1998 Yamaha R1 Carburetor Conversion

[Coil Coyle]

  :)
     Last winter I started planning a Carburetor conversion, looking for some modern CV carbs. The nearly downdraft R1 carbs from 1998/2000 looked like a good place to start so I started putting in low bids on sets at EBay using  www.AuctionStealer.com.

     After loosing a lot of auctions I eventually bought a throttle cable to boots to air box set for $31.00 plus 17.47 USPS shipping.  :o  They have 40mm throttle plates, 41mm slides and were designed to feed 250cc cylinders with good throttle control.  8) Two spare carbs are included in the deal.

     The plan for this attempt is to use a pair of them mounted "sideways" and vertical.

      Another attempt with them oriented like the stock Vision with parallel throttle shafts will only be tried if there are issues with the float bowl levels when braking or accelerating.  ???  A lot more fabrication would be required for the linkages etc if this was the plan.

     This is a list of the work done so far.

1. The carbs were split by removing the through bolts and rethreading the bolts.
2. The right outer side and the left outer carburetor were used to make the pair. Right to the rear, Left to the front. This pair has the throttle cable between them pointing to the right. The throttle position potentiometer on the throttle shaft is to the rear. I want to keep the pot to try R1 ignition in the future.
3. The carbs have tubular manifolds that connect two pressure signals and the fuel supply to each carburetor. On the front side of the pair a 1/8 NPT thread was cut in the Vacuum Signal and Fuel ports of the carburetor body and 5/16" hose barb fittings were screwed in.
4. The centerline of this set is 82.25 mm.

    The primary issue is the centerline of the carburetors. To increase the centerline to the 122.6 mm spacing that the Vision requires these changes are needed.

1. The float vents are connected with a "T".  They could be connected with separate rubber tubes.
2. The top through bolt needs a 40.35mm long 6.5 mm bore spacer
3. The bottom through bolt spacer must be replaced with one 83.35mm long x 6.5 mm bore
4. A Diaphragm Vacuum signal balance tube 113 mm long needs to be built.
5. A Diaphragm atmosphere vent tube 70 mm needs to be built.
6. A fuel tube 77 mm long needs to be built.
7. The rear throttle shaft needs the 40 mm added between the body and the balance adjuster because the front carburetor has the cable mount. Support of the throttle shaft extension may be a problem. This is a design issue.

    I'll post pictures when I get a home up here and a new internet provider.

$0.02
  ;)
Coil

[Coil Coyle]

1. The float vents are connected with a "T".  They could be connected with separate rubber tubes.
2. The top through bolt needs a 40.35mm long 6.5 mm bore spacer
3. The bottom through bolt spacer must be replaced with one 83.35mm long x 6.5 mm bore
4. A Diaphragm Vacuum signal balance tube 113 mm long needs to be built.
5. A Diaphragm atmosphere vent tube 70 mm needs to be built.
6. A fuel tube 77 mm long needs to be built.
7. The rear throttle shaft needs the 40 mm added between the body and the balance adjuster because the front carburetor has the cable mount. Support of the throttle shaft extension may be a problem. This is a design issue. 

Update to this work list.

1. Separate tubes are the way I'm going. Pressing tubing into the carburetor body for the vent hose is the plan, no size for the tube to date.

2. Made this part from the original bottom through bolt spacer by facing its length to 40.35mm.

3. Bought 3/8" aluminum rod, drilled and faced to 83.35mm length.

4. This Vacuum signal tube does not connect to any of the carburetors control signals. It is just the equivalent of a vacuum hose from the left to right of the R1 motor. This part, although I made a very nice one in about 2 hours on the lathe, is completely unnecessary.

5. This should just supply air box air or cleaned air to the other side of the diaphragms, I'm building the connector. A couple of small vent filters would probably work or two hoses to the air box with 90 degree fitting like the one on the side carburetor could connect to the air box.

6. Two hose barbs with 1/16" pipe thread could replace the fuel connection. I've built a longer one on the lathe. The two stock tubes could be siamesed with hacksaw, drill and JB Weld if no lathe is available. Just slip the smaller OD of one into a drilled hole in the larger OD tube.

