Dellorto carb problem
 

Hi

Trying to set the idle screws on the carbs the other day, and I adjusted all
of them apart from one. The idle screw for number three cylinder does not
affect the engine at all, no matter how far I screw it in or out. I checked
the idle jet, which I thought maybe blocked, but it is fine. What could the
problem be?
I have also noticed when the engine is idling, it sounds as though it is
missing, and it is the same under light throttle. But when I put my foot
down it picks up and goes great. Have I got a blockage somewhere in the
idle circuit? What can I do to remedy this?

Cheers

>From: "Gareth Edwards"
>
>Hi
>
>Trying to set the idle screws on the carbs the other day, and I adjusted all
>of them apart from one. The idle screw for number three cylinder does not
>affect the engine at all, no matter how far I screw it in or out. I checked
>the idle jet, which I thought maybe blocked, but it is fine. What could the
>problem be?
>I have also noticed when the engine is idling, it sounds as though it is
>missing, and it is the same under light throttle. But when I put my foot
>down it picks up and goes great. Have I got a blockage somewhere in the
>idle circuit? What can I do to remedy this?

Might be a vacuum leak at the base of the carb. Some people will use carb
cleaner spray and spray at the base of the carb to see if maybe there is a
vacuum leak. Others use a gas like propane and aim it near the base of the
carb.
Both are done with the engine running and done carefully!! I have never tried
the propane gas method. <g>

Does your Dellorto have separate vacuum ports for each throat? If so then check
the vacuum on that port and compare with the others.
If not then there is a carb balance tool that measures vacuum at the top of the
throat of the carb.
Some use a hose holding one end to your ear and the other end over the throat
then listen and compare with the other throats.
Pull that plug wire to see if it makes any difference in the running of the
engine.
Adjust valves, do a compression check and report results here.

Hope this makes sense! <g>

later,
dave
(One out of many Daves)

On Mon, 20 Dec 2004, Gareth Edwards wrote:

> Hi
>
> Trying to set the idle screws on the carbs the other day, and I adjusted all
> of them apart from one. The idle screw for number three cylinder does not
> affect the engine at all, no matter how far I screw it in or out. I checked
> the idle jet, which I thought maybe blocked, but it is fine. What could the
> problem be?
> I have also noticed when the engine is idling, it sounds as though it is
> missing, and it is the same under light throttle. But when I put my foot
> down it picks up and goes great. Have I got a blockage somewhere in the
> idle circuit? What can I do to remedy this?
>
> Cheers

OK, maybe I am wrong here, but these are a pair of 2 barrel carbs,
1 on each side. There should only be 1 (one) idle screw per side. I don't
believe you set the "idle" for each seperate cylinder. 1 screw should be
idle and the other a mixture screw. Unless I am totally off here......*8-}


--
the Grokdoc
Tom Malmevik
all that groks is god
67 Baja "marti"

> Trying to set the idle screws on the carbs the other day, and I
adjusted all
> of them apart from one. The idle screw for number three cylinder
does not
> affect the engine at all, no matter how far I screw it in or out. I
checked
> the idle jet, which I thought maybe blocked, but it is fine. What
could the
> problem be?


Floats are probably too high and fuel is getting pushed past the main
jet circuit. Had the same thing happen on a 40mm webber right out of
the box. Once I adjusted the floats the problem was gone.

