Apologies for the on-topic post, I havent got a MoHo to talk about.

My SO Guzzi V50 is becoming a right pain to fix.
Runs great for around 4 miles, then cuts out on the LH cylinder.
New LH coil fitted last week. Electronic ignition. Carbs have been
balanced and cleaned.Valve clearances checked, all fine.
When cold, it starts fines, runs well for 3 miles, starts spluttering,
then goes onto 1 cylinder. I've suspected a too strong mixture
(flooding) as the plug is wet, slightly, when I stop and take it out,
however, if it isnt firing for a few hundred metres, the plug will have
unburnt fuel on it anyway wouldnt it?
Getting a rich mixture on that carb shouldnt really cause it to cut out
though should it, as before that there should be black smoke etc before
it cuts out?
Once cooler, it starts again fine.
Heat causing the ignition module to fail? - not sure, as it isnt that
cool when it starts up again, and seems to be sparking well.

Any pointers?
Thanks.

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On 04/09/2023 18:55, Alan Lee wrote:
> Apologies for the on-topic post, I havent got a MoHo to talk about.
>
> My SO Guzzi V50 is becoming a right pain to fix.

<http://www.maydavid.co.uk/mainjet.jpg>
Rather than flooding, I reckon it is running too lean. this is backed up
by the state of this main jet, which was cleaned 6 months ago. Both
holes are full of gunk. Starngely, the plastic filter is clear, so this
shits is so fine it gets past the filter.
Time to get the new tank out, this one is full of shite, mostly old
Petseal which has flaked off. I've known about this for ages, but never
got round to changing it.
Oh well, shit in the carbs is the main suspect now. Should have checked
first, as its a 1 minute job to take the float bowl off.

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On 04/09/2023 18:55, Alan Lee wrote:
>Apologies for the on-topic post, I havent got a MoHo to talk about.
>
>My SO Guzzi V50 is becoming a right pain to fix.
>Runs great for around 4 miles, then cuts out on the LH cylinder.
>New LH coil fitted last week. Electronic ignition. Carbs have been
>balanced and cleaned.Valve clearances checked, all fine.
>When cold, it starts fines, runs well for 3 miles, starts spluttering,
>then goes onto 1 cylinder. I've suspected a too strong mixture
>(flooding) as the plug is wet, slightly, when I stop and take it out,
>however, if it isnt firing for a few hundred metres, the plug will have
>unburnt fuel on it anyway wouldnt it?
>Getting a rich mixture on that carb shouldnt really cause it to cut out
>though should it, as before that there should be black smoke etc before
>it cuts out?
>Once cooler, it starts again fine.
>Heat causing the ignition module to fail? - not sure, as it isnt that
>cool when it starts up again, and seems to be sparking well.
>
>Any pointers?
>Thanks.

In my experience ealier this year, it was a gungy fuel cap vent gave
identical symptoms which had got gradually worse. Try running with the cap
loose, ajar, without a seal or whatever...
HTH

Chris

--
XV750SE & GS550T

Alan Lee <alan@darkroom.plus.com> wrote:
> Apologies for the on-topic post, I havent got a MoHo to talk about.
>
> My SO Guzzi V50 is becoming a right pain to fix.
> Runs great for around 4 miles, then cuts out on the LH cylinder.
> New LH coil fitted last week. Electronic ignition. Carbs have been
> balanced and cleaned.Valve clearances checked, all fine.
> When cold, it starts fines, runs well for 3 miles, starts spluttering,
> then goes onto 1 cylinder. I've suspected a too strong mixture
> (flooding) as the plug is wet, slightly, when I stop and take it out,
> however, if it isnt firing for a few hundred metres, the plug will have
> unburnt fuel on it anyway wouldnt it?

Yep.

> Getting a rich mixture on that carb shouldnt really cause it to cut out
> though should it, as before that there should be black smoke etc before
> it cuts out?

The mixture would have to be exceedingly rich to cause the cylinder
to cut out completely. But ignition failure would result in a wet
plug from no spark.

> Once cooler, it starts again fine.
> Heat causing the ignition module to fail? - not sure, as it isnt that
> cool when it starts up again, and seems to be sparking well.

