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Old 11-29-2019, 07:11 PM
Mrmonk7663 Mrmonk7663 is offline
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Default Tav 2 help

Ok guys I need some insight. This is on a minibike but it is for the tav 2.

Build:
196
Head shaved .070
Ported/polished
18lb springs
32 degrees timing on stock flywheel
Billet +.020 rod
Stock piston
Mikuni vm22
Staged Header
Upgraded msd wire
3910x plug
Cl1 cam
Rider+bike=260lbs

Tav 30 series, 6” driver with white springs, 3100 rpm engagement
19” tires.

Gearing- 50/8, 50/9, 72/10

I ran the engine first with 50/8. Driven on middle setting with green spring. Bike hit 41.x mph. Rpms were about 4800. I thought maybe I needed more gear to gain rpms. Switched to 72/10. Bike hit 5100 rpms, still showing 41mph, and did NOT feel as peppy. Switched to 3rd hole on driven...still same. Switched to 50/9 on 3rd hole. Bike felt peppy like it did on 50/8 but still 41mph.

Tried moving main jet up and down. Still 41-42mph.

Bike isles great, mid range is great, top end doesn’t break up and it isn’t excessively popping. Seems good.

What is preventing the bike from going faster? I know the cam is small and I have a lager 265 cam on order, but I still don’t understand why the bike won’t rev higher. I thought the lower 72/10 would make it rev deeper but all that did was shift to OD quicker.

Am I missing something. The fact that I’ve tried huge variations in gearing along with different driven settings leaves me at a loss. All I can fathom is the head work and mikuni are too much for the small cam.

Thanks!
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Old 11-29-2019, 09:24 PM
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is that a 7" driven? or the std 6"?

to check where your peak torque currently sits,
you might be able to just swap back to the original weight/garterspring set
(engagement 2200) without changing the gear ratio

to see if the bike accelerates as well, better or worse.

that gives you a rough idea about if the torque was shifted up as expected.

talking of which.. any chance you know what your original timing was set at?
different clones have different stock settings (anything from as late as 20 BTDC to as early as 28 BTDC is still possible)

How was your 32 set?
relative (+8 of stock timing with the assumption it had 24)
or absolute to 32 carefully setting the timing disc to TDC?
or just by popping in a bought offset key?

reason I'm asking is you might have your engine firing too late/early for your setup..
maybe the key is the wrong wa around, maybe the timing dial slipped,
maybe your engine was at 28 to begin with and all you got is a 4 advance in the end...

Unable to tell from here, but it might be worth checking.
especially since you say idle and mid range are great but top end lacks power.

Oh wait.. if you got a tachometer.. set the idle as low as possible!
that can also give you a clue about the current timing..
Assuming a stock engine (idling @ 1400 rpms with stock timing [1800 on some clones])
it should need about 1500-1600 rpms with an 8 key at least to idle just as well.
a swapped 8key can bring your idle down to 1200 rpms without it struggling...
essentially 200 rpms of difference as a rule of thumb either way.

and while increased compression and cam do change the idle as well,
timing is still a major factor and could give you a clue if your timing is off.

I'm not going to tell you what a stock flywheel and 18lbs springs can cause,
I bet you heard all that more than once already.. .. I just want to remind you that you ought to be cautious

I mean for now with only 5k max at any given setup.. nothing much to worry about really,
if you however manage to crack the 6k rpms you might want to think about a billet flywheel IMHO.

So with that out of the way,
if you double/triple checked the timing is correct (at 32), and the
swapping of garter springs indeed verified the torque to be shifted towards mid/top end further
(sluggish acceleration with blue springs)
oh keep in mind that a lower rpm always has a "gentler" acceleration of course it should still feel "as or more powerfull" less punchy though.
more rubber band, less mallet smacking so to speak

then all there's left is to check your fuel mix..
floor it as long as you can under load,
and then flip the killswitch and as quickly as possible get a spark plug reading
(take a set of good photos of the business end)
Do not forget to bring your gloves.. it'll be toasty after a few full speed minutes

Might be you just need a slightly larger jet...
might be you need a bigger carb entirely but IMHO a vm22 should be good *headscratch*.

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Old 11-29-2019, 09:56 PM
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Engine was a coleman 196. Timing is assumed 24 degree. I was told some of the clones even came at 18 degrees...so yes it’s an assumption. I used 9.1 degrees advance over whatever it originally was.

Bike will idle sub 1000. I can have it idling at 900 flat if I want...which surprised me actually. So you are saying this might be an indication of the key backwards?

