ET: Engine (Twin) Uneven Running in Lower Gears

[nigsey]

if should be stamped on the top of your slide
its a measurement of (I believe 1/16" increments) no metrics here

I’m ok with imperial measurements. I appreciate your help, I’ll look for the stamp. Just as a matter of interest, I guess trying to ‘file’ the cutout manually to the next size would be too crude and inaccurate?

 

[nigsey]

I beleive it to be the oposite - air will always find a way in and usually makes things lean. When the pilot jet is blocked, that metered amount of petrol can't get through, so the carb draws it from the main jet as the throttle is opened,, causing unstaisfactory low speed running. Unblock the pilot petrol passage, set the air screw to 1 1/2 turns and it will be fine. Needle jet really doesn't come into the mix until after 1/4 throttle.

In which case, it does fit the description of the symptoms I’m suffering.

 

[Jim Bush]

On the 276 carbs, the main brass jet block is sized with the pilot jet integral, it is not a separate jet. It is high lighted in yellow belwo. You can see on the cut away diagram there are a number of passages that each is to be be clear. It will take some time and patience.

 

[ClassicBiker]

I’m ok with imperial measurements. I appreciate your help, I’ll look for the stamp. Just as a matter of interest, I guess trying to ‘file’ the cutout manually to the next size would be too crude and inaccurate?

Nope, you can do that. When I was setting up my Mikunis I wasn't able to get a largest enough cut away. So I used trigonometry to determine at angle to set slides at on a 5 inch sine plate and how much to mill off. At our section meeting a brought along photos to show how I did it and my notes and calculations etc.... Dave Matson looked at it all and said "I just scribe a line hold it in a vise and file it." Talk about wind being taken out of your sails.

 

[oexing]

Tickover speed is said to be allright, so the pilot jet will not be blocked. What´s more, if the pilot jet was blocked you get less of fuel into the engine as air through the pilot system is still available. So rich running at quarter carb open is not the typical symptom then. No, my bet is an oversize needle jet after a million miles, slide cutout next try, when having the needle one step lower does not get you satisfaction.

Vic

 

[chankly bore]

I'm too stupid to do links, but this subject was covered in great detail in May 2017, on this Forum.

 

[oexing]

unlikely

Vic

 

[greg brillus]

Did it have the problem before you removed and cleaned the carb's..........

 

[rapide049]

Sorry for the answer (ATD) I completely read the discription wrong

 

[nigsey]

On the 276 carbs, the main brass jet block is sized with the pilot jet integral, it is not a separate jet. It is high lighted in yellow belwo. You can see on the cut away diagram there are a number of passages that each is to be be clear. It will take some time and patience.

View attachment 59168

Tickover speed is said to be allright, so the pilot jet will not be blocked. What´s more, if the pilot jet was blocked you get less of fuel into the engine as air through the pilot system is still available. So rich running at quarter carb open is not the typical symptom then. No, my bet is an oversize needle jet after a million miles, slide cutout next try, when having the needle one step lower does not get you satisfaction.

Vic

I'm too stupid to do links, but this subject was covered in great detail in May 2017, on this Forum.

I'm too stupid to do links, but this subject was covered in great detail in May 2017, on this Forum.

Thanks CB, I’ll see if I can find it.