Dellorto flaw

[Deleted member 12676]

yeah I think that was the culprit after all. I really should do a retest on the boost bottle.
Fabian, due to manufacturing tolerances some carbs will be worse than others. That's why I suggest people take the carb off and check it with a flashlight to see how much clearance there is. Then if there is any just apply a little JBWeld, an easy fix.

 

[Deleted member 12676]

Turns out "the fix" is not sufficient for my engine. It still needs the .45mm diameter hole in the lower part of the fuel column to idle right.

 

[lazylightning@mail.r]

Turns out "the fix" is not sufficient for my engine. It still needs the .45mm diameter hole in the lower part of the fuel column to idle right.

I have the Dellorto 16.16 SHA with the 66cc engine. I used a .71mm drill bit to drill the small hole at the bottom of the column. The same size as the hole above it. The bit just fits into it. Coincidently.
It still seems to come down from a high rev to a decently low idle rather slowly at times though. I still haven't gotten around to checking to see how much play that slide has.

 

[Old Bob]

I think you are trying to over compensate for a problem that isn't a problem in the real world.

Even if there is an air leak, so long as it is a consistent air leak, it can be compensated for by slightly altering the jetting to restore a perfect air/fuel ratio.

I have tried the genuine Dellorto and it worked acceptably well, though when the NT and genuine dellorto and clone Dellorto were jetted correctly, they all worked the same; not one of them gave any better performance over the other, and the diaphragm carburettor fitted to the intake tract on my bike does not give any better performance that the previously mentioned float style carburettors, but it is much, much easier to tune.

Its a fix for a non existant problem.
dellortos are not known for issues like this. Amal on the other hand have a just deserved reputation for excess slide to body clearance but only when worn.They would wear faster than normal due to the poor metal that was used.Its a far stretch to imagine clearance for the cable would cause this issue, from experience with Amal I know its not.They are equipped with boots to seal the top and they engine does not run any different with or without the boot in place. It serves to keep dust and dirt of the exposed cable not seal airflow as its not needed.
A new Dellorto does not have this problem so its not a design issue.
Judging by the quality or lack thereof of the rest of the conveyance the issue is self inflicted,not a Dellorto problem.

 

[Deleted member 12676]

Bobby boy, you obviously haven't looked inside a Dellorto. If you would you could see (with aid of a flashlight) how big the air leak is past the slide and that it leaks to the air filter. What can come into it past the cable is maybe a tenth of a percent of what can come in by way of air filter. And if you've ever dealt with air leaks upsetting the idle mixture you would know that it takes a very small passageway to make a very big difference. It has to be 100% sealed to run right. Between the slide and the engine there can be no leaks to outside air.
My Dellorto is a genuine one. Maybe the people who made the copied version fixed that problem. I doubt it but it is a possibility.

 

[Fabian]

Have to agree with you Old Bob. I never had any idle issues or transition issues with my genuine Dellorto carburettor. The only reason why i returned the Dellorto to the place of purchase is because it didn't give any better performance than the standard (correctly jetted) NT, even though i was told the Dellorto would give better performance or my money back.

 

[Deleted member 12676]

Strange turn of events; turns out the o-ring I use between the carb and the manifold had shrunk a bit and was allowing some air in. So probably without that problem I wouldn't of ever noticed that there was a small air leak past the slide. It's not enough to cause the engine to race at idle but it is enough to throw the idle jetting off a bit. But not enough for normal people to notice. But I believe that anyone that uses JBWeld to fix it will notice a new power increase at low rpm and a stronger idle.
Man, I can't wait for the Mikuni to arrive. Finally an adjustable carb!

 

[Fabian]

But why waste your time with a Mikuni when you can install a diaphragm carburettor and have a truly adjustable and leak free carby.

 

[Deleted member 12676]

Mikunis are "truly adjustable" and as "leak free" as any other carburetor. But I might have tried out the $80 15mm Walbro if I'd known JNMotors was selling it along with adaptors for the Rock Solid reed valve.

 

[lazylightning@mail.r]

I think part of the idle problem on the Dellorto SHA is due to the slide covering the atomizer holes. Until I put a hole in that fuel column at the bottom, it really did idle very fast. Fast than at half throttle. It raced. I've heard that others had a problem with that model.