Help K & B engine fuel problem
 

I have a K & B .45 Sportster engine built for RC planes. The muffler does not have a nipple for the fuel tank pressure line and the documentation with the engine says that the fuel tank needs to be "vented to the atmosphere". How do you vent a fuel tank to the atmosphere when the plane may be upside down at times? Won't the fuel leak from the vent? I am unfamiliar with any system that does not have a pressurized tank using exhaust pressure. Somebody help me please???

RE: Help K & B engine fuel problem
 

I would most probably do one of these things:

1) Drill/tap the muffler, insert pressure fitting, and run with muffler pressure.

2) Purchase an aftermarket muffler that already has a fitting, and run with muffler pressure.

3) Drill/tap the backplate, insert pressure fitting, and run with crankcase pressure.



That said, I've run with "no pressure" before. (An older K&B, oddly enough... with a Perry carb)
I ran the pressure(or in this case, "vent" ) line through the firewall as normal, then downward
until it was just about flush with the bottom of the fuse. I used a forward facing 45 degree angle cut
on the hose, to lessen the chance of having a vacuum pulled on the tank while flying, and to lessen
the chance of fuel getting sucked out while inverted.

Never had a moment's trouble out of that setup.
I believe the forward facing cut probably provided a little positive pressure from the airflow, and
combined with the suction from the carb, I doubt I ever lost a single drop. (If I did, I never knew it)
You can always try it that way, but I just feel better with a more positive source of tank pressure.

RE: Help K & B engine fuel problem
 

Duane:

You can go either way on the tank system. I would visit my LHS or mail order store and get a nipple to go in the muffler. Not hard to do. Then run muffler pressure.

But so far as the fuel running out is concerned, it doesn't happen. The engine is pulling fuel from the tank. the tank has to get air to fill the space where the fuel was, so as long as the engine is running there will be a flow into the tank through the vent line.

The one big thing to watch with the K&B Sportster engines is the oil in the fuel. The Sportster is a plain bearing engine, there is no synthetic that will give proper lubrication to the crankshaft. Granted, it will run for a while with 100% synthetic, but for maximum engine life be sure to to use a fuel with castor oil as at least part of the lube mix. My choice is Omega, but there are others available.

Enjoy it.

Bill.

RE: Help K & B engine fuel problem
 

Is there a plug where a pressure fitting belongs ? K&B uses a special
(larger than any other) pressure fitting, and you can only get them K&B.
I've never been able to find a tap for the metric fittings. I've heard of drilling
a slightly smaller hole, and pressing in a piece of tubing, but I've never tried it.

FBD. ;)

RE: Help K & B engine fuel problem
 

I feel better with the positive pressure in that fuel tank as well so I may try to drill the muffler and tap in a pressure nipple. Any idea where I can buy the nipple and the appropriate tap??

RE: Help K & B engine fuel problem
 

Thanks for your reply. I'm going to try drilling and tapping the muffler so I can add pressure o the fuel tank. I've checked some of the supply houses but haven't run into any opportunity to buy the pressure fitting or tap yet. If you have any ideas where these things can be bought please let me know. Thanks a bunch.

RE: Help K & B engine fuel problem
 

K&B is at MECOA....you can get the fitting from them, and it is an
American size....and uses a common tap size. :D

Dave. ;)

RE: Help K & B engine fuel problem
 

The muffler that came with the engine has no opportunity to add the pressure fitting at all. I have checked with K & B and they do not sell a muffler for this engine with a pressure fitting already present. I have only one or two options at this point I guess. Fly with the fuel tank vented to the atmosphere or drill and tap the muffler for a pressure fitting. If I can find the fitting and a tap I think that is what I will do although I have some doubt that this will be successfull. My doubts are founded on the belief that the muffler wall is probably too thin to take a tap very well. We'll see. Thanks for your help and if you have any ideas where I can buy the pressure fitting and correct tap please let me know.
Sincerely
Duane

RE: Help K & B engine fuel problem
 

Thanks Dave. I'll see what K & B can do for me - - probably today. Thanks

RE: Help K & B engine fuel problem
 

The fitting are about 3 bucks. There should be a fat area to drill and tap.
Here is where it is on a K&B .61. :D

You should have a pressure fitting for the tank.....without it your engine
will lean out while accelerating, or in climbs and could overheat . [:o]

FBD. :D

RE: Help K & B engine fuel problem
 

A closer inspection and disassembly of the muffler finds bad news. The wall of the muffler is approximately .30 thick and it is uniform throughout - - no thick area for potential drilling and tapping. I have sent a message to K & B to see how they can help. I don't believe there is enough "meat" on the wall of the muffler to allow a tap to work but I'll see what K & B has to say. Thanks so much for your time and efforts to help me. It is obvious that this forum is filled with people of great knowledge a desire to assist other R/C folks.

