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Does anyone know the correct thread spec for the Predator 3500’s gas tank cap? I’d like to replace mine with a vented cap, but even though the aftermarket vented caps for portable gas tanks that i’ve found in stores are the correct diameter, their threads don’t quite match the threading on the Predator’s tank filler opening.
Did you ever figure this out? I have the same question.

Thanks
 

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New member here, but decades long forum user, hello all!

I wanted to post this here since this is the top google search result for 'Predator 3500 forum'

I bought my generator in July 2018 with the 2 year extended warranty, to power my brand new camper at the racetrack - I go to Motorcycle, Nascar Xfinity, Trans-Am, IndyCar, NASA / SCCA and Vintage racing event that are four days long. The generator stands now at 441 hours on the clock. It's always run great until I got it out 2 weeks ago...

A little back story - I broke this generator in with Mobil Super 5000 10w-30 conventional oil, changed at 2h/5h/18h. I ran that same conventional oil for my first real race weekend in August 2018, ended up at about 75 hours, then I switched to Mobil 1 10w-30 full synthetic. I service it every 60-100 hours - change the oil, remove the spark arrestor, and clean both pieces with a propane torch and air compressor, clean and re-oil air filter. I put the recommended NGK plug in it when first got it. Never seize and dielectric, of course. Generator is stock, no charcoal canister delete, no oil door air mods. Totally stock. I'm in Ohio at about 1000AGL and use the generator between 45F and 95F.

So anyway, two weeks ago, I fired it up and ran the camper AC for 15 minutes in my driveway to make sure all was well before I left for the race weekend the next day. It pulled the AC fine and seemed to be running great, like it always has, until I shut off the AC. With little to no load it had a distinct surge, rev up, slow down, etc. It was much more pronounced in ESC on / ECO mode. I ran the AC again and it was fine under load, perfectly smooth. I chalked it up to last years fuel that was in it, and figured it would clear up once I filled it. I carry two 5 gallon translucent motocross style fuel jugs to the track, and I always use Sunoco 93 octane, and treat with Star-Tron fuel treatment. Same fuel procedure the whole time I've owned it.

So before I left for the races, I changed the oil, popped in a fresh NGK plug, cleaned and oiled the air filter. No change still running rough under light load only.

So I get to the track and even after it used all the old fuel and I filled it with fresh treated 93 octane, it was the same story - ran perfectly normal under heavy load, but sounded pretty sad under light or no load, idle constantly hunting, rev up, stumble, rev-up... Yuck! I found that cracking the fuel cap helped it run a little smoother but still it clearly wasn't happy. I put about 40 hours on it that weekend. I was assuming I'd have to pull the carburetor and clean it up...

So I get home from the races and sat down to work on it. I hit the starter button. NOTHING! Pull battery put the meter on it, and it's at 12.95v. Hit the starter button again, nothing no crank, no click nothing. I was so surprised I couldn't believe it. I figured a wire had to have vibrated lose on the control panel. So, I pulled the cord and it fired right up first pull. It was running the same, poor at idle. I shut it off and a bit later decided to try the electric start again, this time I got a click but it wouldn't turn it over. At this point I am like oh man what has happened to my once great generator! I was so frustrated. I am still within my two year extended warranty, but I know I got a good generator, 441 hours of proof. I hated the thought of getting a bad one on exchange, but I was considering it...

I decided to take the right side cover off, where the pull cord is as I knew the starter and starter solenoid is on that side, because I had to replace the starter solenoid within the first 30 days of ownership back in 2018. No big deal. Anyway - as soon as I pulled that cover, my eyes were drawn to the small 1" x 4" epoxy potted electrical box mounted to the bottom of the frame. At first glance the surface of it looked slightly melted! Upon closer inspection it had a small amount of engine oil pooled up in it, and the areas that looked 'burnt or melted' were just bits of grass or debris trapped in the oil. And that oil had wicked up into the square 4 pin molex connector also!

I checked the Harbor Freight parts list, it's part 120 labeled as 'LIGHTER' and it's not available. I looked at the Northern Tool parts list, it not available there either and they call it 'IGNITION'...

