Dellorto SHA Clone - Running rich

[Deleted member 12676]

Saying that a NT carb that doesnt even have a separate idle circuit is equal to all other carbs is insane. Any other carb will let the engine idle better. If idle is unimportant to you then stick with the NT. Other carbs, other than the SHA, also have replaceable jets so you can adjust it to perfectly match your engine. The NT only allows needle position adjustment, so that when it is adjusted right for WOT it is wrong for low and mid range RPM.

The SHA sucks because it is designed for a particular engine, being basically non-adjustable. I had one and adjusted it by drilling jet holes. But then I replaced it with a Mikuni 18mm and have been very happy with it. Click on my signature link to read about all the options available to you if you want a "complete" carburetor that is fully functional.

 

[Fabian]

Never had an issue with idle quality from a stock standard NT carburettor. That said, i have jetted richer than many on here say is necessary, with my current engine using a No 86 main jet, and the previous engine requiring a No 78 jet to achieve an optimal air/fuel ratio for max torque.

To compensate, i simply place the circlip (some might call it the "e" clip) to the highest position on the needle, thereby restricting fuel flow when the carburettor slide is in the idle position.

 

[HeadSmess]

The NT only allows needle position adjustment, so that when it is adjusted right for WOT it is wrong for low and mid range RPM.

dont make me click on your signature link, find your link to gordon jennings "two stroke tuning guide" and then cut and paste the section on carburettors, please...

pretty sure its repeated in every carb tuning manual, as well...

needle taper(s). needle jet (not the main jet but the tube it screws into). slide cutaway. fuel height in bowl.

thats four methods of adjusting the idle and mid speed operation. still havent even touched the eclip, thats five....


so who really needs the extra complication of a low speed jet in a low performance engine that lives at WOT? 6 with the jet...7 with the air screw...

it does the job


edit sorry...four...needle jet is for full on total fuel flow... i quote from memory "the main jet will not deliver more than the needle jet will allow, no matter how large it is made" (and then some blah blah about removing the main jet altogether to test...) scratch that one from the list.

 

[Fabian]

so who really needs the extra complication of a low speed jet in a low performance engine that lives at WOT?

So perfectly written

and why bother with extra fuel circuits when the standard NT works adequately as supplied from the manufacturer, and furthermore, it's a dead simple carburettor that's easy to adjust due to "lack" of complexity.

 

[Fabian]

If you want to add complexity (that works) then make the move to a diaphragm carburettor.

Ultimately, programmable electronic fuel injection is the logical choice, and i would buy such a kit (in an instant) if a manufacturer were to design a suitable system, tailored to these low capacity 2-stroke engines.

 

[Leroybrown420]

10 points each for the Australians. Great info guys. We get surface rust here in AZ. See check out this old AZ bug I'm looking to buy.

 

[570rm47]

sorry mispelt abero should be arbeo
http://www.mopeddivision.com/sha-15mm-clone-carburetor-lever-choke-for-tomos-mopeds/

This Carby is a bit big i think fo my 46cc ive got .58mm approx for petrol and it performs pretty close to my nt with petrol .7mm the original seems ok for my homemade methanol but i have not tested it more than to know its better than the nt for the methanol think its got something to do with the air-flow

 

[HeadSmess]

Methanol or Ethanol?

i can understand Ethanol using only a slightly larger jet to petrol or even the same...but Methanol... no. way too lean.

methanol/ethanol are both less volatile than petrol and benefit from better atomisation at the jet, nevertheless.

 

[570rm47]

Thanks for the info HeadSmess my turbo 500
http://stillspirits.com/products/turbo-500-still
produces very very clean solvent, it reccomends to remove 50ml from the head but i was occasionally getting a hangover so I err to the side of caution heavily and take 150ml+ (i dont have a decent measuring cylinder yet so really im making ethanol denatured with methanol about methanol:ethanol 1:2).

I think my jetting is slightly too rich still .5 was to lean .55 was so close with just a touch tail wind or a little downhill i was around 90km/h least thats what really p/o motorists were screaming it just happens that the only bit available to me after .55 is .58 and its just too rich now.
Its a learning curve to now understand how so little difference between what i think should be .56 and what is .58 can result in half the speed i was getting but it doesnt get hot on top now. I was privileged enough to have a real carburetor specialist tell me that my jetting could be as much as .01 out and has offered for a bottle of my correctly proofed and bourbon flavored ethanol to let me use his instruction and little jewelers lathe and more complete set of bits. 0.58 - 0.7 is a bit of a jump for petrol it craps along at about 35km/h like that.
I have tried 1mm with my own fuel and dellorto clone as suggested for the nt carb at
http://motoredbicyclehacks.blogspot.co.nz/p/ethanol-bike.html

it ran like S#*%

Please would love some pointers

 

[HeadSmess]

the flow of an orifice (jet) is controlled by diameter...AND length. if the .56 isnt big enough, then slightly counterbore it, reduce the length of the jet orifice, let it flow slightly more. conversely, bog em up with solder, drill em out larger, and dont counterbore the solder all the way to brass... also finding super fine copper wire from a transformer, tack solder one strand in the (oversize) jet at a time...

no idea how to read a plug on alcohol

whole temp curve changes, pipelength changes...powerband will be at diff rpm to petrol, fo sho!


what oil you mixing with it?

and, thats another one...the oil can tweak your mixture too