Driven is std. 6”. It revs to 4600 rpms almost instantly after takeoff and remains there until overdrive at which point it creeps a few hundred rpm more. I have a 140 jet in it now. I tried a 155 but didn’t see any change.

Timing key was installed properly I THOUGHT...maybe not. If I launch the bike it will literally flip over backwards. It has power. Just not the rpms.

I’m going to swap to an aluminum 3.1 pound clone flywheel when The new cam arrives. At that point I’ll recheck to make sure the key is correct.

As far as the carb...if I was overly lean I would expect some breaking up and hesitation...but it doesn’t break up at all. It’s very weird. Maybe it will turn out to be something as simple as the key in the wrong position. Fingers crossed it’s something as simple as that, but I distinctly remember having the step toward the front of the engine and rotating the flywheel clockwise to rest on it. Maybe it rolled back before tightening. I’ll find out later this week I guess.

Thanks Sid
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Old 11-29-2019, 11:36 PM
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Quote:
Originally Posted by Mrmonk7663 View Post
Bike will idle sub 1000. I can have it idling at 900 flat if I want...which surprised me actually. So you are saying this might be an indication of the key backwards?
might be an indication at least..
@900 rpms most clones will certainly have a sincere hiccup

by coleman 196 you mean a coleman bike with some sort of gx200 clone?
IDK what's on there tbh.. but rato r200 and Loncin lf168 idle at 1800rpm stock.. (Lifans and Ducars as well as Hondas @ 1400 IIRC)
sooooooo yeah quite a difference..


18? quite possible on low speed setups (fixed half speed engines and such)
but you used a relative offset (via key)
so you should be fine with the key correctly oriented.
just to be sure:
key should offset the flywheel in a clockwise manner.
(notch to the left if keyway is pointing up)

And with the rest of your description I think this is amongst the first things I would want to have checked

140 main frankly IDK.. sounds right to me.. but that's my guts speaking

Since you are currently on the highest ratio listed (9->50 you said, right?)
swap the garter springs to the blue ones,
you won't gain speed, but lighten the load on the belt significantly
and get an as powerfull but smoother acceleration I bet.
chances are with the mods you have you might even be able to run @ 5:1 (10->50)

especially since your engine revs as low as it does,
you are just wasting rpm band at the moment

Or test the timing advance w/o removing the shroud or startercup...
there's a notch in the starter cup and a cut in the airshroud
(well on gx200s and the clones I have that is...)
That marks TDC with stock timing since the cup is indicated on the flywheel...
remove the spark plug and use a stick poking out the sparkplug hole
to see if the piston is rising or dropping as the notch passes the mark on the shroud..
if it's still rising just after the notch passed the mark your timing is advanced..
it it's already dropping before the notch apsses the marking you inadvertently retarded timing instead.
(man I hope I haven't messed the logic up...)

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Old 11-29-2019, 11:53 PM
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Haha I understand what you mean. I need 3100rpms currently to get going...have no upper rpms...so might as well lower engagement.

Engine is off a coleman bike. Hisun 196cc

I just finished taking the flywheel off. Key was orientated correct I believe. Flywheel was almost 6lbs. New flywheel is 3.1lbs. I’m using a new offset key with it. Per the supplier it should put me right at 32-33 degrees. I’ll hold the other side of the crank to make sure the flywheel rests against key. It’s also been suggested to shove a toothpick in the keyway void to prevent the flywheel from rotating back while tightening...couldn’t hurt I guess.

Only other thing is coil gap. I was running around .090...maybe I should tighten it up to around .050. I have read anecdotal stories on big coil gaps causing retard in upper rpm range...maybe that’s what was going on. Any idea what the stock clone coil gap is with stock flywheel? This definitely could be part of the issue now that I think about it.

Here is a picture of how my key is oriented to make sure I haven’t lost my mind just yet.
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Old 11-30-2019, 10:07 AM
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yeah that is correct installation..

increased coil gap makes a weaker spark.. but all around for all I know,
if it retards timing in upper rpms noteworthy IDK.. never heard of that before.

coil air gap on Honda GX200 is 0.4 to 0.2mm (~ 0.016 - 0.008")
on clones IDK bit I doubt five to ten times that is okay let's say.

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Old 11-30-2019, 10:37 AM
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Wow the gap on the gx200 is incredibly tiny. I didn’t know it was that small. I set it up like I did my arc flywheel in another engine. I’ll tighten it up and see what happens.

