Fuel Pump Conversion Issue

[crosbyman]

drifter…

I did a pressure test 3-5 lbs psi on the pulse nipple of a B&S pump…well I did get loss of pressure upon release my pump indicating loss of air from the gold screen. plugging it with my finger holds pressure a bit longer but it does drop to 0 psi

This would probably explain your loss (leak) of fuel/oil being pushed out of the engine air nipple into the pump cavity

although I can not explain why you get so much juices from your crankcase….. the alternative is to try a different pump and see what happens. not being on site makes things a bit hard to evaluate.

let us know if you find a cure

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[drifter]

Update…..Today I installed the square Mikuni pump and had success! I ran the motor for 25 minutes with zero issues.
Observations: 1) There was still some bubbles of fuel mix in the pulse line but there was no indication that they caused any issue with performance.
2) The pump pulled fuel well (at all speeds) through 7 ft. of line even with the tank sitting on the ground.
3) This motor runs well but today’s runs was superb. Prior to today starts cold in 5 pulls but initially runs very rough (like heavily flooded or dropping a cylinder) for 2 or 3 minutes,
then smooths out. Idled well, but a bit sensitive on needles. Today with the Mikuni pump, it started in 3 pulls and was dead smooth. Idle was “pokata pokata pokata slow! No
sensitivity in the needle settings.
4) Prior to today, there was no oil droplets on the surface of the water after extensive running. (I thought this odd as I’ve always had some oil spots floating on the surface of the test
tank with all of my other motors). Today, the oil spots were there as in the past with all of my other motors.
I will need to get creative as to mounting this pump.

Thanks again for all of the great input. After many years at this hobby I know two things. 1) Great people in AOMCI and 2) I’m still learning every day.

• This reply was modified 3 years, 6 months ago by Mumbles.

[crosbyman]

great news great feedback … i’ll be watching for the round B&S pumps in the future ! I have a Jubile ready to test next spring….

the Mikuni probably does not allow a pressure drop on the pulse going in so the engine can’t push the juices up the pulse line due to an air-lock effect

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[drifter]

Update…..Not one to give up, I pulled out my 1958 Johnson 7.5hp and made the exact conversion using the blocked right hand port and the same fuel pump. The pump worked well and the engine ran great, but, there was still some fuel mix entering the pulse line. No where near the amount that was seen in the 5.5hp Johnson. The fuel mix never actually oozed out of the gold center vent when on the 7.5, but the vent did get wet and the fuel mix was seen traveling up the pulse line to the B&S pump.
Since the 7.5 has removable bypass covers, I decided to tap off of the bypass pulse. Using this method of obtaining a pulse worked perfectly. The pulse line remained clean. The pump easily pumped fuel through a 7 foot line with the tank sitting on the ground. After a 20 minute run almost all at slow idle, there was not a hint of a problem.
This conversion does not require any disassembly of the intake plate. Just blocking off the pressure line. Conversion back to two line system is as fast as blocking the bypass line and connecting the two line fuel/air fitting back up.

[crosbyman]

the 5.5 I sold to a neigbour with the modified channel trolls all day long yet…he does mention that the plugs foul up faster than he likes.

Obviously the unburnt fuel oil mix which should,,…just drain out the purge valve are causing an overly rich mixture but the pump works fine

yours seems to be pushing juices it out the “reassigned” pulse nipple normally these juices would end up back in the pressurized tank via the air line.

I am still suspicious that your crankcase drain valve and/ or internal crankcase drain orifices may not be doing a good a job as they should ending up as excess juices in your pulse line

pressure pulse wise I don’t think a fuel pump would care if it was being pumped with… liquids or just air but your B&S pumps don’t seem to like it . I can see the gold screen as an atmospheric balance feature to let the diaphragm flex both ways but why fuel actually leaks across the diaphragm and reach the screen is odd to say the least . could be crappy diaphragms being destroyed by the fuel ….

if you plan to junk the B&S may as well open one up and look-see inside..for us!

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[rudderless]

I have read 4 stroke pumps are slightly different than 2 stroke pumps.  4 stroke pumps have that screen/filter thingy to keep crankcase oil from filling up the pulse line.  The pump on a 4 stroke should be mounted higher than the motor fitting and pitched back  so the pulse line can drain.  That filter thingy will allow air in so the crank oil can drain back….what the article said…

[crosbyman]

interesting…   but does not explain why so much fuel oil  is pushed into the B&S  pump from the pulse nipple…

 

I wonder what would happen if a check valve was in line with the pulse line to allow  vacum only to reach the B&S pump with fuel oil being  stopped from  progressing to the pump … the check valve acting like a reed valve.

wonder if they make  ” vacum  impulse only” pumps….  that should solve all these  fuel conversion issues on the CDs .

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[rudderless]

 

…just use the rectangle Mikuni pump for a 2 stroke on a 2 stroke..

…maybe seal the vacuum breaker/filter/thingy with some epoxy fir use with a 2 stroke..

 

• This reply was modified 3 years, 5 months ago by rudderless.
• This reply was modified 3 years, 5 months ago by rudderless.
• This reply was modified 3 years, 5 months ago by rudderless.

[crosbyman]

sounds like a plan .. the blocked screen should air lock the juices from reaching the diaphragm area of of the pump

Joining AOMCI has priviledges 🙂

[rudderless]

The 4 stroke version of the Mikuni rectangle pump has a very small hole that serves the same function but the pulse line must be pitched back towards the pulse fitting.,.

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