Tuning issue.

[lykan]

OK to start I am working on a T-maxx 1st gen.
It has the mach .15 engine with an OS 10E carb.

I'm having a problem with it overheating.

I tune it in so it's got a good amount of smoke, and seems to be running ok. Idles well, takes off good, and looks like it is a bit on the rich side.

It will run great for a few passes, then suddenly heat up. This is all within the 1st half of a tanl. For tuning purposes I kept it full.

I have just replaced the fuel line, as they were chaffed and had a hole or two in them.

It's like I just can't find the sweet spot. It's either too rich to get decent power, or so lean it gets hot. I checlked fopr leaks, none in the fuel lines or connections Tonight I pulled the carb apart, and everything looks A-ok in there.

I am running a short fuel pressure line (from the header). Could this be the possible culprit? Will too short of a return line make it hard to tune?

I also noticed it's power band seems to be right out of range for the low end grunt. once I get to a decent roll it has lots of power, but gutless until then. I have a piston and sleeve for it, but I don;t want to put it in until I figure out the tuning problem

It's about 50 degrees, and I am running with the lid off, because it heats up. I am afraid of the summer, it gets hot around here.

Open to any and all suggestions

 

[SkyMaxx]

Let's see what we can do here...

1. Do you know what the factory presets for the needles should be? If so, start there. The low end grunt issue is most likely related to the LSN (which should be flush with the carb casing). You can tune it from there, but do it in very minor steps. A little tweak on the LSN goes a really long way.

2. How do you know it is overheating? Are you running with a temp gauge or using a temp gun? What are the symptoms that indicate an overheat, as far as you are concerned?

3. Fuel lines should be between 6 and 9 inches in length. They should also be about the same length, meaning that the pressure line and the fuel feed line should be about the same length. I would recommend keeping them near the 9 inch length. The shorter you make them, the richer the engine will tend to run. Make them too long and the engine will lean itself out. So keep it between 6 and 9 inches.

4. Do you have a fuel filter? If so, check it for leaks and cleanliness. A leaky or partially clogged fuel filter will restrict fuel flow and cause a lean condition.

5. Make certain that the glo-plug is seated. It will work with the glo-plug slightly loose, but this will cause an air leak at the cooling head and a loss of compression. Both can lead to a hot runner.

Well, that about covers it for now. Get back to me with some answers to my questions and we will see what we find.

 

[lykan]

1. I was given the default settings for the carb. The engine is a mach 15 from a Losi. I am begining to wonder if the carb is aftermarket. I don't know what carb came with the losi so that is just a guess.

2. I do not have a temp gun, and ATM don;t have the cash to grab one. I belive it is overheating, because the water drop on the head sizzles after a WOT run. It will also stall, and not start back up until it cools. On a rare occasion I can hear the fuel sizzling in the carb.

3. The pressure line is 8" the fuel line to the carb is about 6 1/2 inches. They reachm but just barely. They also pass close by the header. (I hear longer pressure lines even out the flow. Any truth to that?)

4. I had a fuel filter in line, but thought that might be the cause of an air leak. I removed it to troubleshoot. Straightlines to the tank now.

5. Glow plug is seated, and used a new washer. Also a new plug. Not sure of the rating.

6. I sure appreciate your help

Did any of that help to narrow it down? I'm new to tuning, but have the hang of it on the xtm stadium truck with the .18

**edit**
I have a THS racing pipe on it, if that makes a difference. Lots of turbulance in the tank, meaning lots of pressure

 

[SkyMaxx]

1. You listed the carb as an OS carb. You may want to get the needle settings for that particular carb, vice the settings for the Mach .15 engine. That would be a great place to start.

2. The water sizzle method is not very accurate. Why? Unless you are sitting their with a stop watch, the measurement you are making is subjective, meaning entirely up to your perceptions. The other symptoms you listed are spot of for an overheating engine.

