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Weird engine problem.

Old 06-07-2008, 04:11 AM
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Default Weird engine problem.

Hi guys,

I have a ASP.70 4 Stroke. Everyone keeps telling me it's really a magnum with a different label so I'll go with that

Anyway, it's got a slight tuning problem but I have it running pretty well except for a couple things. It doesn't idle for long and believe me I've tried a lot of different things, including new plugs ranging from OS 'F' to Saito plugs to ASP's own brand. Obviously I've played with the needles as well.

I will change out the plumbing today in case there may be a slight leak.

OK, I can probably deal with the above but there is one thing that is bothering me with this engine. It reaches full power at 2 thirds throttle. I mean the carb is open 2 thirds but I get no increase in power for the remaining third of the carb. No change is engine tone, it's at full power.

I am getting full power from it, I mean it's not like it's lacking that third but I should not be.

Example. I will get 9400RPM with a 13x6 or 9000 with a 12x8 at 2 thirds but no change at full. I think you may agree that's full power from a .70?

I hope I've explained it clearly and you get what the hell I'm trying to say

Any suggestions please?
Old 06-07-2008, 04:52 AM
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Default RE: Weird engine problem.

When you say the carb is open 2/3, do you mean the throttle stick on the transmitter or are you visually confirming that the carb is open 2/3?

How do you have the engine mounted? How far from the fuel tank? What muffler are you using?

You might be losing too much pressure in the fuel tank if the exhaust pressure line is too long or has a hole. If you're not using the stock muffler, or have a long header installed, this can also affect fuel tank pressure.

You may have an obstruction in the fuel path thats preventing additional fuel flow. I'd take the carb off, break it down and clean and back flush it.

At full throttle, is the needle valve effective? How far do you have to turn it to get it to reduce RPM? Are you certain you're running it to the rich side?

The problem you describe at idle could also be due to a blockage.

Brad
Old 06-07-2008, 05:14 AM
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Default RE: Weird engine problem.

Thanks man,

Yes I should have mentioned. I'm visually confirming the carb.

The engine is new, just run in and had about 8-10 flights and it's side mounted. The plumbing is as short as I can make it and the tank is correctly installed with the carb height.
It won't maintain a decent idle unless I'm at about 3500 rpm.

Any lower and it will die. Mixture needles always give good response, couple clicks will rich it or lean it, also the muffler is stock.
Old 06-07-2008, 02:10 PM
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Default RE: Weird engine problem.

As the ASP and Magnums are the same engine, that carb has a bit of a quirk on the mix control and if your engine isn't setup correctly, it can be a rough running engine.

Check the manual for inital carb settings. Note that the mix control doesn't screw into a stop, but out to one. If you get the hIgh speed to rich and the mix to lean, it is not a good running engine. I about took a hammer to my Mag 70 when I first got it.

Set your carb to inital settings then after warming up the enigne, peak the high speed jet then go back rich by 500 RPM. Now set the throttle as slow as you can get it and keep the engine running. At this point, lean the mix control for maximum RPM.

Go back and do the high speed and then the mix again.

IF the transisition isn't good, tweek the mix control 1/16 turn at a time until it jumps to the throttle. My Mag 70 will bark like a gasser. If the enging dies when you jam the trottle from idle, the mix control is to lean. If it stumbles and slowly gains RPM, the mix control is to rich. Adjust acordingly.

By the way, the four strokes have little change in rpm over the last 1/4 throttle opening. I usually put some expo on the throttle to make the sitck more linear to the rpm changes.

Don
Old 06-07-2008, 02:18 PM
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Default RE: Weird engine problem.

I missed the idle at 3500. That is a sure sign that the mix and high speed are not balanced. Try my tune up and see if you arn't happy. My Mag 70 sill put put along a 2000 RPM for about as long as you want. After I got the carb adjust right. Before, it was at leas 3500 on the idle and the more I played with the carb the worse it got. That engine forced me to learn how to turn a 4 stroke. The key is starting form the factory settings.

Like I said in my first post, you can end up with a rich Highspeed and very lean mix control and at this setting, you will find the top end is sort of OK, but the idle sucks.

By the way, this engine is slow to break in. Keep the top end at least 500 RPM off peak to the rich side for the most of your first gallon of fuel. Then you can peak it a bit more to 300. Chances are though that you will not need to as you almost never fly full throttle and 200 rpm wouldn't be noticed anyway.

Don
Old 06-08-2008, 02:42 AM
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Default RE: Weird engine problem.

Thanks Campgems,

I will go back to factory settings, if I can find em

I'm sure I have the manual somewhere.

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