skinny z

That's the question. I'd like to use a bypass regulator to keep the fuel circulating past my mechanical pump. I haven't found one the spec'd to work with a mechanical pump although one of the techs at Holley suggested that I MAY be able to use their 803BP regulator.
Anyone have any experiences in this regard? Thanks.

naf

iTrader: (7)

Why are you not using the stock style mechanical pump with it's own return?

skinny z

That's a good question. I suppose it's because I was looking for a pump with enough capacity to keep up with whatever I throw at it. The Edelbrock 110 gph unit looked to fit the bill so I picked one up and have been running it for a couple of seasons.
I suppose the next question is what's the capacity of the OEM unit with the return line?
I'll have to look into that.

Joe Tag

iTrader: (4)

Carter M6626 is rated at 120 GPH IIRC.

Joe Tag

iTrader: (4)

http://www.summitracing.com/parts/crt-m6626

naf

iTrader: (7)

even cheaper at Rock Auto: $11.64 minus discount

skinny z

That's what I like about this forum.
Thanks for the info guys. I'll be checking into it.

skinny z

Figured I bring this thread back as I've tried the Carter M6626 and it's not up to the task.
So, back to my original question, has anyone used a bypass style regulator (like Holley's 12-803BP) with a mechanical fuel pump? It says the installation guide (in bold text). 12-803BP is not to be used with mechanical fuel pumps!
I need to do something to keep the fuel moving. Either that, or back to the old school cool can.

naf

iTrader: (7)

mechanical fuel pumps are self regulating, the pump spring is sized so that when the needle seat is shut the pump diaphragm doesn't move fuel. You would essentially have to set up the bypass regulator's pressure below the "no-pump" pressure of the mechanical

skinny z

That I understand.
The problem with "dead heading" the pump is that the fuel, at idle or a low consumption condition, is staying relatively stationary in the supply and discharge lines to and from the pump. On the supply side, if the fuel gets hot enough, such as when it's in close proximity to the exhaust as it is on the drivers side header (in my car), it will vapourize. The pump isn't able to draw from the tank due to this happening and a vapour lock is the result. On the discharge side of the pump, the heated fuel, under pressure and still liquid, will instantly flash to a vapour once it hits the unpressurized atmosphere of the fuel bowl. These are both common conditions of the old school, returnless mechanical fuel pump systems. What's needed here is a way to keep the fuel circulating thereby keeping it cool. Any mechanical pump I've been looking at, short of the non-performance orientated Carter that I'm using, doesn't have a return line to accomplish this. That's why I'm looking for a bypass style regulator that's compatible with a mechanical pump. As you've stated, it's important that the pumps output is higher than the setting of the regulator. At idle, that shouldn't be a difficult thing to accomplish.
The only one I've found is the QFT 30-899.
http://www.quickfueltechnology.com/b...tor-w-jet.html
This regulator has an adjustable jet on the bypass that will allow the correct pressure to be set. That's the route I intend to go.
I think.

naf

iTrader: (7)

You're exactly right. The carter will have a return port that will continually cycle fuel through the lines, but not between the pump and the carb. This can still cause problems as the fuel in the lines will pick up heat from the pump and the exhaust. The factory installed a helper pump in the tank to prevent vapor lock in the lines during shut down and hot soak conditions. On my 87 I have no provision for the mechanical pump rod, but use a mechanical pump as a return regulator. In addition to the in-tank pump that the 87 comes with (too low pressure to use on its own) I've installed an in-line pump that feeds fuel through the stock fuel lines to a non-functioning mech pump, retaining the factory return plumbing. I have also installed heat shielding on the fuel lines that run adjacent to my headers.

In the past, prior to the heat shielding I experienced fuel boiling issues on extended highway trips. Usually in the Spring, perhaps exacerbated by winter fuel mix (lower vaporization point-I'm told anyway). I have not had that problem after the heat shielding, but haven't had any long trips since it was installed, so no definitive results.

The best solution I can imagine, would be to install a decent in-tank pump, re-route the fuel lines away from the exhaust and use a fender well mounted return regulator with a direct feed line to the carburetor. Avoid all of the heat sources. I haven't had to go there yet.

