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Old 08-24-2019, 07:25 AM
onionfmr onionfmr is offline
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Default Trailmaster MB200-2 Engine RPM, TAV & Gearing

Looking for some advice, pointing in a direction. I've been working on this build for approximately a year. Getting close, but kind of hit a wall in terms of performance. Here's the general information of the build:
Tillotson 212 Hemi.
Billet flywheel and rod.
.010 head gasket.
CS 265 cam, 7000 max RPM.
26# valve springs.
Mikuni VM22-133 with 20 pilot and 140 main jets.
Chinese TAV with 146 gram weights, white garter springs. Driven spring in 3rd hole.
10 tooth jackshaft sprocket and 50 tooth rear sprocket.

Engine will hit a top RPM now of 5,500 RPMs at full throttle and then fall back to around 5,200 RPMs if the throttle is help open. Top speed at approximately 550 feet on a GPS is 45 MPH. RPMs top at 5,500. That's it. I'm guessing that I might pick up a little RPMs and top speed if I held the throttle open over a longer distance. Based on the feel of the engine, it isn't pulling hard at this point. Kind of flat.

I would like increase my top speed to around 51 MPH over this distance. I'm thinking of changing to the blue/silver garter springs and to yellow spring in the driven unit. Realizing that I can change gearing to accomplish more top end, but will lose on the low end. I would like to get more RPM out of this engine maintaining my existing gearing. Here's the question. Would swapping to a different cam, head work, etc.., allow me to build more RPMs or am I stuck because of the TAV and the gearing and need to change gearing (60 tooth rear sprocket) to get more out of this engine package? Thanks in advance for any comments and suggestions.
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Old 08-24-2019, 09:17 AM
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easy to find out..
easy to tell if you can/should change the ratio..
if the TAV is in overdrive at full speed (best clip an actioncam at your front frame and have it point towards the uncovered TAVKit.
That'll show you if you reach overdrive and can be held there.

if it cannot be held in overdrive you are lacking torque.
and thus should not gear any higher (youd be slowing down instead)
instead you can try to gear ever so slightly lower to keep the torque,
sometimes when you're right on the edge a lower gearing indeed results
in higher top speeds since the engine can rev to higher rpms.

hows the ignition timing? non-adjustable ARC flywheel? [i.e. 8 advanced]
or what?

I think we'd need a wheelsize and total weight (you and bike)
to get a better calculataion.

what I don't understand is why someone wants 4000 rpm pass unused
to use nothing but the upcoming 1500,
especially since all that does is ruining the belt.. exact same ratio with a lower engagement speed is as fast maybe a hair quicker but much easier on the belt.

I'da lso check for takeoff speed tbh..
since that's a very important value most ignore entirely..
"but I want 60mph" so the kart has to go @ 40mph the instant I hit the throttle since I only have 1400 rpm to work with (sounds familiar?)

So.. if I'm not mistaking the MB200 has a 19" rear wheel..
that makes a 5:1 geared engine @4000 rpm 50+mph fast! (in overdrive)
and you need ~20mph to even fully engage the clutch)
so you just burn the belt until you reach 20mph essentially..

swap to the stock weights, that'll drop engagement speed to 3100 rpm with the white garter springs that'll drop the engagement speed to 14.some mph which I say is a much nicer value

Post a pic of your belt please.. I'd love to see how it held up to your abuse.

How you got the rpms read btw..
since frankly if you haven't cracked the 50mph yet..
you couldn't have revved up to 4k rpm yet
you sure the governor is removed?
since 45mph very much sounds like it is intact

(top speed @3600 rpm and 5:1 ratio tavkit on 19" wheels means 45.22 mph... rings a bell?)

