81 Special

One a good note the engine lives! Yesterday I installed the carbs and filled them with gas. I didn't try to start it yesterday as I had concerns about fuel leaks. I wanted it to sit overnight as see if I had any. And yes for you eagle eyes out there I know the float bowl screws are too long, I have shorter ones coming and they will not be button head they will be normal allen head.
This morning no fuel leaking from the float bowls or crossover tee. Put in a freshly charged up battery,set the choke and hit the starter. It started instantly, she was running after the first compression stroke. Yippee! After running for 10-15 seconds went to half choke. It was idling way too fast, just had to back off the idle screw. After less than a minuet took the choke off completely and finished setting the idle. Motor sounds great, no noise from valve train, no cam chain. I have not checked anything in the engine other that it had compression, with only 973 miles on it it should all be fine. I'm sure eventually I'll check the valves and cam chain. Feeling the exhausts it seems the carbs are balanced pretty good.
Speaking of the choke I was concerned as to how it was going to work because I had drilled the that little hole out in the float bowl to get it clear. I thought at worst it would flood when trying to start it with full choke. It didn't, it started great. I'm sure it's richer than what it was from the factory. Also even though it's very cold outside my shop is 70F. So I think the choke will be ok.
So far so good.
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Hmmm, maybe you've stumbled upon a little improvement "mod" for the BS34s. I know my BS34 equipped '83 didn't start as easily and quickly cold as my BS38 equipped '78. Did you note the drill bit size you used in your post? I forget.
 
5twins said:
Hmmm, maybe you've stumbled upon a little improvement "mod" for the BS34s. I know my BS34 equipped '83 didn't start as easily and quickly cold as my BS38 equipped '78. Did you note the drill bit size you used in your post? I forget.
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#60 smallest I had that would reach. .040 on my calipers.
Unless you have spares I would wait until I have some more time to test it. Which will be spring.
 
Yes, I'll wait. According to DogBunny's post back on page 2, that #60 drill is over twice as big as the original size (about a #79 drill, or .0145"). Maybe I'll experiment with something in between, if I have a bit long enough.
 
5twins said:
Yes, I'll wait. According to DogBunny's post back on page 2, that #60 drill is over twice as big as the original size (about a #79 drill, or .0145"). Maybe I'll experiment with something in between, if I have a bit long enough.
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Yes would be best to experiment with smaller bits. I used what I had that would reach. Come spring time I'll find out if it's too much. I do think at the worst I may have to use half chock to start it or make it so it can only go to 3/4 choke.
 
Well, congrats on getting this carb set refurbed, you did hit quite a few snags along the way, lol. But, the BS34 carbs are a very good set, once you jet past their factory leanness. They're lighter and more modern than the BS38s, and I think that in the future, eventually they will come to be regarded as about the best stock carb set for these bikes.

The P.O. of my '83 said he always had carb issues, and when I went through them, I think I discovered why. He didn't do a 100% overhaul on them. He didn't replace the mix screw o-rings and they were toast (hardened up and deformed) or the butterfly shaft seals. I could see he attempted to do the shaft seals because a couple of the Phillips screw heads were buggered up. Apparently he couldn't get them out so the seals never got replaced. I did manage to get them out without too much trouble, using the proper tools (good Vessel J.I.S. bits in a T-handle holder and by grinding the peened backs off the screws). The carbs came out nice and worked well for me. Experimenting with the jetting got them running well, especially that air jet. With that, I was able to dial in the smoke ring on the plugs to just where I wanted it (about ¼ of the way up the porcelain), both when I first got the bike and it was (almost) stock and later on, after changing the exhaust and switching to pods.
 
5twins said:
Well, congrats on getting this carb set refurbed, you did hit quite a few snags along the way, lol. But, the BS34 carbs are a very good set, once you jet past their factory leanness. They're lighter and more modern than the BS38s, and I think that in the future, eventually they will come to be regarded as about the best stock carb set for these bikes.

The P.O. of my '83 said he always had carb issues, and when I went through them, I think I discovered why. He didn't do a 100% overhaul on them. He didn't replace the mix screw o-rings and they were toast (hardened up and deformed) or the butterfly shaft seals. I could see he attempted to do the shaft seals because a couple of the Phillips screw heads were buggered up. Apparently he couldn't get them out so the seals never got replaced. I did manage to get them out without too much trouble, using the proper tools (good Vessel J.I.S. bits in a T-handle holder and by grinding the peened backs off the screws). The carbs came out nice and worked well for me. Experimenting with the jetting got them running well, especially that air jet. With that, I was able to dial in the smoke ring on the plugs to just where I wanted it (about ¼ of the way up the porcelain), both when I first got the bike and it was (almost) stock and later on, after changing the exhaust and switching to pods.
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I think the 34s are probably a good carb for the later motors. Being smaller they will react better with the milder cams in them. I think they used they the 38's for better performance in the early engines. The 256 cams are a bit different than the latter 447 cams. A good running 256 cam from a XS2 will give you a punch at 5 grand that feels like a 4 barrel kicking in. I know from experience my 750 doesn't have the 5 grand punch that it did with a early cam.
 
GLJ said:
I think the 34s are probably a good carb for the later motors. Being smaller they will react better with the milder cams in them. I think they used they the 38's for better performance in the early engines. The 256 cams are a bit different than the latter 447 cams. A good running 256 cam from a XS2 will give you a punch at 5 grand that feels like a 4 barrel kicking in. I know from experience my 750 doesn't have the 5 grand punch that it did with a early cam.
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I didn't realize there is a cam profile difference. Interesting.
 
