Long list of strange, miscellaneous questions...

[GTLabs]

I'm going back and forth about a lot of things on this build-up. What do you guys think?

Stuff I have to work with

GX160 Jiangdong clone.
GX200 Genuine Honda.

What would you build as an example of a "mild" alcohol motor? I want to use the fuel, but not for high revving shenanigans. This is more of a study in torque. The challenge is to make ample torque off of idle, opposite of high rpm usage. The bike does 40mph already, but has a little trouble off the line getting there. A TAV is about the only modification I would consider to increase top speed. This thing at 75mph would be a death trap and already is getting a GS425 front brake.

The Good Doctor runs very well with very little modifications to the motor. I wanted a small showcase of alternative fuels that wouldn't kill me or interested folks that want a ride. I also wanted it to be easy to maintain.
I'm mostly happy with the bike's performance with just an open element filter and a header. A rejet and timing bump is all I have planned for basic, cheap mods.

The bike runs great even geared down to 5:1. I'm purposely limiting the top speed. What's funny about this is the amount of torque available. I've done practically nothing to the motor and it almost seems too fast already. If it needs any help it's just off idle with that numerically high gearing.

Thoughts? I think there's plenty to be had with just a timing bump. I think a high compression, low rpm build might be "too much." I don't want the bike to walk off and leave at idle like it does on nitro mixes and an open choke. I want a motor dialed in before stripping the chassis for paint.

-Should I consider a GX160 carb on a GX200 for torque?
-Would just a GX160 head on a GX200 be plenty to raise compression? Maybe keep the smaller carb?
-Would just a timing bump, GX140 emulsion tube, and rejet be all that's needed for better low end on -5:1 gearing? On cam it's fine, but off cam it's a bit of a dog at 5400ft. elevation.
-How would you make a lot of torque below the 3600rpm stock rev limiter for cheap?

 

[Oldschool]

I have a some Liffan clone 14cc heads on some engines in development and one running right now on " La Vache ".
Yup they make low end torque! But they need to be massaged a bit for better flow so a mild port clean up and some unshrouding. The effect on compression is about 1/2 to 1 full CC of extra space but you make up for it in better flow.
Valves seem to be holding up and this head on an otherwise stock motor works well with a timing increase of about 8 deg for 28 BTDC.
Header I have a small 3/4 inch header on 20 inches long. This may be a bottle neck at higher Rpm but its not hurting low end torque. I think the length of the header is more important than the size at this point.

One engine is going to use a more agressively ported 14cc head and the Honda thin ring Flat top for about 11.5:1 compression. This is a good combo and will still be gasoline ( although some doctoring with Xylene may be required for 91 octane ).

SO yes ...

 

[GTLabs]

Will I burn up the clutch faster with more torque off idle and these high gears?

 

[Oldschool]

From that picture in your Icon thats a stock MB615 with a stock clutch and jack shaft right?
The higher gearing will not make the clutch's life any easier

Well its not a strong chain, jack shaft or clutch so be prepared to replace them. Don't go nuts with power and the TAV it was not designed for more than 8hp in mind.

Keep it simple stay with gas buy the TAV and improve the engine with a better carb and stronger internal parts so its safe and reliable.

And you won't have torque off idle that you can notice. These engines need to wind up a bit to start feeling the difference. I notice the extra pull staring around 3000 RPM. Below that the clutch doesn't work right and slips anyhow.

 

[GTLabs]

It's a Mini Baja with the jackshaft removed. It's straight back to the 50T gear from a 10T stock clutch. Is a tuneable clutch any tougher? I've never used one and they're cheap enough to be affordable. I liked the ones listed on your sponsor sites. Are they handy to have a few of?

Other little stuff on my list was on those sites, too. The adjustable Honda mixture needle and a GX120 emulsion tube looked like further little improvements. I'm not looking for outright power. Off-idle does sound a little useless now that you guys mention it, though. Do the clutches kick in around 1500-2000rpm? A timing bump, rejet, fuel change, intake and exhaust sounds well rounded for the combo. It's meant to be mild-ish and still reliable. A TAV might even be too much for the bike. 8-10hp is indeed what I had in mind, but maybe 20 ft/lbs of torque instead? Possible?

I have a new chain but haven't installed it yet. It's a meaty sucker. Right now the chain is long and unsupported in the middle. It does oscillate but has never jumped off. I think I can fit an idler gear where the jackshaft used to be, but wasn't sure if it was needed. I tried to find gears for the 2-1 reduction on that stock jackshaft, but didn't find anything locally.

 

[65ShelbyClone]

If you want something less difficult to maintain than methanol, look into E85. It's not the greatest fuel in the world, but it's easier to get than methanol, usually costs less, and has 100-105 octane depending on the blend.

My guesstimate for a "diesel" build would be high compression, increased timing, a stock or very mild cam, ratio rockers, and perhaps some mild intake port cleanup with the stock valves.