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Old 08-24-2019, 09:49 AM
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Quote:
Originally Posted by itsid View Post
pointless quote removed
Thanks for your reply,

Last edited by itsid; 08-24-2019 at 09:33 PM.
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Old 08-24-2019, 12:54 PM
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So basically you are not in overdrive it sounds like. My kart with the tab does the exact mph that my gear ratio and tire size and rpm indicate. With enough power, which you have, you should also. I think SID is correct about changing the springs.
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Old 08-25-2019, 07:11 AM
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Quote:
Originally Posted by Mrmonk7663 View Post
So basically you are not in overdrive it sounds like. My kart with the tab does the exact mph that my gear ratio and tire size and rpm indicate. With enough power, which you have, you should also. I think SID is correct about changing the springs.
I've tried different weight and spring combinations in the drive unit. With stock weights and white springs, the best that I've gotten with RPM was 5,000 RPM @ 41 MPH. I'm starting to think that there may be an issue with my driven unit not working or opening correctly?
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Old 08-25-2019, 07:38 AM
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I think we still need to know what size your wheels are
and while we're at it,
we also need to know what kind of weight has to be moved
(bike and butt)

Since we need to find out what torque requirements you have
and where that falls short.

I cannot imagine the heavier weights preventing a full rev (not at a decent gear ratio that is)
and i cannot seem to believe that your 5:1 ratio is that bad

Now, please check again the toothcount on both sprockets
what it says on the sidewall of the rear tyre
and of course what your bathroom scale says about you and the bike

Post a few pics, of the bike and TC (cover removed.. we like to see your belt and the state of the sheaves)

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Old 08-25-2019, 02:28 PM
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I thought that I posted list of answers to ITSID's questions yesterday morning?

Tire size is 19"
Governor has been removed from engine as I'm running a genuine Mikuni VM22 -133 carb with 20 pilot and 140 main jet.

Combined weight of bike and rider is 340 lbs.
Flywheel is ARC with 32 degrees advance.
Jackshaft sprocket is 10 tooth and rear sprocket is 50 tooth.

Running CS 265 cam. I talked to Dyno Cam personnel and they indicated that @5500 RPMs, I'm just starting to get into the power curve of the cam. I need to run in the 6500 RPM range to get to power curve.

Chinese TAV that was standard on the mini bike when purchased. Running 146g weights and white springs in the drive unit. Driven unit spring is in 3rd hole, delayed opening of driven. With stock weights and white springs in drive unit, the best that I've gotten with RPM was 5,000 RPM @ 41 MPH.

RPMs are measured using a tach. MPH is calculated using a GPS in my phone. I've tested both the tach and GPS for accuracy against other units and they are all producing results at approximately 99.7% of each other. Example, one GPS unit shows 45.1 MPH the other 45.0. One tach showed @ 5500 RPMs, the other @ 5480 RPMs as max RPMs.

I appreciate any and all assistance. Thanks in advance.

I'll add some pictures later.
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Old 08-25-2019, 02:53 PM
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It has to be the torque converter/gearing (not necessarily a bad converter) . 41mph at 5k rpms is not in the .9 overdrive range with 19” tires and 50-10 sprockets. I’m not as knowledgeable as SID but I would try 2 things if it was my bike.

The first thing I would do is change to a 9 tooth sprocket. On one of my karts with a 6” driver (Heavy Kart) I was hitting 37mph max. According to my gearing and tire size I should have been about 5mph faster. I dropped the jackshaft sprocket down one size and increased driven to 7” (both lower top speed) The result was the same mph as before with much more torque. The difference was now the mph I reached matched the mathematical speed calculation. Basically my gearing and weight were not allowing me to fully get into overdrive.

2nd thing is get a fresh cheap ($20) driver and see if anything changes. I’d personally do the 9t first. Available on Amazon from Azusa for about $14.
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Old 08-25-2019, 03:56 PM
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I appreciate the replies, information and advice. I'm thinking about going the 9 tooth jackshaft route. However, I have a 60 tooth rear sprocket and some extra chain. So, I may just give that a try. Bike is stripped down for now as I am testing everything including exhaust. Overall plans are to fabricate a real gas tank, new fenders, seat setup, etc.... However, I'm not doing anything until I get it running correctly.

Here are some pics. You can see the 50 stamp on the rear sprocket. Looked in my notes, the belt in the pictures probably has 12 hours of hard testing on it.