7. Ok, the cables mount to the front carburetor and the push/pull throttle pulley is on the back carburetor. The pulley also has the tab that moves the balance adjuster screw on the front carburetor. The back carburetor has a threaded end for the pulley mounting nut. Current plan is to make a shaft extension that will screw onto the rear throttle shaft and extend the cable pulley over to the front carburetor, where the throttle cables mount. This will leave the rear carburetor shaft without an idle screw tab and the throttle return spring will not have a connection to the throttle linkage. The idle screw mount and the return spring mounts are on the rear carburetor.

8. The new issue is a throttle shaft mounted return spring plate with an idle screw tab included.

9. Airbox adaptors that cover the outer carburetor throat and connect to the Vision airbox are necessary. The inside diameter of these two adaptors will allow the R1 velocity stacks to enter the airbox.

      As I write this it looks to me like the items included in 7, 8 and 9 are the pieces that would be most the useful parts to outsource if there were a lot of these conversions to do. Everything else could be done with typical skills and equipment.

;)
Coil

[Coil Coyle]

          The throttle extension shaft is done except the idle arm. I'm simplifying the construction of my design but the set looks great and balance adjusting is OK.       

          I brought the engine I got from Odium to the shop to trial fit the spread carburetors. The bodies of the R1 are wider right above the mounting spigot so the carbs hit the heads before slipping into the rubber manifolds.   :P

          This weekend I'll try spigot extensions for the R1 carbs to raise them above the manifolds. This is going to change the carb to airbox floor connection.

          We may move soon and then I'll post pictures.

[Coil Coyle]

Here are thr R1 carbs spread to the Vision Centers.

http://s164.photobucket.com/albums/u28/coilPBcoyle/XZ%20Width%20R1/?

If that doesn't work search XZ Width R1 at www.photobucket.com.

Note the "ports" are aimed to the inside of the carbs, the Throttle Position Sensor is not usable, the idle screw has no lever and the throttle shaft extension has yet to have the flats milled on the sides to mouint the throttle cables pulley.

Coil

[Coil Coyle]

OK, once I got to the Boot it became obvious that the stock R1 width was the best solution. Less mechanical problems, better port flow and other manufacturers Carbs for the R1 could be used.

Reckon got me going on the boot building and to date I have positioned the Carbs so that the Stock Air Box connection style will fit with another boot built for the box floor. The Air Box floor will be cut and a rubber adaptor will fit the large part of the carb body to the new holes in the air box floor.

Here is the "Port" that will be inside the new R1 Boot.
http://s164.photobucket.com/albums/u28/coilPBcoyle/Vision%20R1%20Boot/?

;)
Coil

[Coil Coyle]

No progress on the boot, I'm waiting for tech support from a couple of Silicone Manufactureres to recommend the best product. I have been busy commuting weekends to Cal. and trying and sell the house there.

Ron_McCoy sent me a recommendation to get the settup mounted in a frame to verify clearances. Early on I just did an outside dimension comparison with the stock carbs and, when I saw that they had room, just kind of dropped that aspect of my planning.

           He is doing a similar project and cautioned me that I need to verify that the throttle cables and linkage will work at the mounting position I have worked out for the port and the airbox. The issue is frame clearance with the side cables.

           So, this week end while I stay in Oregon I'll fit the plaster ports and R1 carbs on the top of my 83RK (rod knocker) to get pictures and lay out for the problems that Ron pointed out.

           Also, a part number for a most gasoline resistant RTV 2 part Silicone Rubber would be nice  :) but I'm probably going to find that a heat vulcanized rubber is the way to go for a manifold on a gasoline engine.

Gratefully,
;)
Coil

[Coil Coyle]

Let's see;
   
       It's been a busy year but I got moved, the plants running three new lines and I'm ready to get back to my hobby.

       On the CROV September ride an old friend of mine and Ron's, Denny Lack, came along on his BMW. He had built molds for Newby Rubber in Bakersfield for a while and passed on a lot of good information about molding rubber. I became convinced that the clamped and heated mold and vulcanized rubber is the correct way to do a boot.

       I'm thinking that I'll change the carb side of my boot model to a spigot, make the manifold rigid and use the stock R1 boots for the connections. I can build the manifolds with Epoxy and fiber for the prototype and get on to the rest of the project. Build a rubber one later.

       Ron McCoy's working on a throttle linkage for his similar conversion, he thinks that pulleys should be the last resort. I'm just ready to set up the dummy engine in the dummy frame and start working on that part of the conversion.

       I should have pictures of the dummy setup this weekend and will post at the Photobucket site.