My 85 TA, with only the mechanical pump (a carter btw) has never had any of these fuel related issues, and it has been on several extended trips. It has factory manifolds though, which may not pass as much heat to the fuel line. My hedman's are coated though on the 87.

In your situation, I would try the small holley fuel pump mounted in the rear feeding the stock fuel lines and keep the carter up front. Then apply some heat shielding. I used the sock like stuff with the DEI heal shielding tube over it. 3' was enough to apply to both supply and return where they passed close to the headers.

Wife'sCar

iTrader: (1)

I had issues with my bronco vapor locking, I added a small electric helper pump at the tank, helped but still had an issue. I mounted a mr. Gasket return style regulator as close to the carb as I could. After playing with the adjustment enough I've got the fuel flowing to keep it cool, engine runs great, and no more vapor lock. Whether or not this will work for something track driven I'm not sure, but every day driving I've run this for a year or two now no sweat. Runs great. Mr. Gasket reg was pretty cheap from summit as well. Make sure you get a line adapter and a gauge to adjust the pressure.

You may even benefit from ditching the mech pump and running just an electric pump and a return reg togther. I plan to eventually.

skinny z

I've been exploring a number of options.
What I've found is that there's only one bypass style regulator on the market that's specifically designed to work with a mechanical pump. That's QFT's 30-899 which has a tune-able jet in the return line. It's been suggested more than once that a conventional bypass regulator can be modified to incorporate a carb jet in the return line. Something I may look in to.
Then of course, there's always going back to my old Holley blue pump. Noise and all.
I figure that keeping the fuel moving is the best plan as opposed to the heat shielding but I may to do both. Racing here in the summer isn't much fun with the DA approaching 4000'+ at times. Kills the performance. That's why I'd to get something done before the season closes in mid-October. Nice cool fall evenings and more horsepower.

skinny z

40 GPH. Runs out of steam for me before the top of 2nd gear (and that's with the bypass closed). I had hoped it was the 120 GPH I thought it was.

skinny z

Wait. There's more!

http://www.kse-racing.com/TechDocs/K...stallation.pdf

https://www.demoncarbs.com/Assets/do...LIT715rev2.pdf

-=Z28=-

iTrader: (3)

Skinny, old thread I know. Ive been doing some looking and reading and wondering what you ended up doing. My mech pump is pre set for 6psi but I really want to benefit from using my return line, cooler fuel, etc. Did you get the reg from kse?

Thanks man.

skinny z

No sir. I abandoned the mechanical pump altogether for several reasons not the least of which is that the fuel pump pushrod almost sawed the cam in half! Long story with pictures available.

I ended up going back to the Holley Blue Pump with their by-pass regulator. Kept the OEM 3/8" steel supply line and added a -6 AN return that's connected to the factory 5/16ths fitting at the tank. While I haven't raced in a while, it was trouble free with solid and consistent fuel pressure. The car has been parked for the last while pending a fresher shortblock.

I have plans for the fuel system, which will maintain an electric pump but one that's quieter. That pump is sitting in a bin on the parts shelf somewhere...

NoEmissions84TA

iTrader: (1)

Crap - I had planned to use the M6626.
But thanks for saving me from the aggravation.

-=Z28=-

iTrader: (3)

Right on. Yeah, I'm thinking about going electric now... I dont need anything crazy, prefer a inline style pump so I dont have to deal with anything in the tank. Still learning about the matter... and carb tuning. That in itself is a lot to take in. Car is rich. Burning eyes horrible rich. What I dont get is nothing has changed sense dyno sessions. Engine dyno. I did figure out the secondary needle and seat was shot and fuel was dumping out of the boosters. Fixed that but still seems rich. Tomorrow, well today, later today, I'm going to mess with idle valves and go down the list. 4150 dbl pump, mec secondary. Hope to have it figured out.

Thanks for the reply.

skinny z

I had best results with the Edelbrock 1721 mechanical 110 gph pump. Except for heat soak issues. I did a post years back.

https://www.thirdgen.org/forums/carb...edelbrock.html

Best advice with regards to carb tuning when it's been worked on and the thread appears lost is to start from scratch. Reset the transition slot and go from there.
I suppose the very best advice would be to suggest a wide band O2 / AFR gauge. There is no substitute.

-=Z28=-

iTrader: (3)

think I'm ordering the aem. 200 bucks but it's well worth it from what I've been reading.

