Starting Point For Idle And Main Jets

[Hellion]

I've been eying the 6 or so inch long curved ones. Any advice or recommendation about that?

How much of a curve? There’s a few guys trying to run the U shaped ones (to where the carb is above the engine and out of harms way) but it does something funky to the A/F mix and the charge. Requires more tuning and Excedrin.

 

[Wicked_Daddy]

The issue with the curved manifolds is that they are 22mm. At least the one I have is. So it seemed a mismatch/waste to fit a 22mm manifold on a 24mm carb. The Nibbi manifold is made for the carb. That said, the intake port is about 20mm but the intake valve is 25mm. I ported my intake with a Dremel to match the manifold and taper it into the 20mm remaining distance to the valve. In theory, this would cause a venturi effect that will speed the flow of mixture into the chamber and provide the associated increased burn rate of the flame front for more complete combustion - thus my lean condition until I provided a richer mixture.

 

[OneTimeUser]

How much of a curve? There’s a few guys trying to run the U shaped ones (to where the carb is above the engine and out of harms way) but it does something funky to the A/F mix and the charge. Requires more tuning and Excedrin.

The ones I've been looking at are a bit less than 90 degrees and horizontal. "Some" say that the extra distance is better for atomizing and performance.

I'm over my head at this point 'cause I only understand the basics of carburetors.

 

[Whitetrashrocker]

Yes, long intake runners have better low end torque.

 

[panchothedog]

WTR,

You were spot on. I had leaks at both ends of my cheap Amazon manifold. The rubber gaskets are junk. I fixed one by tightening, but the other remains despite some torque and some gasket sealer.

It is better over all, but I'm now on the hunt for a new manifold.

I've been eying the 6 or so inch long curved ones. Any advice or recommendation about that?

Thanks again.

Yes. Don't buy the Amazon cheapie. We usually get what we pay for.

 

[Edwin Spangler]

Welp, I went to a 48 idle jet yesterday on the 212. I feel like that needs to be said after my previous comment.

 

[Edwin Spangler]

Yes, long intake runners have better low end torque.

I have found that they help the cheap carbs run better also.

 

[Edwin Spangler]

Yes. Don't buy the Amazon cheapie. We usually get what we pay for.

GPS sent me a manifold with both faces bowed. Light shown thru both sides.

Since then, I have resurfaced all intake mating surfaces that I mess with. Just glass and 220-400 sandpaper.

Trying to "tighten the leak out" has been the cause of several intake stud re-tappings.

 

[OneTimeUser]

GPS sent me a manifold with both faces bowed. Light shown thru both sides.

Since then, I have resurfaced all intake mating surfaces that I mess with. Just glass and 220-400 sandpaper.

Trying to "tighten the leak out" has been the cause of several intake stud re-tappings.

This.

I torqued to the max (calibrated wrist) and plan first to resurface as you mentioned and find new orings for both ends. Chinese rubber parts seem to be especially bad. Bellows boots on things like master cylinders and cable ends seem to last about 6 months.

These days I see the same Chinese-made items on Amazon, and also often at Lowes, Tractor Supply, and even some auto shops.

 

[Edwin Spangler]

Chinese rubber parts seem to be especially bad.

Yes! Ive noticed its affected by gasoline MUCH worse than rubber from Nibbi or something.

Removing the bowl for example. If I get gas on the o-ring of one of the Chinese carbs, its a huge hassle to get it to fit again. The Nibbi on the other hand, I just remove that bowl full, gas all over the o ring, no problems.

 

[OneTimeUser]

Yes! Ive noticed its affected by gasoline MUCH worse than rubber from Nibbi or something.

Removing the bowl for example. If I get gas on the o-ring of one of the Chinese carbs, its a huge hassle to get it to fit again. The Nibbi on the other hand, I just remove that bowl full, gas all over the o ring, no problems.

I've had the same experience. Come daylight I'm going to hand lap the cheap Amazon manifold and go in town to the air and pump guy who has a seemingly endless assortment of orings (and other such things). I think with a bit of hand lapping and a new oring I can solve my immediate problem leak while I do some more research about a new, longer, and curved, manifold.

I'm just about done building this cart. A new center-mounted solo seat will finish the job.

