Duel fuel pumps

[ctomkins]

Anyone heard of or installed duel fuel pumps.?

I'm wondering if it would give more flow besides having a backup.

[seerex]

Well I am sure one electric would give plenty of flow and pretty reliable. Unless you are gonna just mount 2 in the rear <electric ones> I don't think having a mechanical and electric would work . Besides most setup unless you are running triple 50 or 52 mm carbs or a throttle injection unit I am not sure if it would do anything other than cause problems .

[beandip]

I am not sure what you are asking. The '73 &74 came from Nissan with two pumps. I tried a RX-7 pump on a stroker with tripples and it supplied them with no problem . I am runnng one elect only on my 280ZX engine with SUs and havent had any trouble . The only reason to run more than one pump that I can see is for redundancy . One single pump will supply more than enough. You can only run up to 5 psi. with carbs.

[ctomkins]

My carbs (tripple Mikunis) are stumbling on tight right hand corners.

The floats are at 6mm. Mikuni manual recommends 12mm.

At present I'm using a Carter electric good for 4-8 psi

According to my pressure reulator I'm getting 3.5 -4 psi.

There seems to be lots of flow.

I thought the second pump for whatever reason might help with the stumble and add redundancy.

I'm wondering if my Holley pressure regulator could be the prob.

[panchovisa]

Chris, I have dual electrics on my car. Main reason is to pull fuel from both pick-ups in my fuel cell. Second reason is for redundency.

You should have one pump for each pick-up, NEVER tee two pick-ups together to get by with one pump! I've tried it and you WILL have problems.

You CAN, and should tee the lines together AFTER the pumps.

With one pump use ONLY one pick-up in the fuel cell.

[ctomkins]

I heard installing a surge fuel tank might solve the problem.

[Phred]

Clairify your float setting. If you are measuring the float level with the float lid upside down and measuring the gap between the float and the lid, your float level is too high. The stumbling you refer to is a classic high float level symptom. The high fuel level in the float bowl will slosh over into the jet well in right turns, flooding the air corrector jet. This causes a temporary stumble created by a rich mixture. You should be able to get all the HP you are capable of producing with 3 1/5 psi provided your pump has enough volume. Pressure over 5 psi will start to blow the needle off the seat and cause a rich unstable condition.

Phred

[panchovisa]

Chris, a surge tank is very good. A built into the fuel cell surge tank is best. ATL sells cells with surge tank and also surge tanks that can be fitted to existing cells.

Still you do not want to run multiple pick ups to one pump.

From my experience: I had two pick ups tee'd before a single low pressure Holley pump. My car died while driving around the block. The pump had gone bad. Replaced the pump and even with 12 gallons in a 15 gallon cell I couldn't get fuel to the carbs. I had to physically prime the fuel line before the pump to get fuel to carbs, even though the pump was mounted at a height equal to the BOTTOM of the cell.

Think of it this way. Two dash 6 lines into pump, one dash 6 line out. The pump can only maintain head pressure on one of the dash 6 pick up's. The second pick up is one giant leak!

Teeing the lines together after multiple pumps (which each act as one way valves)allows you to scavenge the corners of the fuel cell (the poor mans surge tank) and stops the "leak". Multiple pumps do NOT increase flow because that is a function of the size of the final fuel line to carbs. A single dash 6 line to your pressure regulator will only flow what it can, at your pressure setting, regardless of how many pumps.

[preith]

Clairify your float setting. If you are measuring the float level with the float lid upside down and measuring the gap between the float and the lid, your float level is too high. The stumbling you refer to is a classic high float level symptom. The high fuel level in the float bowl will slosh over into the jet well in right turns, flooding the air corrector jet. This causes a temporary stumble created by a rich mixture. You should be able to get all the HP you are capable of producing with 3 1/5 psi provided your pump has enough volume. Pressure over 5 psi will start to blow the needle off the seat and cause a rich unstable condition.

Phred

IMO the stumbling cannot be corrected by running a lower float level alone. Beleive me, I have tried it. If there are others out there that don't have any problems I'm all ears. I road race my Z and feel the higher G-forces inherent with race tires enhance this problem even more. Wolf Creek Racing modifies the carbs extensively to correct this.

Unfortunately I don't have any pics, but what I ended up doing was epoxy'ing another piece of aluminum on the float cover so it seated against the rib in the float chamber. I then drilled a single hole in each cover above the jet area for venting and epoxy'd a 90 degree vacuum fitting in it. Seemed to do the trick.

Also, Dave at Malvern Racing told me they always ran 4.5psi with a 2mm seat in every one of their road racing cars. Just an FYI, but Dave passed a few years ago now and the business has subsequently folded.

As for the dual pumps question, I have a two pick-up fuel cell and originally had a pair of solid state Facet pumps. I found that even with two it wasn't able to maintain enough fuel pressure at higher rpm's. I switched to a single Carter competition pump (which flowed more than both the Facets) and don't have the issue anymore. I also have two pick-ups feeding to the single pump and do have problems once the fuel gets low. I'm going to install a surge tank this winter to correct that.

[tholt29]

Chris, My car used to have a right hand turn stumble and I lowered the float levels to th epoint that I was starving on long straights... (not recommended). I ended up send the carbs to Rebello for a professional rebuild (Mainly because I couldn't get left and right barrels of each carb equal at low speed). They criticized my low float levels and told me I need to add external bowl vents to keep the fuel from sloshing into the air jets (or some other undesired bypass). They did that and the problem was solved... If you think it would help, I will try and post a couple of pictures...

Tom

[preith]

Chris, My car used to have a right hand turn stumble and I lowered the float levels to th epoint that I was starving on long straights... (not recommended). I ended up send the carbs to Rebello for a professional rebuild (Mainly because I couldn't get left and right barrels of each carb equal at low speed). They criticized my low float levels and told me I need to add external bowl vents to keep the fuel from sloshing into the air jets (or some other undesired bypass). They did that and the problem was solved... If you think it would help, I will try and post a couple of pictures...

Tom

Basically that's what I was trying to point out in my previous post, keep the fuel off the jets. It sounds like my modifications are diferent from Tom's, but accomplishing the same thing.

[ctomkins]

Excellent info guys. Thanks.

It sounds like I have to vent the bowls.