I really don't see a way for heat to be causing the carburetor to
richen up. This really sounds like either fuel starvation (in which
case the plug probably wouldn't be wet) or more likely a heat-related
ignition failure.

You might try temporarily fitting a spark plug indicator lamp such as
this one, to confirm the cylinder is cutting out due to loss of spark.

https://www.amazon.co.uk/Sealey-SEAQF-VS526-Ignition-Multicoloured/dp/B00S6C94VA

If it's a Dyna aftermarket ignition (or similar) there's probably
not much you can do besides trying a replacement "points plate"
as it appears the whole works is contained within the two trigger
module assemblies.

https://www.dynaonline.com/dyna-s-ignition-system-for-1979-1987-moto-guzzi-v35-v50-v65-ds5-1/

Does each carburetor have its own fuel tap?

--
FJR1300A, GL1000, KLR650A6F, EX250J9A, DR200SE, Vespa Ciao

On 04/09/2023 23:13, Mark Olson wrote:
> I really don't see a way for heat to be causing the carburetor to
> richen up. This really sounds like either fuel starvation (in which
> case the plug probably wouldn't be wet) or more likely a heat-related
> ignition failure.

See my other post. Fuel starvation through a blocked float chamber and
main jet. And, what has surprised me is that I got the cylinder that
wasnt firing totally wrong, I thought it was the left, it was the right.
Totally dry, white plug. I thought this because the LH cylinder was
giving an intermittent spark, so had its coil changed, hence when it
spluttered afterwards, I thought it was the same cylinder.
What didnt help was that it ticked over and ran well enough in the
garage, carbs were well balanced, and it would always start.

The main jet isnt used until around 50% throttle opening, and one of the
other ports was partially blocked, so its no surprise (once I'd found
it) that it would tickover, but 3 miles must be the limit for the float
blockage, and it must have used the fuel in there, and couldnt get
enough back in to supply the cylinder.
Turn off, pull over, wait 30 secinds and the float bowl was partially
refilled, but struggling to run, leave it 5 minutes, and all was well again.
Frustrating, as these carbs were cleaned 6 months ago, it's the shite in
the tank that is causing the shite in the carbs.

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Alan Lee <alan@darkroom.plus.com> wrote:
> On 04/09/2023 23:13, Mark Olson wrote:
>> I really don't see a way for heat to be causing the carburetor to
>> richen up. This really sounds like either fuel starvation (in which
>> case the plug probably wouldn't be wet) or more likely a heat-related
>> ignition failure.
>
> See my other post. Fuel starvation through a blocked float chamber and
> main jet. And, what has surprised me is that I got the cylinder that
> wasnt firing totally wrong, I thought it was the left, it was the right.
> Totally dry, white plug. I thought this because the LH cylinder was
> giving an intermittent spark, so had its coil changed, hence when it
> spluttered afterwards, I thought it was the same cylinder.
> What didnt help was that it ticked over and ran well enough in the
> garage, carbs were well balanced, and it would always start.
>
> The main jet isnt used until around 50% throttle opening, and one of the
> other ports was partially blocked, so its no surprise (once I'd found
> it) that it would tickover, but 3 miles must be the limit for the float
> blockage, and it must have used the fuel in there, and couldnt get
> enough back in to supply the cylinder.

Yet, you said:

"Carbs have been balanced and cleaned."

I took that to mean, that you had taken the carbs apart after
discovering this behavior and found that they were pristine inside. So
that's my fault for inferring something that wasn't the case.

> Turn off, pull over, wait 30 secinds and the float bowl was partially
> refilled, but struggling to run, leave it 5 minutes, and all was well again.
> Frustrating, as these carbs were cleaned 6 months ago, it's the shite in
> the tank that is causing the shite in the carbs.

As I said above, "sounds like either fuel starvation (in which case
the plug probably wouldn't be wet) or ..."

I admit that it was bad advice to you that it was more likely to be
ignition related. Any time I hear of a bike running OK for a short
bit, then recovering after a short stoppage, I immediately think of
a fuel problem which is why I asked:

"Does each carburetor have its own fuel tap?"

I've seen fuel flow issues on my missus' bike due to the tank vent in
the fuel cap being blocked by a rubber coated underside of a tank bag.
It behaved much like yours, would run fine for a while but eventually
sputtered to a stop, but would recover after sitting for a few minutes
and start the cycle again.

