Common 670 Solutions

[slonomo]

So far I have found the Predator 670 to be a very good engine for the money. With that said, it has some faults. I figured I'd start a thread about some of the common issues and solutions.

If you have or have had a 670, please post your experience with issues and the solutions here.

[slonomo]

The first issue I ran into was the idle air screw adjusters. First off they were hidden with caps, an EPA requirement so people don't mess with the air fuel ratio and cloud the earth with carbon. Whatever. All these do is make it impossible for the diy mechanic to adjust the carb, because we all know they don't stay adjusted correctly, ever!

Most of us already know that you can take the little metal caps off to expose the idle air screws. (see blue arrows)

All I did to remove mine was just drill a small hole through the cap, then use a finish nail to pry the cap out. They popped out super easy, they are just lightly pressed in there.

This will expose the low speed air/fuel adjuster screw. The screws on my carb were way off and it wouldn't barely idle.

Adjusting them is quite easy. I first gently bottomed out the adjuster, then backed each one out 1.5 turns as a baseline. Then I started and idled the engine at about 2200 rpm, let it sit and idle to warm up to full temp. Then I adjusted the screws until the engine sounded smooth, and the idle speed reached a peak, around 2500 rpm for me. When the idle speed started to slow down is the point where I went too far, so I backed up to the previous setting. Then I backed the idle speed screw down to get it to idle around 1000 rpm. I also used a temp laser gun to measure the exhaust manifold and head temp to double check the settings. More fuel = lower temps and less fuel = higher temps. The temp maybe had a 150 degree swing from one end of the spectrum to the other. Not super scientific, but it's just something else to look at, worked for me.

The only other way to get the air fuel ratio correct is to use a sensor, which I don't own, and neither do most people. But that's the only way to get it "spot on" by the numbers.

There are carb tuning videos galore on YouTube, I suggest watching and learning as much as you can before you attempt this.

[slonomo]

Another thing I found to be a problem was the stock 670 fuel pump. I was getting air in the fuel (I think) and it was causing irratic fuel supply and running issues, was driving me crazy.

To test the pump I simply removed the rubber fuel line from the carb, stuck it into an empty water bottle, and cranked the engine for 10 seconds. I watched the flow and measured the amount visually. There were some bubbles and the stream was weak.

I changed the pump out to a Briggs and Stratton pump, a direct swap. I've been using these pumps for years on every small engine I run (under 25hp). They have been great and super reliable. They do wear out but only after years and years of use. (See the photo for pump part #)

I retested with the water bottle and the fuel coming out had no bubbles and the stream was much stronger, and the volume was 2x that of the stock pump.

While I was in there I took apart the vacuum pulse line filter and found some bits of plastic and some metal shavings in there.........I guess that's supposed to be some kind of filter. None of the engines I've ever used have ever had a filter for the pulse line, so I just cleaned all that crap out and reinstalled it. I don't know if this had any effect on the pulse quality or not, but it sure didn't seem right to me. Very strange.

[slonomo]

Spark plugs.....this is a hot topic.

Everyone will likely have their own preference for brand, but I think we will all agree that the stock "Torch" brand plugs that come in the 670 are garbage. I've never heard of them until I removed them from this engine, but apparently they are a legit brand. Ok. Not for me. I swapped mine out to an equivalent in NGK Double Platinum. Did it make a difference? Yes. The stock plugs would fuel fowl fairly easily. Every now and then I'd have to remove the plugs and dry them off and then the engine would start. That was my indication that they were a weak link. Shouldn't have to do that once a week or every 3rd time I started the engine. After I changed the plugs I have never had to remove them again. It's been months.

My recommendation.....just replace the Torch plugs with a cross referenced brand of your choice, whatever you like. I've always liked NGK, plus it's all the local parts store had other than AC Delco and Denso.

[PharmGuy85]

Great thread idea. Did you go with the NGK-BPR5EGP? I am leaning towards that or the BPR5EIX (iridium) stock NGK replacement being BPR5ES if anyone needs that.

I am going to be replacing the stock predator oil filter next after initial break in for piece of mind. HF Manual lists Fram PH4967 or STP S4967. I am leaning towards the STP but have cross referenced and may choose a different brand altogether.

[slonomo]

Originally Posted by PharmGuy85

Great thread idea. Did you go with the NGK-BPR5EGP? I am leaning towards that or the BPR5EIX (iridium) stock NGK replacement being BPR5ES if anyone needs that.

I am going to be replacing the stock predator oil filter next after initial break in for piece of mind. HF Manual lists Fram PH4967 or STP S4967. I am leaning towards the STP but have cross referenced and may choose a different brand altogether.

I failed to record the part number I just took the Torch plugs into the parts store and picked out a plug. I just remember it was NGK Platinum. I thought the guy said "double platinum" but those are Bosch. I just know the difference was substantial. I can't think of anyone that likes the Torch plugs.

Fram....they have a terrible reputation. Try and cross reference that to a Wix or Napa.

[kellett5261]

Originally Posted by slonomo

The first issue I ran into was the idle air screw adjusters. First off they were hidden with caps, an EPA requirement so people don't mess with the air fuel ratio and cloud the earth with carbon. Whatever. All these do is make it impossible for the diy mechanic to adjust the carb, because we all know they don't stay adjusted correctly, ever!

Most of us already know that you can take the little metal caps off to expose the idle air screws. (see blue arrows)

All I did to remove mine was just drill a small hole through the cap, then use a finish nail to pry the cap out. They popped out super easy, they are just lightly pressed in there.

This will expose the low speed air/fuel adjuster screw. The screws on my carb were way off and it wouldn't barely idle.

Adjusting them is quite easy. I first gently bottomed out the adjuster, then backed each one out 1.5 turns as a baseline. Then I started and idled the engine at about 2200 rpm, let it sit and idle to warm up to full temp. Then I adjusted the screws until the engine sounded smooth, and the idle speed reached a peak, around 2500 rpm for me. When the idle speed started to slow down is the point where I went too far, so I backed up to the previous setting. Then I backed the idle speed screw down to get it to idle around 1000 rpm. I also used a temp laser gun to measure the exhaust manifold and head temp to double check the settings. More fuel = lower temps and less fuel = higher temps. The temp maybe had a 150 degree swing from one end of the spectrum to the other. Not super scientific, but it's just something else to look at, worked for me.

The only other way to get the air fuel ratio correct is to use a sensor, which I don't own, and neither do most people. But that's the only way to get it "spot on" by the numbers.

There are carb tuning videos galore on YouTube, I suggest watching and learning as much as you can before you attempt this.

which screw is what?

[slonomo]

Originally Posted by kellett5261

which screw is what?

The one in the photo It has a blue arrow pointing to them. There are two. They have caps covering them that have to be removed, as mentioned in the post. You'll find some videos on YouTube as well.

[kellett5261]

i was referring to the idle screw, i tried your little experiment over the weekend with 1.5 turns out and try to match with a heat gun.

100 times better than it was but still needs little more attention but no longer is popping on me and flowing plugs(yet at least)

ill put some miles on it and see how long it turns out, i also did the fuel pump and the filter on the vacuum line too. Not sure ill need a aftermarket carb now. but ya never know Lmao thanks Slonomo

[smackley]

This is great info, and great timing for my own 670 project. I was racking my head around the idle issues. Thanks for taking the time to make this.

Also, what the heck is the cranks shaft bolt thread and size? Nothing in my random bolt bucket is threading in. I googled a bunch of verbiage that I thought would turn up results easily but I only saw info for predator 212cc 3/4 shafts.