Dirty carbs

Earlier on today, I removed the 2 930 Monoblocks from my 750 Commando to service.
The bike has been standing A LOT, and quite a few times it was either started in the garage, or fuel was poured in the carbs but the bike was not / did not start.
Any way, after dismantling I noticed the RHS carb bowl was much - much filthier than the LHS one which was actually tolerable.
Am I missing anything obvious here? Why this huge difference?
Thanks, Aris

What side does the fuel feed from? Perhaps that has something to do with it???
Do you use an inline fuel filter?

Both sides really, as there are two fuel taps; one main and one for reserve.
When I open, I always open both taps, do my in garage firing / testing routine, and then I shut both.
Thanks, Aris

Kool_Biker said:

Both sides really, as there are two fuel taps; one main and one for reserve.
When I open, I always open both taps, do my in garage firing / testing routine, and then I shut both.
Thanks, Aris

Click to expand...

Not sure how your hoses are routed but is the dirty side the side on reserve? If so, is it possible to be getting more gas from the 'bottom' of the tank on that side?

Yes, the dirtier carb is on the side of the reserve.
But the two carbs are fed together, by same fuel line(s), extended by 1 or 2 cm ...
Thanks, Aris

The reserve side takes the gas right off the bottom of the tank, so it follows that it will bring in more dirt and gook than the running side which feeds from an inch or so off the bottom.
JD75

Is this the type of setup you have? If so, you will still get the majority of gas from the same side of each petcock to the respective carb. The crossover is there to get gas to both carbs when only one petcock is opened. When both are opened as you are doing, it is basically a straight run down into each carb. You might want to runs some gas directly from the reserve side through some white cloth into a glass jar. Do the same on the other side and compare. I avoid the reserve as much as I can. I would prefer that any sediments that are in the bottom of the tank stay right where they are.

http://www.oldbritts.com/1972_g9.html

Yes, avoid reserve ,it is for getting you to the nearest fuel fillup only. When was the last time you changed the float needles ? Plug colours ?

OK, thank you all.

I am in the process of rebuilding my carbs with new kits so they will soon be spotless again.
In the future I will take the 'reserve' more seriously ...

Going forward should I install an in line fuel filter, each side?

Cheers, Aris

I can't argue against fuel filters as I must run one on my mower and all my cars got em and my special will have one but I put factory fuel hose on my Combat 2 yr ago and ain't had any reason to clean carbs but did check in for sticking ticklers not to see much in bowl bottoms. There is already a pretty fine screen in the feed banjo that is also a fuel feed baffle for level control. Unless fueling from old cans or stealing gas off bottoms of tanks by siphon hose, another inline filter is over kill. Most the crud that plugs pilot or show ups in bowl is not from the gasoline but from oxidation of zinc like the white stuff on coaches noses. No hydrocarbon solvent can touch it only mild acids or strong alkali which can dissolve whole carb given some time or just scratch or rub of wire poke it clear in pilot after a manual for the drill size.

Yes the addition of more fuel filtration is overkill. The tank taps are fine mesh screened as well as the 2 bowl entry screens means it should be adequate. IMO external line filters are less than attractive too. As Steve states carbs that have sat a Lot are in danger of plugged-up pilot jets ,that is a big factor. Torque values are so low with these delicate gas-air metering instruments that warpage can occur if not adhered to. Plus fuel eats up rubbers n' gaskets n' plastic floats n' ...

Ah, what a difference a thorough clean and synch of the monoblocks does ... my bike now sounds and goes so good.

In the end, the only explanation 'I' could find, possibly explaining the big difference between between the state of my two monoblocks:

The float of the much dirtier RHS carb was correctly set. But that of the LHS was set lower by another 2 mm (a total of 4 mm from the top of the bowl !!!).
So the RHS carb was always getting much more fuel than the LHS ...
As I was not really running the bike for so long, this did not register so much as a running problem.

Any way, this has now been corrected by carefully tapping the corresponding needle seat and as mentioned above the bike feels and goes sweet.

Thanks everybody
Aris

Kool Aris, where do your pilot jet turns land now? When I'm anal i try to bump float level so pilots land closest to ideal 1.5 turns out as base line fuel supply to rest of the range. Yet I know Trixies float are way low d/t expedient fix of stuck ticklers yet starts and idles and responds from low down to top end so nice its not worth bothering about till something else makes me take carbs off. I'm not sure I believe the lower or higher floats flowed extra fuel to collect more sediment or oxidants as the flow should be the same on each jug's mixture consumption. Hope its a long time before either of us has reason to open bowls again.