FWIW I'm very pleased with the electric start Tilliotson 212. It's stronger than the Predator I had and quieter too (go figure--because it has the same exhaust on it that the Predator had). They were on sale for a while for about $350. I snagged a couple of 212 predators when they were on sale for $99. They are spares that will most likely end up on the log splitter or a generator when the time comes.

I'm resisting the urge to hot rod the Tilliotson with a cam and stuff 'cause it's plenty fast for me now and I don't want to compromise it's reliability.

 

[Hellion]

Hey we could all benefit from a pic or link of the cheap a amazon manifold(s). Show us what you’re working with. O.T.U. or E.S., don’t matter who

 

[Edwin Spangler]

Hey we could all benefit from a pic or link of the cheap a amazon manifold(s). Show us what you’re working with. O.T.U. or E.S., don’t matter who

PWK 24mm and 34mm.

 

[Edwin Spangler]

View attachment 164569View attachment 164570



PWK 24mm and 34mm.

Also, I DO NOT recommend these things. Theyre terrible. You have to be SO GD precise with tuning. Ive been thru several now with various engines and I havnt found one that runs acceptably whereas the name brand equivalent runs smoothly even with poor tuning.

If at all possible, avoid and get name brand.

 

[Wicked_Daddy]

Pics:
- Nibbi on a curved Amazon manifold (22mm) - worked good, no leaks. I was also concerned about the vibration being amplified by the manifold and ultimately weakening the threads in the head.

- Nibbi on a Nibbi manifold - held together with a rubber sleeve (comes with it). This one is on a 196cc that I built and currently doesn't have a home. (searching for a minibike roller I can refurb).

- Nibbi on a Nibbi manifold - all bolts. This is my current Kart engine and it screams. The picture is just a zoom in so, excuse the clarity.

 

[OneTimeUser]

OP here. This is a 24mm round slide Nibbi mounted on a Amazon manifold that originally came with the very cheap Amazon 22mm carb that I first tried to use.

After a bit of hand lapping, and with the help and advice of a few of y'all, I got the carb mated properly with no leaks. BTW, the original Amazon carb had the same problem since I first put it on--namely, I couldn't get the A/F mix properly and it ran at high idle even with the idle adjustment all the way out. Apparently, the cheap manifold was the problem all along.

That's why you see some hot glue holding the red adjustment knob on to the idle screw itself. With no tension on the idle adjustment screw I was afraid it would back out and fall off. At one point I had a length of fishing line tied to the red knob in case it rattled out.

My vacuum leak is now gone, the idle adjustment now works, and all is well in Whosville.

I'm still pondering on getting a longer curved manifold. I'm told it will increase low end torque, though I don't understand how that might be the case.

 

[OneTimeUser]

And, here is what AI has to say about a longer manifold.



A longer intake manifold increases low end torque because it enhances air velocity and improves cylinder filling at lower RPMs. This design allows for better performance in the low and mid-range powerband, making it ideal for street vehicles.
jegs.com team-bhp.com

Impact of Longer Intake Manifolds on Low End Torque​

Air Velocity and Cylinder Filling​

A longer intake manifold enhances low end torque primarily by improving air velocity. This design allows for better filling of the engine's cylinders at lower RPMs. The mechanics behind this involve the following:

• Pressure Waves: Longer runners create a more favorable environment for pressure waves, which help in drawing air into the cylinders during the intake stroke.
• Increased Port Velocity: The longer the runner, the faster the air charge travels, resulting in higher port velocity. This is crucial for effective cylinder filling.

Performance Characteristics​

The characteristics of longer intake manifolds make them particularly suitable for specific applications:

• Low and Mid-Range Power: They are optimized for performance in the low and mid-range RPMs, which is where most street vehicles operate.
• Torque Production: By maintaining higher air velocity, longer runners contribute to stronger torque production at lower speeds, enhancing overall drivability.

 

[Whitetrashrocker]

Chrysler used a long ram intake back in the 60s on their land yacht cars.
They needed all the torque and these old boats felt peppy because of it.

 

[Denny]

Unfortunately top end suffers. Even the Chrysler cross ram started running out of breath around 5,000 rpm. By 6,000 it was way past done. And that was a multi-cylinder engine.

 

[Edwin Spangler]

Its always a trade. If you want high RPM power, your low end will suffer. If you want low end power, you wont get much RPM.