Dellorto SHA Clone - Running rich

Discussion in 'Performance Mods' started by Leroybrown420, Nov 17, 2013.

  1. Leroybrown420

    Leroybrown420 Member

    Hello everyone,

    Just took my latest build out for a test spin. The bike had no power over 25% throttle position. However, if I turned the fuel off it runs great until the bowl goes dry. I ended up taking off the metal air filter (more like a choke). If runs okay now, I have the proper Air Filter on order. This is my first experience with the SHA carb. I don't think this carb is running right. The auto choke will not come off, I'm not real sure how that system works. This project is on hold until I get the filter. In the mean time; I want to get the choke working and figure out why is running rich.

    Does this carb have adjustable jets? 20131114_175927.jpg 20131114_175915.jpg

  2. jaguar

    jaguar Well-Known Member

    take the filter off and look at the flap that closes or opens the intake pathway. then move the choke lever to see which position is closed and which is open.
    if a filter causes the engine to run too rich then there is no jetting problem with the carb. filters should not restrict the intake, but many of them do.
    if you have a foam filter and you oil it too heavily then it will be too restrictive.
  3. 570rm47

    570rm47 Member

    I have a very similar carburetor, but also has a small brass screw.
    It has abero sha 15.15 on the side.

    I think it is a little big for my 46cc but i will have a better idea when i get my new exhaust, i let someone convince me they should drill a hole in it and add an extra stringer. It is better with methanol than the stock nt.

    I would appreciate any info, suggestions.
  4. Leroybrown420

    Leroybrown420 Member

    The air filter came in, done! The SHA carb has a Semi-automatic strangler starting system. I did not have the cable adjusted properly, after I backed the throttle cable off the choke released at WOT. The bike is running better now but I think she needs a colder spark plug. I'm running a NGK BP7HS. I'm out of BP6HS and the B6HS ran like dog poo. I'll keep you posted and get some photos up when it's done.

  5. Leroybrown420

    Leroybrown420 Member

    The correct spark plug made a world of difference. I laid a rooster-tail through the front yard. Semi auto choke is cool when it's working too.

    Here's a few photos of the finished bike, hope you like it as much as I do.
  6. Fabian

    Fabian Well-Known Member

    I fitted that exact same banana pipe to my bike as a test. All i can say is that the thing was horrendously loud; so loud that it was not a viable option for road use. Worse still was that it didn't improve power in any meaningful way over a stock exhaust system with modified internals.

    A diaphragm carburettor is a much better option than a float style carburettor, such as the Dellorto SHA and clone variants.
  7. Leroybrown420

    Leroybrown420 Member

    I'm not in love with the exhaust but it's not as loud as the smaller expansion tubes I haves used in the past. I had the exhaust and it fit so, I when with it. It gives the bike an aggressive look and sound even if there are no true power benefits. I have already put the bike up for sale so if the new owner want to purchase a different exhaust system they surly can. I have more than 12 motorized bikes in stock, I need to have lot's a variety to keep people coming back for more. As we all know, everyone is different and likes different things. Just because I like something does mean everyone is going to like it. Variety is the spice of life.

    I had one customer special order a trike from me, I built it the way he wanted it. Two weeks later he showed up with a box of parts and asked if I wanted them back? Hell yeah, he gave me back tires, tubes, grips, pedals, chain guide & seat post. I then purchases a non-running motorized huffy for $40.00 on CL, fixed it up with all the free parts. I sold it as a "rat rod" for $350.00 (see my Rat Rod photos below)

    Thank you for your input I do appreciate it.
    20131108_113451.jpg 20131108_113510.jpg 20131108_113251.jpg

    Couple of the trike where the parts came from
  8. Leroybrown420

    Leroybrown420 Member

    SHA is coming off. I'm going back to my NT
  9. Fabian

    Fabian Well-Known Member

    Tried most of the float style carburettors and when all were jetted correctly they didn't offer any performance or drivability improvement over a correctly jetted NT carburettor.

    The same goes for the difference between a Walbro style diaphragm carburettor and the NT (when both are jetted optimally) - no power advantage between one or the other. It's just that the diaphragm style carburettor doesn't leak fuel and has external air/fuel adjustment screws, which makes jetting changes a 2 second affair "and" without the mess of a float style carby; spilling fuel everywhere (typically all over the garage floor) when changing jets; trying to zero in on the perfect air/fuel mixture, which is then no longer the perfect air fuel mixture the next day when atmospheric conditions change; requiring you to repeat the previous process; spilling even more fuel over the garage floor.

    The NT benefits from a simple modification, consisting of 3 small o-rings (perfectly sized to fit the internal step) that are then slipped inside the carburettor intake throat, at the point where it seals against the engine intake pipe.
    This modification prevents air leaks between the carburettor clamp and intake pipe; allowing a stable idle as well as giving good transition when rapidly opening the throttle.
    Last edited: Dec 22, 2013
  10. HeadSmess

    HeadSmess Well-Known Member

    couldnt agree more.

    for all round, set and forget (most of the time) use, the NT does it, and its all i use on these engines now, having fiddled with just about anything i could find other than the normal "hopups" available.. mikuni vm18, walbro 13, 16, and a 20... got a 28mm zama somewhere...

    the one other benefit of a good walbro/diaphgram type, other than the simple mixture setting (get the right model, BTW) is that the fuel is pumped rather than using simple venturi/pressure drops.

    in other words, when set correctly, with an intake port that allows it, you can stick a RIDICULOUSLY large bore diaphgram carb, where a "flooded bowl" (ie, slide type) carb, will just stall and die when opened up fully...

    there is no point using anything over 17mm on the HT anyway. thats all the port is.... work on deburring and matching more than anything. theres usually some nasty welds on the z-bends! and im yet to see a manifold thats port matched from the word go. its virtually impossible if youre welding one, the studs are just too close together. i say virtually, not entirely ;)

    best NT mod i ever made was the VERY slight taper i bored in the throat :) theres not much there to take off, but i like the idea of a properly tapered venturi! it was a BREEEEEEEEZE to jet afterwards.

    shame it eventually busted at the other end! :shout: i guess i could do it again one day...meh!

    seriously...does anything go rusty in AZ? :jester:

    if its not slathered in grease its falling apart with rust round here... makes everything look like sh...
  11. jaguar

    jaguar Well-Known Member

    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.
  12. Fabian

    Fabian Well-Known Member

    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.
  13. HeadSmess

    HeadSmess Well-Known Member

    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.
  14. Fabian

    Fabian Well-Known Member

    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.
  15. Fabian

    Fabian Well-Known Member

    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.
  16. Leroybrown420

    Leroybrown420 Member

    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.
    plate.jpg my bug 2.jpg
  17. 570rm47

    570rm47 Member

    sorry mispelt abero should be arbeo

    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
  18. HeadSmess

    HeadSmess Well-Known Member

    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.
  19. 570rm47

    570rm47 Member

    Thanks for the info HeadSmess my turbo 500
    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 :ack2: 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

    it ran like S#*%

    Please would love some pointers :tt1:
    Last edited: Dec 28, 2013
  20. HeadSmess

    HeadSmess Well-Known Member

    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 :confused:

    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 ;)