I've built a 12 volt generator for my motorhome, 3.5 horsey vertical shaft
briggs and stratton engine, running a 70 amp alternator from a pug 306,

I've converted it to run on lpg, but it's running rough.

The engine is electric start, and i've got it on a key switch to start if
from inside the van, with a throttle controll next to the starter switch,
i've used a few relays as i need to disconnect power from the alternator
whilst the engine is cranking or the alternator self exites and stalls the
engine.. anyway it all works on petrol.

the gas supply to the engine comes from a 80 litre vapour take off tank,
through a regulator set at 37 millibars, got autogas in the tank.

The gas pipe goes to a solenoid valve which is only opened when the engines
ignition is on, from the solenoid the gas goes to a Garretson fuel
controller bought from edge technology,

From the outlet of the fuel controller the gas goes to the carby via a
'spud' basicaly a bit of pipe on a right angle fitting, got that from tinley
tech... edge would have to make up a mixer for my engine, and i wanted to
get this thing up and running fast, so i went for the pipe in the inlet from
tinley as i was going past there today.

I've removed the choke from the carb, totaly.. pulled the butterfly out and
removed the spindle and blocked off the hole in the top where the spindle
went,
the carb has a tin air filter plate that bolts onto the end, and there's a
round disc that sits about half an inch away from the carb mouth, this is
part of the duct from the engine breather so the engine sucks in the oil
fumes,

i drilled a hole in that disc for the spud to go through, tried the spud
through the air filter outer cover first, so the end of the spud sat about
2mm inside the disc, no go, wouldent suck the gas through.

So i put the spud through the disc so it's a good inch into the carb mouth,
prolly where the venturi is, the engine will start like this now, but it's
very rough, it will run on full throttle but it's surging on the governer
all the time, go below half throttle and it drops the revs, almost stalls,
catches and revs up again, wont idle or owt.

I've tried spacing the spud so it's not in the carb so much, no differance,

i've ran it with the air filter in the housing, and out, no differance, tho
i did notice whilst i was running without the filter in, housing in place,
when i placed the filter over the inlet for the filter the engine seemed to
rev up, so i'm guessing i'm running way too lean.

I have modified the air filter housing, Basicaly i have blocked up the stock
air inlets that were around the outside of the housing, and put in some 50mm
drain pipe on the cover, this is so i can run a pipe to the filter from
outside the generator box i'll be building later to enclose this genny (with
air flow of course)

but with the air filter air inlet mod, the engine ran perfect on petrol,
exactly the same as it did before i did the mod, all i've done is change
where the air comes into the filter box anyway.

I've tried adjusting what i believe is the mixture screw, on the back of the
fuel controller, above the big fitting for the gas inlet there's a brass
plug, unscrew that and there's a screw down there,

But i've had that wound right in, and right out, and it makes absolutely no
change to the way the engine runs.

When the engine starts up it really chuggs away and gradualy picks up speed,
if it were a 2 stroke i'd say it was 4 stroking, i.e. sounds way too rich,
but once upto speed it's surging as if it's too lean.

Any suggestions on what to try next??
i would really love to replace the entire carb for a gas one, but that'll be
expensive and prolly impossible, this carb is really small,
i'm wondering if i need a mixer on the carb mouth rather than the spud
fitting i have, but i've been assured by the bloke at tinley tech that he
converted his lawnmower with a spud, and it runs fine.

Any suggestions welcome,

Anyone know of a lpg place that does small engines near where i live?
Grantham, near Newark and Nottingham, searching on goole throws up very few
places that do generator/small engine lpg bits.

CampinGazz wrote:

Any suggestions welcome,


I'd guess that the demand valve cannot sense the tiny suction from this
baby engine. Can you increase the vacuum on the inlet ?

Its exactly the same problem I had with the V8 in my Landrover - fixed
using three plastic panscrubs in the air inlet....

