Bump stick of choice?

[roadrash]

[**Billet flywheel in hand, mikuni carb arrived today; billet rod and 18# springs should arrive this week along with a few timing keys.… The Plan is to put those in and take it for a spin (or 2…or 3…test’n’tune).]

In the mean time I’m looking into cams and stuff.

The Isky Black Mamba cams seem hot: SMALL ENGINE CAMS (310)769-6880 - STORE

Dyno cams has a list of different cam profiles: DynoCams Cam Profiles

I’m new to world of the small engine building and having trouble trying to determine where the line gets drawn between mild and wild?

At the same time I have no concept of the different class’s. Who is the authoritative governing body if I wanted to read about the various classes?


Thanks!

 

[buckeye]

Classes???

We have Gumpit class, "just put a clone on it".

We have the Square Chopper class. Supports Gay Rights.
We have the leathernun class, nuttin but flannel seats.

We have several classes, if that's what ya mean.:laugh:


Black mamba seems to be well thought of.:thumbsup:

 

[gumpit]

Buckeye class: Runs on hot air... Nothing ever happens though...

 

[buckeye]

Oh yeah, the best class. First Class.:laugh:

 

[Txpowdercoater]

I love the dyno 310, but the motor needs to be built to flow enough cfm's and wind high enough to get the full benefits of the cam.
at 4k rpm's or so its like a switch is flipped and the front of my mini starts going up in a power wheelie if on pavement (at 30-35 mph, you have to lean forward to keep it down), if on dirt its trenching a rut. Love the combination I have now, it belongs in the class of "WTF!"

 

[incogrhino]

 

[roadrash]

Thanks txpowdercoater, thats helpful. Sounds like a blast!




HAHA you guys are funny. You forgot Old Skool'n class.....

I like that kind of free spirited thinking.

Yeah man, I'm not trying to build to a specific "class". I'm just gonna build what what feels good and thats where it will end up. Just trying to figure out if there was any method of madnesss to classification. At what point does it stop being "mild" and become "wild". Gotta stroke it and run alcohol? (that sounds wild....could ya push the limit some more?)

IMO, If Im not questioning that I'm still in control or slightly scared to crack it open some more, then its not moving fast enough. I'll sign up for that class....


I'm not planning to hang out at the strip, however "test and tune" night could be a blast.... I plan to ride the yard a bunch, some dirt track action through the woods, and the occasional WOT down a back country road to smoke my friends.

So, I guess I'm having trouble trying to place my practical application in some cookie cutter build range. And maybe that is my FUNdamental problem and I should just build what ever I want. Yeah, I want it full on ape, all out nutty. BUT at what point does the diminishing return effect kick in? I'm never going to race it for trophy's and cash prizes (side bets dont count, lol).

How wild can I go before I hit the wall of practical diminishing return? I'm not talking unlimited capital or a full service machine shop at my disposal, I'm asking about practical. There must be a point of reasonable diminishing return, after crossing that... yeah you can make more power or squeeze a little more out, but at what cost? Follow me?

At that thought is where I get hung up on cam selection. I guess If I'm not happy with the cam I can easily buy another and swap it out and keep playing that game (I mean, they are "cost effective" all things considered).... Lil tweak here, lil tweak there... that didnt pan out, back up and tweak something else.... CUSTOM...

I'm just trying to learn from other's past experiance.

Next question would be head related, but thats another thread (maybe).

 

[funky ole]

[**Billet flywheel in hand, mikuni carb arrived today; billet rod and 18# springs should arrive this week along with a few timing keys.… The Plan is to put those in and take it for a spin (or 2…or 3…test’n’tune).]

In the mean time I’m looking into cams and stuff.

The Isky Black Mamba cams seem hot: SMALL ENGINE CAMS (310)769-6880 - STORE

Dyno cams has a list of different cam profiles: DynoCams Cam Profiles

I’m new to world of the small engine building and having trouble trying to determine where the line gets drawn between mild and wild?

At the same time I have no concept of the different class’s. Who is the authoritative governing body if I wanted to read about the various classes?


Thanks!

with these parts, especially the 18 lb. springs, a good choice would be the mod 2 from dyno. you could use the mamba jr. from isky also,if you choose not to rev real high,or trail ride more where your on and off the throttle. both mamba cams use 26lbs. springs.
your parts with the mod 2 and 1.3 rockers would be my choice.
OR switch to 26 lb. springs and the mamba jr with your parts.

