Topic: What are the differences between carbs?

[Dusthawk]

I have 3 sets of Carbs, they are marked 086A, 657B and 7A. The 086A set I want to keep and mount on Rita, but they have 105 main jets. The 657B carbs had 110 mains and the 7A carbs had 115's. Is there something different about the carbs themselves that require the different jets? The previous owner of the 7A carbs said they came off a stock bike, the 086A set were rebuilt but never used, don't know if they were for a stock rebuild, and the 657B set came off Rita but I don't know the history on those carbs. The PO of Rita did no work on her, only rode her for a few months and sold her to me.

I am running drag pipes and will be running a custom airbox so I planned on running 120 main jets. I don't know if the cam is a hot cam or not and I don't have the proper tools to check rise and duration.

[Lars]

I think the carb house is pretty much the same, maybe only different numbers on different periods. Far as I know, you can change to other mains if you like on any of them.

[CycleRanger]

I have 3 sets of Carbs, they are marked 086A, 657B and 7A. The 086A set I want to keep and mount on Rita, but they have 105 main jets. The 657B carbs had 110 mains and the 7A carbs had 115's. Is there something different about the carbs themselves that require the different jets? The previous owner of the 7A carbs said they came off a stock bike, the 086A set were rebuilt but never used, don't know if they were for a stock rebuild, and the 657B set came off Rita but I don't know the history on those carbs. The PO of Rita did no work on her, only rode her for a few months and sold her to me.

I am running drag pipes and will be running a custom airbox so I planned on running 120 main jets. I don't know if the cam is a hot cam or not and I don't have the proper tools to check rise and duration.

Aside from insignificant external differences the 7A, 657A & B are essentially identical.  (At least the ones I have are.) 
I haven't personally examined an 086A set but they appear to be the same as the earlier carbs.

Here's a quick chart:  http://www.hondachopper.com/garage/carb_specs/carb_specs.html

Honda changed the mains over the years to adjust for emissions and performance.  These changes and the carb numbers are documented in the manual and supplements.

[Dusthawk]

Some carbs or heads have different sized mounting rubbers I think?

Rotortiller, all the mounts, head mounts and airbox mounts, are the same for all sets of carbs. Airbox sides are all 39mm and the head sides are all 40mm. I tried my new carbs mounting rubbers to all three sets and they fit all three.

I actually found 2 differences, the 086A set has a different throttle return spring mounting than the other two.  The 086A is the first pics, the 7A is the second. The 657B is the same as the 7A set, they both have that extra lobe the spring mounts to, the 086A set does not have the lobe and the spring is longer.

The other difference I have found is that the mating plate for the carbs is slightly different between each set. On the 086A set, the idle adjust screw is on the right when mounted to the head, the other two sets are on the left when mounted. Other than the difference in the plates and throttle arms, I don't see any other differences.

[CycleRanger]

Some carbs or heads have different sized mounting rubbers I think?

Rotortiller, all the mounts, head mounts and airbox mounts, are the same for all sets of carbs. Airbox sides are all 39mm and the head sides are all 40mm. I tried my new carbs mounting rubbers to all three sets and they fit all three.

I actually found 2 differences, the 086A set has a different throttle return spring mounting than the other two.  The 086A is the first pics, the 7A is the second. The 657B is the same as the 7A set, they both have that extra lobe the spring mounts to, the 086A set does not have the lobe and the spring is longer.

The other difference I have found is that the mating plate for the carbs is slightly different between each set. On the 086A set, the idle adjust screw is on the right when mounted to the head, the other two sets are on the left when mounted. Other than the difference in the plates and throttle arms, I don't see any other differences.

Yes, there are differences with the stay plates, what you refer to as the "mating plate", but that's a whole 'nother subject!   The carburetors and the stay plate are two separate things.

Btw, don't lose that throttle return spring from the 086A set. That spring is unique to the '75F and '76K&F stay plate and is no longer made.

[CycleRanger]

Hey I was just told if I wanted to install older carb assemblies on my engine to consider the mounting parts between the head and carb assembly because there was a change in inside diameter. I'll see if I can dig out the data.

What year is your bike?  There is a difference for '77 and '78.