I pulled the screws that secure it, and sprayed it down with electrical contact cleaner, dried it off, and it looks perfect. It was absolutely not melted or burnt at all thank god. I sprayed out both sides of the molex connector as well, used air to dry it up, and put everything back together.

I hit the electric start, it fired up instantly, and the generator IS NOW RUNNING PERFECTLY!! Wow! Perfect idle with no load, just like always, and still runs perfect under heavy load.

I was totally shocked that this was the cause of all my issues! That oil must have been shorting some of the contacts together intermittently, and causing the stepper motor that runs the throttle on the carb to wander, causing the poor up and down idle under light load. It was also interfering with the electric start, as I have started and stopped it about 10 times since with no further issues with the electric start. I keep starting it and running it for about 10 minutes using a big 52" belt drive drum fan for heavier load (7A), and a small floor fan for light load (1.5A).

I am convinced it is all 100% fixed. Wow. Oil in a molex connector caused all that crazyness, who would have though it...

The part number on the electrical box in question is:

TJ113-2009-1
180303

If you google that what comes up is extremely similar, has the same large capacitor, and several smaller caps, but it doesn't have the right number of wires. But the part is called an AVR - automatic voltage regulator rectifier.

So I think the oil was causing the voltage to fluctuate intermittently, so the stepper motor was reacting to that, and thus causing the idle to wander to chase an apparent electrical load that appeared to be coming and going, but which wasn't really there.

In all the researching i did prior to starting to chase down this problem - YouTube videos, forum posts - absolutely no one noted this issue. So I wanted to get this info out there for the community of Predator 3500 owners!

The only remaining question is how the oil got there. I can't answer that.

I've included two pics, one of the location of this box in the frame, and one of the box with the oil and debris in it before I cleaned it. I don't have a pic of it after I cleaned it up, but it looked perfect after clean up.

Here is a YouTube video of how terrible it was running with no load before the fix. I hope I never have to hear it run like this ever again! : )


View attachment 7918

View attachment 7919
The green wire coming from the rear of the motor is the low oil sensor wire. There’s a bullet connector halfway down. The oil seams to seep out and down the wire. I’m going to try and clean the Lighter #120 on the parts list (22212) and I’ll add wire and make a loop so it will drip down and not run down the wire into the Lighter.

The AVR is not the same, it’s a Auto Voltage Regulator. I have the 22212 Lighter on back order from Harbor Freight but I have also found one from AliExpress in China for about the same price but $8.00 shipping. I’ll order one if the Harbor Freight one stays on back order once I stop traveling.
 

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Unless I'm mistaken, the Predator 3500 is an inverter generator. I doubt it uses that particular part, which looks like an AVR for a non-inverter generator.
Yeah, I don't think the inverter model of the Predator 3500 has an AVR. But apparently HF did make a Predator 3500 that uses one. We probably need more info about this gen...
 

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I found a Chicago Electric 3500 generator, a HF sub-brand. Could be this one.


The last picture shows the round alternator end-cover. That's usually where you'll find the AVR.
 

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Thanks for the help. Here is a pic of the actual generator and it is a invertor type. Basically what happened is while connecting it to the home power fed back in to the generator and obviously that's when it quit working. It starts and runs well but the overload light comes on right after it starts and it doesn't produce any power. Does anyone know what part is bad and do you think it's worth fixing? Thanks again! Danny
 

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Basically what happened is while connecting it to the home power fed back in to the generator and obviously that's when it quit working.
Well, that probably killed the inverter assembly. A new inverter is likely about $350-$450. Check with HF customer support and see if they will provide the wiring diagram for the gen. Get the price for a new inverter assembly too.

I don't know if there might be anything else that could have been destroyed on the output but looking over the wiring diagram might help clarify that if you post it.

And, as you have probably already figured out, you need an interlock kit installed to prevent this in the future.
 

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Well, that probably killed the inverter assembly. A new inverter is likely about $350-$450. Check with HF customer support and see if they will provide the wiring diagram for the gen. Get the price for a new inverter assembly too.

I don't know if there might be anything else that could have been destroyed on the output but looking over the wiring diagram might help clarify that if you post it.

And, as you have probably already figured out, you need an interlock kit installed to prevent this in the future.
Thanks for the update. I'll look for a schematic online.
 
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