mikuni bni 40 fuel line routing

[nitrosport_5]

Hi, I recently purchased a set of bni 40 carbs used. They were on a 96 gsx. I am cleaning them up to use in a buggy with a skidoo engine and I want to verify the fuel lines are correct. I have a set of bni 38s on my other buggy and the bottom port on each carb is hooked together and the top ports are the returns. On the 40s, the top port on the pto carb went to the bottom of the mag carb, and the bottom of the pto and top of mag were returns. What way is the correct way? I had thought the 40 and 38 were the same besides the size of the throat. My 38s seem to work great the way they are set up. This iis why iI want to verify what way is correct or if it even makes a difference. Thanks iin advance

 

[racerxxx]

I believe yours have accel pumps.

 

[nitrosport_5]

I don't believe they do. They look and have identical internal parts as my bni 38s, but have a larger baseplate opening. So it looks like the lines were wrong when I got the carbs? I tried to post a pic but it wouldn't let me. I'll try again.

 

[racerxxx]

Your carbs are wrong. Your pumping fuel from the MAG carb to the PTO return. Surely a quick way to melt a PTO piston. Make them the way in the pics I posted. Also, lose the grey fuel line. Then inside will break down and clog the internal filters, again, leaning out the engine and melting down. The "Y" goes on the return port.

 

[soccerdad]

And now you need to post pictures of your toy when it is running. Or now...

 

[nitrosport_5]

Your carbs are wrong. Your pumping fuel from the MAG carb to the PTO return. Surely a quick way to melt a PTO piston. Make them the way in the pics I posted. Also, lose the grey fuel line. Then inside will break down and clog the internal filters, again, leaning out the engine and melting down. The "Y" goes on the return port.

Thank you, I didn't think they were correct but wanted to ask to.make sure. I am planning on all new lines when I rebuild them.

As for pictures, my first buggy with a 670HO skidoo engine and bni 38 intake setup runs awesome. It is a 1989 honda pilot. The downdraft mikuni carbs give much more transmission clearance than a typical snowmobile carburetor so I could mount the engine low in the frame vs up high like others typically do.

The one I am building now, is the same 1989 Honda pilot, but iI have added long travel suspension, power steering and a better seat. It also runs a 670ho (for now) because iI had one on the shelf from a sled I parted out. I wanted to try something different so am going to do 40s on this one. Someday it will get a fuel iinjected 2 stroke etec when iI can find one affordable lol.it is further along now than it is in the pics. Just haven't had much time to work on it so spending an hour here and there

 

[nitrosport_5]

Also, I was told to never run a fuel filter inline between tank and pump on these carbs as it will cause them to run lean. Is there truth to that? It makes no sense to me, because a filter before the pump should not restrict the flow to the carbs as that pump will be supplying the pressure they need at all times.

 

[soccerdad]

Well a lot of us use inline filters before the carbs without issue. And they are on 787cc 110 HP motors. Yours should be a great toy. I cut my teeth racing Honda Odysseys back in the day. Then ran the Mickey Thompson Stadium series and SCORE desert series for several years in what we termed Stadium Superlites. It was really a 360CC odyssey motor turning about 10,500 rpm. Never dyno'd it but it was about 65 HP we thought. Long travel suspension and all the toys.

Good luck and have fun! The dunes are a great place to play.