Category: PC800 Fuel Injection

A post from Jerry on the IPCRC brought up the point that the throttle bodies that the VT750S uses have a 90 degree bend in them to allow for a side air cleaner box.  That won’t work very well with the PC800 setup.

Looking at the PC800 microfiche, I wonder if I could use the PC800 throttle body and carbs with some heavy modification.  I could drill out the jet ports to install the fuel injectors.  All of the random diaphragms and other parts could then be removed and the various leftover holes could be sealed with JB Weld or Hondabond High Temp Engine Sealant or screws or metal plates, etc.  It wouldn’t be as good as a purpose-made throttle body but it might work.  And it wouldn’t require any modification to the stock air box.

Now if only I had a spare set of PC800 carbs laying around to experiment with…  I fear I will be removing the carbs on my bike several times to take measurements and figure things out in the coming months.  I’d rather have everything ready to drop into place once.  It wouldn’t be so bad taking apart the bike all the time except for the small problem of me not having a garage.  I do all of my work in a parking lot outside the fraternity where I work (I’m the house dad).  I have to button up the bike every time I’m not outside working on it.  That becomes tedious very quickly.

I wonder if there are any automotive throttle bodies with fuel injection that would be the right diameter.  Or maybe motorcycle throttle bodies.  Surely there must be some vehicle with the same diameter intakes.

NOTE: I have created a new category where I will be posting research, information, and eventually a how-to for installing fuel injection on a carbed PC800.  I’ve given quite a bit of thought over the last year of PC800 ownership about adding fuel injection.  I finally decided the time is now to start figuring things out and moving forward on this project.  Is it crazy?  Yes.  Is it possible?  Yes.  But it will take lots of determination, some money, and me being crazy enough to subject my poor PC to modification and tuning.  Let the fun begin!

My First Brilliant Idea

As the new Honda Shadow VT750S has fuel injection on-board, swapping that system onto a PC seems promising. The VT750 shares heritage with the PC800 engines. I
was looking at the parts microfiche for the PC800s and VT750S. Everything on the engine up to where the carbs would bolt on looks the same (ignoring the PC800 being tuned more “sportily”).

I need to find someone with a new VT750S who would be willing to look at the bike and take some measurements for me.  Specifically, the carb insulator boots (or I guess
these would be fuel injector insulator boots?) interest me. They have different part numbers (PC800: 16211-MR5-670 vs VT750S: 16211-MFE-640). However, looking
at the microfiche they sure do look similar. The big question is if the tubes that lead into the cylinders are the same size between the bikes. (Basically where #7 is pointing on Page 5-4 of the Service Manual)

If they were the same, then it becomes much more reasonable to pursue using the VT750S fuel injection system. PowerCommander already makes a unit that will interface with the VT750S Honda ECU which will allow tuning for the higher RPMs that the PC800 uses.

Another Good Idea

Otherwise, there are several companies that make custom fuel injection systems or I could do it myself and learn the black arts of fuel management. Obviously, I’d prefer sticking with Mother Honda, even if the parts weren’t exactly made for the PC800.

The best system that I’ve seen so far is the MegaSquirt.  It is a do-it-yourself hobbyist controller for fuel injection.  Just buy your injectors and a few other parts, throw it all together, and start tuning.  Or something like that anyway.  One of my friends, Michael Q, happens to be a member of the hobbyist community built around the MegaSquirt.  He has already offered his help.

If I went with the MegaSquirt, I could also eventually add ignition timing control and possibly expand to have cruise control and someday nitric oxide injection.  This is a list of things that I will absolutely need to make it work.