Blowing out of Carburettor

[Collector Inspector]

Does the carb have the screw on bell mouth?

If not, it will spit and fart about like an Old Ships Cat.

Post some pics and a vid of it doing nasty.

Will help aye.

B

[Collector Inspector]

Does the carb have the screw on bell mouth fitted?

I think 1/2" is what you need..........your engine number is?

If not either, it will spit and fart about like an Old Ships Cat.

Post some pics and a vid of it doing nasty.

Will help aye.

Not hard.

B

[Gannet]

Thanks Bruce,
Yes, it has the bell mouth fitted (why and how did Villiers manage to plate the outside and leave, with most of them that I have seen, unplated on the inside?).
FV6353 fitted with a 7/16" carburettor.
There won't be anything to see on a vid, but you can certainly feel it - the 'fog' as has been described.
Apart from Jon suggesting that exhaust restricion/water level can influence this feature, what else does encourages this?

Jeremy

[headdownarseup]

to try and help explain this "phenomenon" the best way would be to say these engines are "open circuit"
that is to say that when the piston is on its "power stroke", it has already sucked in a charge of air/fuel mix. as the piston continues to return to BDC, the piston will start to close the cylinder port window, BUT because there is no valve to speak of to prevent any fuel/air charge coming out of the carb the wrong way, that is why these villiers carbs "sneeze" or "cough" a little bit.
the larger amal 46n carbs do exactly the same.
the problem with seagulls compared to "modern" 2 stroke engines is that they dont have any REED VALVES which act as a crude one way valve. so with the INCOMING CHARGE (fuel/air) being under a partial vacuum, until the piston is at TDC, when past TDC, the opposite happens. hence you get a bit of "blow by" from the carb.
reed valves would help massively, but very restricted as to how small to make these valves to keep the air/fuel inside the cylinder where it belongs?
make sense?
dont worry about it too much, just make sure the carb is fairly clean in the main jet and the needle itself isn't bent.

jon

[Gannet]

Thanks Jon,

I have checked the ignition timing after resetting the baseplate location screw into the recess. it was stiff to move, so I wasn't sure whether it was correct before.
I have given it another run, but starting it on 3/4 throttle. Seems to be good at that rather than full throttle.
Then running it at no more than 3/4 throttle, at which the coughing/sneezing is hardy noticeable. So I am happy with that.
It sounds ok, although it doesn't idle down to low revs, although slow enough to not pump water.

Jeremy

[Stelios_Rjk]

Did you do anything else on the motor apart from reseting the baseplate?

[Collector Inspector]

3/4 throttle sometimes is best.

Not all Gulls or similar makes actually go the 100% "Hand Throttle" setting.

There are different diameters of throttle with which a cable can be tied around at your hand end.

Something there for all of us aye.

If 3/4 gives all out best result then settle at that.

Old Dears just need to breath "enough" no matter what.



B

[headdownarseup]

absolutely.
why bother with flat out when 1/3 to half throttle acheives the same results.
especially with something as old as an FV.
these "old dears" should be treated with a bit more love rather than abuse!
steady as she goes i reckon?

j

[james c]

hiya i am new member to had this problem as well as carb reving up and down could not control reves was jet blocked in center piece littel hole on side all blocked up dont know if this will help but did with mine

[Keith.P]

My FVP runs perfectly well whatever the revs, it will handle full revs for as long as I want it to, its a 50's motor not 30's.
Would you drive your vintage car or bike in third gear, just in case, its a seagull, that's what they are made for.

[Horsley-Anarak]

If 3/4 gives all out best result then settle at that.

I have a number of featherweights that run better at just under full throttle, you can hear the revs, bit like model aero engines.

H-A

[Gannet]

The 'FV Port Timing' topic did flag up that blowback out of the carb would occur with large inlet timing duration.
The engine which has this problem - FV6353 - has a long inlet duration of 155 deg. This compares with three other FVs which have much lower durations of 132, 139 and 144 deg.
This last result of 144 (from FV2682) does have some small degree of blowback when tested in a tank with the prop on. I have yet to run it on a dinghy, so I don't know if it in reality suffers from this. I think this is relevant as speed/load/throttle setting certainly affects the amount of blowback (if any).

Following the information in 'FV Ignition Timing' post, I have got FV6353 running and starting better. The advance with the baseplate engaged in the dimple and with 0.020 points gap with this engine was 58 deg. This is an excessive amount. I have moved the baseplate to give 46 deg and am running it at this setting.

Jeremy

[planesilly]

Jeremy,

I have just bought my first seagull, a 40 plus, from e-bay. It has had some problems although it was stated as up and running and ready to go. One was carb blowing and after checking the plug and points gap, which where well out, I decided to adjust the needle adjuster on the carb piston. It is a 10;1 oil mix and after looking at this site, with all the good tips, I decided to turn the screw in. It stopped the carb blowing and and it runs perfect. My next teaser is the amount of oil/slurry in my wheelie bin. I am using bio oil tc-w3 and would have thought there would be less mess. Maybe I will reduce the amount of oil but as its running perfect I would have to say wait and see.

Brian

[Keith.P]

Seagulls are well known for the oil slick, now its running better you may not get so much of a slick, but try not to reduce the oil mix as it will just reduce the life of the motor, no matter what modern oil you use.