Chris

"dave" > wrote in message
...
> >From: "Gareth Edwards"
> >
> >Hi
> >
> >Trying to set the idle screws on the carbs the other day, and I adjusted
all
> >of them apart from one. The idle screw for number three cylinder does
not
> >affect the engine at all, no matter how far I screw it in or out. I
checked
> >the idle jet, which I thought maybe blocked, but it is fine. What could
the
> >problem be?
> >I have also noticed when the engine is idling, it sounds as though it is
> >missing, and it is the same under light throttle. But when I put my foot
> >down it picks up and goes great. Have I got a blockage somewhere in the
> >idle circuit? What can I do to remedy this?
>
> Might be a vacuum leak at the base of the carb. Some people will use carb
> cleaner spray and spray at the base of the carb to see if maybe there is a
> vacuum leak. Others use a gas like propane and aim it near the base of
the
> carb.
> Both are done with the engine running and done carefully!! I have never
tried
> the propane gas method. <g>
>
> Does your Dellorto have separate vacuum ports for each throat? If so then
check
> the vacuum on that port and compare with the others.
> If not then there is a carb balance tool that measures vacuum at the top
of the
> throat of the carb.
> Some use a hose holding one end to your ear and the other end over the
throat
> then listen and compare with the other throats.
> Pull that plug wire to see if it makes any difference in the running of
the
> engine.
> Adjust valves, do a compression check and report results here.
>
> Hope this makes sense! <g>
>
> later,
> dave
> (One out of many Daves)

Adjusted valves, still same problem. Pulled the plug wire and the engine
note is the same. Also shorted the plug wire to ground to check for spark,
so I'm thinking it must be something to do with the carb (or at least one
side of it).

There are separate vacuum ports for each throat, I will try and compare the
vacuum a.s.a.p., along with testing the carb for leaks with some carb
cleaner. Am I right in thinking that when you spray this around the base of
the carb, the engine will pick up if there is a leak present? Or is it just
a visible thing i.e. will I see it bubbling around the carb seal?

Thanks Dave

> Adjusted valves, still same problem. Pulled the plug wire and the
engine
> note is the same. Also shorted the plug wire to ground to check for
spark,
> so I'm thinking it must be something to do with the carb (or at least
one
> side of it).

Gareth,

If the engine speed did not change at all when you pulled the plug wire
then I would suggest pulling that spark plug and inspecting it. You
should see a very pronounced change in the idle quality if you pull a
plug wire. No change at all means you just found a dead cylinder.

You say you verified the valves are set correctly, the next thing I
would check is the plug wire and the spark plug itself. If the plug is
saturated with gasoline and/or black it could still be a
float/carburetor issue, and you would need to clean or replace the plug
to restore the functionality of the ignition in that cylinder. It also
may be as simple as a bad plug wire, I've seen bad wires act up at idle
but once the engine speed is increased they clear up and the misfire
goes away temporarily.

Chris

"Hal" > wrote in message
oups.com...
> > Adjusted valves, still same problem. Pulled the plug wire and the
> engine
> > note is the same. Also shorted the plug wire to ground to check for
> spark,
> > so I'm thinking it must be something to do with the carb (or at least
> one
> > side of it).
>
> Gareth,
>
> If the engine speed did not change at all when you pulled the plug wire
> then I would suggest pulling that spark plug and inspecting it. You
> should see a very pronounced change in the idle quality if you pull a
> plug wire. No change at all means you just found a dead cylinder.
>
> You say you verified the valves are set correctly, the next thing I
> would check is the plug wire and the spark plug itself. If the plug is
> saturated with gasoline and/or black it could still be a
> float/carburetor issue, and you would need to clean or replace the plug
> to restore the functionality of the ignition in that cylinder. It also
> may be as simple as a bad plug wire, I've seen bad wires act up at idle
> but once the engine speed is increased they clear up and the misfire
> goes away temporarily.
>
> Chris
>

Spark plugs are new. Thought it may be a problem with the plug so I
replaced them all as it was due a service anyway. I have not renewed the
plug leads for a while though, so it may be possible that one of these is
bad. I will check this as soon as I can.

How do you do a compression/leakdown test Dave?

>How do you do a compression/leakdown test Dave?

http://www.misterfixit.com/dyncompr.htm

http://www.vclassics.com/archive/leakdown.htm


later,
dave
(One out of many Daves)

Gonna be busy with work and Crimbo for a few days, but as soon as I get
chance to test it out, I will let you know the results.

Cheers for the links mate.

"dave" > wrote in message
...
> >How do you do a compression/leakdown test Dave?
>
> http://www.misterfixit.com/dyncompr.htm
>
> http://www.vclassics.com/archive/leakdown.htm
>
>
> later,
> dave
> (One out of many Daves)