Performance Carburetor Options

Carb size

The 14 mm carb sounds a *lot* more workable for a 'happy time' engine (ref. to a 22 mm. That size generally goes on something - street-ridden - between 90 and 125 cc)
examples: Yamaha 60 cc two-strokes (early 70's) usually ran 16 mm carbs. The two I recall either used reed or (in the case of the one I worked on) rotary valve induction. Both turned 6000+ rpm. Case in point: the rotary valve one had a wider powerband and pulled surprisingly ***hard***. (Take that for a hint, inscrutable oriental happy time manufacturers!)

The chief advantages with the del'orto (spelling?) are 1) higher precision overall. This means longer life (parts don't rattle -> wear out) and more precise mixture control. 2) You can *get* jets, needles, throttle slides, etc, unlike the 'factory' carb. With those things, you'd best have a lathe, mill, and a *good* assortment of reamers, drills, brain lubricants (?) and related things.

Hope this is of help.
 
:cool:Davesmotors.com has a 4-petal reed upgrade for the DELLORTO carb on my pocket bike engine for $95. It's supposed to help the carb flow better, and is an improvement over the stock 2-petal reed induction.

I think I'll get the 4-petals.

Myron
 
anybody know anything about mounting a reed induction system on the happy time engine? I saw a deal on ebay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7242102416
that i thought i could make work, however it looks like you might need two of the oval looking piece (one for each side) in order to make it work, which means that unless the seller can hook it up, the only option is to buy two in order to make one. the upside of this is that spare parts will be abundant...however, the seller will not give me the dimensions of the holes in the intake manifold so I cannot check to see if it will fit the cylinder or not...to say nothing of the space required to do so. A reed system would be pretty badass though, anybody? and 5-7, you are using a pocket bike engine on your bike? do you have pics?
Reeds aside, the carb in question should provide much more adjustability, which will definitely come in handy once I port and polish the cylinder and intake this weekend.
 
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reed valve

Fitting a reed valve to an otherwise unmodified engine would *reduce* power, not increase it. Why?
1) A reed valve permits 'ready' flow in one direction, and little or no flow in the other. By 'ready', I mean with little restriction (vs. no restriction in an unobstructed intake tract).
The intake timing of a happy time engine is sufficiently 'short' that backflow, save at the very lowest RPM, isn't going to be an issue - unless, of course, your porting radically increases that timing event. (necc. for higher RPM operation)
2) use of a reed valve (on an otherwise piston-ported engine) is associated with other efforts to 'increase power' (higher up the rev scale, as a rule) - longer intake, exhaust, and transfer events, AND added ports (in some cases.)
Use of a reed valve permits a very useful type of boost port, one which comes straight from the back side of the reed cage. This type of porting uses the 'suck' action of a properly tuned expansion chamber to improve scavenging and breathing.

Now for a 'dumb' question: How much metal is present at the intake side of the cylinder wall above the intake port? The reason I ask is that adding one or more small 'finger ports' fed from holes drilled in the piston would help power and longevity - power, in that the lower back side of the cylinder would receive scavenging flow, and longevity, in that the wrist pin (bushing) would get fresh oil-rich mixture on a regular basis.

Hope this is of help.
 
I have no idea how much metal is there I haven't had the thing apart yet. I've only had it running for about 3 weeks. That is interesting that a reed valve doesn't do much for these engines. I just assumed from my experience with dirtbikes that it could only help, and when I was first running the engine I was getting some gas back through the carb into the air filter. That is what made me think of reeds, but then I ziptied my fuel line at the tank and carb and the "spitback" stopped. So you are suggesting that additional ports can be drilled into the cylinder wall? That is crazy! I wouldn't even know the first place to start on that. Can you explain that concept in more detail?
So no go for the reed valve...Cool that will save me money!
 
anybody know anything about mounting a reed induction system on the happy time engine? I saw a deal on ebay http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7242102416

and 5-7, you are using a pocket bike engine on your bike? do you have pics?

Ian, no way in **** is that reed induction going to fit onto a happy time engine. you need a 2" square port in the engine block to just fit the box.

Yes, I am using a 49cc pb engine with reed induction. I originally ordered just the DELLORTO carb and manifold. I didn't realize my engine had reeds until i pulled the stock manifold. When I installed the new carb, the reeds had to be removed and couldn't fit the new manifold.:confused:

When I found the 4-petal reed induction on Dave's catalog, I was ecstatic. The reeds not only can be reinstalled, they can be upgraded to 4-petal system. Moreover, this kit is made specifically for the DELLORTO carb I'd just installed!

Pics later, when my bike is roadworthy.

Myron
 
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Th' 14mm sha dellorto knock off carb works....OK......I installed one on my 47cc pocketbike schwinn spoiler.( #90 jet worked best) But, I prefer th' (modified) stock pocketbike carb. (reamed jet with medium-sized safety pin) It felt more gutsy.:cool: Th' 14mm sounded and looked cool.........but its NOT tuneable!:eek: (save for jetting) It IS a good basic carb for pocketbike racers that dont want to tear their bikes apart (between races) just to tune it.:confused: I will say this.....a real dellorto 16mm phbg carb would probably work best on a fairly stock "happy time" engine. This carb will provide ample tuneability.......and be ALOT more precise. (throttle response!)
 
Carbs - and ***carbs***

I was looking up dell'orto carbs yesterday (I think it was yesterday) and learned that some of them are a good deal more tuneable than others. If I recall correctly, that 'knockoff' carb is a copy of one of the less-tunable variety, one where only the main jet is readily changeable. There's another 'type' with more letters which has replaceable needles, slides, main jets, pilot jets, etc.

Once I learned that, I thought to look up mikunis. I knew the sixteen millimeters were being made currently (some smaller atvs use them) but when I found a place selling them, I nearly choked at the price!

100$! (ouch!)

Odd, though - an eighteen mm example is only seventy, and based on what someone (don't recall who, beyond they documented it on the list somewhere) said, it might be possible to jet that size so as to run *decent*. (he managed with a 20mm - oh, he said the engines were coming apart in a hurry, and *Dax* was speaking of his modifications causing them to do so - or so I recall.)

Hope this is of help.

I still suspect a sixteen (or slightly smaller) will give best low-end performance. Had we more than one 'gear', I'd argue for fitting the 18mm.
 
Prism, Ill be frank....I have used a 20mmcarb on my 70cc.....and it works! The ONLY problems I had from experience are from trial and error: 1st engine died six months later AFTER using 32:1 oil/fuel ratio suggested from other moto site.....plus.... I broke it in using SYNTHETIC which was reccomended in the instructions! 2nd motor died ( actually the bushing worn out) from running in 20 below temps and not adding ADDITIONAL oil to the standard 5oz after breakin . 3rd engine went past 500 miles....... but blew gasket and oil seal from using TOO MUCH OIL and running it wide open for miles on end. (Hey, that "does 35-40 mph" sales pitch STILL lingers in my head) The 4th engine went WAY past 500 miles.......it died when the upper roller bearing fell apart...and grabbed the piston at idle(???). The fifth engine was a stocker with VERY LITTLE mods.....had 7oz oil in it .....ran slow as **** and wtf .....the roller bearing died and wedged bearing pieces about the motor. What dax mentioned about modifications was ......PORTING...SHAVING HEADS....CHANGING PISTONS. And dont try to play all innocent like........virtually everyone on this site WANTS BETTER PERFORMANCE and HAS MODIFIED SOMETHING. Youre STILL suggesting a LARGER carb yourself.
 
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