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Old 12-12-2010, 06:03 PM   #1
mjf1604
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Smile EZ GO ST350 2004 (MCI engine) running rough and smoking

Hi Everyone,

I have two EZ-GO ST350's which I use around the yard to move tools and materials etc, one is a 2002 (with Pre-MCI engine), the other a 2004 (with the MCI engine). Neither are high hour machines (700 and 600 hours respectively).

The 2004 one is running rough, with almost a rattly sound compared to the older vehicle. The engine has a reasonable amount of power, and compression test seems ok (just over 150 psi per cylinder). It is also creating a lot of smoke when first started, this clears after a 5 mins of driving it. It doesn't seem like it would be a piston ring problem as if it were the compression would be considerably lower.

Older vehicle is low on compression, only around 55psi when cold, but runs perfectly, smooth, no smoke, powerful - but with this reading I dont know how!

In the newer problem vehicle have replaced the spring in the driven clutch (and ran the engine without the drive belt - and it still made the same rattle/rough noise, so I know it is not the axle / driven clutch). I have changed the engine oil, checked the valve adjustment and adjusted to the specified 0.004", and I have also replaced the timing belt, and checked timing and still no better.

Apart from tearing the engine apart, and doing a complete re-build, I don't know what else to do? maybe check the exhaust box for back blockage, causing excessive back-pressure? I have had this on a old mower before, where it smoked badly on start up, but fine when warm, after cleaning the exhaust box out with petrol, it cured the problem.

Anyone have any suggestions what could be causing my engine to rattle, and for it to smoke so much?

Thanks
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Old 12-13-2010, 04:46 PM   #2
caddymankc
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

If the oil is overfull it will smoke and run rough, also adjust the valves, it will help alot if they are out of wack.
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Old 12-13-2010, 05:12 PM   #3
mjf1604
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

yes I have checked the oil since it was changed, and its half way between min and max, and also check the checked the valve clearances and are all fine.

Should have said before, the smoke is more white than blue and smells nasty, its not particularly an oily smell. I am not sure what causes white smoke on an air cooled engine - I know on water cooled units white smoke is usually a split head gasket so coolant is able to enter the cylinders, but here this obviously isn't the case, as there is no coolant.

I have checked the spark plugs and they are back and sooty (not ideal) but yet not wet and oily, so again wouldnt suggest oil burning...

I am fast running out of ideas...any suggestions would be greatly appreciated - particularly as getting spares here in the UK is rather difficult so need to be sure of what is wrong so I can work out what I need before ordering parts
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Old 12-13-2010, 05:22 PM   #4
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

I would almost say the white smoke would be a carb problem like too much fuel "too rich". Just a thought but really not sure!

The noise your sure is in the engine and not something vibrating on the side of it or around the body of the cart?
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Old 12-13-2010, 05:41 PM   #5
caddymankc
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

Is the choke opening up all the way? and is your oil vent tube pinched on the motor?
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Old 12-13-2010, 05:58 PM   #6
mjf1604
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

the carb is something I have not looked into to much to be honest. I removed the float bowl and it had lots of brown gunge at the bottom which I cleaned out. I also sprayed some carb cleaner spray down it, but apart from this I have done nothing more - I guess my next step should be to strip the carb down when I have time for a more through clean to sort out the fuel mixture issue.

The oil tube is defiantly ok, I just replaced it as the original was showing signs of splitting.

As for the noise, I am pretty sure it is the engine and not the body rattling. I know the engine mounts are tight, as I had to remove the front one, and loosen the rear 2 to drop the engine down in order to remove the drive clutch to replace the timing/cam belt. But yet the noise persists...its sounding more like a diesel than a petrol : (
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Old 12-14-2010, 11:36 AM   #7
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

Have you checked to make sure that someone didnt put deisel fuel in the gas? It would run like crap and smoke badly if so.
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Old 12-14-2010, 12:57 PM   #8
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

Hello MJF,

The chokesystem could be the white smoke.
Are the plugs the right type? (bad burningproces)
Are both cylinders working, so not walking on one leg?

Rattling:
Are the valvesprings broke?
Are the retainers in their place?
Is the valve timing okay?
Look with a torch for scratches through the sparkhole. (signs of valves touching the piston)

Are the rods tight on the cranck, so not loose or damaged.
Look with a screwdriver through the sparkhole if you can feel clearance on up or down.
Look also in the oilfilter if some aluminiumpieces are in it.
In that case its for sure the rod / cranck.

Is the ignitiontiming okay, so no to early ignition?

Benno
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Old 12-14-2010, 01:46 PM   #9
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

Check for a loose baffle in the muffler??
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Old 02-21-2011, 01:11 PM   #10
mjf1604
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Default Re: EZ GO ST350 2004 (MCI engine) running rough and smoking

Thanks for all the replies guys, its been a while but I have at last had the time to tear it down properly:

Firstly, the exhaust seems fine, a little clogged with carbon deposits but this is nothing that cant be cleaned out using suitable solvents.

During the teardown, I found many things which could be causing the rattle, including loose bolts on the cam belt cover, a dent in the cam belt cover causing it to fowl on one of the cogs, an ignition wire toughing the fan, worn piston rings and connecting rods causing some piston slack.

The bottom end is in a poor state, the bottom of the crankcase was full of thick sludgy oil/grit, perhaps from past oil changes being missed, and not drained correctly out the sump plug and just out the filter hole or contaminated oil being used. (I purchased the machine used, so cant say for sure).

This has created some wear on the connecting rods between the crank and the pistons, and on the cylinder walls. While there is no deep scoring (on the walls at least), signs of wear can be seen and a slight ridge at the top of the bore).

I am unsure at the moment if I should rebore and fit overside pistons and rings, or just fit a new set of standard rings. I could see a little oil pushing up past the rings turning the engine over with the head off, so I guess this explains the smoke problem I had!

Before the teardown compression was reasonable, a little over 150psi on both pistons, so I am considering just replacing the worn rings with a new set or standard ones, does anyone have any thoughts on this?

Also the connecting rods, have signs of wear (although the crank looks fine), does anyone have any idea if these can be re-machined or do they need replacing?

If anyone has ever experienced this, and has any suggestions they would be greatly appreciated so I know which bits I need to replace and which bits can be salvaged

Thanks in advance
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