LCGB Forums

Hi
Just rebuilt my lambretta, was up and running
It's booked in for its mot Friday, filled the tank up, tried to start it tonight won't fire up, strong smell of petrol, changed plug and it's got a strong spark. Took carb rubber off petrol all on the inside and petrol was dripping off the engine cowl
Any ideas please
CB

Some thoughts;
Float stuck
Float needle worn
Float needle seat mucky,(clean with a cotton bud).

Pete

Cheers matey will try that tomorrow night
Will let you know how I get on
CB

what carb do you have fitted charlie ?

if its a Jetex it could well be the float sticking caused by rough casting of the float and friction on the spindle or the float rubbing against the float spindle brackets.
Jetex carbs all need to have some careful finishing work carried out on them and a key area to get working smoothly is the float,... splindle and needle assembly .

Its worth fitting a proper fuel filter between the carb and fuel tap. You'll be surprised at the amount of fine silt that gets through the fuel tap filter.Most of this silt is fine rust particles that the fuel washes off the inside of your fuel tank when its not been used for a while. Check the carb filter and the bottom of your fuel bowl for sediment

Careful on the fuel filter as some are designed for pumped systems. I had the "devil's own job" trying to start with an inline filter from Halfords.
Jetex get bad press but some TLC around the float assembly pays dividends. Run a small drill bit by hand through the hole that the pin sits in. They nearly all bind here.

Also with the plug out kick all the fuel out that's accumulated in the crankcase and the retry it with choke and NO throttle.

I always turn off the fuel tap when not in use, this could help.
(BTW - I had a faulty tap that passed fuel even when I thought it was off - this sometimes flooded my carb..)
Additionally, I picked up a good tip on this forum from another thread: - I have affixed a small but strong magnet underneath the fuel tank near the tap - the idea is that the fine rust particles stay inside the tank, attracted where the magnet is located.

CHRIS in MARGATE wrote:.
Jetex get bad press but some TLC around the float assembly pays dividends. Run a small drill bit by hand through the hole that the pin sits in. They nearly all bind here.

.

I also find its worth using a bit of wet n dry to both sides of the float spindle brackets where they rub against the carb splindle brackets. Difficult to describe in words isn't it

Someone ought to do a tutorial as the Jetex carbs are excellent once they have been fettled

Inline fuel filters are a lot more trouble than they are worth imo.

Rich Oswald wrote:Inline fuel filters are a lot more trouble than they are worth imo.

hows that then Rich ?

you only have 2x very crude filters using an early Delly carb ...one in the carb inlet manifold /banjo and the other on the fuel tank tap neither of which will remove sediment like fine rust from the fuel.

I picked up a good tip on this forum from another thread: - I have affixed a small but strong magnet underneath the fuel tank near the tap - the idea is that the fine rust particles stay inside the tank, attracted where the magnet is located.

Does this really work?

I have magnets on my metal tanks and I agree that inline filters are asking for trouble as they clog up fast and restrict fuel flow, not what you want when tanking down the motorway.

the only filters that clog up quickly are the ridiculously small filters that people seem determined to fit to their scooters and bikes because they look discrete.

A sensible sized inline filter would never clog up in years and gives complete protection and peace of mind against the tineiest of particulate matter.

The alternative (no filter) doesn't seem any kind of sensible option to me when you consider the amount of wasted time and inconvenience blocked carbs and jets cause out on a run when your scoot won't start and run
Pretty it ain't but it does the job
[url][URL=http://s130.photobucket.com/user/peanutNboo/media/filter_zps2ipnshvw.jpg.html][/url][/url]

If a filter clogs up,its because your tank is full of crap.The size of filter only prolongs the problem.Personally,I think if A small one clogs up,sort the problem

point I was making is that they restrict fuel flow, any restriction in the line restricts flow. On motors that don't rev over 7k rpm its not often noticeable, I run 400 float valves, most people use 300 valves and many use 250 valves, I would expect that after a few months of running an inline filter that the flow through the carb float valve to be reduced. After all if you feel the need to run the filter then you feel there is something to filter which means that what ever your filtering will be staying tank side of the filter and therefore restricting flow!

its a good point Eden. For those runing high performance big bore motors with a tiny fuel filter it could conceivably have an effect on fuel flow .
However I would have thought that if a large filter had a significant effect on the fuel flow rate then either the fuel tap is too small or blocked or the motor is using way too much fuel.

The filter that I use on my scooter (pictured) I also use on my 650cc 55bhp motorbike which has 2x 38mm carburettors and it doesn't limit flow to them !

When I did a flow test on my filter it was flowing well over a litre a minute ! at that rate the tank would be empty in less than 5 minutes

Have you done a flow test from the base of the carb fitted in place after using the filter for a few months on your lambretta?

Just interested to find out how much difference there is if any.

no I haven't and you're right ..that would be the acid test wouldn't it.

I suppose I should also remove any restrictions like the carb banjo filter... which is redundant now.

I might give it a go this weekend seeing as the weather has brightened up a bit !

Any news on this one.
stag

Charlie last looked in on the 21st July without posting so I imagine he has either solved the problem or couldn't find what he was looking for.
Pity not to have some closure.... if it was sorted the solution could be useful for others

Thanks for that.
stag