I've talked to individuals at two well known mini bike shops indicating that they are seeing 6,500 RPMs running Trailmaster mini bikes with built 212 engines and TAVs. They also claim to be getting into 40-45 MPH range easily with Stage 1 engines with stock gearing. Some say they are running 60 tooth rear sprockets, other says 36/38 tooth rear sprockets. One claim was with a Predator 212 and a Stage 4 engine build, TAV with 146 gram weights and white garter springs, 36/38 tooth rear sprocket and 240 lbs. rider, they are seeing 6,500 RPMs and 64 MPH. I'm not disputing anyone's claims. I'm just trying to make sense of it based on my actual testing results.
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Old 08-25-2019, 07:29 PM
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Have you tried setting the driven in the middle hole?
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Old 08-25-2019, 09:19 PM
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I'd swap to the much stiffer and sturdier aluminium cast backplate IIWY..
I'm not too confident that pressed sheet metal thingy is going to like a high weight/torque application too much..
It'll eventually fail IYAM.. and I'd swap it before it does

Anywhoo
yeah if the cam need 6500 to get into it's comfort zone.. you are pretty much screwed as of now.
that'd be ~82 mph on the current setup
and to reach such you'll need upwards of 21 horses.. which you certainly do NOT have
(and unlikely will be able to squeeze out of that engine)

So.. lowering the gear ratio according to your applied weight is the single option you are having
I suggest a lower than 6:1 ratio to be honest since you are not exactly skinny
nine tooth up front and 55 tooth on the wheel would make it a 6.11:1 ratio
and with 6500 rpms that would give you ~66mph
(IF you have upwards of 12 horses in that setup)
if you don't then your speed limitation will drop of course
exact same setup with just 10 horses might not allow you to reach more than 62mph
etc...
Oh forgot.. you loose 20% in the Tavkit
(Id say maybe even closer to 25%) so your overall power needs to compensate for that.
so ~16 horses for 66 mph and 13.5 ish for 62 mph etc...
[max speed is estimated and NOT based on gear ratio but on air drag at speeds alike!]

Sorry, that's not too good news is it?
And it get's worse.. if 6.5k is the minimum rpm for the cam to be of use..
that's not even going to cut it really.. is it?
you want 7000 rpm max at least to even see the cam doing anything.
and with that you need to gear even lower..
like 6.6:1 (9T tavkit-> 59T wheel) for a 16horse
and 7:1 (9T -> 63T) for the 13.5 horse

frankly.. what a stupid cam for a bike like that!

ah well...
I would swap to a much milder cam tbh and gear accordingly.


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Old 08-26-2019, 08:42 AM
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Thanks for the replies.

Mrmonk7663 Have you tried setting the driven in the middle hole?
I'm going to try the middle hole for the spring on the driven.

ITSID - my goal in this adventure is to get a top speed of between 51-55 MPH. So, based on your information, I should not have a problem getting there by changing gearing?

I don't understand your comment about the pressed steel backplate thingy. The driver unit is bolted directly to the engine crankshaft and the driven unit is bolted to it's own jackshaft which is braced and welded to the frame. I do eventually plan to replace the driver and driven units with genuine Comet products.

Regarding the engine. This 212 Tillotson engine supposedly started out at 10 HP according to the seller. I don't believe it! I changed it out with the clone 6.5 HP engine that came with the mini bike and didn't find a noticeable difference in performance.

The CS265 cam selection came about from recommendations by GPS, OMB Whse and Dyno Cam personnel based on the mini bike and my goal of mid-50 MPH performance. Looking at the specs. on this cam, it is good to 7000 RPMs. My target of 6500 RPMs was for some margin of error in top ending the engine. Dyno cam personnel informed that I can run to 7000 RPMs without issue. I was also told by the suppliers of parts that I used in this engine build, based on a 212 clone 6.5 HP, this engine should be producing approximately 13.0 HP to 14.0 HP. I DON'T BELIEVE IT!!! What cam would you recommend?

Regarding total weight. Bike weighs 165 lbs. You can do the math on my skinny weight addition to the project. LOL.

