Fuel Systems

[tborisch]

I have noticed alot of talk about going away from gravity feed fuel systems to using a pump, and getting the weight of the fuel tank into the boat.

What pumps do people use? Crank Case pressure operated?

Anyway, any info would be great! Just looking to get educated?

Thanks,
Tom

[hydroplay]

You can put the weight of the fuel tank wherever you think it will hurt you the least or help you the most depending on your point of view. Not all are in the boat. Assuming you are talking about Yamato motors, all pumps that I know of are crankcase pulse operated. We have used both OMC and the rectangular Mikuni pumps with good success. We've won Nationals in B and C Mod H with both large and small OMC pumps and the Mikunis. We originally used just the small OMC pumps and fed the carburetor directly. This system worked well and was used on our CMH for a number of years but we eventually changed to the larger OMC pump because OMC even changed to it on the generation of 15 hp motors made after our A motors. The small pumps worked well in racing conditions but had problems feeding the motor after the race when you came off plane and tried to idle back into the pits. I think this relates to low crankcase pulse pressure at lower speeeds with the Yamato reeds. We now have eliminated the small OMC pumps and just use the either the large OMC or Mikuni pumps with an overflow system. Either pump works well. The OMC has some mounting advantages on the 302 as it has three bosses just waiting for it. Here is a pic of out last year's 20SSH with a large OMC pump set-up. As you can see, the tank is not in the boat.

[tborisch]

Thanks!

Thanks for the great info! Do you have the part number for the big omc and the mikuni pumps. Also, What do you mean by overflow. Is there a bypass built into the pump?

I have a yamato 80. Is there a port to run the pump off of, or do people drill and tap the crank case? Will the OMC mount up nicely to the 80?


I would like to build a system, And i figure i will tap into others knowledge instead of trying to figure it all out myself.. cheap R&D so to speak!

Thnaks!
Tom

[hydroplay]

There is nothing already on Yamatos for crankcase pressure. You will have to drill and tap your own opening but there are some thicker bosses available. I use the pulse port as the mounting place on 80/102 motors with OMC pumps. I thread a short pipe nipple into the tapped hole and thread a small aluminum mount (maybe only 2" x 1/2") on the other end to screw the pump to it. I originally used ordinary brass pipe nipples but eventually found some Schedule 80 SS ones that are much stronger even though we never broke a brass one. I don't know any part numbers. I used to get the pumps from sources at OMC and now have a friend at Bombardier. But the larger OMC pump is on the 92 and up 15 hp motors newer 25 hp motors and has been used forever on 40-75 hp motors although the three cylinder versions may need a hole drilled and a port plugged as they run a separate pulse line rather than mount directly to the crankcase. They are as common as could be if you talk to a service guy nicely. You can find the Mikunis at any kart shop as it is a common pump used on shifter karts. Don't get the round style Mikuni as it pumps less volume. Mikunis also need some mounting system.

Overflow refers to the system used to regulate fuel pump pressure to the carb. The Mikuni carbs on Yamatos are intended for very low, gravity pressure. The overflow system keeps the pressure at regular gravity level and returns excess fuel to the tank. It is separate from the pump. I used to modify the OMC pumps for lower output pressure and just run the pump directly to the carb. It was worked fine and confounded the great eastern Yamato expert who said it wouldn't work and insisted on a floatless carb or a top-feed float bowl cover- both only legal in MOD when he used a fuel pump. But I eventually went to the overflow system when we had multiple engines to keep track of. Both Jerry Davids and I use the same principle but mine includes a small reservoir which aids starting when you need someone to "tickle" the float needle to prime the motor. I run a fuel line from the fuel pump to the carb and T it with a line that goes up as high as the tank used to be. There I have a very small reservoir for any excess fuel the carb doesn't need. Fuel enters it and 2/3 up there is a larger port for the return to the tank and at top is a check valve that prevents gas from leaving but will allow air to enter. The Davids approach ties the fuel in, fuel return and check valve all on a T fitting. The check valve is not absolutely necessary for the system to opperate well under running conditions, but if you don't include it you will soon when you try to live without it.

It really is pretty straight forward once you decide to do it. And makes the motor look much less antiquey.

[tborisch]

Correct pump?

Is the pump OMC P/N 438562 the correct one?



Also, how big is your hopper tank, and why did you mount it in the old location?

One more question. What size tank do people run. is 1 gallon enough?

Thanks!
Tom

[hydroplay]

The pic is a big OMC pump but it is not obvious if it is the style that mounts directly to the crankcase or is the remote mounted 3 cyl version. If you flip it over the pulse hole will be between the mounting holes if it is the direct mount type. Reservoir volume is not critical, some is good, more is not better 2-3 oz is plenty. It is mounted at the smae height as the original tank so it results in the same pressure to the carb.

1 gallon is a nice tank size.

[Matt Dagostino]

Sam.......................

Why is the tank on the stearing bar?? Is that the boat you had at Wakefield you sold to Donny??

FYI. Val is in a sling with no broken bones. Hope you and Bill are well.......

Matt

[hydroplay]

Because weight farther back is generally a good thing for Yamatos, esp 80s. And besides, I had a neat genuine Dick Fickett tank that needed to be polished and used again. That pic is from Christy Allen at Wakefield and Donnie did buy the boat for JrJr so we'll have to be on our toes to be competitive with him this year. We've got two new ones since then so hopefully we've made enough improvements to stay ahead. I told Bill about Val's crash Sunday afternoon and I thought he called her and wished her well. Glad that she came out of it reasonably well.

[hydroplay]

Here's a couple of pics showing the fuel system on a 80 and a 102. You should be able to see al details except the check valve on top of the reservoir.

[hydroplay]

pushed the right button this time, hopefully!

[tborisch]

Thats perfect! Thanks for all the help.

I will probably look into trying that out pretty soon.

Thanks again!

Tom

[94H]

If you use the Mikuni pump, make sure it has the clear plastic diaphram and not the tan colored one. I'm told that the clear diaphram is for gasoline / oil.

The square Mukuni pump number is DF44-211 and the repair kit is MK-DF44.

[les]

Pumps

Tom,
I have some parts that integrate a Mikuni DF-44 with the small tank if you're interested. The stock DF-44 is shown below for reference.

[jeff55v]

My el-cheapo pumper setup...

Twenty some years ago I was doing a lot of river racing with a B Utility runabout (usually at night). It was very difficult to refuel my 80 motor while floating down the Mississippi river! So in the garage, I took off the carb and reeds, stuffed the crankcase with clean rags. Then drilled and tapped the crankcase just behind the reedcage to accept a hose barb. I routed this "pulse" line to an old fuel pump from a late 1950's 35hp OMC.
Upon my first test, I found that the stock carb couldn't take the pressure the pump put out. So, I made a slick little adapter for a Merc KC (1-1/16 venturi) carb. this setup worked great for my "marathon" runs up and down the Mississipi river. The best part is, it cost me nearly nothing since I had all the stuff on hand already.

[Al Peffley]

Pump Info

Wow guys,

Thanks for all of the technical info and pics -- I am building a C-Mod setup and the information quality in this thread is awsome. Thanks also for a great question to start the information flowing, Tom!

Al Peffley