Im getting tired of pulling this carb

[artificialreef]

I tried to rebuild a mikuni sbn44 on a 92 waverunner 111. Upon first install (after first attempt at carb rebuild) i had no vacuum. Went over the blow up schematic and noticed I didnt put the checkvalves in with the stripe pointing up. I installed a new jet (the one with the removable seat) and corrected the checkvalves, reinstalled and same thing. The rebuild kit had the fuel pump diaphrams which I installed as well. The ski has pretty good compression 135lbs. both plugs. There is a decent pulse. No I did not put the hoses back wrong. Pulse to the block, upper to the supply , lower to the return. I used an external tank which removes all the fuel lines from the equation and still the same thing.
I believe it still has to be the carb (fuel pump) but this schematic does not look that complicated. Most of the fuel pump gaskets and diaphram look to only go together one way. I can spring for a new carb but damn do I feel stupid. Has anyone here had the same prob before? I also got a primer ball and it fills the filter (new) and the ski runs until the filter is dry. No vacuum. Thanks for your help.

 

[Jeff Walkowiak]

Re: Im getting tired of pulling this carb

get a small gage that shows vacuum, connect it to the fuel pump suction side and see if it reads any suction.

 

[artificialreef]

Re: Im getting tired of pulling this carb

I ran a hose right from the carb input into an external tank and it did not pull fuel in. Then I put my finger on the end of the hose and felt nothing. I would think this would prove that there is no vacuum at all. Please dont be offended that I didnt purchase the vacuum gauge, just that I am tapped out right now and thought my trouble shooting logic made sense. Any ideas on why no vacuum?

 

[Jeff Walkowiak]

Re: Im getting tired of pulling this carb

well if you have the pulse tube connected to the pump and the pump won't work you messed up someplace when you did the pump,, no other reason other than the cylinder where the pulse tube goes from has no compression.. place your finger on the pulse tube end and crank the engine you should get 3 pounds of vacuum and 3 pounds of pressure from that pulse tube if it has both it is the pump that isn't working

 

[Dryon]

Re: Im getting tired of pulling this carb

Do as Jeff said and confirm you have press/vac at the pulse tube coming off the engine. If there is adequate pulse then the next thing to check is the pump diaphragm. It should hold 4 psig for 10 seconds when pressure is applied to pulse nipple on carb. If pressure drops then replace diaphragm.

The next thing to check is the fuel pump valves which are easy to test if they're operating correctly. Here is how to test them. If the test results are opposite of what is called for below, then the check valves are installed on the wrong side. If neither side will not hold pressure nor vacuum, then possibly they have been damaged or flipped over wrong. They are very delicate and the blue strip side indicator will rub off easily when you handle them.

Fuel Inlet Side:
1) Connect a tube to the inlet nipple.
2) Apply pressure & vacuum with your mouth...
Should release with pressure & hold vacuum.

Fuel Return Side:
1) Connect a tube to the return nipple.
2) Apply pressure & vacuum with your mouth...
Should release with vacuum & hold pressure.

 

[artificialreef]

Re: Im getting tired of pulling this carb

I think i found the problem, unfortunately after buying a new carb. If you read my first post it says I have the upper carb hose going to the supply and the return on the lower. When I put in the new carb it still wouldnt run. (except when i poured fuel down the throught) I pulled upper hose that I thought was the supply and fuel squirted out so I guessed that is the return. I did label them before i touched anything so the previose owner must have messed around with them. I swapped them and it stays running. Sounds like only 1 piston though. Hopefully I just fouled a plug, or need a wire.(hope its not the ignition) but I'll figure that out. What a nitwit. I probably rebuilt the old carb just fine. 200$ lesson. The manual shows supply on the lower nipple too. Sound right to you guys? Thanks for your help. I am bummed, but maybe if i get it firing right and get on the water Ill feel better.

 

[Jeff Walkowiak]

Re: Im getting tired of pulling this carb

top lines are the return lines and bottom are fuel supply so be sure the bottom hoses are going to the correct carb inlets ,, do not go from the front carb top to the second carb bottom,, I have seen people do that, bottom to bottom, top to top, to return line to tank.