QD-15 with FP conversion- carb running out of fuel

[mixin]

Background- I am pretty well versed in basic mechanics from being a shade tree auto mechanic for the last 20yrs. BUT, this is my first outboard motor-so I am learning alot here. Bought motor last month, has new coils, points, condensers, and a less recent carb rebuild from previous owner. This previous owner also converted the dual line to one line with fuel pump. Pump is a Minkuni (sp?) variety.

Problem- I can feel needle and seat in carb close once I pump the bulb (BRP assembly) several times. Motor starts on first pull. Motor runs ok in the barrel. Idles down low, revs up ok. But carb isn't getting enough fuel and the engine will stall after awhile unless I pump the bulb right before it stalls out. (note: I did not have the tank vented previously and thought that was it, I vented the tank and problem still exists during repeated tries)

So, I figure I have an air leak in my fuel line as per other sticky threads I have read here. I substituted vinyl between the carb and FP outlet- no bubbles going to carb. I put vinyl between the FP inlet and motor side tank hookup - no bubbles coming from tank side. BUT when the motor stalls, the inlet of the FP burps a bunch of air backwards into the vinyl line that is feeding it. Where did this air come from? (note: when switching the fuel lines for vinyl, the inlet barb of the fuel pump pulled out of the pump body, it had some old sealer on it. I put a little gas-proof permatex on the barb sides and tapped it back into the pump body with a hammer - motor still had same problem afterwards)

Either my FP is leaking air internally or the FP conversion was done wrong by the previous owner and caused the FP to go bad?

What is my next step? I think I should replace the FP, but I don't know why it went bad (if it is) and I don't want to damage a brand new one.

Pics show setup with vinyl substituted between FP inlet and motor side fuel hookup. Top of vinyl tubing filled with air once motor stalled and then bubbles continued to come from FP inlet.

I only get to work on the motor about once a week, so I appreciate your patience in waiting for me to try suggestions out. I will respond to any questions ASAP though. Thanks for any replies at all, I really appreciate your time!!!

Mike
Grand Rapids, MI

 

[F_R]

Re: QD-15 with FP conversion- carb running out of fuel

So, is the fuel pump getting it's crankcase pulses from the bypass cover or the intake manifold? I can't tell from the pictures and am not well versed in the Mikuni pump. If it is getting it's pulses from the intake manifold, the question arises: Did he do it right by blocking one of the pulse passages? Or did he even go in and do anything to the passages? You can't simply attach a hose to the fitting and expect it to work.

Personally, I don't think much of doing it that way, but that is another subject.

 

[mixin]

Re: QD-15 with FP conversion- carb running out of fuel

So, is the fuel pump getting it's crankcase pulses from the bypass cover or the intake manifold?

The vacuum/pressure hose is attached to the intake manifold port beneath and behind the carb fuel inlet. I think this is the port that formerly provided pressure to the tank.

If it is getting it's pulses from the intake manifold, the question arises: Did he do it right by blocking one of the pulse passages? Or did he even go in and do anything to the passages? You can't simply attach a hose to the fitting and expect it to work.

There are some clues that show the intake manifold has been removed and reinstalled. The previous owner did report to me that he followed the instructions he saw online - since he used the Mikuni pump, maybe he used the Duckworks page below - let's hope so as it pretty clearly illustrates the pitfalls of the job.

http://www.duckworksmagazine.com/05/columns/max/5/index.cfm

Personally, I don't think much of doing it that way, but that is another subject.

At this point I can see why! But alas, here I am with an inherited quandry to resolve.

After some research, I have found that the FP does have a rebuild kit available. I think I will disassemble the FP and inspect the diaphrams and gaskets for tears. Maybe it can be saved. But the question remains, why did it fail?

To be safe, I might have to go through the process of the conversion again and check all previous work done.

 

[F_R]

Re: QD-15 with FP conversion- carb running out of fuel

Yeah, that duckworks article is where people are getting the idea. Sure is the complicated way to install a fuel pump.

 

[mixin]

Re: QD-15 with FP conversion- carb running out of fuel

Yeah, seems pretty involved - but I guess it's the only way on some motors that were never made with fuel pumps like the 7.5 or had other oddball case casting issues like the 5.5.