I don't envy you the tank cleaning process. And I don't recommend simply
fitting a filter, this never works well on a gravity feed system, which
is why carbed bikes without fuel pumps invariably have just a fine screen
in the petcock and do not employ inline filters.

I would De-rust the tank and optionally coat it with epoxy, although
I have had less than good results with one of the popular treatments
(Kreem). I've heard of some good results with POR-15 but I think
now I would opt for mechanical agitation with something inside the
tank to dislodge loose chunks, followed by chelation rust removal,
and finishing up with phosphoric acid to treat the bare steel surface.

--
FJR1300A, GL1000, KLR650A6F, EX250J9A, DR200SE, Vespa Ciao

On 05/09/2023 10:34, Mark Olson wrote:
> Alan Lee <alan@darkroom.plus.com> wrote:
>> On 04/09/2023 23:13, Mark Olson wrote:
>>> I really don't see a way for heat to be causing the carburetor to
>>> richen up. This really sounds like either fuel starvation (in which
>>> case the plug probably wouldn't be wet) or more likely a heat-related
>>> ignition failure.
>>
>> See my other post. Fuel starvation through a blocked float chamber and
>> main jet. And, what has surprised me is that I got the cylinder that
>> wasnt firing totally wrong, I thought it was the left, it was the right.
>> Totally dry, white plug. I thought this because the LH cylinder was
>> giving an intermittent spark, so had its coil changed, hence when it
>> spluttered afterwards, I thought it was the same cylinder.
>> What didnt help was that it ticked over and ran well enough in the
>> garage, carbs were well balanced, and it would always start.
>>
>> The main jet isnt used until around 50% throttle opening, and one of the
>> other ports was partially blocked, so its no surprise (once I'd found
>> it) that it would tickover, but 3 miles must be the limit for the float
>> blockage, and it must have used the fuel in there, and couldnt get
>> enough back in to supply the cylinder.
>
> Yet, you said:
>
> "Carbs have been balanced and cleaned."
>
> I took that to mean, that you had taken the carbs apart after
> discovering this behavior and found that they were pristine inside. So
> that's my fault for inferring something that wasn't the case.
>
>> Turn off, pull over, wait 30 secinds and the float bowl was partially
>> refilled, but struggling to run, leave it 5 minutes, and all was well again.
>> Frustrating, as these carbs were cleaned 6 months ago, it's the shite in
>> the tank that is causing the shite in the carbs.
>
> As I said above, "sounds like either fuel starvation (in which case
> the plug probably wouldn't be wet) or ..."
>
> I admit that it was bad advice to you that it was more likely to be
> ignition related. Any time I hear of a bike running OK for a short
> bit, then recovering after a short stoppage, I immediately think of
> a fuel problem which is why I asked:

Unless it's a Morini when "it's always ignition".

Except when it's only cutting out on one cylinder when it might be
carburation.

The no spark when hot scenario usually affects both cylinders on those
and almost always the ignition winding on the stator on its way out.

Theoretically possible to be one transducer or even the pickup. Standard
diagnostic on those is to swap the components around and see if it
transfers the issue to the other cylinder.

Best course of action with the Guzzi tank might be a POR15 treatment.

--
Moto Morini 2C/375
Gilera 175 Sport, Husqvarna 401 Svartpilen
Honda CB250RS (Not Waynetta!)
"Do not adjust your mind, there is a fault in the reality"

On Tue, 5 Sep 2023 07:08:24 +0100, Alan Lee <alan@darkroom.plus.com>
wrote:

>On 04/09/2023 23:13, Mark Olson wrote:
>> I really don't see a way for heat to be causing the carburetor to
>> richen up. This really sounds like either fuel starvation (in which
>> case the plug probably wouldn't be wet) or more likely a heat-related
>> ignition failure.
>
>See my other post. Fuel starvation through a blocked float chamber and
>main jet. And, what has surprised me is that I got the cylinder that
>wasnt firing totally wrong, I thought it was the left, it was the right.

You didn't do the "Ouch! that one's OK..." exhaust pipe test, then?

