Dellorto carb leak

tom3c75

tom3c75

Hero member
Location
Cape Town South Africa
Since rebuilding my series 1 Jota there?s been an intermittent and slight drip from the alternator side carb.  Only seems to happen when the engine is hot.    All the jets, seals, float needles & seats, etc. were replaced during the rebuild and the float levels were reset.   

My first reaction was to tighten the float bowl nut and, when this did not help, to change the float bowl o-ring which, surprisingly, did show signs of wear.  Also checked the floats for binding, etc.

During a ride over the weekend the bike started misfiring and when I stopped there was fuel pouring out of the suspect carb.  I removed the float bowl, but found nothing amiss.  However, I could not refit the bowl, as the rubber gasket, which had popped out of its groove, had expanded in length by about two cms!  The thickness of the gasket seemed to be unaffected, but the material did appear softer.  I cut off the excess length and placed the join at the rear high point of the bowl.  This cured the leak and the misfire.  I?ve now fitted a Viton replacement.

A few questions:

1.  What else can cause the carb to leak/flood, other than the gasket, float height or a needle & seat problem?

2.  Could the gasket, which clearly was not fuel resistant, have allowed fuel past the sealing surfaces, or even
    have become dislodged, while the float bowl was in place? 

3.  Is there a vent hole/overflow on these earlier Dells and, if so, where is the vent? 

4.  What is the preferred method of adjusting the float level?  The Dellorto manual says to bend the float arms,
    but some folk say to adjust the tang that the float needle rests on.     

Thanks
Tom
 
tom3c75 said:
4.  What is the preferred method of adjusting the float level?  The Dellorto manual says to bend the float arms,
    but some folk say to adjust the tang that the float needle rests on.     

Thanks
Tom
Click to expand...

I prefer to bend the float arms as to bend the tang the float needle sits on may cause the needle to become pinched or not seat properly and thereby flood the bowl.. Just my 2c.
 
Tom,

Early Dellortos have the vent about half-way up the side of the mixing chamber, there's a little "roof" over the hole.  Later carbs had one each side of the mixing chamber, later still, a little tube was fitted that carried hoses to transport excess/overflow away.

At the angle at which the carbs are fitted, it is not uncommon to have the float bowl o-ring leak a little.  The fuel level is at about the same height as the joint, a new o-ring usually cures the leak.

Bending the float arms for adjustment is easier, very often they are at different heights anyway... probably due to owners trying to fettle carbs still mounted to the bike.

piet
 
Could the expanded float bowl seal be due to fuel contaminants/additives or possibly inferior rubber quality?
 
tom3c75 said:
4.  What is the preferred method of adjusting the float level?  The Dellorto manual says to bend the float arms,
    but some folk say to adjust the tang that the float needle rests on.   
Click to expand...
well, i'm normally just an arm bender kinda bloke.  (drink)

but,, a couple of times i've had to first reshape the needle tang back to close to what it should be.  'cause a couple of floats have shown serious bending abuse and also had a couple of 'banana' shaped arms to compensate for the poor needle tang position.  no, not pretty.
also worth checking the vertical tang that's about perpendicular to the forked needle tang.  this tang prevents the float from dropping down too low when the fuel level is too low.  i've seen some float needles that almost drop out the bottom of the float valve body when the floats are sitting too low. this often can cause the float needle to jam in the body when it tries to rise back up to cutoff the fuel flow.
IMG_1210cr.jpg

also good to check the floats are all the corrrect and same weight.  i.e.  10 grams or 14 grams?
& i've seen some new'ish white floats that are only 8.5 grams??

sorry, don't know much about what float weights should be with what carbs, with what float levels.  :-\    :-\
i just check what came out, clean or replace, and adjust to the DellO manual, and it kinda works.
 
I have now replaced the float bowl gaskets with Viton units and also reset the float heights by adjusting the arms.  The needle tangs were indeed out of shape, esp on the problem carb, so these were straightened out as well.  The vertical stop tangs were OK.    Ran the bike for about 100kms and there was no leakage.

Regarding ethanol in ZA fuel:  it depends who you ask, but it seems that our fuel contains about 2%. 
However, there is talk of increasing this to 10 or 15% in a couple of year?s time.    Regardless, most rubber products claimed by local vendors to be petrol resistant do not hold up to the new fuels, so one needs to be very specific when buying such items.

Thanks for all your inputs.

Tom
 
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