So, here's my plan, I'm going to order a 9 tooth jackshaft gear/sprocket. I'm going to start with installing the 60 tooth rear sprocket that I have (since I have 5 foot of extra chain) leaving everything else unchanged and see what I get for performance. At that point, I will decide what to try next including changing the driven spring hole to the middle position.

I will update this thread with my results as I go.
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Old 08-26-2019, 09:35 AM
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Quote:
Originally Posted by onionfmr View Post
Combined weight of bike and rider is 340 lbs.
Quote:
Originally Posted by onionfmr View Post
One claim was with a Predator 212 and a Stage 4 engine build, TAV with 146 gram weights and white garter springs, 36/38 tooth rear sprocket and 240 lbs. rider
And that's what I thought would get close..
I was assuming the bike to have about 110 to 120 lbs

Quote:
Originally Posted by itsid View Post
since you are not exactly skinny
Quote:
Originally Posted by onionfmr View Post
Thanks for the replies.
Regarding total weight. Bike weighs 165 lbs. You can do the math on my skinny weight addition to the project. LOL.
my apologies for making you 50 lbs heavier than you are

Now...
38 sprocket.. no fricking way, not without a compound gear ratio..
that with 6500 rpm would mean 107+ mph on the wheel
So he likely didn't have a TC but a compound jackshaft installed instead.
(too lazy to calculate his first stage reduction)

Cam-wise I'd pick one that puts peak torque ever so slightly above engagement speed.
So down to 4100-4200 if you want to keep the light flyweights;
and down to 3500 if you want stock weights with white garters.

None of that matters if all you want is 50mph
you can do that with a proper setup at 5500 rpms and with 7000 rpm
with a matching setup as you like
I prefere the slower engine tbh.. but that's just me

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Old 08-27-2019, 07:57 AM
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sid - thanks for your reply and advice.

Quote:
Originally Posted by itsid View Post
Now...
38 sprocket.. no fricking way, not without a compound gear ratio..
that with 6500 rpm would mean 107+ mph on the wheel
So he likely didn't have a TC but a compound jackshaft installed instead.
I agree. This commentary came from an individual at a renowned mini bike/go kart shop. He claimed to be running a genuine Comet TAV setup, Stage 4 Predator 212, and everything else stock on a Trailmaster MB200-2. I asked him 3 times to clarify what he was running. Same answer each time. He did however offer to build me the exact same Predator 212 engine he was using for $1,000. LOL

I'll change the gearing on my mini bike and then post results. Thanks to all for your input and assistance, especially sid.
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Old 09-10-2019, 07:04 AM
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***UPDATE*** I ordered a 9 tooth Comet jackshaft sprocket to try, however, the side pucks of the sprocket are narrower than the existing 10 tooth sprocket and would cause chain and TC belt alignment issues. So, I decided to replace the 50 tooth rear sprocket with a 60 tooth sprocket. Big difference in performance and I picked up approximately 250 engine RPMs. The mid-range improved markedly and the bike was a lot more fun to ride! I'm going to make some spacers and also give the 9 tooth jackshaft sprocket a try, also. Once I get some more time, I'll use a GPS and post some top end results.
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Old 09-10-2019, 08:06 AM
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thanks for the update,
good to know that you notice a noteworthy difference,
with just the measly* 250 rpm gain
[* since you were heading 1500 more rpms, 250 doesn't sound all too much ]

yeah, I bet with a 9->60 (6.67:1) you will make a much bigger step in the right direction;
I'd say that'd be enough to pass the 6k rpm mark..

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Old 09-11-2019, 07:18 AM
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Quote:
Originally Posted by itsid View Post
thanks for the update,
good to know that you notice a noteworthy difference,
with just the measly* 250 rpm gain
[* since you were heading 1500 more rpms, 250 doesn't sound all too much ]

yeah, I bet with a 9->60 (6.67:1) you will make a much bigger step in the right direction;
I'd say that'd be enough to pass the 6k rpm mark..

