Monobloc problem

[Trefor]

I'm trying to pin-point a problem with missing on my G80 - some questions about Monobloc carbs.
I read somewhere the float level can be checked by unscrewing the cap on the idle jet and attaching a clear tube to and comparing the level with the dot on the float chamber. I did this the level is below the dot. Is this a correct check?
Unlike my other two bikes with monobloc carbs holding the tickler down doesn't make petrol flood out of the carb.
If this sounds like a problem with the float height how is it adjusted, is something missing from the assembly or does it sound like some other fault?

[Mick D]

Hi

That's the correct method to check the fuel level in the float chamber, you can adjust it up by adding a fibre washer between the fuel inlet and the carb body.

Tickling the carb should cause fuel to flow out around the tickler and if over flooded the carb air inlet.

Other possible issues:

Punctured float, give it a shake and listen for fuel sloshing inside it - replace float if punctured.

Sticking float pivot - clean and ensure operation is free, (there should be a small brass spacer tube fitted on the hinge pin between the float and the chamber cover, if this is not present the float can jam).

Regards Mick

[Duncan]

Unlike my other two bikes with monobloc carbs holding the tickler down doesn't make petrol flood out of the carb.

Have you checked that your petrol taps are not blocked and that there is a good flow of fuel getting to the carb, the orifice in a fuel tap is quite small and can be easily blocked with corrosion/debris in the petrol tank

[SPRIDDLER]

This pic may add to MickD's comment that there should be a small brass collar on the float hinge pivot.
Some floats can jam up or down at the float bowl resulting in either a lack of fuel or flooding.

Monobloc float chamber flooding (518x598).jpg

[Trefor]

Thanks for the suggestions. There is no washer fitted under the 'needle seating' on my carb and the Amal site helpfully says 'where fitted'. I'll give the float chamber a going over, check for those faults and try a washer under the seat.

[Mick D]

Hi

The fibre washer was originally fitted but dropped at some point and is no longer fitted to new carbs. If your carb is contemporary to the bike it would probably have had the washer fitted.

Regards Mick

[Reynard24]

I think you've got that the wrong way round Mick - originally they did NOT have a fibre washer under the float needle seating and the modern ones do, certainly the last one I bought did.
Spriddler's point about the jamming floats is a good one, in my experience the worst "stickers" are the all black plastic ones which seem to foul on the float chamber. Once again the original were brass then this changed to a plastic/metal hybrid where the float was plastic but the hinge was metal, then on to fully plastic and now back to plastic/metal hybrid (I think these are termed "stay up") types. I source original brass ones and fit those - no problems so far.

[Mick D]

Hi James

You've got me thinking now, the spares list details the fibre washer and I have it on my contemporary carbs. The new carbs I have bought are without the washer and the 2018 Amal catalogue doesn't list them

Burlen supply a kit to set the fuel level:

http://amalcarb.co.uk/monobloc-series/3 ... ttors.html

Which says the level is set by a washer

Regards Mick

[Groily]

I think you've got that the wrong way round Mick - originally they did NOT have a fibre washer under the float needle seating and the modern ones do, certainly the last one I bought did.
Spriddler's point about the jamming floats is a good one, in my experience the worst "stickers" are the all black plastic ones which seem to foul on the float chamber. Once again the original were brass then this changed to a plastic/metal hybrid where the float was plastic but the hinge was metal, then on to fully plastic and now back to plastic/metal hybrid (I think these are termed "stay up") types. I source original brass ones and fit those - no problems so far.

I think you're right on both counts R24, as new carbs I have bought HAVE had the washer, while my originals don't/didn't. Which doesn't mean they do or don't NEED a washer though, to get the fuel level right!
And I agree about trying to find decent original brass floats, I also find them better, in conjunction with viton-tipped needles. The all-plastic floats I don't like either for the reasons given; the hybrids I have no experience of. Is it that they are filled with stay-up flotation 'stuff' maybe?

[Reynard24]

Hi Mick
If you look in Fred Neill's service books, the illustration of the monobloc does include a "seating washer" but this is drawn as going below the filter gauze under the banjo and not underneath the needle seating. Modern gauze filters have a combined washer/filter so this could account for the confusion with the drawings.
The 1955 parts list (first year of monobloc also shows a washer above the needle seating which is listed as 14/175 - "banjo seating washing" (washing?) but interestingly does not illustrate or list a filter to go under the banjo. There is no washer shown under the seating in the diagram or listed.
Regards
James