proanti1

My Feedback: (2)

I am having a hell of a time getting this thing to run right. It runs great for about 2 minutes, but gradually leans itself out to the point of choking at quarter throttle. I richen it up blubbery rich, it runs good for another 2 minutes, then leans itself out. Eventually It's adjusted so rich that it chokes and pops at WOT, and wont stay running. The smoke trail this thing leaves is incredible, right up until it leans itself out. I dont think it has anything to do with temps, because this thing never really gets hot. The needle and the eccentric low speed adjustments are not moving from vibration either, and stay in the same position until I adjust them. I have rebuilt the carb (retardedly frustrating process), tried different props, tried probably 10 different plugs, some with idle bars... nothing makes a difference. It does not have the stock muffler, it has an older strap style one... I dont think that's the issue though, because it looks to have been mounted to the engine from the beginning. Even when warm, the engine has great compression. I did pull it apart to find HEAVY castor staining and pretty extensive coking on the head/piston. The cylinder wall looks good, and there is no serious scoring on the piston.

This engine is on an airboat.

Anyone have any idea why this thing is doing this? I'm about 3 tantrums away from just swapping it out for a magnum and calling it good.

vpresley

My Feedback: (162)

Hi

Sounds like you have an air leak some where. Check all your engine case and head bolts for tightness. Then check your fuel system for leaks, clunk included, high speed needle, and make sure the tank is not fuel foaming. Start with a new glo plug also. Also make sure there is no GUNK in the carb.

Vince

proanti1

My Feedback: (2)

Carb is spotless, all passages have been blown out with compressed air. All fuel lines have been changed, including the ones in the tank. There is a slight air leak along the crank, but that is to be expected since it's bushing supported, it's also very minimal compared to other perfectly fine engines. All the plugs I have been trying are new. I have tried every single heat range I could think of. It seems to run best with a cold O'Donnell long reach car plug.

The throttle cylinder in the carb seems to have a slightly loose fit, a bit more loose than I have seen.

Edit: Oh yeah, I'm running 15% Omega plane fuel. I tried 10% and it ran even worse.

Sport_Pilot

What fuel, plug, and prop are you using.  Sounds like it may be detonating, or on the verge of detonation.  Are the carb O rings tight?  If not the needle or disk could be moving.

AERORICH73

Well, it seems you have done all you could with the existing carb. Suggest you think about installing a Perry carb. The one thing I noted in your write up is whether you purchased this engine new. Also, if it was purchased used, did it show signs of having been run, or just well oiled and clean. Removing the back cover and checking for any signs of running may show up on the back of the cover, My .45 engine began having the same problems, and I came up with the same idea of changing the carb out. With a supply of other engines to choose from, I just repackaged the .45, and put it back in the cabinet. This has not been the only engine which I purchased new that came with a defective carb. My new Super Tiger .45 had the same problems, and I installed a Perry which brought the engine to life. There maybe more info on this website as to what other carbs woud fit your engine. If by chance you have one of the engines in stock, you could just swap out the bad carb, and try the one from you other engine.

I am a retired aircraft mechanic, and enjoy solving engine problems. As in your case, there is an additional cost to correct a defect, and moves one to just buy another engine at only a small amount of more funds.

Let me know what you decide to do, and if a carb change fixes the problem.

[email protected]

earlwb

Hummm, the engine runs OK, until it heats up and then leans out and dies on you?

That would imply there is a air leak occurring so that as the engine heats up the air leak gets worse and so on.
We don't have a lot of places for a air leak to occur. There is the backplate gasket, the cylinder base gasket, the base of the carburetor and the crankshaft bushing area. As the engine heats up the metal expands and a air leak could develop then. But when cold the metal shrinks and the air leak can't occur. Although there is a head and a head gasket maybe, if it leaks it is pretty obvious with the fuel and oil being pushed out.

What you can do, is coat the engine with something like oil and run the engine and keep on applying it as needed on the joints to see if it stops the air leak or not. For the crankshaft bushing it is trickier as you may have to grease up the crankshaft and bushing to see if it is the culprit or not. The grease being more thick would reduce peak RPMS some, but it should stay thick enough to not get pushed out of the front of the engine until you have determined if that is where the air leak is coming from.  The carb to  crankcase intake point usually has a O-ring or gasket and you can grease up the base of the carb and put it back on to see if that eliminates the air leak or not.

Finally a casting flaw in the crankcase may result in a void or space that as the metal heats up it opens up a hole for a airleak. Sometimes cracks in the crankcase can do it too.

Anyway, I would suspect the backplate or cylinder base joint as being where the airleak is likely at.

proanti1

My Feedback: (2)

No, the engine was not new. I actually found this airboat in an abandoned house. The engine had been run, but still has incredible compression. I don't have any other engines of this size, so I don't have another carburetor I could try. I was looking at the Perry carbs, and they seem pretty affordable, so I think I may order one of them just to see what happens. Thanks for the tip.

I saw a couple other replies talking more about air leaks. The carb is sealed up good, I replaced the dried out original o-rings with new ones. I can plug all holes, apply a vacuum, and no leaks will occur. The back plate is sealed, the cylinder is sealed, and the head is sealed. The only oil leaking from anywhere is a very small amount at the crank, which is FAR less than my LA25 spits out. I don't think it is detonating, it sure doesnt sound like it. I am running a 11x6 prop currently, but it still does the same thing with a 10x6 and 10x8.

gyrocptr

Using muffler pressure? Perhaps reducing the size/diameter of the muffler outlet would increase pressure to the fuel tank.
Stock muffler had a series of internal baffles to reduce noise; the baffling also provided an increased muffler pressure.
Also, the carb sits high on the engine. May want to check to see if centerline of tank is properly aligned with level of the needle valve.
Another consideration: Early versions of the engine had wide cooling fins; engine would run "cold". Later versions had the cooling fins ground down to allow the engine to run hotter.

proanti1

My Feedback: (2)

The fuel tank is actually below the engine. Could that have something to do with it? Because it will run great with any amount of fuel in the tank... it will just only run great for 2 minutes. Then Once it gets down to ambient temperature, it will run good for another 2 minutes.

