Spaco PHBM 28 Carburettor

Picture courtesy: Dellorto Tuning Manual by Jet-Tech Motorsport

For the project "free flow", I have been looking for a good carburetor to upgrade to. Considering my bull's engine inlet and exhaust ports were redone (/expanded) a year ago and the bike is running with bigger jets (on stock carb), it makes sense to switch to a carb with bigger venturi to match that of the inlet port. In short, I decided on the carb which came with Machismo A-350 AVL. The only issue was, that model of Machismo had a very short run and a much shorter carburetor that came with it. But all hope was not lost and I had asked a friend to scan Karol Bagh's market for a used piece if he can't find a new one that is. Much to my luck he got hold of a box packed one from one of the vendors. I had a call with the vendor to ensure the item he was having at hand was indeed the one I was looking for. Long story short, that was the carb  I had been looking for. This model of the carburetor was manufactured under license from the Italian carburetor manufacturer Dell'Orto, for Royal Enfield. Spaco was the OEM manufacturer of this one. Considering EFI (Electronic Fuel-Injection) systems have already replaced (and will continue to do so) the old school carburetors on all upcoming higher cc motorcycles, a shining new box-packed carburetor is gonna be a rare sight in the coming years. Or at least that's what I thought. So why not get some close-up shots of my new toy before I get it on my bike. So here are some of the photographs I shot. Unfortunately, I didn't have a size 14 spanner handy, so couldn't open the bowl/floats chamber.

Spaco (India) cardboard packaging

The cab is seal packed in thick plastic (so no tampering is possible)

That's a neat-looking vintage part in my (humble) opinion :) LEFT SIDE (Air Filter side)

FRONT SIDE: You can call it a "Mechanical GUI (Graphical User Interface)" :D This stays on the right-hand side of the motorcycle and you would see me fiddling with it in the middle of nowhere when my bike stalls :/ (very rarely though)

RIGHT SIDE: Connects to the engine inlet

BACK SIDE: This one stays towards the battery on the motorcycle and is usually not accessible. The fuel line connects to the grooved metal pipe facing up.

BOTTOM SIDE: That bolt allows the drainage of the fuel if loosened slightly or the bowl to be opened completely.

TOP VIEW: The throttle cable goes here and connects to the slide

Top section opened

The slide, the needle, and the metal stay which locks one end of the throttle cable

Main jet opening

A closer look

Air intake side with idle air intake vents

Choke (starter) lever neutral/off position

Choke (starter) lever ON (/engaged) position

Side view: when the choke is ON

Main needle with adjustment washer set to 2nd slot

Assembling the top portion: Needle, Slide, Spring, Top cap

Pilot jet fuel passage

Slide half open (this happens when you have the throttle rotated one-quarter turn). For most of the older bullets, we cruise at this state at around 2000-4000 rpm (roughly).

Slide fully closed (when no throttle is given and the engine is idling)

The air filter goes on the left and the flange connects the carb to the engine inlet.

This carb is already been put on my steed and it is currently being tested during my daily commute. Yeah, I am taking the bike to the office to run this new carb in and troubleshoot any glitches. So far it's doing great and along with the free flow exhaust, there is a change in overall performance, I could feel, but I will hold my comments until this bad boy goes on the highway. Hope you enjoyed watching the photographs here. 

Update[06/03/2017]: At this point, the motorcycle (along with the new Carb) has done a little over 5000 KMs and doing absolutely great. As part of the test runs, I switched to a 95mm jet (instead of 110mm which came as stock) and that has been doing its job well. Initially couldn't find replacement jets for this model in the market as the thread size of the main jet was completely different (i.e. larger) from what we have from other makers available in the Indian market. After lots of research and lost hope, I ended up on EDC brakes' website and noticed they make aftermarket jets for Dell'orto. Upon enquiring, found the helpful guys at Motousher (one of the authorized retailers for EDC Brakes in India), who could import some jets for me from EDC. A big shout out to Motousher for helping me with this. You guys (reading this blog post), check out their website for all high-quality aftermarket accessories/parts for your motorcycles. The reason for my recommending them is simple; their response to my request (of a few carburetor jets which may not be much in terms of sales amount), shows their attention to the customers and to the motorcycling business as a whole. I wouldn't think twice before buying anything much expensive from these guys in the future, due to this first-hand experience. Now coming back to the carb, I am running with the new 95mm main jet (instead of a souped-up 95mm jet fitted with a plastic tube around to fit it into the carb's thread). The performance of the carb (along with other mods) has been excellent however, there have been a few issues as well. For instance, there are these petrol stains on the fuel filter side of the car all the time. This means there is some fuel evaporation from that side. Also, I use a cap at the point where the throttle wire meets the carburetor from the top cap, otherwise, there were a few instances where water got into the carb due to rain or pressure wash at the service stations. None of this was a deal breaker, as I could ride 5-6 days in heavy rain during my northeast trip and never had any issues (with the cap in place). And the stains look bad, but it's on the inner side of the bike, so doesn't bother me that much. All in all, I am happy with this change. I will continue using it, and if I come across anything worth sharing, will make an update to this post.

Cheers!!

Sid