RE: Help K & B engine fuel problem
 

Drill a hole for the fitting and put a nut on the inside of the muffler for the fitting to screw into.

jess

RE: Help K & B engine fuel problem
 

If you vent the tank from the top and exit at the top of the plane, fuel may run out inverted, but if you run the vent from the top of the tank to the bottom of the the fuse there is no way fuel will run out.

RE: Help K & B engine fuel problem
 

Thanks Jess - - - perfect solution. Guess my inexperience might be showing a bit now eh?
Duane

RE: Help K & B engine fuel problem
 

You can always drill and tap the muffler extension that bolts to the engine. That should be thick enough for a tap.

RE: Help K & B engine fuel problem
 

Or just buy Du-Bro's number 241 6-32 pressure fitting. It comes with a nut to go on the inside end. $1.45 MSRP.

Bill.

RE: Help K & B engine fuel problem
 

There are some excellent ideas above for how a pressure tap could be added to the muffler. While I don't personally like adding a nut on the inside wall of the muffler to retain the tap (Murphy seems to dictate that things that can come loose in mufflers often do..and then end up inside the engine :( ) I also think the main point may have been missed. The reason K&B doesn't have a pressure tap on the muffler, and the reason they say just to vent the tank to the atmosphere, is that they were DESIGNED to run best that way. having run one of the .28 sportsters, I can attest that even though I too had to TRY some form of pressure boost on the fuel to the carb, the engine just plain was easier to set up with the tank vented to the air.

As for concerns about fuel running out of the tank, all one has to do is to run a line from the vent on the top of the tank, straight down, and out the floor of the plane. When the plane is upright, the vent is above the top of the fuel in the tank...no fuel running out. When the plane is inverted, the END of the vent line is STILL above the fuel in the (inverted) tank, so it still can't run out.

Just my thoughts...

Lee

RE: Help K & B engine fuel problem
 

All good points so I thank you for your reply. I have decided to try venting the tank through the bottom of the fuse and go from there. If I get the feeling that pressurizing the tank may have benefits I am going to try installing a pressure fitting on the muffler. It has all boiled down to experimentation and performance for me I guess so I will start with the least intrusive action and go from there. I don't think I will buy another engine that involves venting to the atmosphere though. I got surprised by this purchase and actually favor the pressurized tank. Thanks again.

RE: Help K & B engine fuel problem
 

If you mount the engine on it's side, you can help minimize the evils
of a non-pressurized system. Some engines....four strokes especially,
can run fine without pressure....mainly due to the fact that the carb is
located close to the centerline.

An upright mounted two stroke will be troublesome without pressure.
I might consider an inverted two stroke without pressure, living on an
abundance of gravity flow.....

....but given the choice, I'll go with the pressure. [sm=thumbup.gif]

FBD. :D

RE: Help K & B engine fuel problem
 

No room to mount the engine on its side so I'm kinda stuck (SIG Kadet LT-40). Could potentially mount it upside down but at this point I think I will try it without pressure in the tank and if I can't get the performance I need then I will attempt to add the pressure fitting to the muffler. The worst I can do is end up buying another muffler. Thanks for all your help.

RE: Help K & B engine fuel problem
 

For many years I flew C/L stunt with unpressurised tanks. I either aimed the vents foward or cut them at a 45 degree angle facing the air flow.

My first experience using pressure was when we started using crankcase pressure in C/L combat.

Should you decide to add a pressure fitting to the muffler I am confident you will be able to do so with no difficulty by the "nut on the inside" method or by tapping the thicker extension part as suggested by Sport Pilot.

jess

RE: Help K & B engine fuel problem
 

You dont' want to run muffler pressure with this engine. Muffler pressure will "supercharge" the engine and cause it to get too much fuel. It will backfire, throw props, quit running while flying for no reason and the high speed needle will be virtually impossible to set. Run a vent line from the top of the tank down below the fuse. When inverted, the vent line will still be above the tank and will not leak. Been running the sportsters ever since they came out like this and it is what they need.

Carl

RE: Help K & B engine fuel problem
 

Your suggestion to vent the tank through the bottom of the fuse is where I am headed for now. I prefer a pressurized tank so won't buy another Sportster. But we'll see how this works and thanks for your help. Its good to know that folks like you are there to back up us "newbies".