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Discussion Starter · #1 ·
I have cleaned this carb with ultrasonic cleaner, it is the original carb, the machine has only 850 miles, I have a new plug, I have adjusted the pilot screw numerous times. The issue is that it seems to run fine and then it doesn't. I think I have found the magic carb setting and then the next day, it runs like crap. I pull the plug, it is soaked with gas, then I think I finally have the carb setting right because the plug is dry and the insulator is white and life is good. The next day, it bogs and the plug is black again. So,....... I pin the throttle, it bogs like crazy and at that moment I turn the headlights on and the thing immediately sings the high rpm. I then shut the headlights off and it bogs like crap. Switch the headlight on and it sings again. So.... I have read somewhere that this means the rectifier is bad. Can someone clarify or tell me how to test? I figured that this has to be an ignition issue because it simply is completely inconsistent. It has been driving us nuts, but I hope we just made a breakthrough discovery. Thoughts? Thank you.
 

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It’s a bad regulator/rectifier. $25 on Amazon. The repair manual tells how to test it, but I don’t recall. But since you have to remove the front rack, shifter cover and knobs and front plastic to test it, you may as well just swap it out. You’ll probably need to make a custom bracket to mount it since the aftermarket units don’t mount the same as the OEM.

If it’s a big deal to you to test it, I can take a photo of the procedure from my manual. Let me know.
 

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Here’s what you’re looking for. You can see how I mounted mine. This is how far in you’re going to dig, other than you leave the rear plastic, rear rack and floor boards on.

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To test your rectifier/regulator use a multimeter and do some voltage tests at the battery while your bike is running. At idle you should be getting around 13.0 - 13.3 volts, and 13.8 - 14.0 volts when revving the engine. If the voltage readings are way above or way below those readings then your rectifier/regulator is most likely the issue.

And the rectifier/regulator is not in that hard a spot. It’s typically located round the handlebars affixed to the fame behind some plastic cowling. It’s just bolted in place and connected via a quick plug.

Also, make sure all of your electrical connections are clean, corrosion free, and tight. That includes your main ground to frame. Poor electrical connection can cause all sorts of electrical issues.
 
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Discussion Starter · #6 ·
Great info!! Thank you so much. We bought this quad used. We noticed that they made a hole in the plastics behind the battery. Not sure why. Maybe to get to what looks like a solenoid behind the battery? Is this common. I thought it could be the rectifier, but it clearly looks different than what you posted. Thanks so much and we will tear off the front plastics again. Thanks.




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Discussion Starter · #7 ·
BTW, is Amazon approved for this? I made sure I bought a used quad with an OEM carb. I didn't want to go down the road of the Chinese carbs. Are cheap rectifiers good enough for this application. I think OEM is $225.
 

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The round device with the two nuts on top on the right (as you face the bike, looking through the hole someone has cut behind the battery box) is the starter solenoid. The neutral safety relay is about four inches to the left. The regulator/rectifier is nearly the size of your palm and mounted a bit higher, about where the horizontal “vent” is in the front plastic.

I bought a cheap aftermarket regulator/rectifier and it lasted about 5 years. I get to do it again. As you mention the OEM costs quite a bit more. I’d say it’s a personal decision, realizing the aftermarket unit likely won’t last 15 or 20 years like my OEM did.

As to the “main” ground location, I’m not sure. When you remove the front plasticfollow the negative (black) lead that connects to the battery and see where it connects to the frame.

If you want to check the neutral safety relay, I just posted that info on the site for another member on 21OCT22. Search under my user name and you should find it.

BTW I always use anti-seize to reassemble all plastics and rack nuts and bolts. Sure helps the next time you have to take it apart.

Good luck with it all.
 

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Discussion Starter · #10 ·
Great. Thanks. The plastics will come off fine. We just had them off for other reasons and touch up painting the frame. I already ordered the Amazon one and we'll see how it goes. If nothing else, it should help with diagnosis. Thanks again.
 

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Cheaper aftermarket electrical components are really a matter personal preference as stated. Though you need to keep in mind that cheaper usually means shorter lifespan. Sure OEM is more expensive, but it is often more superior in terms of quality and durability.

For electrical components I myself stick with OEM. Generally because I don’t like to cheap out on electrical components specifically. Though that’s just my personal preference.
 

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Discussion Starter · #13 · (Edited)
With the original rectifier, volts reached a peak of 18v. With the Amazon, it peaks at 14v. Sounds like the rectifier is the issue. Quad seems to idle and no longer bogs under throttle. I have a nice video of how it was behaving with lights on and off. Will 25 sec vid post to this site or is it too large? That way it helps the next guy. I thought I was chasing a carb issue until I tried the light trick. BTW, the one that I purchased bolts right in, no need to fab a bracket.
 

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Great, glad to hear it. Could you attach an image or link of the R/R you bought? Maybe I can get the same one. Right now the one I gave in my cart is roundish, eightish sided. Does yours have one plug? Or two plugs? Thanks.
 

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Post your video on YouTube then copy it’s link into this thread as a post. Glad your new rectifier solved your problem. 18v is definitely on the high side. Your were basically creating a overcharging scenario. This essentially overwhelms the electrical system thus causing a variety of issues such as bogging, backfiring, poor idling, etc.
 

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Discussion Starter · #16 ·
This rectifier is plug and play. There are other brands that look the exact same. I will get the video posted to Youtube. Thanks.

 

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Discussion Starter · #18 ·
Ugh, I spoke too soon. The quad runs much better, will rip through the gears and handle aggressive driving, but the idles slowly dies and then you have to peg the throttle and spin the starter for 15 seconds to get it to light. The plug was black. So, still not running right. I think I will make it 1/8 of a turn leaner, unless you guys have a better idea. Thanks.
 

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I’m not so good on carb issues. Seems like you’ve got one of those too.

Not your issue currently, but you’ll likely have it at some point, the diaphragm in the vacuum actuated fuel pump like to go out on these bikes. It will keep it from running right. I “fixed” it once, but that was short lived and I bought another OEM pump which is still ticking away.

IIRC, way back when mine was under warranty (3 year free warranty at the time, I think), the fuel tank petcock had the diaphragm in it go out. It kept the bike from idling correctly. I think it might have made it hard to start too.

Good luck, you’re getting the bugs worked out.
 

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What year is your 300 again..?
 
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