1977D carb settings

[griennehornette]

Howdy.

I just introduced myself in the Clubhouse. I'm trying to resurrect a mildly modified 77D I restored about 15 years ago. I was a newb (still am, really) and made mistakes. When I cleaned the carbs, I found that I had the wrong type of pilots installed; BS30/90 series, size 45. The mains were 132.5. And I had lowered the clip on the needles.

Don't remember what I was thinking, for all that. I've got pod filters, stock head pipes and some cheap harley mufflers with the baffles knocked out. Not major mods.

The pods were cheap Emgos. With them strangling the bike for air, and the ridiculously rich jetting, it's a wonder the bike actually ran. I did notice the plugs were rawther dark and wet...

So I've ordered and installed 27.5 VM22/210 pilots and 127.5 mains. Raised the needle clip to the very middle position. And bought larger pods from XS650Direct (which is just a couple of hours north of me). Don't have it all back together yet, and the wheels are at the shop getting new rubber, so I won't know for sure how well it works for a week or two.

But I thought I'd post, and see if any of the carb gurus cared to render opinion on whether I'm at least in the ballpark. Guess it's hard to say for sure. But I'm happy to receive any and all opinion!

Thanks in advance!

 

[5twins]

Yes, you sound like you're in the ball park, but those pod filters may give you tuning problems. The K&N pleated type pod doesn't work well on these CV carbs. If you must use pods, the foam type are better. Most of us use the UNI foam ones.

Your CV carbs rely on a smooth flow of air to operate the slide properly. The pleated pods give a turbulent flow. This can cause break-up, especially in the upper midrange, say from 4 to about 5.5K. Now, break-up is often a sign your jetting is off, too rich, but it could be the pod instead.

 

[griennehornette]

Cool! 5twins himself has responded! (Like, you wrote the book. I downloaded it and have been using it.) Thanks man. Will the K&N style pods do any damage? It's just that I've blown a fair amount of $ so far, and can live with something that is perhaps irritating; but not dangerous to the bike. For awhile, anyway. I'll save me pennies and get me some foam pods when I can.

 

[5twins]

It shouldn't hurt the bike, it just may make it difficult to tune perfectly. I started out myself with K&N pods. I love K&Ns and have used them in one form or another on every bike I've ever owned. I even put them in my cars and trucks. But, this was the first time I ever put the K&N pod style on a CV carb. I had used airbox replacement K&Ns with CV carbs in the past and had no problems. The pod style though, well, it just doesn't work right on a CV carb.

I struggled with tuning my 650 carbs for the first few years I had it using K&N pods. I had it tuned OK but it wasn't perfect, and I couldn't get it any better. It seemed like another size up on the mains was called for but when I did that, it caused break-up through the upper midrange. And this was with the needles already leaned a step to compensate for that. Well, I read about the UNI foam pods on these boards and how they worked better so I finally gave them a try. Problem solved - I was immediately able to go another size up on the mains and got no upper midrange break-up. So, it wasn't the main jet size causing the problems, it was the pleated style pod filter.

The UNI pods aren't that expensive, only about $15 each. You don't need any special oil for them either, just use a 50-50 mix of gas and motor oil. For your BS38s, you will want the UP4200 or UP4200ST (dual layer). They have a 2" I.D. mounting flange and are a perfect slip fit on the BS38s.

 

[griennehornette]

The question may be whether I'll actually be able to tell if anything is wrong ;-) But I'll cross that bridge when I get to it. Like... what do you mean by "break-up"? What is it that I would notice? Does the engine hesitate or fire differently? I have no doubt that it was doing stuff like that, when last my bike was on the road; and I didn't even realize something was wrong.

So much to learn... I sort of get that the pilots, the needle jet and the mains handle slow, medium and fast. But I'm pretty sketchy on exactly what it is they're doing.

That's why I'm so grateful to have people like this, willing to help enlighten the ignorant. (That would be me.)

 

[5twins]

Oh, you'd notice. "Break-up" is just what it sounds like. The motor doesn't increase speed smoothly as it should. It stumbles, stutters, or misfires. This is most noticeable under heavy or full throttle applications, and the more gas you give it, the harder you push it, the worse it gets. If you ride very gently and easy, you may not notice the problem too much. These CV carbs are rather forgiving and will mask over minor jetting glitches unless you push them hard. Obviously, you don't normally ride that way, at full throttle all the time, but you must do it for jet testing. You need to work the carbs hard to uncover the glitches.

 

[griennehornette]

Ah. Yep, even I would notice that. Been so long since I last rode it that it's hard to remember; but I do have a vague memory of something like that happening. Can't recall when/where during acceleration that it happened. But then, if stumbles, stutters or misfires happened, I would most likely have backed off the throttle, rather than gunned it.

Huh. I've always wanted to become a more confident rider; i.e. not so timid and willing to open it up. I'll take this as a recommendation to do so!

"Honestly, officer. I have it on good authority that I really have to push the bike to accurately test the carb jets and get it tuned well. That's all I'm doing. Seriously." ;-)

Thanks again 5twins. It's amazing to be able to get expert advice like this. I hope someday I'll be able to pass along some of the wisdom.