I got a pro .15 nitro engine that powers my nitro sport. I was having some problems with is cutting out bogging ect. I took the engine into my local hobbie shop and they tuned it. the guy told me that the problem of it cutting out and boging was still there, just not as bad. to get the engine to run WOT i have to steadly press the throtle until i have it it WOT. i checked the motor for air leaks and there are none. There are new fuel lines and a new plug installed in the motor. The problem is not as bad is it was, but it is still there. Any ideas as to what it could be? this is really really starting to get on my nerves. is it a leak in the gas tank maybe? This engine only has 1 gallon run thru it, so i really don't want to buy a new engine. thanks for your help.

One thing I have had problems with on the pro 15 is air leaks, especially on the backplate. How exactly did you check for air leaks?

Why not pull the backplate and clean things up there, seal it good with a sealant. Also pull the carb and clean it very well, replace the o rings ($2.00 for O-ring kit), put it back on and seal it with sealant also.

There are a couple easy and inexpensive things to do right there, and quite often they are the problem. I would also make sure the gas tank has no leaks on the seal. Pinch the line going to the carb and blow air into the line that connects to the exhaust, it should hold a little pressure.

were is the back plate and how hard is it to seal. Also what type of sealent should i use?

the back plate is a good place to start on my .21 it would idle fine mid throdle it run great at wot it would die. it came out to be the exhaust gAsket it was not giving the fuel tank enough pressure to run wot.

well mine's fine unless i go from idle to wot other wise it is perfecfectly fine. If it really starts to get bad all probably will just deal with it. I was running it for three hours today, and it was running good enough do drift across some packed dirt; now that was cool! it is starting and running better than it ever has. i Want to check the back plate, so how could i tell if it was leaking air?

Oh I don't know.....but I'd richen your LSN as a start.

It seems you want to nail the throttle and see it scoot....what we all want. But yours doesn't like that for some reason. Could be an air-leak, but I'd start with tuning. Can't be tearing down engines every time they don't run right.

If it takes off with great gusto and then abruptly dies, your HSN is too lean

If it takes off but can't seem to wind up, your HSN is too rich.

Now.....if you notice, those last two sentences are what's happening a little while after you nail the throttle, not instantly after.

Prior to that, at the instant you nail the throttle, the mixture going through the engine has been defined by the LSN.

A sluggish take-off and then it gets better can mean a rich LSN setting.

Having to feather the throttle lightly can mean the LSN is too lean....this is what I think your problem is.....see below for an explanation.

There's a lot of interpretation. You can get similiar symptoms for completely different problems, but if you didn't notice other clues, it's easy to find out. Try something and see if it gets better or worse. Richen your LSN....if it gets worse, try leaning it a bit instead...that sort of thing. In fact, you can get bogging or quitting from either too lean or too rich an LSN setting. You look for other clues to help determine which, or you just make an adjustment and see if it makes it worse or better.

Explanation: A cold engine needs a rich mixture, but doesn't get it.....so when cold it's too lean....and you can't nail it without it quitting. Once the engine is warmed up, it takes the throttle fine. Most people experience this with their RC at one time or another. Now imagine that it is too lean even when warmed up. That means it will always show the symptom of quitting when you suddenly open the throttle.

Again, I'd try richening your LSN a bit...maybe 1/4 turn CCW for a start.

Now, troubleshooting over the net is always a guess. Best advice I can give you is to stop taking it to the LHS and start tuning yourself. Even if you do get the LHS to tune it perfectly, a week later and the weather changes, your engine may not run right again.

Befor you start screwing around with the carb like alot of people have told you, could you give us some other info???
What fuel are you using??? The °nitro in the fuel will also have alot to do with the performace of your engine.
What glow plug are you using as this will also enhance the performance of your engine. It could also screw up the performance of your engine.
I see your running a small .15(2.5cc) engine. I have a Tamiya NDF01 that likes to run on Sidewinder 25° fuel usung a O.SA5 plug.
In the beginning I tried sidewinder 16° but it would just bog down at medium to high revs, tried all sorts of tuning tricks but nothing was helping untill I filled the tank with higher percent nitro. Runs like a mad beast now.
No problem with sealing nothing.
Keep us informed as to how you get along.
P.S.
What is the temperature of your engine during use, it wants to be around the 120°C.

I know I'd try a few screwdriver adjustments before I went and bought different fuel and glowplugs.

If an easy to try, and "free" carb adjustment doesn't work, then by all means look for airleaks, try different fuels, glowplugs, etc.

I always start with the easiest thing first.