Yes, the early cams are "hotter". Just like many new bikes, the performance is greater for the first few years, then they tend to get "de-tuned" a bit. The early 650s had that hotter cam, along with slightly more retarded timing. I think this timing difference helps with the performance as well, and it's something you can do to the later bikes quite easily.
 
Or there are several mild performance cams that will give similar performance, perhaps with a more modern take on entry ramp length/angles.
I have kinda thought Yamaha coming from peaky 2 strokes thought ALL riders wanted peaky high RPM power bands, But street riders coming from Harley and British twins had different ideas of "best" engine characteristics.
 
TX650A Van Islander said:
I didn't realize there is a cam profile difference. Interesting.
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Yes the early cams have a more aggressive profile. Depending on what you read the 72 is the best. some say 71 is better. I can tell you from experience a 75 cam is more linear than a 72. By that I mean a 75 cam pulls constant to 8 grand with good low end. A 72 pulls ok at the lower rpms but at 5000 hang on.
 
GLJ said:
Yes the early cams have a more aggressive profile. Depending on what you read the 72 is the best. some say 71 is better. I can tell you from experience a 75 cam is more linear than a 72. By that I mean a 75 cam pulls constant to 8 grand with good low end. A 72 pulls ok at the lower rpms but at 5000 hang on.
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Hmmm...now you've got me wanting to do a back to back ride test comparison. Come on Spring time! :bike:
 
Today I started her up again, ran it for 15-20 mins. Fired right up on 1/2 choke and still no leaks. So then I pulled them back off. Reason being I was not real happy with the float bowl gaskets that came in the carb kits that I got from China. They feel really good. Very supple, even have a bit of a rubbery feel to them. The problem is they are a little bit too wide. Do not fit into the carb body on the sides. I tried to trim one and that didn't go well for me. So I decided to do 2 things. First install them as is and see if they work. Second was to order 2 OEM Yamaha gaskets so I could compare them and see for sure that they are wider. New OEM gaskets came in today. Sure enough they are wider. Off came the carbs. Like I said they didn't leak. They do compress enough even with the extra width to leave a impression on the ends. Going to keep using them and see how it goes.
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One other problem I ran into is the springs for the mixture screws are a little bit longer than the originals. With the new spring and washer for the mix screw the o-ring could not reach the part on the screw where it needed to be on. Yes I could have held the carb upside down and put it in but then I couldn't be sure the o-ring was where it needed to be and not pinched. No big deal just used the old spring.
Are the kits a good deal? If the needle and seats, and the floats turn out to work ok then yes it's probable a good deal, if the gaskets hold up even a better deal. If you need diaphragms and know how to change them then even better. Plus you are getting 4 kits not 2. You will still need to get the correct jets for your carbs. Come spring I hope to be able to ride the bike and find out for sure how the stuff holds up.
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GLJ said:
Today I started her up again, ran it for 15-20 mins. Fired right up on 1/2 choke and still no leaks. So then I pulled them back off. Reason being I was not real happy with the float bowl gaskets that came in the carb kits that I got from China. They feel really good. Very supple, even have a bit of a rubbery feel to them. The problem is they are a little bit too wide. Do not fit into the carb body on the sides. I tried to trim one and that didn't go well for me. So I decided to do 2 things. First install them as is and see if they work. Second was to order 2 OEM Yamaha gaskets so I could compare them and see for sure that they are wider. New OEM gaskets came in today. Sure enough they are wider. Off came the carbs. Like I said they didn't leak. They do compress enough even with the extra width to leave a impression on the ends. Going to keep using them and see how it goes.
View attachment 260056View attachment 260059View attachment 260070
One other problem I ran into is the springs for the mixture screws are a little bit longer than the originals. With the new spring and washer for the mix screw the o-ring could not reach the part on the screw where it needed to be on. Yes I could have held the carb upside down and put it in but then I couldn't be sure the o-ring was where it needed to be and not pinched. No big deal just used the old spring.
Are the kits a good deal? If the needle and seats, and the floats turn out to work ok then yes it's probable a good deal, if the gaskets hold up even a better deal. If you need diaphragms and know how to change them then even better. Plus you are getting 4 kits not 2. You will still need to get the correct jets for your carbs. Come spring I hope to be able to ride the bike and find out for sure how the stuff holds up.
View attachment 260071
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👁️👍
 
Exhaust day. Yesterday I removed the exhaust system. I was amazed the crossover pipe came apart. Had visions of cutting it apart. I had sprayed rust penetrate on it a few times a few time last week. It came apart with no drama. I then de-greased everything, knocked off the big rust and then polished it some. It came out ok. I used the Gunk engine degreaser first (it's good stuff, you don't need gloves but wash your hands before going pee). Next was Quick-Glo on the headers and the tops of the mufflers (thanks @jetmechmarty ) that stuff works very well. Not so good on the heavy stuff for that I used the Dremel and brass wheels. Finished with my favorite wax.
It came out ok for what I had to work with. As I was cleaning it up I could see what I already knew, it wasn't going to be perfect. When you have your face 6 inches from something you see every blemish. From a few feet it looks good. I could feel mission creep. I went and looked and I can buy new head pipes and good mufflers for less than $200. I had to remind myself what I am doing. The goal is to end up with a presentable bike that runs and rides like new. Not a show bike. New pipes would look better and maybe make the bike run better. At the end of the day I do not see a gain in value to justify the expense.
Next up swing arm.

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