Subaru Robin Carb Problems

l008com

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After about 20 years of running really well, my Manco Dingo's engine started running poorly. It was clearly carb problems and rather than clean it and probably break it, I just bought a new one. I've had very good luck buying cheap ebay carbs for lawn mowers, snow blowers, etc.

I've had other threads about this cart before but it's time for a fresh start.

So I put the new carb on and here's what happened.

For a while, every time i started the cart, the engine would run away. Sometimes gradually, sometimes suddenly. Yes, the last time it did this, I had to run after it and it almost drove away.

Then after doing that for a while, suddenly it stopped. Now it's new behavior is that it can't idle. As seen and heard in the video. If I raise the idle really high, it will stay running with tons of pulsing. If I try to lower the idle to something more normal, it will just conk out if you're not actively on the gas.

So what do you think is going on here? It makes me nervous because even if it starts to behave normally, I'd be afraid it would randomly start to run away again. And runaway engine means runaway go kart. Is the carb just a dud?

Stage 2: Engine can't idle
https://youtu.be/3X0VlpEvIuA
 

karl

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I've had very good luck buying cheap ebay carbs for lawn mowers, snow blowers, etc.
Yup.

Many people bring their equipment to me, after installing a new ebay/ amazon/ typical suspect carb.
See about 1 a week.

"Cant be a carb issue, its brand new" "wont run right" "leaks"

Briggs, tecumseh, kohler, subaru, seen it all. If they did not throw out their old carb, I can clean it and get them going.
As long as the "installer" did not break anything else on their attempt.

If not, gotta find a roached OEM carb and rebuilt it, or get billed for a new one (if still available)

Installing a china carb for a customer practically guarantees a bring back.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Anyway, you got fresh fuel? You can shine a light in the gas tank, and no breakdown/ sediment/ debris in the bottom?

The fuel was pumped less than a month ago? The throttle linkage moves free, no binding? Did you force the throttle rod,
slipping the governor arm on the shaft? Vacuum leaks? Did you use the gaskets that came with the kit? Over tighten the carb nuts, and crack the insulator? The possibilities are endless.
 

Karttekk

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Agree with karl here. Buying those Taiwan carburetors is a gamble. I just finished up a kart with a Predator engine that took a while to straighten out. Bought one of those cheap carbs as I was going through the process of elimination. Ends up the coil was the problem but the engine would surge up & down then quit with the new carb installed. The mixture screw didn't seem to do anything and it was hard to start after it quit. Took the original carb apart, cleaned the jet and emulsion tube, reinstalled it and the kart ran fine afterward. Took the new carb apart, didn't see anything wrong with it but it wouldn't work right. Maybe start here to help find and OEM carb or at least learn which carb you need. I put an OEM carb on a Robin/Subaru engine along with new factory governor springs, thing ran great. Sold it & the customer is still using it. Had to toss the original carb due to internal rust and corrosion. There could be a multitude of other things going on but at least start with a quality carburetor to eliminate that as a possibility.

 

Fallingdown

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After about 20 years of running really well, my Manco Dingo's engine started running poorly. It was clearly carb problems and rather than clean it and probably break it, I just bought a new one. I've had very good luck buying cheap ebay carbs for lawn mowers, snow blowers, etc.

I've had other threads about this cart before but it's time for a fresh start.

So I put the new carb on and here's what happened.

For a while, every time i started the cart, the engine would run away. Sometimes gradually, sometimes suddenly. Yes, the last time it did this, I had to run after it and it almost drove away.

Then after doing that for a while, suddenly it stopped. Now it's new behavior is that it can't idle. As seen and heard in the video. If I raise the idle really high, it will stay running with tons of pulsing. If I try to lower the idle to something more normal, it will just conk out if you're not actively on the gas.

So what do you think is going on here? It makes me nervous because even if it starts to behave normally, I'd be afraid it would randomly start to run away again. And runaway engine means runaway go kart. Is the carb just a dud?