By the way, you might want to check the integrity of your fuel system external to the engine. That means no exhaust leaks, no cracked pressureline, no cracked fuel tank, properly sealing fuel tank lid, etc. Again....easy to check, and doesn't cost anything

Well everybody thatnks for your help, but now i have more bad news; my EZ start and slipper clutch are broken(scream) .I am trying to deside if i should sell it or repair it. I know that most people would say fix it, but every time something starts to work on good on this car something else breaks. Basically all the info that i have is that if i punch it it dies. I don't really have the slightest idea on how to re place those parts, but i really Don't want my LHS Charging me 32$ an hour eather.

20% bryons race blend gen 2nitro fuel, traxxas super dudy plug (cold), and it runs about 275 (which is aparently good for a nitro sport)

If your temperature is about right then your tuning is about right.
Change the plug for something a bit warmer.
If you sell it, get your self a new KYOSHO MP7.5 RTR and your problems will be over.+/-.
By the way, is the nitro sport a 1/8 scale or a 1/10???
Could also be that your buggy is to heavy for that little engine.

Is that the Traxxass(trash-ass) nitro sport. If it is, you bought yourself a real P.O.S. Sorry, dont want to insult your buggy(yes I do),
really, get yourself something good, you deserve it, its X-mas(almost).
A real good place to start is the kyosho MP7.5, I've had one for years and it still beats the crap out of many and without problems.
Try the one with the GX.21 engine. you dont want the GXR.28, to many difficulies where as the GX.21 is race legal little screamer that kicks ass when I've done the modding.
Use the Trashass as a paper waight, but dont put to much paper on it.[:@]

You should be running a hot plug with 20% fuel. I ran Traxxas plugs for a long time and found the McCoy's are better. I run MC59 plugs in all of my engines..

So you know it's a P.O.S. but you don't know whether it's a 1/10th or 1/8th scale truck? Sounds like you've never even seen one, so how did you form such a strong opinion on it?

i helped a kid brake in a .15 engine from a nitro sport. he was going to kill it if i wasnt there (way lean)

i blame it on user error.

check/ replace fule lines, check tank, remove and check glow-plug, replace it as they foul very quickly after break in, there are two bogging sounds a engine will make one is a deeper almost gurgle, one is almost like it cuts out, typically the gurgle is caused by the high speed being too rich, the cut is from too lean a high speed setting or low speed being too lean.

once you replace glow-plug, glow plug igniter battery, and lines, start it up then quickly pick up the car, and revv the engine, a medium cloud of smoke should pour out, and have just a slight hesitation, followed by a very rapid and fast rev, if not, adjust the high speed, if it starts to rev quickly then bogs, with little smoke, richen it up with 1/4 turns counter clockwise, revving it up each time. if it bogs a long time with thick smoke and revs high, it is to rich, lean it by turning 1/4 turn clockwise.

once you get that set, now its time for the low speed, adust the idle set screw at manufacture specs, or slightly higher for this adjustment, if the car burbles and wants to die and with acceleration it either stalls or it bogs then clears up it is running rich, turn it in 1/8 turn clockwise, each time blipping the throttle, get it to a nice steady idle. if it revvs high and wants to die, and if you blip it it either stalls, or it takes off then bogs it is running lean, richen the low speed needle 1/8 at a time, blipping each time.

once you get it to idle, now get it warm by taking quick passes, it should have a nice light smoke trail and should provide decent acceleration and good top end, if not and it produces low amounts of smoke and wants to stall at high rpms, richen it up 1/16 - 1/8 counter clockwise, if it produces alot of smoke and not much acceleration, lean it out 1/16 - 1/8 at a time clockwise.

once you have that sorted out, make a few passes, and bring pinch the fule line, it should rev up within a second and die under 5, if it takes too long to die, lean the low speed needle 1/16 clockwise at a time, if it dies very quickly, richen the low speed needle 1/16 counter clockwise at a time

and there you have it, a well running engine!

No offence taken it really is a Piece of junk. I tryed using a hot plug but the stupid Ez start wire that heats the glow plug didn't wnat to work with it. Now it needs new clutch shoes and a new clutch spring the ez start sometimes works, other times it doesn't. Wish that i Had got a HPI savage x after all.

So a McCoy hot plug would work fine with my engine?

I would say the OSLC3 is the best for your pro 15. It's a hot plug, lasts a long time, and your EZ start wire will easily plug into it.

Some glow plugs have a tip that's too big for the EZ start plug and it won't go on without jamming it on and damaging the connector.

OK i'll get a hot glow plug and see it that makes a diffrence. I can't run it now because im waiting for parts from traxxas.</p>