Dellorto carb problem

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.

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!

later, dave (One out of many Daves)

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"

adjusted all

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

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

I believe that they designed the Dellortos to be set up like motorcycles. One vacuum gauge to each carb throat's vacuum port so the vacuum of each throat could be read at the same time. I am not sure if you can adjust each throttle plate separately on just one carb.

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?

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.