Steve

In message , CampinGazz
writes
I've built a 12 volt generator for my motorhome, 3.5 horsey vertical shaft
briggs and stratton engine, running a 70 amp alternator from a pug 306,

I've converted it to run on lpg, but it's running rough.

The engine is electric start, and i've got it on a key switch to start if
from inside the van, with a throttle controll next to the starter switch,
i've used a few relays as i need to disconnect power from the alternator
whilst the engine is cranking or the alternator self exites and stalls the
engine.. anyway it all works on petrol.

the gas supply to the engine comes from a 80 litre vapour take off tank,
through a regulator set at 37 millibars, got autogas in the tank.

The gas pipe goes to a solenoid valve which is only opened when the engines
ignition is on, from the solenoid the gas goes to a Garretson fuel
controller bought from edge technology,

From the outlet of the fuel controller the gas goes to the carby via a
'spud' basicaly a bit of pipe on a right angle fitting, got that from tinley
tech... edge would have to make up a mixer for my engine, and i wanted to
get this thing up and running fast, so i went for the pipe in the inlet from
tinley as i was going past there today.

I've removed the choke from the carb, totaly.. pulled the butterfly out and
removed the spindle and blocked off the hole in the top where the spindle
went,
the carb has a tin air filter plate that bolts onto the end, and there's a
round disc that sits about half an inch away from the carb mouth, this is
part of the duct from the engine breather so the engine sucks in the oil
fumes,

i drilled a hole in that disc for the spud to go through, tried the spud
through the air filter outer cover first, so the end of the spud sat about
2mm inside the disc, no go, wouldent suck the gas through.

So i put the spud through the disc so it's a good inch into the carb mouth,
prolly where the venturi is, the engine will start like this now, but it's
very rough, it will run on full throttle but it's surging on the governer
all the time, go below half throttle and it drops the revs, almost stalls,
catches and revs up again, wont idle or owt.

I've tried spacing the spud so it's not in the carb so much, no differance,

i've ran it with the air filter in the housing, and out, no differance, tho
i did notice whilst i was running without the filter in, housing in place,
when i placed the filter over the inlet for the filter the engine seemed to
rev up, so i'm guessing i'm running way too lean.

I have modified the air filter housing, Basicaly i have blocked up the stock
air inlets that were around the outside of the housing, and put in some 50mm
drain pipe on the cover, this is so i can run a pipe to the filter from
outside the generator box i'll be building later to enclose this genny (with
air flow of course)

but with the air filter air inlet mod, the engine ran perfect on petrol,
exactly the same as it did before i did the mod, all i've done is change
where the air comes into the filter box anyway.

I've tried adjusting what i believe is the mixture screw, on the back of the
fuel controller, above the big fitting for the gas inlet there's a brass
plug, unscrew that and there's a screw down there,

But i've had that wound right in, and right out, and it makes absolutely no
change to the way the engine runs.

When the engine starts up it really chuggs away and gradualy picks up speed,
if it were a 2 stroke i'd say it was 4 stroking, i.e. sounds way too rich,
but once upto speed it's surging as if it's too lean.

Any suggestions on what to try next??
i would really love to replace the entire carb for a gas one, but that'll be
expensive and prolly impossible, this carb is really small,
i'm wondering if i need a mixer on the carb mouth rather than the spud
fitting i have, but i've been assured by the bloke at tinley tech that he
converted his lawnmower with a spud, and it runs fine.

Any suggestions welcome,

Anyone know of a lpg place that does small engines near where i live?
Grantham, near Newark and Nottingham, searching on goole throws up very few
places that do generator/small engine lpg bits.


I'm not overly familiar with small engines but I thought the Garretson
is designed to run directly from a vapour take-off, not through another
regulator. Sounds as though you are getting insufficient gas through at
peek demand.
--
hugh
Reply to address is valid at the time of posting

"Steve" wrote in message
...
CampinGazz wrote:

Any suggestions welcome,


I'd guess that the demand valve cannot sense the tiny suction from this
baby engine. Can you increase the vacuum on the inlet ?