--

-Pip

On Tue, 5 Sep 2023 12:38:09 +0100, Pete Fisher
<peter@ps-fisher.demon.co.uk> wrote:

>On 05/09/2023 10:34, Mark Olson wrote:
>> I admit that it was bad advice to you that it was more likely to be
>> ignition related. Any time I hear of a bike running OK for a short
>> bit, then recovering after a short stoppage, I immediately think of
>> a fuel problem which is why I asked:
>
>
>Unless it's a Morini when "it's always ignition".
>
>Except when it's only cutting out on one cylinder when it might be
>carburation.

Common ignition on a Vee?

I had an early (points) model of XS750 that would lose one cylinder
when hot. Three separate ignition systems, timed 120deg apart. Turned
out to be a faulty condensor that died whenever it got hot.

--

-Pip

On 05/09/2023 17:37, Pipl wrote:
> On Tue, 5 Sep 2023 07:08:24 +0100, Alan Lee <alan@darkroom.plus.com>

>> See my other post. Fuel starvation through a blocked float chamber and
>> main jet. And, what has surprised me is that I got the cylinder that
>> wasnt firing totally wrong, I thought it was the left, it was the right.
>
> You didn't do the "Ouch! that one's OK..." exhaust pipe test, then?

No, couldnt tell the difference at all. It had been running for 10
minutes or so, so up to temperature, and air cooled engines seem to take
an age to cool down.
I've just taken it out, 15 miles trouble free today. What a lovely
little bike it is, handles brilliantly. But christ, its slow.
It's being sold, hopefully, tomorrow. If not, I'll be riding it up to my
new house in Scotland one day next week.

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On 05/09/2023 17:40, Pipl wrote:
> On Tue, 5 Sep 2023 12:38:09 +0100, Pete Fisher
> <peter@ps-fisher.demon.co.uk> wrote:
>
>> On 05/09/2023 10:34, Mark Olson wrote:
>>> I admit that it was bad advice to you that it was more likely to be
>>> ignition related. Any time I hear of a bike running OK for a short
>>> bit, then recovering after a short stoppage, I immediately think of
>>> a fuel problem which is why I asked:
>>
>>
>> Unless it's a Morini when "it's always ignition".
>>
>> Except when it's only cutting out on one cylinder when it might be
>> carburation.
>
> Common ignition on a Vee?
>
> I had an early (points) model of XS750 that would lose one cylinder
> when hot. Three separate ignition systems, timed 120deg apart. Turned
> out to be a faulty condensor that died whenever it got hot.
>

The transducers are independent and the pickup might be dodgy for just
one connection. Much more often it's no sparks at all due to low output
from the stator winding (about 20-50 volts AC at kickstart speed).

The Ducati Teletrotecnica system is WEIRD. Often killed completely by
'helpful' breakdown folk applying 12v DC to the transducers.

--

Moto Morini 2C/375
Gilera 175 Sport, Husqvarna 401 Svartpilen
Honda CB250RS (Not Waynetta!)
"Do not adjust your mind, there is a fault in the reality"

On 05/09/2023 18:48, Alan Lee wrote:
> On 05/09/2023 17:37, Pipl wrote:
>> On Tue, 5 Sep 2023 07:08:24 +0100, Alan Lee <alan@darkroom.plus.com>
>
>>> See my other post. Fuel starvation through a blocked float chamber and
>>> main jet. And, what has surprised me is that I got the cylinder that
>>> wasnt firing totally wrong, I thought it was the left, it was the right.
>>
>> You didn't do the "Ouch! that one's OK..." exhaust pipe test, then?
>
> No, couldnt tell the difference at all. It had been running for 10
> minutes or so, so up to temperature, and air cooled engines seem to take
> an age to cool down.
> I've just taken it out, 15 miles trouble free today. What a lovely
> little bike it is, handles brilliantly. But christ, its slow.
> It's being sold, hopefully, tomorrow. If not, I'll be riding it up to my
> new house in Scotland one day next week.
>

"If in doubt pull one of the plug leads out" If it doesn't run at all
then you have your 'smoking gun'.
--
Moto Morini 2C/375
Gilera 175 Sport, Husqvarna 401 Svartpilen
Honda CB250RS (Not Waynetta!)
"Do not adjust your mind, there is a fault in the reality"