While jogging my memory trying to figure out why the FP diaphram could be possibly ruptured, I remembered while the seller was trying to start the motor unsucessfully (because the Attwood primer bulb was junk), he thought maybe he had the plug wires reversed. Upon switching the wires and pulling the starter, the motor backfired through the exhaust (and probably the intake too) not once, but twice.

That caused me to remember how I blew out the power valve in my holley carb on my Chevelle with a precise backfire through the carb once upon a time. If this is what happened, I might try to rebuild the FP and have another go at it with the current set up. It is possible that the conversion was done ok, as if the carb was getting no fuel at all, I don't know that it could run for 2-3 min on just the gas in the bowl?

If this doesn't work, I'm pulling the whole thing apart and putting ALL OMC stuff in it!

Like you F R, I like to keep my OMC all OMC if I can. There's a reason why the OMC FP is engineered to work on the motor. I am also leary of using a fuel pump designed for a snowmobile/4-wheeler/ultralight aircraft/go cart when an off the shelf OMC setup could be used instead. But I have no time for this project, and if I can make it work with what I have, I'll try to run it for awhile--at least until I have more time.

I'll post an update later, Thanks for the advice!

Mike

 

[mixin]

Re: QD-15 with FP conversion- carb running out of fuel

Took Mikuni FP into a motorcycle dealer to get it checked out. I had the parts guy pull a rebuild kit for it. The kit consisted of 2 gaskets and a thin plastic diaphram. Upon disassembly and inspection of my pump, there was only one gasket and the plastic diaphram. Since I could not know exactly how the three pieces from the rebuild kit fit into my pump body, I elected to just replace the whole pump for $23. But of course there's not one in stock. So while looking at pics of ones online I see that the inlet and outlet ports are CAST as a part of the pump body. (Remember when I said that the inlet nipple pulled out?) The MACHINIST seller that I bought this motor from must have broken the original inlet off and drilled out the FP body and machined a new aluminum nipple to press into the pump body (he also made new transom screw grips from billet aluminum too - which are nice actually).

So I have a FP with a loose inlet nipple (constantly under vacuum and possibly leaking air into the fuel supply) and an insufficient number of parts inside it! (I love buying projects, don't you!)

The up side is that the motor actually ran a little while with this cobbled, crappy pump, so I won't to get too optimistic, but putting a new pump on this motor couldn't make it run any worse right? The best possible scenario is that this could prove that the seller did the conversion correctly and all it needs is a pump that is working properly. *knock on wood*

*NEW PUMP IS ORDERED* here goes nothin'!....

 

[mixin]

Re: QD-15 with FP conversion- carb running out of fuel

Finally got the new pump, slapped it on, and the motor runs great! I pumped the primer ball after a while and it got firm right away letting me know that the FP is keeping the carb full now.

One issue is that when I disconnect the fuel line from the connector on the tiller handle, all of the fuel from the carb, fuel pump and lines dumps out (like maybe 1/4 cup or more!). The next time I did this I DC'ed the fuel line from the tank first and pumped the primer for a few minutes until the motor ran out of gas - then it was much less. If there is another way besides running the motor out of gas first, I'd love to hear it!

Also at the same time I lubed all of the throttle linkage as it seemed stiff. WELL, the previous owner zip tied the plug wires together and routed them along the side of the motor instead of the factory location on top. This caused the wires to be unable to move freely with the mag plate! No wonder that throttle was stiff to operate! Then to boot, he attached a spring to the spark plug wires to "pull" them out of the way of the swinging engine cover. This was the culprit of the engine always wanting to idle fast when you released the grip - yanked that damn thing off! I now have the plug wires routed in the factory location and the throttle seems to work amazingly better - I never knew it could work that smoothly!

We took the boat out with a 50lb trolling motor for a 45min cruise and she did great - no leaks, my wife and 3yr old son loved it! My son says "Daddy, now do the green motor! Turn that thing and makes it LOUD!!! *does his best, deafeningly loud outboard motor impression*" - gotta love it! I decided to wait until we got the boat registered though.

I got the boat registered today and slapped the new license numbers and 2012 sticker on her!!! Now the final test! This weekend we're going camping and we're throwing the boat on top of the pop-up and heading out. There's a 400 acre lake nearby and we will be able to launch and tie up right to our campsite...I CANT WAIT!!! I'm literally counting down the hours. I'll see if we can't burn through that six gallon tank! Wish me luck!


Mike