2016 Hisun 500 runs rough no power

[CapnWalleye]

Just picked up a Hisun 500 that had shift issues (corroded fan gear) which I fixed. It also didn't seem to be running smoothly then all of a sudden it got worse. It seems to miss on both idle and when pushing the gas pedal to the floor and doesn't seem to be running at full power. I've been working with a local person who is walking me through some steps, but I'd like some input from this group as well. What I've done:

- drained the fuel tank and replaced it with 93 octane fuel and added heet to help with any water problems.

- replaced the fuel injector.

- disconnected the battery (several times) to allow the module to reset.

- set the valve clearance, both intake and exhaust, within specs ... intake was tight but exhaust seemed fine.

- replaced the battery.

- replaced the O2 sensor.

Nothing has helped. Not sure what the next steps are, but would appreciate any expertise that can be offered here.

 

[Steve G.]

Only thing I can think of that you haven't already done is look at the fuel pump. There is a filter on it but you have to pull the pump to look at it. If that is the problem consider installing an inline filter before the pump.

[Alien10]

Just a thought here...how is compression?  Too tight exhaust can burn a seat and leave you with poor compression. 

[CapnWalleye]

On 3/30/2025 at 4:00 PM, Steve G. said:

Only thing I can think of that you haven't already done is look at the fuel pump. There is a filter on it but you have to pull the pump to look at it. If that is the problem consider installing an inline filter before the pump.

Thanks for this. I pulled the pump but cannot find a filter or screen. I didn't want to disassemble it without knowing more. I'll look at installing an inline filter ... good idea.

[CapnWalleye]

8 hours ago, Alien10 said:

Just a thought here...how is compression?  Too tight exhaust can burn a seat and leave you with poor compression. 

Thanks. I tested compression which is over 100. Since my most recent post I've also looked at the fuel system and wondering if there's something that is affecting fuel flow. I pulled the lines and blew them out but could not find a filter.

Also, I wonder if I made a mistake when adjusting the valves. Intake was tight but exhaust was still good. After doing it, though, I fear I didn't have it at TDC. I couldn't find the marks so spun it around to just after the exhaust opened and closed but before intake opened and closed. TDC is on the compression stroke if I remember correctly (I'm not a mechanic, just a guy who isn't afraid to get his hands dirty) which would be between intake opening but before exhaust, right?

[Steve G.]

10 hours ago, CapnWalleye said:

Thanks for this. I pulled the pump but cannot find a filter or screen. I didn't want to disassemble it without knowing more. I'll look at installing an inline filter ... good idea.

Mine had a small plastic sock kinda thing on the end of a tube. It was all clogged and broken down. Maybe some are different.