Outer Limits 4x4 Board

GQ carby gas - 270ks. I'm running dedicated gas (no fuel tank and electonic dizzy advance curve modified for 20 deg initial) so I don't need the original carby.

It looks as if the Impco 300A unit is on the way out as the idle fluctuates between 800 - runs fine and 500 - runs a bit rough. I think it is not holding vacuum - even after a clean. Power at cruise is fine.

What carby / mixer options are available for the GQ manifold? I'm not really chasing huge horsepower, I'm just after a more simple and efficient system. Otherwise I'll replace the 300A.

Thanks,
Duncan.

been there done that. stick with the 300. right on the very top you will see a 13mm nut undo that and there will be a gas idle adjust screw, try that. pulled mine apart on the weekend there is nothing really to go wrong with them.

I'm running a OHg x-450 mixer, i changed over to a EFI manifold, still on a carby block. Straight LPG now. Soon to be blow thru turbo.

The 300A series 1 & 20 is a brilliantly basic unit that should easily last 20 odd years of service ................. provided its SERVICED !

By the sounds of it, its way over due for the converter to be serviced.

Rough idle, altering idle, hard starting are usually signs that the converter is in need of a clean out. What is causing the drama is that there will be a "wax build up " between the diaphram and the converter body which prevents the steady flow of vapour to the mixer @ idle.

Simply unscrew the cover plate on the converter body to remove the diaphram, then wash the diaphram and body in warm soapy water, dry it off, and then reasemble..... if you want to be particularly fussy then replace the diaphram just to be 100% safe.
The last diaphram I bought was $9 from memory.

Kingy

p/s
the diaphram is easily damaged so HANDLE WITH CARE !

Thanks for the info. I've gave the mixer an external clean with a solvent and I couldn't see any wax build up.

It's booked in for a mixer rebuild and a tune. Hoping to get better than 4km/L.

PS. apparently if you can't miss match converter and mixer brands (impco converter with gas research carb doesn't work).

Cheers,
Dunc.

4km/l lol, thats what i get, i think i might do the same to mine and see if it improves, my idle on gas varies and my economy is woeful, although i run 33s on 4.6s daily

Guys Guys Guys....


Before you waste ya hard earned money it AINT the mixer....... its the

CONVERTER

that needs attention.

Keep talking V8Patrol - I'm listening.

What's the deal with the converters?
I can easily see that the carby mixer is prone to wear and tear.

Please explain.

ps. I have Impco converter as well.

Dunc.

There are two main types of LPG "feed" systems.....
& before we go any further......
there are 2 main things under the bonnet which deliver and control the gas, they are ...
A/
The MIXER..... its sole purpose is to mix the gas with air as it enters the intake manifold
B/
The CONVERTER ..... is converts the LIQUID LPG into a vapour using heat from the engine ( usually through the engines cooling system IE: hot water )

There are obviously other bits under the hood too ... a safety switch which stops the flow of LPG when the engine is killed and also a LPG lockout valve.... it too stops the gas when the engine is killed.
But thats about it !


Back to the 2 types of systems.....

1/
COMPLEX.
The complex system uses a complex converter which does ALL the metering of LPG into the engine via a "Simplex" mixer. The simplex mixer usually is a ring setup that sits between the carby and air cleaner.

2/
SIMPLEX.
The simplex system uses a simplex converter, its only job is to convert the liquid LPG to a vapour. Its the complex mixer that meters the flow of vapour LPG to the engine, this complex mixer usually sits ON TOP of the carby and uses a replacement airfilter system

Rules....
You cant run a complex converter with a complex mixer ..... not compatible
You cant run a simplex converter with a simplex mixer .... not compatible

Generally.....
COMPLEX systems are used on small engines.... IE: 4 & 6 cylinder motors
SIMPLEX systems are used on larger engines ... IE: V8's and some of the larger capacity sixes.


The IMPCO 300A series is a SIMPLEX system.
The CONVETRER simply converts the LPG liqiud to a vapour and its then the MIXER which metres the flow into the engine.

As for why the CONVERTERs of both systems "play up"..... the fuel companys mix other gasses, perfumes, etc and in some instances add even more water to the "LPG", as a result the LPG over a long period of time "WAXES UP", this build up of grunge in the CONVERTER limits the amount of movement that the feed diaphram has....... therefore limiting the amount of vapour availiable to the mixer.

This in turn either effects the ..........
1/ Starting of the engine ( too lean a mix of air / LPG )
2/ Poor idleing ( too lean mix of air /LPG)
3/ poor inital acceleration ( too lean a mix of air / LPG )
4/ difficult to acheive hard acceleration ( too lean a mix of air / LPG )
5/ lack of top speed ( too lean a mix of air / LPG )

Pending on which direction the feed diaphram is limited to, its either a
"leaning out" problem or a "Flooding" problem.

The problem is more easilly spotted in winter or cooler than normal atmospheric conditions, reason being that the "WAX" doesnt melt anywhere near as quickly as it would in more temperate conditions ..... IE: SUMMER !

Hope that answers your question

Kingy

V8Patrol, thanks for the extensive reply.

Q: What is inolved in cleaning or rebuilding the converter of the Impco simplex system ?

The only problems I'm noticing are:
fluctuating idle and maybe a little lack of full power.

I have the flow control valve on the mixer 3/4 to rich.


Dunc.

Sorry - just saw this thread..........

http://www.outerlimits4x4.com/PHP_Modul ... hp?t=54373