Stage 2: Engine can't idle
https://youtu.be/3X0VlpEvIuA
Had this issue on a Robins 2 stroke motor before. I was told by everyone it was because I replaced the original with a cheap one off the web. Well just like you, Ive bought the cheap carbs and had luck with them on everything so far. After trying to adjust the high and low idle speed 10 times with no luck I decided maybe it's bad fuel. Bad gas cap. Neither of those. What it was and believe the scooter ran better then new after I figured it out. But I had the lines coming from the carb to the fuel tank crossed and used same size fuel line for both air inlet and fuel inlet. i switched the lines to the right connections on carb only and that fixed it. Decided to put right diameter lines after and didn't change much. Runs like a champ now. The obvious is always where my mistakes are made.
 

l008com

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Believe me, if I had a good place to bring my small engines, I would. But here in the suburbs, we don't really have many places. Just some random signs for lawnmower and snow blower repair stapled to telephone poles. That's a little too iffy for me, I'd rather take my own changes.

And regarding OEM carbs, it's over $100 for an OEM, vs $15 for an ebay. So even if the dud-rate is high, it's still a lot cheaper to go with the ebay carb. if I end up buying another one, I'm still only in for $30.

As for the fuel, it was fresh when this started and i'm pretty sure it was stabilized too, but at this point I don't even remember how long this was going on. So it's probably best do burn all the old stuff, put some nice fresh fuel in there and then go from there.

It may be a while before I get to that step because ironically, this go kart is heavy enough that I'm currently using it as an anchor to hold up a roof support while I replace the roof.
 

Karttekk

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"And regarding OEM carbs, it's over $100 for an OEM, vs $15 for an ebay. So even if the dud-rate is high, it's still a lot cheaper to go with the ebay carb. if I end up buying another one, I'm still only in for $30.

And if the next $15.00 carb doesn't work you're out $30.00 with a kart that still isn't running. Get the correct carb # then see if you can find an eBay vendor that sells OEM carbs cheaper. We're telling you to go new OEM or repair your OEM because we've been through what you're going through. You came here for help, maybe try our suggestions rather than dispute them.

As far as fresh fuel, anything that's been in the fuel tank longer than a few weeks to a month is stale. The Ethanol in the stale fuel will destroy any rubber parts in the fuel system and corrode the metal.
 

jamyers

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Hopefully you still have the original carb. If so, you can clean it yourself, just be careful and don't force anything. Really, it's not that hard, it's just a matter of taking it apart, paying attention to how it comes apart and goes back together. Use come carb cleaner to blow out ALL the passages, and maybe even boil it in lemon juice for 15 minutes or so (fair warning, boiling lemon juice smells awful).

Then carefully put it all back together, remembering that "Cleanliness IS Godliness", and I'll bet it'll be fine.
 

l008com

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You'd think boiling lemon juice would smell nice, hrm

Anyway, I was messing around with the kart today. I didn't take the carb off, I was mainly changing the oil and replacing the broken starter rope. There is lots of sea foam in the now nice fresh gas so I started it up and let it run for a while to see if it would help. So far it hasn't made much difference but I did get a little more detail on it's exact behavior.

So with full choke, it runs more or less like an engine with the choke on.
With about 7/8th choke, it runs nice and steady but at a very high RPM, high enough to engage the wheels. It never settles down, it stays revving high.
As you approach half choke, it very rapidly changes from smooth high revving, to low RPM revving where it repeatedly almost dies, then revs itself at the last moment.
Then with no choke, if you're not on the gas, it dies right out.
In any choke level, if you start to give it gas, it will rev right up no problem.

This seems like a very odd set of symptoms. If the idle circuit was clogged, why would it rev up with almost full choke? Cutting the airflow should potentially make it rev normally, but racing, I still don't get. It makes me think something else is going on with this engine. But I have no idea what it would be.
 

l008com

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Here's another video where I move the choke from Full to Half. Right in the middle of that is where it revs away. At half or less, it dies.

