Carb / throttle linkage issue, could use some guidance!

[tractorbeam]

So I got the CnC Bored Box Stock Carb from OldMiniBikes along with a filter kit and a few other items for my non-hemi Predator 212.

After mounting the new carb, I noticed the throttle rod, while in a 'resting' position, is pulling the carb wide open:



Then I realized the original stock carb had a built-in return-to-idle spring:



BTW i have not removed the governor. So I'm not sure how to correct this 'slack' with the throttle rod & the new carb.

If I pull the throttle rod until it seats the carb into the idle position (basically taking the slack out of it,) and then twist the throttle, the entire throttle system seems to work perfectly. I've been googling youtube vids and it seems either of these options *might* work, but I wanted to get you guys' opinion or direction:

1) Maybe I could carefully shorten the throttle rod, so that its resting position matches with the idle position?

2) Ive seen several return spring solutions, mounted/positioned in several different locations, but not really sure if something like this is best practice?

Finally: was this 'stock' carb supposed to come with that built-in return spring? Should I attempt to take it off the old carb & put it on the new one?

Thank you for any guidance you could provide.

 

[buckeye]

Number 1, No
Number 2, maybe
Number, find some pics of the stock set up..
Number 4, smash it with,a hammer.

 

[T-Town Mini]

The governor should pull the throttle closed to rest on the idle speed set screw once it's running. Have you started it with the new carb installed yet?

If the engine idles ok without an added return spring then it's not needed. With it running, rev it up using the twist grip and let it snap back to see if the engine then returns to idle. If it does then you're good to go.

If you want to experiment with it go ahead and try to swap the return spring onto the new carb. If it works...then, keep it.

 

[tractorbeam]

I have pics of the stock setup, before I removed the orig carb. Everything's where it should be, but the new carb doesn't have that same built-in return spring. Pretty sure this carb was designed for applications involving no governor/aftermarket linkage kit.

So like, just bash it into submission? ball-peen? Framing hammer?

 

[CarPlayLB]

That tiny spring under the throttle plastic piece does little to nothing. There is not much tension there! It is not needed, and as was stated earlier, the engine governor will bring it to idle once started. None of my carbs have that spring!

 

[tractorbeam]

T-Town, thanks for the advice sir. No I have not fired it up, only because the carb is wide open and throttle does nothing to the carb unless I manually pull in the rod's slack. I will definitely try running it & see what happens.

Don't really want to swap that spring out if I could easily do something like this:

 

[tractorbeam]

That tiny spring under the throttle plastic piece does little to nothing. There is not much tension there! It is not needed, and as was stated earlier, the engine governor will bring it to idle once started. None of my carbs have that spring!

Thanks CarPlay. You're right about that stock spring, it's very weak.

Obviously I'm new with this and I didn't notice the throttle behavior *before* starting. I will fire it up tonight & see what happens.

 

[T-Town Mini]

T-Town, thanks for the advice sir. No I have not fired it up, only because the carb is wide open and throttle does nothing to the carb unless I manually pull in the rod's slack. I will definitely try running it & see what happens.

Don't really want to swap that spring out if I could easily do something like this:

View attachment 95533

That would be better than risking breaking the plastic on your new carb.

Also, be sure to prop the bike up on blocks or a milk crate, etc. before you start it for the first time. You probably already know that but, still...you don't want to experience a potential run-away bike stuck on a full-throttle.

 

[buckeye]

And be sure your kill switch is hooked up.

 

[tractorbeam]

That would be better than risking breaking the plastic on your new carb.

Also, be sure to prop the bike up on blocks or a milk crate, etc. before you start it for the first time. You probably already know that but, still...you don't want to experience a potential run-away bike stuck on a full-throttle.

And that's exactly what would have happened had I not had it propped up. So I did the spring solution I posted earlier. That worked out great... however now I have the won't-run-off-idle issue which I've been researching all weekend, tried too many troubleshooting paths to count.

Will continue researching but just in case you guys have any ideas:

It's a 212 non-hemi with a side-exit header + muffler from hotrodminibikes and a brand-new Race Ready/CNC Bored Box Stock Carb from OldMiniBikes Warehouse, bored to 615, a 22 idle jet w/rubber ring removed, .038 main jet, K&N style filter. Runs at idle with choke on, but choke+throttle it's choppy. Dies immediately when choke is turned off. Will crank without choke and turns over a couple times, then dies.

No vacuum leaks, everything's tight, gas is flowing well to the carb, tank vent is clear, jets are clean of course. I'm about to pull my hair out!

 

[OND]

When you say Idle jet with the O-ring removed....there should be two O-rings on the low side jet and I've never heard of removing them.

 

[tractorbeam]

When you say Idle jet with the O-ring removed....there should be two O-rings on the low side jet and I've never heard of removing them.

I only mentioned that because the carb came with a note from OMBW that said to remove the rubber ring at the bottom of the idle jet after the engine is broken in. No change in behavior whether that ring is on or off anyway. This motor already had about 20 hours on it and ran okay with the stock carb & hotbox muffler.

Based on what I'd read, I thought the .038 jet might be too big. But all the symptoms & troubleshooting seem to indicate it's not getting enough fuel. I'm totally confused and wondering if there's just something wrong with this carb.

 

[naterater]

two words : slide carb

 

[T-Town Mini]

Try looking at the fuel inlet shutoff valve on the carb and check to make sure the rubber seal is not damaged/torn to obstruct fuel flow. Clean it and flush it out with the fuel line removed.

Make sure your inlet needle is working freely. ???

Are you using a fuel filter?

 

[tractorbeam]

Try looking at the fuel inlet shutoff valve on the carb and check to make sure the rubber seal is not damaged/torn to obstruct fuel flow. Clean it and flush it out with the fuel line removed.

Make sure your inlet needle is working freely. ???

Are you using a fuel filter?

No fuel filter, but that will change soon. Gas is getting into the bowl no prob.

I talked to Eric @ OMBW, he said to check that fuel inlet valve & small bowl and he wants me to really inspect the float assy to make sure it didn't get boogered up during shipping.

Also mentioned the carb cleaner test to see if there are vacuum leaks @ the head (I hadn't tried that yet.)

But he mentioned something I haven't seen anywhere else: The plastic spacer thingy that I took off with the old carb. I thought it was part of the old airbox. Fortunately I didn't toss it. He said I need to try installing it.

It's not exactly similar to this, but close:



So I'm going to try these things this evening and see what happens. Thanks to you & everyone else for the suggestions, very much appreciated.

 

[tractorbeam]

It was the spacer.

This is the "Box Stock / CNC Bored" carb. Evidently the stock form factor carb requires that spacer. After looking at the spacer's little vent groove, and remembering the puzzling little vent hole in the gasket & how it lined up with a vent path on the head-side of the carb, I had that "well duh?!" moment. Thank you Eric @ OldMiniBikes Warehouse.

It runs great off choke, but sputters a bit at high RPMs. On to the next learning experience.

 

[Nickj276]

The best thing to is buy 22 mm mikuni carb kit it willl really wake up your engine stock cam and valves works great with the factory jet in the mikuni that my advice the best Angkor. Your buck to


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