[MidnightAuto]

Well I am opening the patient up (see other thread about adding a pusher pump to help with start up) and it dawned on me that I might look at things a bit more holistically.

I dont hit WOT often, but the couple times I have, I get some backfiring out of the carbs at the top end. It happens in any gear, probably around 5000 RPM. My suspicion is that the small rochester bowls are getting drained and i have a fuel starvation problem. I like my tripower, but I know its probably not the best for 1/4 performance after a certain threshold.

So I am wondering if enlarging the fuel block and lines around the carbs to 3/8 from 5/16 would help. It looks like the center carb has an adaptor at the inlet that could be replaced - its currently fitting for the 5/16 inverted flare. the end carbs is a different story and appears no easy ability to open up those inlets. that adapter does not seem like something readily available though. worst case, I run 3/8 fuel block and lines all to inlets that have a 3/8 to 5/16 reducer. Feels like that may defeat the purpose some, but wanted feedback.

thoughts?

reminder on my setup - stroked 421 to 461. KRE 290 CFM. 60919. Headers/3" exhaust. 1/2 inch fuel sending unit and fuel line to regulator. robbmc mech pump. 3/8 line regulator to fuel block. 5/16 lines after that. tripower venturis have been opened up and all the accompanying tweaks from Dick B. 1" spacers under each carb. MSD ign. TKX 5 speed. car is no slouch, but feel something is being left on the table at the top end.

It would be easy to throw a 850 holley and an electric pump and call it a day, but id like to keep the tripower cool factor.

[steve25]

Sell the Tri power set up and get a Edelbrock duel 4 set up .
You will still have the cool factor plus a good chunk more power to play with .

[MidnightAuto]

Ha. Now that is a recommendation! Feels very mopar though?

[MidnightAuto]

I forgot the 421 had dual quads. And i thought the tripower manifold was expensive!

[mgarblik]

I don't think the fuel supply system on the pressure side, past the fuel pump is likely the problem. I have owned a number of 421 HO tri-power cars, a 2+2 and a 9 passenger wagon, and neither of them had any fuel starvation issues in a 1/4 mile drag race. The 2+2 ran 13.60's @ 105 with stock 5/16 fuel lines between the carbs. 3/8" from pump to the first carb. Rochester 2-jets, each 1 has a fuel bowl nearly as large as a Q-jet. So you have almost 3 times as much fuel on hand. I would make sure your ignition system is top notch and the valve springs are not beginning to float in the 5000 RPM range. My 9 passenger wagon ran 14.50's @ 96 MPH at 5050 Lbs. I pulled a 19' Sea Ray with it every summer for over 12 years and can't recall any fuel delivery issues. Check the rubber fuel hoses from the tank to the fuel pump. Make sure they are not being sucked closed.

[MidnightAuto]

Ok I’ll try and look at other variables.

Fuel starvation would manifest as low pressure when its running rough? I need to watch that gauge at wot.

[Goatracer1]

When I started racing my 428 with Tripower I quickly found that I needed a supplemental electric fuel pump to supply the engine. I never had any problem running 12 second quarter mile times with the stock tripower fuel lines as long as I could get fuel to them.

[Kenth]

You think the 850 Holley needs an electric fuel pump but not the Tri-Power?

I cured the fuel starvation for my Tri-Power with an electric fuel pump some 35 years ago and not looking back.
This also cured fuel percolation at engine shut off due to rising fuel pressure in line between the mech pump and float valves from turned off engine heat.
Then Carter P4070 5 psi, now Facet RedTop 480532 with 5 psi spring.

FWIW

[MidnightAuto]

New update- on a hunch I took a look at my rev limiter on the msd box. It was set at 5700. I bumped up to 6500. Test drive at wot, and no backfiring. I was also able to watch the fuel pressure gauge and it did not dip at any point in the pull. So I guess I’m chalking this up to a rev limiter issue.

So back to plan a and a pusher pump for improved start up