freshie impco rich on decel ???

Propane, Butane, LPG, GPL, C3H8, C4H10
Post Reply
jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

freshie impco rich on decel ???

Post by jono »

I'm just back from a test drive with an AF meter running off the tail pipe - my first conversion 25 years ago.

250 ci straight six running dedicated Impco L converter and 225 mixer - no balance tube.

Not really been touched in 25 years - just driven, and pretty rare drive in last 15 years.

I have suspected last few years on very rare times its been driven that it is wolfing the propane down.

OK. I can deal with a 13.3 idle mixture - either adjust or add a ring

driving I get 15.5 to 16.5 cruising and richens up - low to mid 14's while tramping it.

What has me puzzled and reason for this post -

on deceleration been getting 13s and 14s pretty much consistently with the very quick flash of 17 , 19 and 20's

not the regular max out of the 29.9 range of the AF meter
any guesses ?

known symptoms of a converter screaming out for a rekit ?

maybe just a balance tube to go on to see what it does ?

advice from anyone with experience welcome :)

franz
Posts: 1201
Joined: Thu Oct 07, 2004 7:57 pm
Location: Central Texas
Contact:

Re: freshie impco rich on decel ???

Post by franz »

You mentioned you had the sensor mounted at the tailpipe. It needs to be as close to the engine as possible to prevent fresh air reversion. Engines exhaust pulses in normal operation, especially on decel, and raw air dilutes the mixture around the sensor.

Normal cruise mixture of around 15:1 is great, and a very lean on decel is also normal, as there is no air moving through the mixer to trigger gas valve movement, BUT, there is no way of knowing at this point since I suspect erroneous exhaust sensor readings.

Franz

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: freshie impco rich on decel ???

Post by jono »

oh, my mistake Franz - and thanks for coming in so quickly :)

I should have explained that it is a portable on road tail pipe analyser Vane 8020 or the like , used it many times on many different vehicles.

Am used to seeing lean readings at idle when something blows wind up its pipe in a stationary position , and swapped it from a car just before that was giving all the right readings.
This rich on decel sounds like a hole in something and is drawing a rich mix through maybe a diaphragm of the converter?

I have a spare rekitted converter somewhere, don't have a spare 225 mixer, though may be able to pinch something out of a 200 mixer to try.

Sounds like the mixer is quaffing it through :(

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: freshie impco rich on decel ???

Post by jono »

well, I'll be .....

the key to this simple thing, concept kicking about in my head, wondering how the fuel could get richer - sneaking past the diaphragm seat somehow ??? Well, in a complex mixer such as the Impco it is the mixture screw .... ain't it ?? Idle mixture @13.3 :1 . If anything tailpipe analysers get leaner readings rather than richer if vehicle stationary and a breze blows up its pipe. I wound idle screw in for good measure to see mix went richer, then as I screwed it out could just hear it draw breath of fresh air right up to stoich @ 15.5. Sort of loose enough on that idle screw spring to warrant a leaning ring but that would make the cruise a little leaner than needed . Hooked up the vacuum gauge again after um ... is it really 19 years ?? Idle at op temp gave 22 in Hg, backing off only a little better @ 25 in Hg. A run immediately saw mid 20's on backing off (decel) . In fact this beast @ 60mph [nearly wrote 90 mph :) ] could just light throttle up a long haul hill and read 15.5 - no effort on the old 257 cubic inches :)
All sorted guys, due to not adhering to the golden rule of set idle mixtures first !

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: freshie impco rich on decel ???

Post by jono »

:) now...on start up ...can here air passing through the mixer instead of the fuel vapour :)

such a simple thing caused complex problem$

Post Reply