Topic: 087A Carbs on a 78 CB550???

[TowelThief]

Long story short....let a mechanic take my bike while I went into the military. Paid him for the work before hand. (this was almost 2 years ago)

In a rush to get it back and to my new base (12 hours from home) I didnt really look over his work (#$%*).

It had the PD46 carbs when I gave it to him and It came back with 087A (76 CB550) carbs....albeit, all new internals.

Ive ran the bike with them....when it was running....But is there any negative to having them? Is it just a matter of tuning them correctly?

[Deltarider]

Congrats! You can thank your mechanic. 087A carbs are much nicer to work on than those PD carbs.

[Bankerdanny]

No biggie. You lose the bar mounted choke and the fast idle cam that came with the PD series carbs, but you gain carbs that are easier to get parts for and probably improve overall rideability.

[TwoTired]

The 78 carbs work very well with the stock 4to4 exhaust and intake filter box.   
I doubt you still have those, so it doesn't matter.  They must be completely retuned to work with other intake and exhaust components.

The 78 carbs do have the sync ports on the carb bodies.  So, not only are the intake couplers different, but the intake manifold is devoid of intake ports for the carb synch process. Check for screws on the intake runner sides.

With the 087 carb swap you also need the older intake runners with sync ports.

The 087 carbs are sloppier than the 78 PD carbs, which makes tuning for changed breathing components easier.  But don't expect 50 MPG, like the 78 got with original components.  Probably in the 30 ish range now.

Cheers,

[BomberMann650]

Did the tech-mech inform you of the change?

I've seen carbs get wrecked from improper storage.  Also seen lots of broken float pins from whoopsie uh ohs.

[swestleyj60]

Just in the last two weeks, I put a set of 1975 carbs on my 1978 CB550.  The guys are right in that the other things that needed to be changed were the engine manifolds and the airbox-to-carburetor boots, simply due to the fact that the carb bank in 1975 was longer.

I kept the PD carburetor rack, just to teach myself how to rebuild it over the winter, but I'm thoroughly pleased with the 75 rack.  Frankly, I much prefer, for example, the choke switch being on the side of the rack rather than up on the dash and connected by a cable.

I don't think you'll have any troubles & may even find it to be an improvement over time.

[TowelThief]

The 78 carbs work very well with the stock 4to4 exhaust and intake filter box.   
I doubt you still have those, so it doesn't matter.  They must be completely retuned to work with other intake and exhaust components.

The 78 carbs do have the sync ports on the carb bodies.  So, not only are the intake couplers different, but the intake manifold is devoid of intake ports for the carb synch process. Check for screws on the intake runner sides.

With the 087 carb swap you also need the older intake runners with sync ports.

The 087 carbs are sloppier than the 78 PD carbs, which makes tuning for changed breathing components easier.  But don't expect 50 MPG, like the 78 got with original components.  Probably in the 30 ish range now.

Cheers,

You're right. I don't have the stock air box. It came with pods when I bought it (2010). It ran when I bought it and then I got home and it didn't.

So I began to rebuild. Everything on the bike is pretty much knew. Over 7 years the amount of money I've put into it is pretty stupid. And I think I've road it 5 miles, Lol. I'm attached just for the learning experience at this point but have very limited time.

He did not replace the intake manifolds so when I was looking where to hook the mercury meter I had to call him and ask him how he sync'd them. He said he bench syncd them...at this point I didn't expect much less from him.

I bought the manifolds with the sync screws in them. Unfortunately I let gas sit in the bowls for 10 months and they are gummed up and need cleaned.

Thanks for all the replies. Wealth of knowledge here.

[TowelThief]

Did the tech-mech inform you of the change?

I've seen carbs get wrecked from improper storage.  Also seen lots of broken float pins from whoopsie uh ohs.

Well no, he didn't ask me if he could. But when he gave me the printout of what he did I saw it. I'm not sure why he did. Ease? 

I have velocity stacks but am debating on getting one of those steel dragon airbox's for better filtration.

Cleaning the carbs and then figuring out why the battery doesn't charge are my two main goals now. Shotty electrical job on this bike.

[BomberMann650]

Memory is a little hazy, but I think the available breadbox filters are exclusively fitted for the PD carbs.  The rep at cognito moto regrettably informed me their unit did not fit the A series (supersport) carbs.

Looks like you're getting v-stacks.  I think there are some people who stuff a piece of oiled foam filter and rock screen on theirs.  To avoid sucking schmutz into the chambers.