Topic: Where are the "vacuum plugs"??

[natewatkins]

I am looking for the "vacuum plugs" so I can sync the carbs on my 78 CB550. These carbs themselves are from a CB500 stamped 627B and have the stock jetting in them. I received the bike this way from the guy I picked the bike up from. However all the pictures I have found with where the plugs "should" be, I can't seem to find them. Can someone assist me? I hope I am just blind and they are right in front of my face!

Thanks again!

[wannabridin]

there should be a screw going into a hole into the central runner of the carb.  i'm not familiar with 500 carbs, but that screw coming up at an angle looks to be it to me, unless that's the air/fuel screw...

[natewatkins]

If you are referring to the top image and the screw in the upper left hand corner, no that is not it. I assume it would be closer to the cylinder side of the carb but I just can't seem to find it 

[cb550fcafe]

Youre not blind 'cause they aren't there. a 1978 had the sync plugs in the carb, no holes in intake. The CB500's had the sync plugs in the intake, not in the carbs, so when you use 1978 intakes=no sync holes & CB500 carbs=no sync holes, you have no sync holes. You'll either need older intakes which is what I'd recommend or 1977 or newer carbs.

We're not even getting into how good/bad the engine will run with these carbs.

[TwoTired]

The 78 carbs have the vacuum tap/plug on the carb body.

The earlier carbs had the vacuum tap/plug in the intake runner at the bottom near the engine.

 A carb change like that usually is done by bringing the proper manifolds along with the carbs from the donor bike.

[natewatkins]

Well, it runs like crap haha. I had some air leaks in the boots and now that I got that fixed, I can get it to run and all 4 pipes are not getting hot. However, it still runs rather bad so I figure I would sync the carbs. I have already gone them the carbs them selves multiple times. I can assure you all the little bits are cleaned out and there is no blockages. The timing is set good, no blockages from the pet cock. All 4 bowls are getting gas... bummer.

So, until I get a different intake, the chances of vacuum sync is SOL. I have heard of folks bench syncing but have also heard it is kinda hit and miss. Is there anything else I can do with out spending money on a new intake (something I would rather not do right now)?

Thanks!

[TwoTired]

Return the bike for a refund?

Drill and tap your existing manifold?


All pipes not getting hot at idle, or 3000-4000 RPM?  Cold(er) pipe at idle is probably a pilot circuit issue in a carb.

[333]

I'd drill and tap the intake manifolds at this point.

[natewatkins]

I have to say that I agree with all of you. Thanks everyone for the input everyone.

[bradweingartner]

I'd drill and tap the intake manifolds at this point.

Me too!

I didn't think it was possible to put earlier carbs on the late manifolds, as the spacing is different. (Perhaps I underestimated the brute force approach?)  A carb change like that usually is done by bringing the proper manifolds along with the carbs from the donor bike.

I thought that was the 650s with two different spacings and the 500/4 and 550/4 were all the same regardless.

[TwoTired]

I didn't think it was possible to put earlier carbs on the late manifolds, as the spacing is different. (Perhaps I underestimated the brute force approach?)  A carb change like that usually is done by bringing the proper manifolds along with the carbs from the donor bike.

I thought that was the 650s with two different spacings and the 500/4 and 550/4 were all the same regardless.

I went out and measured my spares.  You're right.  The spacing is the same for all the 500/550 carbs.  However, the PDs use different diameter and length carb couplers.

[Frostyboy]

I know this post is getting old, however if you're still looking for a solution, I just found this on ebay.

http://cgi.ebay.com/ebaymotors/1976-HONDA-CB-550-F-CB550-CB550F-Intake-Manifold_W0QQitemZ370365905441QQcmdZViewItemQQptZMotorcycles_Parts_Accessories?hash=item563b873a21

It's got the plugs in the runners for you & certainly cheap enough when I viewed the listing, $9.95