 

madprofessor

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In both videos it acts exactly like the idle screw is backed out too far, starving it of fuel, needs more throttle from idle screw.
Running away with the choke on is to be expected regardless of idle setting. If motor's warm enough to not require the choke (as long as it's getting a little throttle in your case) running fine with no choke at all................
Just run the idle screw in far enough to give it enough throttle to keep running. Don't pay any attention at all to the idle speed with the choke on in any position. Idle speed is set with the choke completely off.
All this talk without action is making folks see gunk and cheap carbs, but the videos both say turn off the choke and turn up the idle screw.
 

l008com

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I tried messing with the idle screw today, no effect. Even with it as far out as it goes, as soon as I flip the choke off, it instantly dies out.

Also running away with the choke on.... is never something this engine has done in 20 years or something any other engine I've ever owned has done. Not sure how you could call that "expected" behavior. But either way, it still dies right away.
 

madprofessor

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".....as far OUT as it goes.......??? Don't you raise the idle by screwing it IN, you know.........clockwise like any common screw. If it was screwed all the way in (that's too far) I'd think it would be hitting the throttle mechanism real good, preventing it from retracting all the way. Would have some pretty raging rpm like that, wouldn't die out. Would probably run away.
I said the runaway expected on the choke thing because in my experience a little choke raises the rpm beyond what it has with choke off. If only a little throttle past idle were needed to get it rolling, that raised rpm from a partial choke would do it.
Have you pulled out your low jet to make sure it's not stopped up? Don't know where that would be on your engine, but hopefully it's as easy as on Predators.
 

l008com

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Well, screw goes in, the 'lever' the screw is in goes out. It doesn't seem like an idle-related problem at all. As far as cleaning the carb, no I have not done that. It is a new carb and i have never successfully cleaned a carb without ruining it before which is why I haven't tried taking this one apart yet.
 

l008com

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Ok I got myself another new carb for all of $14. Before I install, I want to make sure i'm putting the gaskets on correctly. Since the carb installed now is a replacement, I can't know for sure that it's gaskets are installed correctly. Can anyone tell by looking for sure which way they're supposed to go?

gaskets.jpg
 

madprofessor

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Gasket #1 looks way too small of an intake, and would cover up tiny holes that have to breathe.
#2 looks like a Predator exhaust gasket, and has same cover-up situation.
#3 looks like it might stand a chance on carb #A.
 

l008com

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A and B are the two sides of the same carb.

I believe B is the side that faces the engine and A is the side that faces the air filter

And these gaskets are the same shapes of the gaskets that came with the previous carb too.
 

madprofessor

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Gotcha. Just thinking about how pretty much any hole in the smooth face that gets gasketed that leads to interior cavities is there as a part of the functioning of the carb. Don't want to make a blanket statement though, always going to be exceptions.
I hope some others here speak up with thoughts on the openings.
 

karl

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What happened to the original carb and gaskets?
Usually they stick to the carb or insulator , and
Since you had it for 20 years, should be how
It left the factory. That would tell ya quick.

Anyway if you take stuff apart in the future,
Snap a few pics along the way, to avoid confusion. And dont throw out parts until the repair is complete and successful.

If that fails, like the professor said, line up the bowl vent hole with the hole in the gasket, and the mount stud holes. It will only line up one way.
 

l008com

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What happened to the original carb and gaskets?
Usually they stick to the carb or insulator , and
Since you had it for 20 years, should be how
It left the factory. That would tell ya quick.

Anyway if you take stuff apart in the future,
Snap a few pics along the way, to avoid confusion. And dont throw out parts until the repair is complete and successful.

If that fails, like the professor said, line up the bowl vent hole with the hole in the gasket, and the mount stud holes. It will only line up one way.
The carb I'm replacing is not the original. I assume I matched the gaskets on there now with the originals but who knows for sure.
Also which hole is the bowl vent hole?
 
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