Keep in mind that engines get more octane sensitive and there is more stress on parts the lower of an RPM the peak torque occurs at. It might also be cheaper to just buy a bigger engine. A stock GX390 makes more torque than a GX200 could.

 

[GTLabs]

I thought I mentioned E85 is what I would be using. :lol:. Guess not. It's some fun stuff. I can run butanol, E85, and nitromethanol all through the same stock and clone carbs. I'm surprised how well it handles it, too. The jetting doesn't change much among them, either. I use long-chain alcohols so I can get away with nitro usage on smaller jets:thumbsup:. That's why I'm not worried about the motor too much. A teeny tiny splash of nitro does a LOT! This little thing seems to really like fuel, too. It's an oversquare thing.

I hadn't been worried much about the actual carb size as much as the jetting, fuel type, and mild breathing. I think it'll be happy with around a 100-110 jet on the GX200 with alky and nitro. It already tries to walk off and leave and I haven't done anything to the inside of the motor. A hot plug helped a lot with the bottom end and keeping a bit more heat inside the motor. Low compression engines with alcohol are a little different and really not common at all. The notion of more power out of an alky fueled low compression engine is backwards to some and sacrilegious to others. A hot plug and a timing bump do a lot, along with some more gas in the mix. I don't think they like straight alcohol. Unleaded gas helps in that instance instead of detonating.

Here's a weird one--how much timing is too much with a nitro mix? So far I've left it alone and not installed the GX160 flywheel on the GX200. Only on nitro does it try to walk away (<5% nitro).

 

[ezdoesit]

GT, You got any pics of this bike?

 

[Oldschool]

I can't tell you anything on the Nitro front. Its been 25 years since I tried that in a G200 flat head and I am sure its not worth considering for the gains you want.

Compression, timing and improved porting/breathing alone will make 10hp. Even better if you ditch that stock carb and find somethig just a little bigger ( again Tilley 166B come to mind right away for easy adjustment and good low speed performance followed closely by just about anything with a bowl, slightly larger ventury and both adjustable high and low speed jets ).

I don't know what kind of clutch you have but generaly the off the shelf simple drum clutches engage between 2200 to 2500 rpm. Cheap Chinese 35 chain might be a let down.

E85 and any ethanol methanol blend is bad shit, go to a marina and ask anyone who fixes boats. Try and burn pure gasoline it doesn't attack anything in you fuel system and gum things up. unless you to clean and flush your fuel system everytime trouble will find you

 

[GTLabs]

I can't tell you anything on the Nitro front. Its been 25 years since I tried that in a G200 flat head and I am sure its not worth considering for the gains you want.

Compression, timing and improved porting/breathing alone will make 10hp. Even better if you ditch that stock carb and find somethig just a little bigger ( again Tilley 166B come to mind right away for easy adjustment and good low speed performance followed closely by just about anything with a bowl, slightly larger ventury and both adjustable high and low speed jets ).

I don't know what kind of clutch you have but generaly the off the shelf simple drum clutches engage between 2200 to 2500 rpm. Cheap Chinese 35 chain might be a let down.

E85 and any ethanol methanol blend is bad shit, go to a marina and ask anyone who fixes boats. Try and burn pure gasoline it doesn't attack anything in you fuel system and gum things up. unless you to clean and flush your fuel system everytime trouble will find you

The lines are rated for 10% ethanol and I pushed that envelope. The carb float stuck after long storage and eventually the paper carb gasket bites the dust. I purposely left it in there to see what would happen. No problems since. I run an additive that gives the mix a neutral pH and cleans up deposits, but that still doesn't save paper carb gaskets :lol:.

It starts up on the first pull or two even on a mild alky blend. I've used nitro in this motor twice and 4 times in the GX160. Every time it was in small amounts of less than 1/2 tank so I can cut it easy. It needs a bigger jet even at 5400ft. Altitude and low compression is why I'm not anxious to throw a big carb on it. It was fun but I haven't begun to explore these motors outside of really basic stuff. I drain it if there's nitro but unleaded gas and ethanol sit fine for a while.

10hp on this thing really is plenty, IMO. It doesn't need to rev to 9k rpm to be fun. The chain is a 40. The bike is a Mini Baja with a Suzuki GS425 front fork. It's heavy by mini standards but big enough to be fun and stable. Bike + me is about 325lbs. It'll shortly have a GS425 hydraulic front brake so it should stop on a dime. The sprung seat and front bike shocks really make it comfortable.

 

[Oldschool]

Nice seat what is it off off?

I also run a modified MB165 in a slightly more advanced stage of development ( not by much ) with simmilar requirements. Stock front with Baja drum MX handle bars and thumb throttle instead of twist grip

I want to head to Barrie this summer and run the clay circle to see if I got what it takes to play with the older grayer fatter kids....

Bike + me 350 elevation 1420 feet 11.5 compression with HL 166B and some other stuff in the works

:grind:

 

[MiniBike Paul]

"It doesn't need to rev to 9k rpm to be fun."

