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#Post#: 100119--------------------------------------------------
Fuel starvation at high speed.
By: AlmightyBodgeKing Date: December 11, 2015, 2:25 am
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Hello again,
Yesterday evening I managed to reach the dizzy highs of 70mph in
the IIA 109. But after a couple miles she started to cough and
splutter from dual starvation. As soon as I backed off to a more
land rover suitable 60mph she was fine. My guess is she just
emptied the float bowl.
Should I be looking at the fuel pump, or is it just unreasonable
to expect such a vehicle to maintain such a speed? Also, I know
she is running rich at the moment so that could be a factor.
I don't expect to be driving her everywhere at 70mph, I am
generally happy to plod along at 60, or just sit in the wagon
stack. But I was face with a nice empty stretch ofotorway, so I
thought I would she what she would do. The answer is "70, but
not for long".
#Post#: 100122--------------------------------------------------
Re: Fuel starvation at high speed.
By: DarrenH Date: December 11, 2015, 6:22 am
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sounds plausible. only other thing that might recover by
slowing down, reducing fuel usage, is carb icing
#Post#: 100125--------------------------------------------------
Re: Fuel starvation at high speed.
By: AlmightyBodgeKing Date: December 11, 2015, 12:48 pm
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She has a zenith carb, I didn't think they were particularly
prone to carb icing. Also it didn't feel like carb icing, I run
a few old bikes so I am no stranger to the occasional frosty
intake.
Anyhow, I been tinkering today and have soled the carburisation
issues but at a cost. I will make a new thread for that though.
More questions.
#Post#: 100130--------------------------------------------------
Re: Fuel starvation at high speed.
By: Doug_T Date: December 11, 2015, 1:51 pm
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Good news though is that if you're getting a 109 to 70 then the
engine is in good nick.
Does sound like fuel starvation at high revs; could be the pump
(which is easy enough to check - pull the pipe off the carb and
see how well the fuel comes out. IIRC it should be able to fill
a milk bottle before the float chamber drains with the engine
idling) or equally considering the lack of use over the last 30
years you alluded to in a previous topic, it may be that the
flexible hose is breaking down and blocking internally. Possibly
even crud in the tank restricting the pick-up.
A Zenith shouldn't ice at 70; there's quite a lot of heat around
the exhaust manifold area by that speed.
EDIT: from reading your other topic I guess it's sorted now? Was
it leaning out under WOT due to the servo leak? (bearing in mind
the mixture at WOT is defined by the fixed jets and the
accelerator pump, so adjustments to the mixture screw have no
effect under those conditions).
#Post#: 100132--------------------------------------------------
Re: Fuel starvation at high speed.
By: AlmightyBodgeKing Date: December 11, 2015, 1:59 pm
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Engine is definately a good in Doug. She is almost silent at
idle (now I sorted the carburisation issues), has bags of low
end grunt and there is no smoke at overrun or on the power.
But then she has had an annual service despit only doing around
35 miles a year so the oil was always clean.
#Post#: 100133--------------------------------------------------
Re: Fuel starvation at high speed.
By: AlmightyBodgeKing Date: December 11, 2015, 7:39 pm
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Doug_T in reply to your edit. I don't know if it's sorted yet as
I have yet to bleed the brakes after removing the servo so she
hasn't been anywhere this evening. I will report back next time
I get to try her at 70.
Don't want to make a habit of thrashing her though.
#Post#: 100138--------------------------------------------------
Re: Fuel starvation at high speed.
By: prof-pat-pending Date: December 12, 2015, 7:26 am
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Being a 109 is it rear fill ?
If it has the rear tank they have a little filter on the pick up
pipe
These tend to block up with crud and break down with age
If you are just going to be using normal half decent garage fuel
you can manage without it and you will get a better flow
#Post#: 100140--------------------------------------------------
Re: Fuel starvation at high speed.
By: NoelC Date: December 12, 2015, 10:24 am
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Lots of good pointers above. I've experienced this several
times, causes as follows:
1) An old genuine fuel pump with failing diaphragm, then a poor
quality new pattern fuel pump unable to keep up
2) A failing cork seal in the fuel tank changeover tap on a twin
tank military set up
3) Crudded up and corroded gauze at the end of the fuel pickup
pipe
Personally I'd start from the tank and work forwards. If you
have a genuine AC fuel pump and nothing else seems amiss I'd
keep it and fit a good quality overhaul kit. The newer pattern
pumps are quite frankly shite.
And yes, a series should be able to tank along at 70 if in good
condition all day long without coughing and spluttering.
#Post#: 100144--------------------------------------------------
Re: Fuel starvation at high speed.
By: AlmightyBodgeKing Date: December 13, 2015, 1:37 am
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Prof-pat-pending, it has the tank under the drivers seat.
NoelC, thanks for the suggestions. I think I will wait and see
what's what now she is set up with proper fuelling and not
sucking a mix of air and brake fluid into the manifold before I
start tinkering with the fuel pump.
My old SIII would tank along at 70 no problem, all be it bloody
loud, but she would do it.
#Post#: 100148--------------------------------------------------
Re: Fuel starvation at high speed.
By: AlmightyBodgeKing Date: December 13, 2015, 11:25 am
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Ok, so in an attempt to get her running properly now that the
dodgy servo is out of the equation I noticed fuel leaking from
the butterfly spindle on the old zenith carb.
Local landy place didn't have any rebuild kits on the shelf but
did have some copy carbs at £35. Made by britpart. I figured I
would try it, I am well aware of britparts reputation, but
thought it would do as a temporary thing. Also, I have to say
that I have never actually had an issue with anything britpart
myself.
The first thing I noticed was that the choke lever did not
increase the idle speed until 7/8 of the way to full choke. I
made some adjustment to this and bolted it on. After a period of
engine warming and mixture/speed adjustment I had her idling
nicely. I took her out for a quick spin and she seems mostly ok,
but seems a little weak at high rpm / wide open throttle. But is
driveable until I rebuild the original zenith. I may try it with
the oil bath filter back on, I had replaced it with a foam
mushroom type as part oft trying to find out what was going on.
If I remember correctly you can get rebuild kits that contain a
slightly oversize butterfly spindle. I will try and source on of
those. That will be a nice little job for the evenings when the
small people have gone to bed.
She is close, but not quite 100% yet.
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