all immediately saying that the engine is too lean. I've turned the needle as many as 7 turns out in 1/8 of a turn increments and there's been no change. The boat will die after only a 100 yards or so every time! It seems to want to run best at around 4.5 turns out, but it only teases me with that by going just a little further and then it dies again!

The engine is in a Prather Spitfire I rigger. I had been running a stock muffler like the one that comes with the 8935/8950 engines, but recently replaced it with a Silver Bullit tuned pipe thinking that maybe that stock muffler was my problem. It was not. The same problem exists now with the new Silver Bullit tuned pipe.

I am running a gold carb on the engine. I replaced the gold carb with another gold carb thinking that maybe the carb was my problem. It was not. The problem still exists with the replacement carb.

I keep thinking that it is a fuel issue so I have redone the fuel lines twice and have definitely checked for pressure leaks in the system. There are none. I am of course running the fuel pressure line off of the Silver Bullit pipe.

This is my first rigger, and I'm thinking that maybe it's a set-up issue with thrust angle and or prop depth etc. I have asked many who know about these things and have closely followed their advice relative to the correct set-up. The boat still dies!

Currently there is a x440 prop on the boat, and I have been told that this is not the best prop to run for speed. Many have advised that I run a 1740/3 in order to get the best speed out of this hull. I haven't made that prop change as I cannot believe that this would be the cause for the boat to be doing what it's doing. At this point speed is not the issue...getting the boat to go one complete lap is!!!

I have dismantled the engine 3 times. I cannot find anything wrong with the internals. Compression is excellent.

So there it is. Short of your advising me to throw the darn thing in the trash, I would appreciate any and all feedback that can be offered.

Thank you.

 

[topfuel443]

Hey Pete, its leaning out some how. I know thats not want you want to hear, but its what it is.

You either have:

Bad bearings/seal on the front housing (Very common)

A cracked case (Very hard to see)

Or some combination there of

You can send the engine to me if you dont get it figured out. Ill make it run.

~James

 

[SayMikey]

Hey Pete, its leaning out some how. I know thats not want you want to hear, but its what it is.
You either have:

Bad bearings/seal on the front housing (Very common)

A cracked case (Very hard to see)

Or some combination there of

You can send the engine to me if you dont get it figured out. Ill make it run.

~James

How old is the engine? im with James, bearings Does the motor richen sloppy rich on the stand or is it screaming? Can you see fuel spraying out under the flywheel? Mike

 

[Pete Markese]

Hey Pete, its leaning out some how. I know thats not want you want to hear, but its what it is.
You either have:

Bad bearings/seal on the front housing (Very common)

A cracked case (Very hard to see)

Or some combination there of

You can send the engine to me if you dont get it figured out. Ill make it run.

~James

How old is the engine? im with James, bearings Does the motor richen sloppy rich on the stand or is it screaming? Can you see fuel spraying out under the flywheel? Mike

James/Mike....okay, the engine is NOT new that's for sure. I have several of these little K&B 3.5's, and I do swap parts around from one to the other on occasion. BTW, I always keep P/S together as a unit. I have not put new bearings in this motor, although under my cursory inspection, they appear to be in good condition. I do not see fuel spraying out from under the flywheel. I don't run the motor all that long on the stand, but it appears to sound just as you'd want it to prior to launch...not too crisp or too fat. Your suggestion regarding a crack in the crankcase is interesting. As mentioned, I have taken the engine apart several times and have not seen a crack, but I will surely inspect more closely for that. I also have not changed the top bearing, but will do that also (if that's the only way to ensure that there's a good bearing seal in the top housing...is it...or is there something else that I should do there...like maybe change the top housing all together?).

Question...what signs would the glow plug show of a lean condition? Also in your opinion, what glow plug should I be using? I've mostly been using an OS-8. On glow fuel, I've tried everything from 20, 30, 40 and 60%.

Thanks for the feedback. I just might send the engine to you, but of course would prefer to figure it out myself if possible. If I were to send it to you, where would I send it and what's the tariff?

 

[topfuel443]

Hi Pete, the case would most likely be cracked along the bottom. It will be VERY hard to see.

If you replace the bearing, you should definitely replace the housing. The housing/crankshaft clearance is what seals the motor when the oil/fuel mixture is present, NOT the bearings. The bearings just keep everything "in-line" for lack of better wording. To much clearance in there due to scoring on the housing from a worn out bearing will do exactly what you describe.

If you have a lean run, the glow plug element should be pulled and dull colored. If you have an air leak, you may not be able to run the engine long enough to get the plug to show the signs of a lean condition.

There are no tariffs to send me the engine. My address is a US address, but it comes to me in Germany. It will cost the same as sending a package to anywhere else in the states (about 8 bucks via priority mail). Let me know if you need help with the motor. I would be willing to bet, if you replace the top housing and new bearings, and you dont have a cracked case, your engine will run just fine. If you need to ship, my address is as follows:

James Clegg

PSC 2 Box 12548

APO, AE 09012

~James

 

[jaxracer]

Make sure there isn't any trash in the needle valve before you go spending money for a case or bearings. That will cause a lean issue in a hurry. Remove it completly from the carb housing and clean it.

~Mitch

 

[chuck]

By any chance are you running a radio with a fail safe. Maybe its not your motor giving you that problem! Try range checking your radio system! Just a idea!

 

[Pete Markese]

Well thanks to all of you for your thoughts and suggestions. I do really appreciate it. The issue with my engine failure has changed dramatically, and it's now turned to a totally different direction....the boat! Yes, I did say the boat. This engine has been sitting behind a Prather Spitfire I.

I took the engine off the Spitfire and mounted in on a TS2 tunnel that I have. I took the TS2 to the lake today, and it ran like a rocket! The engine performed flawlessly!

