Carburetor question

[pjlogue]

In rebuilding my spare set of 758A carburetors I can't figure out what the middle jet which is between the main and secondary jet is for or how it would do anything. It's the one that has the rubber plug which is held down by the leaf spring keeper that holds the main and secondary jets. The small middle jet is marked 32 and the top side of the chamber the jet sits in is connected to the idle air jet. There are no side ports in the casting of the carburetor (that I can see) to allow any flow through the small jet and the rubber plug, well does just that, it plugs the end of the jet.

Any ideas why they even have a jet there and what is it's purpose.

Thanks for any info anyone can provide.

-P.

[desertrefugee]

Slow jet for the idle circuit - and probably the cause of more frustration among GL owners than any other carburetor component. It meters minute fuel flow for meager idle needs.

[pjlogue]

Hmm, I am going to have to take another look at the bores of the casting where the secondary and primary jets sit and see if there is a hole to supply fuel to the idle jet. Any idea why they chose to plug the end of this tube and use a cross feed hole for supplying fuel?

-P.

[desertrefugee]

I think I remember a discussion Mike Nixon had on the engineering behind the plugs, but kinda forget the details. But, I believe the plug is needed so that the aircut circuit can draw properly on deceleration in the transition back to idle and avoid a lean condition. Mike is the guru, but he ain't around. Hopefully, somebody else can correct me - or expound on the reasoning behind that plug. The '79 CBX carbs have the same plug.

[chewy999]

No matter how much I read about carbs, and all the advice from people here, especially from Mike Nixon, Pistol Pete, Old Fogey and others, I've come to the conclusion that the science behind carbs is bordering on witchcraft!

[pjlogue]

Yes, good carb set up is an art which few people these days know how to do. The carbs on the 750K are quite simple compared to the Goldwing carbs. I'm still learning about these and where the critical points are. The current set of carbs I'm rebuilding are a challenge. I have found the vapor blaster I made does a beautiful job cleaning the bodies of the carbs. Great thing about it is it does not change the any tolerances of the parts and the media is too fine to get packed up in the passages. A series of 3 passes in the ultrasonic cleaner with copious flushes with R/O water between and the carbs look like new afterward and all traces of media are gone. The smaller jets (the 35's) are hard to really clean well. Repeated cycles in the ultrasonic cleaner usually cleans them but with this set of carbs they are so packed I may have to replace them.

Sad thing is that as time passes, fewer people are around that really know about normally aspirated carbs.

-P.

[Sidecar Bob]

No matter how much I read about carbs, and all the advice from people here, especially from Mike Nixon, Pistol Pete, Old Fogey and others, I've come to the conclusion that the science behind carbs is bordering on witchcraft!

Its all pretty simple really https://www.ngwclub.com/forum/viewtopic ... 97#p574597

[chewy999]

No matter how much I read about carbs, and all the advice from people here, especially from Mike Nixon, Pistol Pete, Old Fogey and others, I've come to the conclusion that the science behind carbs is bordering on witchcraft!

Its all pretty simple really https://www.ngwclub.com/forum/viewtopic ... 97#p574597

Worryingly I found that easier to understand!

[Sidecar Bob]

Me too

[desertrefugee]

I went to the link thinking that I'd be enlightened. Come to think of it, I was actually!

[heraldhamster]

and always take good care of yer gnomes, make sure they're always tucked in dry for winter when they're nor werkin'.

[pjlogue]

Had a good look at the cleaned carb and saw the holes between the main jet tube and the idle jet tube that allows fuel to get to the idle jet. I think I saw a few Gnomes scurry past my view while I was looking.

-P.

[Sidecar Bob]

Now you need to encourage the Dwarves to get in there and clean out the passages....