3. Longer fuel lines help out in a lot of ways. They reduce the pressure from the pipe to the tank by allowing the air flow to reach a smoother flow. This same phenomena occurs with the fuel flow.

4. PUT THE FUEL FILTER BACK ON! Of course make certain you clean it out before re-installing it. BUT never run your engine without some kind of fuel filter. A little grime added to the fuel can cause more harm than good...fuel filters stop it from getting to the carb or the engine.

5. Good on you for the glo-plug.

6. No problem.

7. Additional thing to check...the carb itself. Make certain the needles are not fouled. You can remove them and check for any blockage. Blockage on the HSN (especially) will cause the fuel flow to be other than what you think. It may cause the engine to be anywhere from lean to fuel starved.

8. Make certain you pick up some carb sealant or gasket sealant (ask at your LHS they should know what it is and have it in stock). You will want to use this stuff on the gaskets of the carb and any other area that might need it. It helps reduce the air leaks from the carb.

 

[lykan]

I just finished cleaning up the carb. It had the usual grime, but nothing in the needles or the rotatary part. All the gaskets looked good as well.

I'll pick up some sealant tomorrow at the same time I pick up a new filter, and some longer lines.

I'll give th O.S carb settings a shot, the LSN settings are two turns further out, than that for a stock losi.

It just could be the LSN is way too tight. Hence it running good with lots of smoke, but heating up the second I let off the throttle. Does the that sound right?

 

[SkyMaxx]

That is possible. The LSN is for when the throttle is let up...so that might be a part of it.

Give it a try and let us know how it turns out.

 

[lykan]

One last Q, would a very worn motor cause these symptoms, say if it was in need of a piston and sleeve?

 

[SkyMaxx]

Not particularly. A very worn engine would tend to run on the rich side, not matter what the setting. This is due to the fact that a really worn engine would not get the compression required for a complete burn of the fuel. Thus, there would ne residual fuel in the engine when the next compression stroke came along.

 

[Bill Hoskinson]

Sounds like you are trying to tune it before it ever wamrs up. When you fire it up cold, it should blubber, and run like crap untill it gets warmed up good. If you can fire it up cold, and run it WOT without it blubbering, or actling like it runs rich, ITS TOO LEAN.

Fire it up cold, let it idle for about 30-40 seconds, and then pinch the fuel line. If the engine barely revs up when you cut off the fuel, its too lean. It should rev up pretty good, when you pinch the fuel line.

Richen up the low side untill it revs up when you pinch the line. If it trys to stall when you richen the low side, turn the idle speed screw in to raise the idle speed. Keep working back and forth untill you get it to idle smooth, at a low RPM, and making sure the engine revs up when you cut the fuel off.

Then you can start working on the high side. The way you describe how its over heating now, I would turn the high speed needle out at least one full turn, and start from there.

Run it around, warm it up, and keep an eye on the temp. You need a temp gun to know what your temp is. Check it at the base of the head beside the glow plug.

It should be rich enough that you can open the throttle wide open, and it should blubber and run like crap. Just keep leaning it out untill it quits blubbering at WOT.

From this point, you can start fine tuning the low and high speed needles untill you find the sweet spot in the low and high needles.

Hope this helps

and btw....

Fresh engines run hot, and worn out engines run hot.

New ones run hot because of obvious reasons.

Worn out engines run hot because the air fuel mix "blows by" the piston, back into the crank case, causing the engine to "lean out".

Engines with exsess wear in the piston and sleeves will run better on fuels with high oil content. If you can find some fuel with 14-18% oil content, try a quart of it and see how you like it. If you are running a medioum/cold plug, you may need to go to a hot plug with high oil content fuels.

When tuning with high oil content fuel, you can't tune the engine my the amount of smoke you see. Its going to smoke no matter how rich or lean it is. Tune it for power, and temp. If it smokes it smokes, if it doesn't, it doesn't.

Just watch the temp, and listen for detonation. If it pops at high rpm, its either lean, or you have fragged a glow plug, or both.