Predator 212 with mikuni style carb

[Rat]

Thanks for the detailed answer!
Do you think that starting with the springs, rockers and coil (for now) will make an improvement in the RPM?

Springs, keepers and coil definitely, the rocker swap is a safeguard that has no primary connection to performance. You swap so you reduce risks that come with cheap mass produced stock parts.
The stock keepers don't preload the springs tight enough, and also are not intended to contain 18lb springs at 6500-6800rpm and using them at that level is a dropped valve bound to happen

Also -just for my understanding, in order to gain more RPM, do i need a stronger or a weaker valve springs?

The spring weight isn't for gains, it is to reduce loss. Most stock springs are 10.8lb which float at 4k-4500rpm.
If you're floating the valves you are spinning the cam faster than the springs can fully close the valves before the cam lifts them again which is the point you completely stop making more power and risk jumping a pushrod out of it's rocker. The engine makes a distinct stuttering sound when you're floating the valves, and backing of the gas just enough to make that sound stop goes a long way for safety.

Stiffer springs close faster, this makes more rpm potential available. Running 18lb springs can run up to at least 6800rpm no problem.

I haven't really tried spin my 208 harder than that and won't until I can find a better flywheel that still supports the charging stator.

Not all iron flywheels are equal and very few can handle more than 4800 rpm so the fact I spin it as hard as I do says a lot for LCT engines (Husqvarna) probably says I'm batshıt crazy or suicidal to most though.

 

[david-ab]

I changed the iron flywheel to a billet aluminum one, so technically I can run it on higher RPM?

 

[Rat]

I changed the iron flywheel to a billet aluminum one, so technically I can run it on higher RPM?

No technicalities about it. Idk what the billet ones are tested at, but I'm sure it's higher than the cast aluminum PVL flywheels which are all balanced and QC'd to 17k.

It doesn't matter what the individual parts are "capable" of handling if the parts as a whole do not play well together to get there.

Like for example you could put a Dover Coil on a full stock engine, but it serves no purpose because the valves will still float at 4800 or so rpm.
You can put heavier springs in without said coil but you're going to be rev limited by the coil at around the same rpm IF you're lucky (some lose time as low as 4300 others can keep pace up to 5k)

Nothing by itself is useful, but everything playing their part to improve the sum of their whole... that's when the real fun happens

 

[david-ab]

I changed the iron flywheel to a billet aluminum one, so technically I can run it on higher RPM?

I think you didn't quite understand what I was trying to ask, let me rephrase that (English is not my native language )
By changing the stock iron cast flywheel to a billet aluminum one, I can run the engine with higher RPM without the risk of exploding the flywheel, right?

 

[Rat]

I think you didn't quite understand what I was trying to ask, let me rephrase that (English is not my native language )
By changing the stock iron cast flywheel to a billet aluminum one, I can run the engine with higher RPM without the risk of exploding the flywheel, right?

Yes.
High rpm is what the Cast PVL, and Billet ARC flywheels are for

 

[Rat]

I think you didn't quite understand what I was trying to ask, let me rephrase that (English is not my native language )

BTW, I understood the question perfectly fine; perhaps it is you that misinterpreted my response.
I tend to go overboard in detail at times which if one is not a fluent user of English, can be confusing.

You said you got a billet flywheel... and billet is stronger than cast and more uniform at the microscopic level.
I do not know what the QC testing is on billet flywheels, however I do know that the cast aluminum PVL flywheels are balanced and tested by being spun up to 17,000 rpm and kept there for a moment. They either explode or pass that test.

This is where logic and reasonable deduction indictates that if billet is better, than you will never be able to spin it fast enough to even get close to having it frag. If forced to come up with an educated guess, I'd estimate the billet probably being able to handle 30,000 rpm or more.

