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Old 06-25-2016, 07:37 AM
niar98 niar98 is offline
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Engine only runs choke out


New the world of atomic 4 engines. My problem is I can start the engine with the choke fully out and throttle a bit above idle. Engine will run rough. Any attempt to move choke or throttle causes the engine to stall. I tried to let it run for a while till it reached operating temperature and then tried to move the throttle or choke and again stall.

Based on the reading this blog I am guessing the fuel pump is the issue. A electric fuel pump presently installed.

Would appreciate any tips and insights.

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Old 06-25-2016, 02:46 PM
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Welcome to this forum. These guys have been a big help to me understanding my trusty A-4 engine.
If your engine will start, you are not far away from it running right. I doubt your fuel pump is the issue. It could be a number of things. It could be the coil, the distributor, or timing, but my experience has been that the usual cause of symptoms like yours is junk in the fuel, lodging in the various tiny passages in the carburetor, particularly the idle jet or main jet. It may be there is stuff in your fuel tank, and the filters are clogged and passing the stuff into the carb. I personally believe that using non-ethanol fuel and keeping the tank close to full helps keep the bad stuff in the tank and out of the carb.
If you replace the filters, and clean out and reassemble your carb, I'm betting you will fix it, at least for a while. The others on this forum will go into more detail. Make sure you have a Moyer manual. A fuel pressure gauge just before the carburetor can tell you if you are getting enough gas. If you run long enough with the choke closed, the plugs will foul.
Good Luck!
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Old 06-25-2016, 06:13 PM
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Welcome to the forum!
As CAPNWARD suggested, get the MMI Bible. It's a must.

I doubt the issue is your fuel pump.
Is the pump a Manual or Electric?

Another question...
Have you looked at your plugs? How do they look?

Having to run the engine using full choke suggests a lean mixture.
A quick and easy test would be to try turning the idle mixture screw a ¼ turn IN.
See if it makes any difference. If no difference or just a little better, then try another ¼ turn IN.
Continue this exercise until you get a smooth idle.

Remember that the idle adjustment (on top of the carburetor with a screw driver slot) adjusts the air portion of the mixture,
so turning the adjustment IN makes the mixture richer, and backing it OUT makes it leaner.

If adjusting the idle doesn't work, we'll go deeper. One step at a time...
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Old 06-26-2016, 02:12 AM
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Another welcome to the forum.
A fuel pressure gauge between the fuel pump and the carburetor would sort this issue out real quick.


Last edited by JOHN COOKSON; 06-26-2016 at 02:25 AM.
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Old 06-26-2016, 07:09 PM
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Your symptoms are classic for a partially clogged main jet. This can often be cleared by shutting off the fuel, removing the plug over the main jet, and running a fine needle or piece of wire through the jet. Some folks have an adjustable main jet, and clear these clogs (sometimes) by running the needle in and out.
You're going to spill fuel, so smoking lamp is out. I like to jam small towels in the area under the carb to catch the fuel, then hang them on the lifeline to dry.
Keep in mind that all fuel flow is towards the carb, so guess where all the krap ends up? Personally, I try to keep my tank clean, have a big filter before the electric fuel pump, then a small filter between the pump and the carb. I still get the occasional piece of krap that clogs the main jet or gets into the float valve and causes the carb to overflow. I go so far as to keep a second carb on board, cleaned and ready to go. I have good access and the change doesn't take long.
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Old 06-27-2016, 08:56 PM
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Thanks for all the helpful tips. I have ordered a pressure gauge. I am a working/family man so I won't be able to try any of the ideas you all gave me until this weekend. I will report back on my progress.
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