Its exactly the same problem I had with the V8 in my Landrover - fixed
using three plastic panscrubs in the air inlet....

cheers for that,

i put a length of that foil flexi hose on the air filter inlet, about 2
meters long when fully expanded i guess,

got the engine running, was surging like hell, tried stuffing a bit of foam
up the inlet, and that smoothed it out, then it wouldent run on anything but
full throttle,

in the end i discovered that the inlet is very importiant on lpg
conversions, i was able to dictate how the engine performed by expanding or
shortening the inlet, got the hose extended to about 1.7 meters and that
seems optimal, amazing how fussy it is,

But i got there in the end, the mixture screw on the fuel controller
responded to me twiddeling it once i had the inlet sorted out, had to faff
about lots of times making smaller and smaller adjustments, started off on
full throttle, and backed it down, had to re-adjust, but got down to
tickover with it running smoothly, full throttle is fine too now.

the responce about the garretson controller, the one i have is a low
pressure input one, went for that one specificaly as i had a 37 millibar
regulated gas line running past the engine,
seems a lot of people don't know about hte low pressure version, so just ask
for a fuel controller and get the high pressure one, ok when your using a
bottle just for the genny, but in a motorhome where you have a fixed tank
that runs other items, having to put in an unregulated line to the genny can
be a pain,

i'll see how it starts from cold in the morning, but hopefully i have it
sussed, the other half of the problem was getting the 'spud' in the carb
mouth just enough without choking the air flow through the carby, i really
would like a replacement gas carb, but for this size (prolly 20mm if that)
it'll not be worth the expence it seems.

"Steve" wrote in message
...
CampinGazz wrote:

Any suggestions welcome,


I'd guess that the demand valve cannot sense the tiny suction from this
baby engine. Can you increase the vacuum on the inlet ?

Its exactly the same problem I had with the V8 in my Landrover - fixed
using three plastic panscrubs in the air inlet....


This thing is driving me mad, the engine runs so nicely on petrol, but is a
pig on gas.

i really don't like the spud pipe in the inlet thing, seems it's critical to
it's position for the darn thing to work... but, put it in the carb mouth so
the engine starts up, and the engine feels choked, guess it is due to
haveing the already small carb reduced to practicaly nowt due to a pipe
being shoved in it,

Put the sput so it just sits outside the carb mouth, and the engine can't
suck enough to get gas through when cranking,

all ways i've had it set up, it takes a good few seconds of cranking to get
her to fire up, no way i'd like to use the pull start on gas, even when i
use the primer button, it'll give enough gas for a few firing strokes then
die, the controller says to press thebutton for a second then start, maybe
i'll have to rig something up to hold the button in whilst it's cranking,

I'm thinking this spud thing is a very very bad idea, and i really need a
proper mixer to bolt onto the carb mouth, tried a few places that do lpg for
small engines, one never got back to me after asking if by mixer i ment
regulator (wtf was that about, i asked for a mixer that bolts onto a briggs
and stratton 3.5 hp engines carb mouth, don't tell me the bit that lets the
gas into the engine is known as a regulator too)

Of course, now it's easter, so even if i had to get edge to make me one up,
i wont have it in time for going away, my only hope is that one of the lpg
converters is at the peterborough motorhome show and does a mixer for the
briggs engine.

i know it's not all right as the mix screw on the fuel controller has to be
wound almost right out to stop it surging or running rough, it was 3/4 of
the way down the bore when i got the fuel controller, and had a cap that
screwed in the end, that can't be put back on due to the ammount the mix
screw is wound out, so i'm guessing that'd deffo not right,

Anyone any idea's which way is rich or lean on these fuel controllers? not
that it matters too much, i'm adjusting the engine by ear having sold me gas
analizer years ago when i never thought i'd have another petrol engine.