Imcpo 425 power adjustments

[stool]

Men Im after some help on what screw will feed more gas into the engine as it has good power from idle.

But then it feels like it runs out of gas about 3000rpm

The engine is a gas only chev 454 running the 425 mixer on a holly base plate

One more point which makes me think its running lean is its way to good
on fuel for the size of the motor.

[PGS 4WD]

The mixture main screw is the large bolt with a spring under it in the side on older models, it is an allen key in a hole on the later ones. I would suggest if it feels good up to 3000 rpm then it won't be rectified by adjusting the mixture screw as that is an overall adjustment, it is more likely an LPG supply issue, too smaller lock off, blocked filter or gas line. What sort of power does it make, what brand and size gas lock off and lines are they?

Joel

[bazooked]

on a 454 you will probably need twin gas carbs for it to keep up.

[PGS 4WD]

Beware the carburation trap. Too smaller carby won't make peak power but also won't hurt itself, insuficient LPG supply will kill an engine due to lean mixtures. You could fit twin carbs and only make the problem worse if the LPG supply isn't there from the tank.

Joel

[stool]

Thanks for the reply`s

I will have a look at the size of the convertor and the gas lines +tank lock`off
and report back.

Some more info what the car is doing

When doing over 100kph in 5th with load on the engine it seems to surge
and the gas carb makes a screaming sound as you accelerate or when
load comes off the engine

The screaming or whistling sound is also just off Idle which sounds to me like the air passing over the gas valve in the mixer

So whats the best way to work out which gas valve i have as ive read there is
different sized valves to suit engine sizes.

[ronno]

me and another 2 mates run the 425s all 3 off them are on chevs 2 283s and 1 350 they all have a flat spot around 1200 to 1600 revs and all make a whistle sound.Cant figger it out either but all find them to run good.

[create]

I found my 425 whistles a little bit too just off idle. From what I have read I think this is normal.
Have a look at this link it shows the different gas valves.

http://cars.rasoenterprises.com/Propane ... xtures.htm

Have you also removed the gas restrictor also? If you remove the vapour hose connector and look down the hole there is a thing like a washer jammed in there. Pull that out and it should make a difference too.

[PGS 4WD]

The whistle is normal, the flat spot can be rectified with different converter springs and a retune on the dyno.

Joel