 

[davidlamb78]

I found a 14cc head on eBay for $30. It is awesome. Might be another thing to look into. Are you running a stock length rod? I can't remember what cam I went with, CL 1, I think? It is okay. I'm interested in one of those mambas. They sound fun.

 

[65ShelbyClone]

The CL-1 is legal for the box-stock (spec) racing class. It's not really a performance cam at all. The Mambas definitely are.

How wild can I go before I hit the wall of practical diminishing return? I'm not talking unlimited capital or a full service machine shop at my disposal, I'm asking about practical. There must be a point of reasonable diminishing return, after crossing that... yeah you can make more power or squeeze a little more out, but at what cost?

There is no line in the sand answer to this question because the concept of diminishing return can be represented by a graph like this:

Everyone's "pain threshold" is different. I generally think of the lines intersecting around 100hp/L for naturally aspirated engines. The more they make beyond that, the harder it is to improve upon. Take 14,000rpm sport bikes, for example. They make ~200hp/L out of the box. Fully-prepped race versions might make 20% more and increase overall cost by 100%. Add boost, however, and the percentages reverse until parts start breaking.

 

[roadrash]

Thanks for the input!!!!

I used the stock length rod and still have the stock dish piston.
I have considered the higher compression heads, but need to read more.

Think I'm leaning twards the Mamba Jr with 26# springs and upgrade the rods / rockers.

Still fiddleing around with my Fakuni....(seriously considering buying a real one due to the lack of documentation).

I'm having fun with this and learning a lot in the process. Good times!

 

[65ShelbyClone]

It's worth mentioning that all the parts you're talking about have a synergistic relationship. That is to say that together they are worth more than the sum of their individual gains. Suppose a cam by itself nets you 1hp and a ported head by itself nets 2hp. Combine the two and they could net 4-5hp instead of their sum total of 3hp.

A lumpy cam is going to reduce dynamic compression at lower engine speeds, so a bump in static compression would be helpful. High compression with a mild cam and low rpm ceiling will just make the engine octane sensitive.

 

[roadrash]

WOW! Got the carb almost dialed in for the current build, and the bike is running great. Need to get a tach for it and start saving for the next round of upgrades ;-)

Thanks again guys!

 

[novaracer]

well after running the nr 252 0607 it just didn't do it for me I needed bigger so I got the nr 274marine that's a nasty nasty cam very strong but it didn't like to rev comparied to the black mamba jr. for a good minibike cam I would go with the bmjr bang for the buck.

 

[davidlamb78]

It's worth mentioning that all the parts you're talking about have a synergistic relationship. That is to say that together they are worth more than the sum of their individual gains. Suppose a cam by itself nets you 1hp and a ported head by itself nets 2hp. Combine the two and they could net 4-5hp instead of their sum total of 3hp.

A lumpy cam is going to reduce dynamic compression at lower engine speeds, so a bump in static compression would be helpful. High compression with a mild cam and low rpm ceiling will just make the engine octane sensitive.

Awesome! This is the information I love getting from this forum. I have read about the difference in dynamic compression and static compression, but I admit I don't fully understand it. Is this boost in static compression done by keeping the valve open longer to bring in more fuel, which is done with the cam?
I understand how compression ratios are figured. I also understand that high compression makes more heat, and alky is cooler. I also understand that high compression means that the motor has to work harder to compress the air/fuel mixture. This means that you need to get enough fuel into the chamber, and this is done with the larger cam? Am I close? I guess the term static and dynamic are what always confuses me.

I started putting the motor together gradually, and I never intended to put this much into it. It's addictive. I know that these motors have certain parts that work well together, and that some don't work as well together. I probably should have just saved my coins and bought everything at once.

I would love to move up to a BMjr. cam, but I'll have to donate a little more plasma before I do that. The cam is certainly affordable, but I'll need new push rods, valves, and springs. That adds up. What are your thoughts on the stock rockers in a clone?

Thanks again, shelby, for all your advice. I love this forum. Sorry for the bonehead questions all the time, but I promise I'm listening and taking it all in.

 

[jdogg]

Thanks again, shelby, for all your advice. I love this forum. Sorry for the bonehead questions all the time, but I promise I'm listening and taking it all in.

This is probably the best reply ive seen in a while! :thumbsup:

 

[65ShelbyClone]

Awesome! This is the information I love getting from this forum. I have read about the difference in dynamic compression and static compression, but I admit I don't fully understand it. Is this boost in static compression done by keeping the valve open longer to bring in more fuel, which is done with the cam?