'sid
sid - it is very surprising how much the mid-range on the engine picked up with the install of the 60 tooth rear sprocket! Engine is still pulling after 550 feet. I'm going to try the 9 tooth jackshaft sprocket, fluorescent yellow and blue/silver garter springs (in some combinations) and a yellow high performance driven spring. Also, change the spring hole position on the driven pulley.

I'll post results as I go forward.
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Old 09-14-2019, 07:17 AM
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***ANOTHER UPDATE***Had some free time yesterday afternoon to do some testing. Installed the blue/silver garter springs, engine topped out at 6800 RPMs, road five minutes and bang, both springs broke off at the ends. These springs weren't going to work anyways since the engagement point for the CVT was just not workable! Needed too much RPM to get started. Next, tried fluorescent yellow garter springs, engine runs up to 6000 RPMs, launch point is good and the driven unit is definitely shifting. Rode for approximately 1/2 hour. No issues. They appeared to work.

Next test will be making spacers for the 9 tooth jack shaft sprocket. Hoping that that will get me to a consistent 6500 RPMs. I will post an update after I test.

Also, picked up a heavy duty yellow driven unit spring. Anybody have results with this spring? Which hole in the driven unit is best for initial testing with this spring? Thanks
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Old 09-14-2019, 09:28 AM
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help me out a second..
silver/blue is what 5300 engagement speed with your light weights?
and fluorescent yellow was what 4700?

that's rough on your equipment, ain't it
I mean we talk about a take off speed of 18.5 mph for the s/b
(everything below chews on equipment)
for the flr.yellow ones 16.4mph.. (better still a bit much for my taste)

and in real world application that means you must never be any slower than that or
the belt will start to suffer severly.

I find that terribly inconvenient for anything but a race set up tbh.
Next down be the whites you had, right?
then what? blue and purple, no?

Anyways I'd lower the engagementspeed to just below 4k (blue 3700 or so?)
lowering take off speed to just under 13 mph

I (might just be me) like the opportunity to drive slowly especially when public roads are in use.
a toy that cannot but go fast is simply not for off race track use IMHO.

your choice of course, but yeah lowering the ratio would also lower the take off of course (by ~1mph or such)

'sid

PS I'd like to see you using the kartcalc.net web-app
if you store the bike to the database and allow the GPS signal (which is a bit of a pain since ios 9 to cooperate I'm afraid) it allows you to tach and makeshift dyno the bike maybe that gives us a clue about the limits
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Old 09-15-2019, 08:12 AM
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Good Morning sid - I posted a picture of the Comet chart that I used to select the garter springs detailing engagement RPMs. I'm using the 146g weights. I circled the appropriate figures. This mini bike does not perform as expected with any modification. None of the gear ratio speed calculation estimators give me anything close to what I get with actual performance based on RPMs (3 different tachs, same RPMs) and actual speed via GPS. Speed on GPS app has been verified by motorcycle and car testing.

In actual testing, the mini bike starts to move at approximately 3100 RPMs with the fluorescent yellow garter springs and 3300 RPMs with the blue/silver garter springs. The white garter springs would start the mini bike moving at around 3000 RPMs. When the TAV was stock, the mini bike would start to move at approximately 2200 RPMs.

There is no hard launch to start moving the mini bike. The blue/silver garter springs gave too much delay to start, windup. The others that I've tested seem to be acceptable. I've posted pictures of the TAV and as you can see the belt isn't getting destroyed.

From my property, I have access to groomed riding trails with many turns. I road the trails yesterday at slow speed without issue. I can easily ride around at 10 to 20 MPH and then accelerate as desired.

I have some kind of mismatched Chinese 30 series TAV that was provided to me by the Tillotson engine supplier. Once I sort this mini bike out, I will be switching to a genuine Comet setup.

I actually believe that I'm getting this mini bike to perform close to what I was looking for. Based on my testing, the engine seems to be happy up to 6500 RPMs. I'm going to test the 9 tooth jackshaft sprocket and see if that gets me some more engine RPMs. Currently topping out at approximately 6000 RPMs with fluorescent yellow garter springs.

I'm at a loss with this mini bike as to how it performs based on modifications to it!
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