1QwkSport2.5r

My sportster was really finicky with fuel tank placement. Try putting it right behind the engine centered with the spraybar and run it up. Have the idle eccentric screw centered to start with also.

If that doesn't do the trick, then I'd blame the fuel. Not that the fuel is bad, but that it's not all castor. The sportster engines are designed to be used with 100% castor in the mix, not synthetic. Even a 50/50 cas/synth blend at 20% content should have it running better. Mine run a good bit better on castor only fuel despite a very bad carb.

These engines also need to be propped heavy. Mine run hot if under propped or too much nitro. My .65's hate 15% nitro; 5-10% is better. I would think a 12x6 would be a good start on the prop.

proanti1

My Feedback: (2)

Well, the manual says it's meant for a 10 or 11 prop. A 12 is WAY too big for this motor, it barely has enough power to get any usable RPM out of the 11x6 I have on it. I cant run a bigger than an 11 anyways, or it will contact the top of the boat. I also can't mount the tank elsewhere, especially not behind the engine, the rudders get in the way. The fuel I am running is 100% castor, 16% I believe. I have the same stuff (Omega) but 10%, and it runs like crap. I actually ran some 30% boat fuel through it for ****s and giggles, it ran even better... but still ended up lean after a few minutes.

I dunno... I have troubleshooted the hell out of this thing. In between comments I have been running outside, firing it up, and trying different things. I think it's just time to replace it with a cheap ASP or something.

aspeed

Usually airboats have problems with the tank mounted 6 inches below the motor and not being able to suck it up evenly, especially near the end of the tank.  Another problem they have is with the pusher prop not blowing any air over the motor for cooling.  I don't know your setup, but it could be one of those reasons or combinations of what other contributors have mentioned.  A heatsink head could help a bit if it is a pusher prop, like the dune buggy motors use.

Tarasdad

I used to own one of these engines and it was very picky about both tank placement and prop selection. The tank had to be mounted where tank center line was within 1/2" of the needle valve height. As for props mine showed a marked preference for a 10x6 Zinger.

huck1199

I have several K&B .45's and found that they run very well with 10% or 15% Omega with an added 4oz of caster per gallon.  This is a plain bearing engone and needs the castor to run properly and not over heat.

turbo.gst

My Feedback: (8)

My Sportsters took an extended break-in to really develope good manners. They handle great with stock carbs. As mentioned previously, they need extra oil. I have a Sportster of every size and like all of them, but the .65 is my favorite.

turbo

tony0707

HI
I RAN a 45 Sporster for about 10 years-on a Midwest 40 stik
try an 11/5 APC and 15 % morgan omega RPMS w/b 11,800 -12,300-i think the 11/6 is to much prop and is causing heat build up-,an 11/4 might be good if no air is going over the head due to it being a boat
wore the engine out after about 350-400 flights -,one rod change,but loved it's power and lightness
it has a great sound when it starts to scream on the top end and reminds me of the sound of my old u control engines-,that i always loved
hope that will help
BEST REGARDS TONY

tkline

Dang I've been through boerne 4 times today if I would have read this earlier I may have been able to stop and see if I could help you. Let us know what you figure out I'm through there quite a few times every week

gmeyer-RCU

My Feedback: (9)

Try another fuel tank I ran into some real problems with a ST 40 and it turned out to be the fuel tank stopper the tank did not leak at all but once I put a new cap and stopper on the tank everything worked fine.
Greg

Wilson4824

Remove the baffles from the muffler.

I have had both the 45 and 65 both had trouble running..... I agree the tank location is very important.. your find that removing the baffle will let the motor run easier.

spaceworm

Agree that it should run better with the muffler baffles removed, but that will also reduce the muffler pressure to the tank. So, if fuel feed due to low tank is the problem, it will be worse with the baffles out. maybe the solution is a fuel pump, such as the Perry vibration actuated type?

C185Pilot

My Feedback: (25)

How fresh is the fuel? Fresh means open less than a week. Parts of TX are very humid and that will ruin fuel quickly as it absorbs moisture...will cause your symptoms.

proanti1

My Feedback: (2)

As I previously said, it does not have the stock muffler, it has an older strap style one, which has a HUGE stinger. I am fairly certain that the muffler is the problem, and is not providing enough back pressure to pressurize the tank appropriately.

I pulled the tank out and ran it besides the engine, and what do you know... it actually ran good. Since tank location is limited, I am probably going to opt for the Perry pump.

proanti1

My Feedback: (2)

Fuel is close to fresh, probably been open about a month or so. It's stored in my house, which is climate controlled. I am also not in Texas, but I am still in a pretty humid part of the country.

AJRCUSTOMCRAFTEDRC

My Feedback: (70)

I run all of the sporster engines with 15% nitro coolpower fuel all run great, yes at times the carb is bad but AS THE INSTRUCTION SAY DO NOT USE MUFFLER PRESSURE , THIS HAS BEEN THE BIGGEST REASION OF ENGINES RUNNING BAD. and fuel tank must not be mounted low to carb. these are great engines for what they are.

tony0707

hi
a glo fuel tank stopper s/b no more than 3/8 of an inch above or below the center of the carb-,that 's the rule to have the engine run as it should in an airframe
and as close to the engine as is possiblekeeping fuel lines short
i have always used muffler pressure on that engine with the stock muffler and i always remove the baffles from all my two cycle glo engines
REGARDS TONY