Yes, that's what I did, started all over. Set timing to 10deg, all in 36ish. have the front mixture screws out .75 and rear out 1. Achieved 10" of vacuum, runs much better, but still smells rich.
waiting for it to cool so I can take off and look at transition slot. See where it's at.
is 10" ok for a 232/233 106/114cl .545/.547 @.050. Seems low to me.. it will idle at 600rpm but seems to lopey. Nice smooth idle at 700.. fuel pressure gauge is nice and smooth now also. Before it bounced like crazy from 5.5 to 10. Now it's right at 6.

Thanks man.

skinny z

I would think it needs more base timing. That'll wake up the idle. But obviously you'll have to take some out of the mechanical advance. If you have an HEI, you're kind of screwed. Limiting the timing on those takes some fab work. My MSD distributor has interchangeable timing bushings. I run a minimum of 16 initial. It's more like 28-30 because I have my vacuum advance connected to full vacuum. That can be a exercise in tuning in and of itself though.

Do you have full specs for your cam? Advertised duration specifically? I'm running COMP's XR288HR with 236/242, 288/294, 110 LSA. That gives 71 degrees of overlap. With a worn out engine I can muster 10" of idle vacuum at 750-800 RPM. That's with a healthy base timing though.

You won't regret the AFR gauge. You'll be able to dial in the carb in no time. I found it particularly useful for power valve tuning. I have the fuel mixture gauge and a vacuum gauge permanently mounted in the car.

-=Z28=-

iTrader: (3)

I am running a hei now but have a adjustable can. I have a msd 6al programmable, but have yet to install it. Believe I can hook that afr to it as well and log data.

Heres the cam specs.

NoEmissions84TA

iTrader: (1)

The adjustable can is for the vacuum advance. You need to limit the amount of centrifugal advance (springs & weights under the rotor).

-=Z28=-

iTrader: (3)

Yes, thanks. I wasnt thinking right. Been a carb learning session all day. Lol. With vac unhooked, and initial at 12,(i changed it 2*) i get 38* at 3k. Once this afr shows up I'm going to install the msd. I know I have to lock out dizzy, but not sure if I still would use vac. Still fairly green to ignition and fuel delivery. Lots to learn.
I should prob start a new thread. Kinda hijacked skinny old thread.

Thanks for chiming in man.

skinny z

I would be interested to know if the MSD programmable ignition is strictly RPM based or is there a MAP input as well. If you have MAP then you won't have to consider the vacuum can on the distributor. I've adapted a MAP sensor into my carbed 350 and data log with that via an old Innovate interface although I still have to use the vacuum can for tuning.

That's a sizable cam! 293/296, 110LSA. I work out 74 degrees of overlap. Your cam card says 78. Compared to my 71 degrees your 10" of idle vacuum is doing well I'd say. These big cammed SBC's will eat up a lot of idle advance. Just pay attention to spark knock.

EDIT: If you do start a new thread, post a link to it here.

-=Z28=-

iTrader: (3)

That duration is at .006 checking height. If you go down to .050 check height its 232 or whatever. Isnt that how most cam cards are given? (.050)

-=Z28=-

iTrader: (3)

Says 3 pin map hook up. Haven't installed it yet as I'm still learning.... hehe.

skinny z

Yes. Cam cards will list all of the specs that are on your cam sheet. Advertised/.006" duration as well as .050" numbers. Also Lobe Separation Angle and lobe centre lines.
Some builders want the .050" numbers. Others use the advertised numbers. I tend to use both.

That indicates that the MSD will have a full suite of timing inputs. You won't need the vacuum or mechanical advance in the distributor. I may find myself going this route myself. I was always tinkering with the timing and some the processes are very tedious.
As for the MAP sensor, not sure of your current electrical arrangement. The OEM sensor I picked up required it's own 5 volt steady state power supply. Nothing more than a chip I picked from the local electronics store and wired it in. Normally these sensors are powered the ECU.

-=Z28=-

iTrader: (3)

I think its pointless to try and adjust carb until I have msd hooked up. So that's what today's job is. Dont have any experience with that so I may lean on ya if that's ok. Prob pm you about it. Locking out dizzy seems fairly simple, but there are a few things that I may need help with. Prob start that thread.

Thanks skinny.