78 Carbs

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brianinpa

brianinpa

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Every day that I come home from work, I feel like it is Christmas Morning. I am going through all the parts and stuff that I picked up last weekend when I got a 78 parts bike. Tonight's evolution was to look at the carbs and figure out what I have so tonight's question deals with carbs.

The carbs I have are 771A which means they are Emissions Control carbs for 78 and 79. Knowing that the carbs are meant for a 78 or 79, is there any reason these carbs cannot be used with a 77 motor? Since I have both a 77 and a 78 motor, I am looking at things to help decide which motor I am going to use in the bike. Both motors are out of the frames so pulling an engine isn't a concern.
 
the 78 -79 motors as in short blocks are a little better built than earlier yrs ....on the other hand the cams and carbrs and ignition advancer from the 77 are the best for the wing motor in my opinion ....given all things equal as condition ......there are some parts that interchange on the two carb racks ....these things could be done without taking heads off if done right and attension to detail
 
Looking at the underside of the carbs, it appears that some of the primary nozzles are broken. It looks like they were twisted with a screw driver to try and get them removed. :Awe:

Am I screwed or are these parts obtainable, and are they carb model specific?
 
Those I think are air jets. With properly sized micro drills they can be carefully cleared without removal. I think I have the same rack. I'll check later and verify.
 
yep it dont sound good ...post a pic of what you have both racks really .....# 80 micro drill is great for clearing idle jet ...when its impossible to get out ....the carb bodied are different through the yrs 78-79 are totally different than 75-77
 
CM I will keep that in mind.

After reading a lot of Carb stuff over at NGWClub, I think the problems I have are fixable. The broken piece is the bottom of the primary nozzle and it does come out with a lot carb cleaner, some soak time, and a little persuasion. Since I have both a 77 and a 78 motor and 78 carbs, I think I am going to stay with the 78 stuff but I won't know for sure until I can spend some time in the garage without freezing.

IMG 20130202 091338 278

IMG 20130202 091338 278

Carb with broken Primary Nozzle
 
...there just sitting - minus the bellcrank though.
Probably will be minus the air chamber sooner or later. Solidifying a scheme based on what Squirts does in using the air chamber for a single carb conversion.
I end up collecting factory racks. Gotta do something to keep 'em off the street. :)
 
From what I can see Brian it won't hurt it, If just the ear is broken off the screwdriver slot (which I can't figure why it is there in the first place). Push it out from the top through the slider bore.
 
I want to get busy with the carbs, but for now I am waiting on some $$$$ to fund the project. From what I have found and read about them, one ear goine is good, two ears gone is bad.
 
The "ears" on the primary nozzle provide a stop for the jet so as long as the spring clip holds the jet securely you're okay with only one as long as it's sound.

I've seen new nozzles somewhere but I can't for the life of me recall where or when or I'd go back and buy them out.

The way we remove them is to first hit them with pb blaster and then put them in boiling water to soften the goo. I designed a special tool that fits snugly in the slot between the ears but you can file down a screwdriver for the same effect. Once you've got it turning freely you can use a length of thin wooden dowel to push it out from above.

With a snapped off ear it's rather more complicated: you'll have to find a screw extractor that's thin enough that it won't put outward force on the remaining ear but will bite into the inner bore. If you can accomplish this without doing major damage to the nozzle you're in good shape.

In situ nozzle cleaning is an iffy proposition at best because if even one of the teensy emulsifying orifices is clogged or if the passageways from the primary main to the air fuel mix screws and/or bypass holes are occluded you won't get an even burn between the cylinders.

Hope this helps!

OSC
 

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