Post by 90GTVert on Nov 20, 2011 0:49:59 GMT -5
21mm DellOrto PHBG Racing Edition
For the next test, I moved up from the 19mm DellOrto PHBG to a 21mm DellOrto PHBG racing/black edition carburetor. Here's a look at the 21mm DellOrto beside the stock carb. You can get a pretty big increase in venturi size with this one in a small package that fits where the stocker will.
Stock.
21mm. Just like the 19mm DellOrto, this one uses an adapter on the inlet for more fitment options. The 38mm adapter is used here.
Here's a look at the 19mm PHBG and the 21mm PHBG. The whole line of carbs uses the same body, just with larger bores and other differences.
The most obvious difference between the standard and black/racing edition of these carbs is the paint job of course. They also feature a screw on cap instead of a cap that uses two screws to install it. Check the image above if that's unclear. The best difference IMO is the easy access bowl on the racing edition. It makes main jet swaps much faster.
Use a 16mm wrench or socket to remove the plug and then swap out the main jet. It doesn't get much easier.
Of course the bowl must be removed completely to access the pilot and starter jets, as well as other bits.
The 21mm uses the same 5mm main jets and the same pilot jets as the 19mm DellOrto tested previously.
Starter jet, pilot jet, main jet, atomizer, needle, throttle valve.
Stock Specs
Main Jet : 92
Pilot Jet : 50
Starter Jet : 60
Atomizer : 262AU
Needle : W7
Throttle Valve : 40
Connections.
Just as with the 19mm version, it's helpful to remove the locator nubs from the stock intake for a flush mount.
I'm using the same choke used with the 19mm version as well. Everything fits neatly in place.
I used a 98 main jet, 40 pilot, and the needle clip in the next to richest (of 4) positions.
On a 41 mile test ride, I got 62.86MPG. That's the best fuel economy I've seen in all of Project 90 to date. WOT cruising was right on par around 48 - 52MPH, and max speed was 58MPH at about 8,500RPM. Again, the rear pulley just doesn't work quite as it did. The difference in MPH isn't a power difference as best I can tell. I felt no difference in WOT performance vs any other carburetor tested in this phase so far. Acceleration at low throttle positions was greatly improved, as with all of the larger carbs so far. With this 21mm, it seemed like next to no throttle was necessary to stay at 40MPH. I saw increased CHT readings at 40MPH of 240 - 255°F. WOT was 265 - 280°F with 50°F ambient temps. I think the elevated 50MPH cruise temps stem from needle selection and adjustment. Since the throttle is open less to go the same speed, it needs to be fattened up a bit on the low end.
I was pleased that this carburetor showed such great fuel economy as well as improved cylinder cooling. It offers quite a dramatic increase in low throttle power as well. Once again, no noticeable power increase. It's easy to tune with the quick access to the main jet and the wide variety of DellOrto parts available. It's a very nice carb at a reasonable price.
For the next test, I moved up from the 19mm DellOrto PHBG to a 21mm DellOrto PHBG racing/black edition carburetor. Here's a look at the 21mm DellOrto beside the stock carb. You can get a pretty big increase in venturi size with this one in a small package that fits where the stocker will.
Stock.
21mm. Just like the 19mm DellOrto, this one uses an adapter on the inlet for more fitment options. The 38mm adapter is used here.
Here's a look at the 19mm PHBG and the 21mm PHBG. The whole line of carbs uses the same body, just with larger bores and other differences.
The most obvious difference between the standard and black/racing edition of these carbs is the paint job of course. They also feature a screw on cap instead of a cap that uses two screws to install it. Check the image above if that's unclear. The best difference IMO is the easy access bowl on the racing edition. It makes main jet swaps much faster.
Use a 16mm wrench or socket to remove the plug and then swap out the main jet. It doesn't get much easier.
Of course the bowl must be removed completely to access the pilot and starter jets, as well as other bits.
The 21mm uses the same 5mm main jets and the same pilot jets as the 19mm DellOrto tested previously.
Starter jet, pilot jet, main jet, atomizer, needle, throttle valve.
Stock Specs
Main Jet : 92
Pilot Jet : 50
Starter Jet : 60
Atomizer : 262AU
Needle : W7
Throttle Valve : 40
Connections.
Just as with the 19mm version, it's helpful to remove the locator nubs from the stock intake for a flush mount.
I'm using the same choke used with the 19mm version as well. Everything fits neatly in place.
I used a 98 main jet, 40 pilot, and the needle clip in the next to richest (of 4) positions.
On a 41 mile test ride, I got 62.86MPG. That's the best fuel economy I've seen in all of Project 90 to date. WOT cruising was right on par around 48 - 52MPH, and max speed was 58MPH at about 8,500RPM. Again, the rear pulley just doesn't work quite as it did. The difference in MPH isn't a power difference as best I can tell. I felt no difference in WOT performance vs any other carburetor tested in this phase so far. Acceleration at low throttle positions was greatly improved, as with all of the larger carbs so far. With this 21mm, it seemed like next to no throttle was necessary to stay at 40MPH. I saw increased CHT readings at 40MPH of 240 - 255°F. WOT was 265 - 280°F with 50°F ambient temps. I think the elevated 50MPH cruise temps stem from needle selection and adjustment. Since the throttle is open less to go the same speed, it needs to be fattened up a bit on the low end.
I was pleased that this carburetor showed such great fuel economy as well as improved cylinder cooling. It offers quite a dramatic increase in low throttle power as well. Once again, no noticeable power increase. It's easy to tune with the quick access to the main jet and the wide variety of DellOrto parts available. It's a very nice carb at a reasonable price.