If anyone else has info on STOCK coil gaps for clones/predators with stock flywheel please chime in.
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Old 11-30-2019, 12:18 PM
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Rato R200 (196cc) and R210 (212cc yes that is the predator)
according to the Rato shop manual have to be set to 0.4-0.6mm
(0.016-0.024" roughly)

No info on lifan, loncin or ducars so far...

other than that here's a few 'opinions' from 4cycle..
https://4cycle.com/karting/threads/c...uestion.66275/

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Old 11-30-2019, 01:50 PM
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FYI 0.016" is not a tiny air gap. Briggs flatheads are 0.010" as specified by Briggs. Whatever the spec is, just follow it. Manufacturers probably know their engines better than you.
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Old 11-30-2019, 01:53 PM
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Good info Sid. I’ll set it to .020 this time around. Hopefully that’s the issue. Good learning experience if it is.

The gap I was using was based on Arc info. Since they use rare earth magnets it doesn’t apply to stock flywheels. My mistake. I’ll own it and use what sid provided.
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Old 11-30-2019, 08:36 PM
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Air gap set to .021. Flywheel changed to 3.1lb unit. New top speed...same as before. No difference. Same rpm. Safe feel. Same speed. Only other thing I can fathom is the cam is holding back engine. Other than the cam I think I’ve tried everything.
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Old 11-30-2019, 08:43 PM
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huh?
Now I am indeed confused..
I'd almost say you'll have the governor still in place (4100 is still in it's capabilities),
but I doubt that'd be the case really, with a cam mod you certainly have no reason to keep the governor in.

BUT: just maybe the throttle cable itself is unable to fully open the carb..
could you ask a relative to twist that throttle for you
with the airfilter removed and you peaking inside. to see how far the plunger raises?

ideally post a few pics of how the throttle is connected to the carb..
and maybe some views of the engine itself
just so we can get a better idea.

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Old 11-30-2019, 09:01 PM
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Throttle open. Throttle closed. And a couple more pictures. Im lost. The bike is fast. Runs great. But yes its like the governor is in...and it obviously isnt. It is completely removed.
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Old 11-30-2019, 10:22 PM
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Thought-I have a 3203 kart. I initially put a 6” driven on it. Based on tires and gearing speed should have been 42mph. Motor is stage 1. 60/8 gearing 20” tires. The kart would only hit 37 mph.

I swapped to a 7” driven. Kart hit 37mph and matched the theoretical speed for tire/gear ratio.

Perhaps swapping to a 7” driven might help on the minibike as well? Almost everyone who has high rpm issues that I’ve read about use the standard 6” driven. Haven’t seen any minis with a 7” driven.
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Old 11-30-2019, 10:28 PM
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hmm.. and that's throttle opened on the handle bar, right?
(I assume it is, but clinging to some straw )

yeah well.. I'm out of ideas tbh..

No weird sound when it gets up to speed, no 'abnormal' behaviour (like you would get from floating valves, a kicking in governor or a rev limiting coil)
it just won't rev up any further but doesn't miss a pop or start choking...

too strange..

You checked the spark plug already?
(maybe tried a different plug to know yours' not faulty)

The next thing I would do is check the head gasket (peaking under the shroud to verify there's no blow by visible. at worse rattle on the head bolts to check if they're tight,
at best click torque them to spec once more)
recheck the carb manifold to verify no bolt rattled loose leaning the air mix.
doing both with a warmed up engine.
and check valve lash once again..

I'm fairly certain you aligned the markings on the cam/crank correctly..
otherwise I'd be impressed the engine runs as good as it does!
but right now there isn't much left to check IMHO.

if you can jack up the read and mount a tach to the engine,
a very brief top speed dry run would be interesting
just to see how high the engine will rev under minimal load (just the transmission and wheel)
and then a road test thereafter..
just to see what's the exact difference between with and w/o load.

Some issues are load dependend some are not too much...
maybe we can get a better idea of what's going on that way *shrugs*

Anything you forgot to tell us about perhaps?
A tacky lifter fighting you when you swapped the cam?
Excessive need for adjustment of one valve over the other?
you might have forgotton to verify TDC on compression stroke with a feeler gauge
but took the startercup marking as a guide?
IDK and I am sorry that I'm making it sound like you cannot tell left from right..

but
from my guts I'd say that bike should be good for 50-55mph or something
(260 lbs total, right?)
and with just 41mph there's likely something wrong,
and I cannot imagine what that might be.. so I go through all that pops to my mind


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Old 11-30-2019, 10:53 PM
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Haha no it’s a good run down of possibilities but unfortunately all the boxes are checked. Head bolts and manifold just checked. Spark plug-used stock plug and also used 3910x. Same result. No better or worse.

No anamolies while assembling. Lash set on compression stroke at TDC. Bike starts first pull everytime.

