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Tomoto

2009 Hisun Supermach 500, Stalling at idle and hesitating under acceleration

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Hey folks. I recently acquired a pre-owned Hisun 500, carburated. And surprise... it has issues.

When cold, it typically starts without any issues, but once it warms up it tends to sputter and stall out. When accelerating, you can also feel it hesitating occasionally, and when you stop or put her into reverse, she will often stall.  The fuel is clean, I installed a new fuel filter, and the air filter is clean. Though the fuel pump appears to be working ok, it makes a strange knocking sound whenever power is put to it.  I've never heard anything like it, and I'm not sure if its shot or just a cheap Chinese pump thing. I have an aftermarket pump coming, and I've ordered a new ignition coil as well on the off chance that it is faulty. I am hoping replacing these two parts will solve the issue,  and if it does I will post the results here. 

If not, anyone have any other ideas?  Also, I've noticed it is very difficult to find parts for this make... any suggestions on a good source for Hisun parts? I appreciate any comments or insights. 

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16 hours ago, aussie1 said:

Is choke working properly? Also check valve settings.

Thanks for the tips Aussie1. The choke cable appears to be working fine, although I have not measured cable movement to ensure it is within specs.  The machine is ten years old, but it has only 600 kms on it. I suppose I could check valve clearances, but I haven't largely because of the low mileage, and because it goes from running fine to flaming out. When you start it back up, it runs fine at idle as well at higher RPMs. However, once you let it idle again for a few seconds, it begins to pop a bit and then stalls.  If the valves required adjustment, I imagine the problem would be more consistent.

I still suspect either a potential problem with the fuel delivery (I have a new pump on its way), or a faulty ignition coil. I guess I'll see if the problem is resolved once both parts are replaced. 

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I would also go along with fuel or ignition issues.  A lot of "could be this" or "could be that".  Just a few things I would check:

Could be spark plug wires (insulation) breaking down (had that problem on my car once).  Start the engine and look to see if you can see St Elmo's fire around the spark plug wires.  More pronounced if engine is under load.  Best if you can do this at night with very little light.

Could be the fuel pump.  Can you check fuel pump pressure and volume?

Carburetor may need cleaning.  High speed jet may be partially clogged.

The popping could be a sign of sticking valves.  Especially if it sat for a very long time.  Do a compression check.

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44 minutes ago, Dan B said:

I would also go along with fuel or ignition issues.  A lot of "could be this" or "could be that".  Just a few things I would check:

Could be spark plug wires (insulation) breaking down (had that problem on my car once).  Start the engine and look to see if you can see St Elmo's fire around the spark plug wires.  More pronounced if engine is under load.  Best if you can do this at night with very little light.

Could be the fuel pump.  Can you check fuel pump pressure and volume?

Carburetor may need cleaning.  High speed jet may be partially clogged.

The popping could be a sign of sticking valves.  Especially if it sat for a very long time.  Do a compression check.

Thanks Dan B. Great suggestions. Exactly where I've been sniffing around...

Fuel pump was super cheap at $40, so instead of wasting time testing pressures, I replaced it. Intermittent issue persists. 

Carburetor was yanked, disassembled, and  thoroughly cleaned before reassembly and re-installation. I didn't find anything obviously unusual whilst in there... jets were all clean without obstruction. Intermittent issue persists.

Ignition coil including the lead wire , also really cheap at $60, so I'm just gonna replace it too. Then I can be certain that any gremlins go out the door with the old part. 

Spark plug, $5. Turns out the existing plug is actually not the recommended plug as its heat rating is too high. Though I doubt that would cause the issue, its being replaced with a new one at the correct heat rating. 

I was hesitant to start getting into the engine, but if the ignition coil and new plug do not resolve the issue, then valve inspection and  confirmation of their clearances is were  where I was heading. 

Overall, the issue presents like an intermittent fuel or spark problem. Quickly tapping the accelerator to rev the engine repeatedly sometimes results in a major bog, almost to the point of stalling out if you do not let off. But only sometimes... If the valves were out, or there was a compression issue, it seems to me the problem would be far more consistent. I am leaning towards a weak spark compliments of either a faulty plug or ignition coil, so I will post results here when the new parts are installed... hopefully by the end of the week.

Thanks for your actionable input; much appreciated!

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