You're thinking of dynamic compression. Static compression just just the ratio of the cylinder's swept volume to the compressed chamber volume. It doesn't change, hence the name. Dynamic compression is harder to quantify because it is not constant and is affected by things like cam overlap, air density, manifold pressure, intake resonance, and volumetric efficiency.

I also understand that high compression means that the motor has to work harder to compress the air/fuel mixture. This means that you need to get enough fuel into the chamber, and this is done with the larger cam? Am I close? I guess the term static and dynamic are what always confuses me.

A higher static compression ratio does take more engine power to overcome, yes, but that is independent of the cam.

What are your thoughts on the stock rockers in a clone?

Never dealt with them, actually.

 

[youngengines]

My stock appearing engine has stock lifters, push rods, guide plate, and rockers on it. It has Stainless steel valves , aluminum retainers, split locks and 26lb springs. I have turned it 9200rpm on my dyno (valve floats then), but it will turn 8800 to 9000 with no problem. Makes peak hp at around 7500. (around 19hp) Heres a link to the dyno chart:
https://www.facebook.com/barry.youn...05989288.1073741825.1444872408&type=1&theater

 

[novaracer]

Awesome! This is the information I love getting from this forum. I have read about the difference in dynamic compression and static compression, but I admit I don't fully understand it. Is this boost in static compression done by keeping the valve open longer to bring in more fuel, which is done with the cam?
I understand how compression ratios are figured. I also understand that high compression makes more heat, and alky is cooler. I also understand that high compression means that the motor has to work harder to compress the air/fuel mixture. This means that you need to get enough fuel into the chamber, and this is done with the larger cam? Am I close? I guess the term static and dynamic are what always confuses me.

I started putting the motor together gradually, and I never intended to put this much into it. It's addictive. I know that these motors have certain parts that work well together, and that some don't work as well together. I probably should have just saved my coins and bought everything at once.

I would love to move up to a BMjr. cam, but I'll have to donate a little more plasma before I do that. The cam is certainly affordable, but I'll need new push rods, valves, and springs. That adds up. What are your thoughts on the stock rockers in a clone?

Thanks again, shelby, for all your advice. I love this forum. Sorry for the bonehead questions all the time, but I promise I'm listening and taking it all in.

Yes get the bmjr it is a very good minibike

 

[roadrash]

It’s been a while but I’m back. More parts came in - black mamba jr., 26# springs, raceseng S1 push rods, ¼” guide plate, 1.3 stamped rockers, and a 18cc head.

Installed the cam, lined the dots up on the cam and crank. (Although I don’t recall if I made sure it was TDC, if it was not can the cam be installed 180 out?)

Set the valve lash at what I believe was TDC. My feeler gauge only went down to .004, so I used the side wall of a PBR can. (I am picking up a better feeler gauge tonight to recheck the lash.)

It didn’t want to fire without giving it a little gas. With choke on I got it to fire, but it didn’t want to run with the choke off.

Suspected too small of a pilot jet. I swapped jets - replaced the stock #15 pilot jet with a #17.5 and swapped out the main jet that was a #95 but I drilled it out a bit (have to go back and check how much tonight) to a #130 (which may be a bit much, might put a #125 in it, I have one in stock).

Now, it ran at an idle. But the idle was still high, I screwed around with some screws. The screw on the bottom of the carb (which AGK indicates is an air screw https://www.affordablegokarts.com/carburetor-tuning.php ) I got it idling lower, but to low and it would stall (didn’t seem low enough that it should have stalled though). I found another screw on the side of my fakuni, turned it 1/8 of a turn counter clock wise and the idle smoothed out to just around 1600 rpm. Does anyone know what that screw on the side is?

I seem to be running a little rich still….(haven’t moved the needle ring since the cam install, had it goods and dialed in prior to this, might need to lean it out a bit there). And I noticed the occasional back fire on sudden off throttle…

But I have a bigger problem. This thing is an SOB to start; it still wants someone to work the throttle a bit while another person pulls. My arm sore today from pulling last night (no kick back though) lol. I’m wondering if its timing related, or if the higher compression head created an octane sensitivity issue 65shelby clone mentioned. (I’m not sure if the black mamba jr. would be considered a mild or lump cam.) I’ve only run high end pump gas in this motor, no race fuel yet.

If you can get it started it sits and idles, and revs just fine, no bog no lag.

I have an ARC billet flywheel, replaced the stock key with a 4 degree key. I ran that for a while with no issues before the cam and head upgrade.

My throttle cable broke last night in the middle of playing with it… so I’ll grab a new one on the way home and continue to test and tune this evening.

Thoughts? Comments? Thanks in advance ;-)