I performed the freewheel test and I hit 6krpm extremely fast NOT wide open throttle. It’s 11pm and bike is ridiculously loud so that’s as far as I took it. I swear it’s the **** converter. It’s not broken but I think the excessive power makes it go to OD way way too fast or something and once it’s in OD the converter resists going faster. I don’t know honestly. But the engine is good. Of that I’m sure. I have ridden it a dozen times or so. Many full throttle runs. It is repeatable in its performance and repeatable in its rpm restriction.

The freewheel test kind of indicates a load issue...probably from the tav. I just don’t understand it and while I’ve seen it discussed, no one ever had a good solid explanation of the phenomenon.
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Old 11-30-2019, 11:03 PM
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Did oil get onto the belt or pulley faces somehow causing it to slip?
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Old 11-30-2019, 11:19 PM
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No. Good thought but no. Belt is fine and dry. This is a problem that only really is seen with the higher power builds. A lot of folks I am talking to in other areas who drag race have had this issue. It’s something with how the 30 series is designed in conjunction with the overdrive. It’s most likely not a common issue on this forum as it’s mostly karts for the yard or dirt here. Nevertheless I know we have some really talented and educated folks here. Sid is always a great help with technical issues and technical diagnosis.

This might be a better question that can hint at an answer...what does a 40 series do over a 30 series. The 40 is designed for more torque and power. But it’s not a strength issue of 30 vs 40. The 30s don’t blow up and break from more power than intended...so what is different on the 40? It has no overdrive. What else is different? I’m betting that may be the key to answering this problem.
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Old 11-30-2019, 11:59 PM
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If I’m correct, the difference between the 30 and 40 series torque converters is the belt. The 40 series belts can take more power than a 30 series belt.

Now for some stupid questions:
Have you checked the tire pressure lately? That can put extra load on the engine.
I noticed you said you replaced the original ignition wire with an msd wire, is it possible that the connection is bad?
Are all the bearings good (axle, backplate, engine mains)?
Are the chain and sprockets in good shape?

We’ve gone over almost all the engine, it’s probably time to check elsewhere for the problem. I’m pretty sure it’s going to be something that’s so obvious/stupid that it’s being overlooked.
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Old 12-01-2019, 12:21 AM
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All bearings, chains, tires are new. Backplate of tav is new. Crank bearings are not new but low hours and no wear/slim butter smooth. The coil has a good connection. If spark was breaking up I would feel that. When it hits this “wall” nothing out of the ordinary happens. Bike doesn’t begin to hiccup or stutter or miss or anything. No erratic rpms. Nothing that would make you think suddenly you had a spark problem. Exhaust note does not change. Nothing changes...except it doesn’t climb further.

I wish it was something simple and stupid but I really think it’s the nature of the 30 series.

So at this point the game plan is as follows. Buy 7” driven. See if anything changes. Install aluminum weights in driver. See if anything changes. And install new larger camshaft. This will probably take 2 weeks with shipping and what not. After that if I still don’t get the rpms the engine is capable of then I’m leaving it alone, and on my warrior build I’ll just use a clutch and jackshaft setup.

I could potentially swap to a normal stock wire coil just for a Hail Mary, but I just don’t see any indication it’s the problem.

Another question...anyone reading this build a modified engine similar to mine and successfully reach >6500 rpms?

Someone wrote this to me but it went too far away from my knowledge base to understand it all....Sid might make sense of it....

“ The wall your hitting (I’m assuming) is the OD Ratio of the torque converter transferred to the jackshaft final ratio. diameter, length, weight, and counterbalances throughout the drivetrain system all come into play when rotation speeds get up there. You gotta think of all the rotating parts some fixed and Some spring loaded and some engaging with centrifugal compression. So think of all the laws of motion, and then the inertia of each piece of the TAV system, and the constant pull back from the driven pulley, and also belt becoming sticky as it gets hot. Just abunch of opposing forces hittin the point of equal force of the engine output.
So if your want is to achieve +6000rpm while using a TAV look into 2stroke, do the math to figure out what inertia you need at the crank to push past the opposing forces of your drive train at the rpm range your looking for. Try a nitrous system, try do spark plug temps. Get a tri-fuel carb and experiment with different fuel types.

Or just run a smaller tire. If you know you can run past 6k then drop you tire size down a couple inches and you’ll be surprised at the out come.

If your looking to learn some gearing knowledge for low hp high rpm do some research on rally car transmissions.
Also Nissan’s run Tav style trans in a lot of there vehicles so if your lookin for nice spec data and power to weight ratios look there.”
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