 

[david-ab]

UPDATE:
Hey guys, so after a looong wait I finely got the upgrades for my 212 predator - a dover coil, 22lb springs, Performance Valve set and a 1:1 ratio Shaft Rocker assembly.
I have some questions before installing the parts:
1. what is the recommended gap between the flywheel and the coil?
2. what is the recommended lash gap for the rockers?

 

[bob58o]

Stockflywheel? About 0.035” I believe. Let me double check. This document says 0.015” for the air gap on Honda gx style engines. Actually this document says 0.150” so don’t listen to that.

 

[bob58o]

Here ya go.
0.006” on intake.
0.008” on exhaust.
0.016” on the air gap.

 

[panchothedog]

If you have an aftermarket aluminum flywheel set the air gap .040" to .045". For your shaft mounted rockers, set both the intake and exhaust at .003" cold.
.006 and .008 cold is way too loose. At .008 on the exhaust, the compression release will hardly engage.

 

[panchothedog]

The measurements I just gave you are specifically for a predator 212 engine. I have built 7 of them over the last 4 years. I am not guessing. These are measurements that work.

 

[david-ab]

thanks for the info!
I've got a cast aluminum flywheel, what is the air gap for it?

 

[panchothedog]

.040" to .045". A cast aluminum flywheel IS an aftermarket flywheel. Meaning it is not a stock factory flywheel.

 

[david-ab]

Guys I'm in the middle of installing the engine and I need some help.
I got a set of performance valves from eBay ( see attached pic), and before placing the order I checked if some modifications were needed to the valve body, and the seller said no. While installing the valves I noticed that they didn't fit- the stock one have a 4.9mm stem and the new ones are 5.5mm.
Is it normal? Did I get the wrong parts? Do I need to reem the valve body ?

 

[panchothedog]

The early predator engines used valves with 5.5 mm stems. The later ones use valves with 5 mm stems. If you can return for a refund the 5.5's , I would. Reaming out the valve guides is certainly possible, but so is messing them up. Then you need to buy a new head. I don't buy much from E bay, so I can't tell you anything about them. I have purchased 2 or 3 sets of 5 mm stem valves ( the ones you need) from OMB Warehouse, and E C carburaters. Buy the whole set together, as the keepers and retainers for the 5.5's will not fit properly on the smaller stems. Setting the scenario for a complete disaster.

 

[panchothedog]

After looking at the pictures you posted is another reason I don't like E bay. They don't even bother to tell you the stem size. Anybody selling parts for a predator engine should be completely aware of the 2 different sizes. Also the add says machined valves. What are they made of. The ones you buy from legitimate kart supply shops are Stainless Steel. The kind that won't break with stronger valve springs, or at higher rpm. Look for your hop up parts in the right places.

 

[david-ab]

The stock keepers and retainers will not fit this type of valves?
Man I'm so pissed right now, I waited 2 month for this parts and the shipping cost me more than the value of the package...

 

[panchothedog]

I am guessing what you posted is your communication with the vendor. You said somewhere that you have 1 to 1 shaft rockers. Are they champion brand, or the Chinese imitation knock off. The reason I ask is because I run champions on 3 of my engines. They are great. They do not fit under a stock rocker cover. Offering you a 2nd gasket to supposedly gain clearance doesn't sound like enough. You can cut out the baffle in the stock cover. You can purchase a spacer to lift up the cover, or you can purchase an billet aluminum cover that is tall enough.
As I said in post #36, you should be buying your parts from legitimate kart supply shops.

 

[panchothedog]

The keepers and retainers need to correspond with the valve size.

 

[Darren]

You probably require 'automotive style' keepers.
You can buy 5.5mm valve guides but these might not fit your head.
Why did you purchase the valves? Upgrades are normally stainless, but unless your going to do a whole lot of other work on the head, I wouldn't bother.
Get the head flowing the gases first.
Standard progression on getting these little power packs working well, is to use better internals then gas flow the head, de-restrict the inlet and exhaust and alter the ignition timing. At this stage you're still not pushing passed 5500rpm and the engine will have gained 1.5-2hp.