So this engine dying problem that I've been fighting with is somehow rooted in the set-up of this Prather Spitfire. I've shown the boat to several people, and no one immediately picked-up on anything that was a standout problem, but obviously there is a problem somewhere!

Jez' could it be so simple that maybe I have a fuel pick-up problem stemming from the fuel tank set-up? Could it be that the boat hull itself is misaligned causing an undue load on the engine? Who's the rigger expert out there? Anyone got a lot of experience with the ole' Prather Spitfire I hull? If so, I need your help.

Again, thanks to all of you for your helpful suggestions on what could have been an engine malfunction. Even though it now seems that I was barking up the wrong tree, your feedback still presents a great learning experience for someone whose as new to this hobby as I am.

Prather Spitfire set-up expertise now needed..........

 

[moparbarn]

will the fuel tank and lines from the ts2 fit in the spitfire? at least good enough to run a lap or 2? one way to eliminate 1 piece of the puzzle. do you run a fuel filter? is it clogged? i know it's pretty basic stuff, but that's what always kicks my butt :blink: !

 

[tnrcboatracer]

When you ran it in the TS2, did you use the same tank as in the Spitfire? I've had a cracked ube inside the tank before, and it is hard to diagnose. What type of tank is in the Spitfire?

 

[Pete Markese]

will the fuel tank and lines from the ts2 fit in the spitfire? at least good enough to run a lap or 2? one way to eliminate 1 piece of the puzzle. do you run a fuel filter? is it clogged? i know it's pretty basic stuff, but that's what always kicks my butt :blink: !

Interesting thought, BUT I cannot remove the fuel tank from the TS2. It's "Shoe Glued" down to the hull. I am not running a fuel filter (Me bad).

 

[Pete Markese]

When you ran it in the TS2, did you use the same tank as in the Spitfire? I've had a cracked ube inside the tank before, and it is hard to diagnose. What type of tank is in the Spitfire?

No, I did not run the same fuel tank from the Spitfire when I ran the engine on the TS2. the fuel tank on the TS2 is "shoe-glued" down to the hull. I have an 8 oz Sullivan slant tank in the Spitfire.

 

[Bob Kensill]

Get the 1740/3 and your troubles will go away. It will lift the back of the boat and let the engine rev. Been there done that.

 

[tnrcboatracer]

Check the feed tube in the tank; I have a feeling you may find a leak there. Another option is to just replace the tank.

 

[dwb2620]

I ran Spitfire I O/B hydro for years in the 20 hydro class with a Prather 215 prop. Never had any issues like you have been having. It always ran very well. Just threw it in and it would go ( and come back!).

I just thought of something. One thing to check is the turn fin alignment. If it is out of alignment (i.e. not parallel or angled up or down). It will affect the way the boat comes up on plane. My problem was the turn fin got knocked out of adjustment in a wreck. It got knocked back and was pulling the sponson down. It wouldn't plane out at all. In fact, the engine would die after a few yards. It took me a while to figure that one out. Now if I hit or get hit by another boat, I double check everything.

David

 

[Pete Markese]

Get the 1740/3 and your troubles will go away. It will lift the back of the boat and let the engine rev. Been there done that.

Yeah, I got that work from someone else, also. I did get a 1740/3 but had a tough time getting the boat on plane. I know the launch is key with that prop, and I haven't given up on it, but have been having a tough time getting the launch correct.

Thanks for the feedback.

 

[Pete Markese]

Check the feed tube in the tank; I have a feeling you may find a leak there. Another option is to just replace the tank.

Thought about that....replaced the tank. No improvement. Problem still exists.

 

[Pete Markese]

I ran Spitfire I O/B hydro for years in the 20 hydro class with a Prather 215 prop. Never had any issues like you have been having. It always ran very well. Just threw it in and it would go ( and come back!).I just thought of something. One thing to check is the turn fin alignment. If it is out of alignment (i.e. not parallel or angled up or down). It will affect the way the boat comes up on plane. My problem was the turn fin got knocked out of adjustment in a wreck. It got knocked back and was pulling the sponson down. It wouldn't plane out at all. In fact, the engine would die after a few yards. It took me a while to figure that one out. Now if I hit or get hit by another boat, I double check everything.

David

David, very cool. I haven't really paid any attention to the turn fin alignment. When I re-did the paint job on the boat, I obviously removed the turn fin, and did think I got it back on correctly, but you've got me thinking on this one. I really haven't checked it all that closely. You've hit a new note for me there. I'm going right out to the garage to check that now.

Thank you!

 

[Pete Markese]

Well, It's getting kind of tough to do testing with some of the changes that I've made as of late, as my lake is drying up. Yes, Southern California is plagued with one of the worst droughts that we've had in years, and the water level at my local pond is going down quickly. Reeds and other debris is causing havoc on my testing time.

I checked the alignment of my turn fin, and it was off just a touch. I've corrected that. I, again, checked the fuel tank for air leaks and can't find anything there although I did re-position the brass fuel pick-up tube in the tank. It is now located in the right hand back corner of the tank (closest to the engine) looking at it from the stern of the boat.

My last test at the lake, before these changes, the boat did actually get up on plane and gave me a lap or two before it fell of pace and plane. The engine actually kept running, and I was able to get it back up for a short while before it once again fell off. It seems to want to loose pace and fall off plane as I am making a right hand turn. Obviously this is major improvement over past performances, and I am starting to feel as if I am closer to the right set-up. The fact that the motor is keeping alive and not dying is a good sign. Now I need to figure out why it wants to fall off plane while turning right. Maybe that small correction with the turn fin is going to be the fix. I am hoping that is the case.

Won't be able to get to a bigger pond until Sunday, July 8th. Will get back to you all after that.

 

[moparbarn]

the new steering arms will fix it :lol: . on their way to ya.