Dellorto SHA Clone - Running rich

[Leroybrown420]

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?

 

[Deleted member 12676]

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.

 

[570rm47]

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.

 

[Leroybrown420]

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.

 

[Leroybrown420]

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.

 

[Fabian]

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.

 

[Leroybrown420]

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.


Couple of the trike where the parts came from


LB

 

[Leroybrown420]

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

 

[Fabian]

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.

 

[HeadSmess]

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.

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! i guess i could do it again one day...meh!




seriously...does anything go rusty in AZ?

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