Page 1 of 1
Electric fuel pump on a Mikuni U20-resolved
Posted: Wed Oct 02, 2019 9:21 pm
by 2mAn
Just curious what setup people are using for their Mikuni carb'd U20 cars?
Shop said my pump was bad and suggested I go to an electric pump. After installing the pump he is now telling me that the front carb is leaking(??). Carbs were rebuilt in 2017. After talking with Will, we believe that the (I'm guessing) Carter fuel pump is overpowering the pump. Carter runs in the 4-8 range.
I'm thinking that the solution is either a fuel pressure regulator, or going back to the mechanical pump, which may be bad...
I'm dying not driving this car and this dilemma is making matters worse. I hate taking my cars to shops because I always feel like I get taken advantage of and here we are again. big bill and a car that I still cant drive
Re: Electric fuel pump on a Mikuni U20
Posted: Wed Oct 02, 2019 9:27 pm
by Linda
Skip Miller in Pasadena at Miller Sports and Imports can always give a reliable diagnosis. A long time Datsun mechanic with a ton of excellent recomendations from customers.
Also hate getting ripped off by mechanics, and it has happened plenty of times.
Linda
Re: Electric fuel pump on a Mikuni U20
Posted: Thu Oct 03, 2019 12:06 am
by 2mAn
I guess thanks, but the last time I reached out to him to help me he seemed hesitant, so I tried another shop who was closer. I’m not going to send the car to another shop, let’s just say my budget for paying other people’s labor is now dried up.
But back to the original question... anyone help with that
Re: Electric fuel pump on a Mikuni U20
Posted: Thu Oct 03, 2019 8:49 am
by jhayden
The Nissan shop manual (page 51) specifies 3.4lb/sq.in to 4.26lb/sq.in @700rpm regardless of carby type. Plenty of good, reliable choices out there for low pressure pumps that would not require use of a pressure regulator.
Good hunting.
Jon
Re: Electric fuel pump on a Mikuni U20
Posted: Thu Oct 03, 2019 10:06 am
by 2mAn
jhayden wrote: ↑Thu Oct 03, 2019 8:49 am
The Nissan shop manual (page 51) specifies 3.4lb/sq.in to 4.26lb/sq.in @700rpm regardless of carby type. Plenty of good, reliable choices out there for low pressure pumps that would not require use of a pressure regulator.
Good hunting.
Jon
Thank you Jon
Is it possible that this pump (to be confirmed later) is running more than 4 1/4 psi and is causing the front carb to leak ?
Ive read that others have used the Carter pump and havent needed a regulator, but maybe the SUs or later Mikunis can handle a few extra psi, while the early Mikunis that I have arent able ?
(I realize that this probably should be in the tech discussions rather than the quick / stupid question section, feel free to move if you can/ care)
Re: Electric fuel pump on a Mikuni U20
Posted: Thu Oct 03, 2019 11:34 am
by Gregs672000
1-3lbs is about all you want to run. I use a generic "Mr Gasket" #42 which puts out 1-3.5lbs, which I have confirmed in line. Available at Jeggs and the like, probably local too. I have had one fail in 5 years, cheap enough to buy two to have a back up (which I had when mine failed on Mt Rainier 3 yrs ago). It is mounted just in front of the right rear wheel on the frame. They need to be pushers, not pullers so mount it close to the tank. They make a little noise. I too had concerns that fuel pressure was overwhelming the needle valve so I put in a dial type pressure regulator set to 2lbs. I think my changes in fuel ratios noted on my wideband at idle were actually due to an intake leak, but I plan to rebuild the Dells and will replace the needle valves then. There's a plate made for a chevy that blocks off the hole for the fuel pump that works perfect with stock studs/bolts.
Dave Premo told me of a nissan pump he uses but they're a lot more expensive... quiet though.
Hope that helps!
P.s. there are other Mr Gasket pumps that put out more pressure so check carefully (#12 puts out 7lbs... too much).
Re: Electric fuel pump on a Mikuni U20
Posted: Thu Oct 03, 2019 1:06 pm
by 2mAn
Gregs672000 wrote: ↑Thu Oct 03, 2019 11:34 am
1-3lbs is about all you want to run. I use a generic "Mr Gasket" #42 which puts out 1-3.5lbs, which I have confirmed in line. Available at Jeggs and the like, probably local too. I have had one fail in 5 years, cheap enough to buy two to have a back up (which I had when mine failed on Mt Rainier 3 yrs ago). It is mounted just in front of the right rear wheel on the frame. They need to be pushers, not pullers so mount it close to the tank. They make a little noise. I too had concerns that fuel pressure was overwhelming the needle valve so I put in a dial type pressure regulator set to 2lbs. I think my changes in fuel ratios noted on my wideband at idle were actually due to an intake leak, but I plan to rebuild the Dells and will replace the needle valves then. There's a plate made for a chevy that blocks off the hole for the fuel pump that works perfect with stock studs/bolts.
Dave Premo told me of a nissan pump he uses but they're a lot more expensive... quiet though.
Hope that helps!
P.s. there are other Mr Gasket pumps that put out more pressure so check carefully (#12 puts out 7lbs... too much).
Just spoke with Miki (of M's Factory, the shop in question) and he confirmed the pump used is a Mr Gasket pump that isnt pushing much psi, like 4psi max. Still planning on getting the car this weekend, we'll see what happens between now and then.
Re: Electric fuel pump on a Mikuni U20
Posted: Thu Oct 03, 2019 2:12 pm
by JT68
Its most likely simply an issue with the one carb, mis-adjisted, trash in the needle valve etc, not the pump. Doubt the pump is making tons of pressure.