My experience leads me to say that revs are the way to make these bikes/engines really fun!
Starting out, I too figured a TAV would solve the low end/high end conflict; however, the TAV's shift up to their highest gearing prematurly (i know, everyone says you can adjust that but I could not get it to stat lower longer!), so the engine is forced to lug from start to top end. Unable to stop the TAV from doing that, I did what virtually everyone out here seeking performance has done, add a jackshaft and gear down to roughly 10 to 1 (I have 17 inch diameter tires). This gives the bike great acceleration from a standing start, but when I first did it I had engines like you describe, "warmed over clones" I call them, governer removed, bigger jets, an air cleaner and a pipe - but these engines will only spin 5500, so there was still no decent top speed!
The fix, add rpm!!
First I went to 18# springs and that got me 6500. Now, I have 26# springs and the required proper aluminum parts. The light flywheel makes a huge difference, as it does in any engine, in the speed of acceleration, and the 9500 rpm allows gearing changes that yield great acceleration from dead stop to a now very good top speed; and only rpm will do that!
The next steps, if I go further, would be better and more extensive head work, then more cam & dual valve springs, more rpm, better gearing yet! None of this will enable me to beat better riders, but it sure is fun to push the performance envelope!!
You must see an engine like MiniDragBike builds to understand how far this can go - the stuff the rest of us have is "strong" but his are unbelievable!! Running 5 to 1 his will do long burnouts and then reach super sonic rpm and blurring speed.
No offense intended, but you are just scratching the surface - go further, you will love your engine the further you take it - the sound, the feel, the speed!!

 

[65ShelbyClone]

You know what RPM stands for, right? Ruins Peoples' Motors. :wink:

Also, what is "nitromethanol?" Is it nitromethane or methanol? Nitrating methanol yields methyl nitrate which is some very nasty stuff.

 

[olajoe808]

My experience leads me to say that revs are the way to make these bikes/engines really fun!................
No offense intended, but you are just scratching the surface - go further, you will love your engine the further you take it - the sound, the feel, the speed!!

What's so fun about running it on it's edge, dancing, twisting, threading the needle only to say at the end of the day, 'hey, did ya see that'? :thumbsup:

 

[Oldschool]

"It doesn't need to rev to 9k rpm to be fun."

My experience leads me to say that revs are the way to make these bikes/engines really fun!
Starting out, I too figured a TAV would solve the low end/high end conflict; however, the TAV's shift up to their highest gearing prematurly (i know, everyone says you can adjust that but I could not get it to stat lower longer!), so the engine is forced to lug from start to top end.

I assume you tried a stronger garter spring right?
I also think there are heavier weights ( might be thinking a different TAV system ).

Read this it may help
http://www.comettorqueconverters.com/asymapp.htm

 

[GTLabs]

It's 15% nitromethane in methanol--Pink RC glow fuel. It was the lowest concentration I could find. I only ever splash it in or use about a 1/2 cup of it at a time. Butanol or E85, and a splash of the pink stuff is a wicked little combo. Nitro in the mix needs a rejet on the GX200 still. On the GX160 with a GX200 jet + NGK 5-range plug it would walk off and leave with an open choke. 5:1 gearing just didn't matter. I had to sit on it to start it so it didn't go anywhere.

It's been a strange process of turning it up and down with just the fuel and tuning. I can only imagine what this nuttier fuel blend would do with better timing and a higher redline. I didn't WANT a 75mph bike. It was supposed to putt with a bit better oomph and still be simple and reliable.

 

[65ShelbyClone]

Byron makes glow fuel with 0-55% nitromethane, but typical glow fuel is packed with oil....usually 15-20% worth. The synthetics they use don't burn well and the castor leaves sticky gum. There was a thread about glow fuel on 4cycle and I said the same thing there; it's cheaper to mix your own methanol/nitro blends. If top end lube is to be included, I would look into the low smoke/low ash gasoline two cycle oils and use them sparingly.

 

[GTLabs]

I use Klotz Benol. Thoughts?

 

[65ShelbyClone]

........

castor leaves sticky gum.

 

[GTLabs]

That's why I'm learning this stuff on small motors. How fast does that gum form? Inside the combustion chambers does look varnished black, not sooty and carboned. It looks "wet" or almost shiny. Is that the gum you speak of? The clone and the GX200 have both seen small doses of glow fuel mixed with other alcohols--spiking the punch basically :thumbsup:. I can see it pretty easily in the spark plug hole.

I have a small 5cc 4 stroke Saito and a few 2 strokes that have seen Benol. I don't dose the Hondas with Benol, but I dosed the Saito for safety's sake. It's got an hour or two of usage on it. Small motors are a crack habit ut:.

Also, what kind of nitro do you recommend? I use E85 so often I'd just dose that and skip methanol. Methanol cools more, but ethanol has more energy. Nitro likes either. Do you also retard timing at all or change plugs after getting the jetting right?

http://www.klotzlube.com/techsheet.asp?ID=85