Intake boots are different for 1979 vs 1981...

BayArchitect · Post by **BayArchitect** » Tue Mar 06, 2007 1:00 pm

I'm thinking of bolting '79 carbs to my '81 CBX, but there is a different part number for the insulators (intake boots). What is the difference between them? Will the '81' boots fit the '79 carbs, or will the '79 boots fit the '81 heads?

Chris · Post by **Chris** » Tue Mar 06, 2007 2:06 pm

I believe '79/'80 boots will fit the '81 head. Perhaps others can provide additional details.

alimey4u2 · Post by **alimey4u2** » Tue Mar 06, 2007 2:10 pm

I think the boots will fit but something from the dim past tells me that the stock airbox will not align up.....
Maybe someone could cooberate....

LamarX · Post by **LamarX** » Tue Mar 06, 2007 10:41 pm

It was once said to me that the cylinder heads are different, the 81 & 82 have a line on the center of the boots and needs to match horizontatly across the intake for proper angle.

The 79 Head does not require this specific positioning.

I think that's how it goes,

Marc

cbxtacy · Post by **cbxtacy** » Tue Mar 06, 2007 10:49 pm

After reading your post, I went out into the garage and compared a 79 parked next to a 82. Both with original airbox. The manifolds on the 82 are a bit longer then the 79 and angled down just a hair. The carbs appear to be the same size so if you put 79 carbs on a pro link, use the pro link manifolds. If you've replaced the airbox with stage 3 filters, it doesn't matter which manifolds are used (I believe).

Chris · Post by **Chris** » Wed Mar 07, 2007 11:56 pm

cbxtacy wrote:After reading your post, I went out into the garage and compared a 79 parked next to a 82. Both with original airbox. The manifolds on the 82 are a bit longer then the 79 and angled down just a hair. The carbs appear to be the same size so if you put 79 carbs on a pro link, use the pro link manifolds. If you've replaced the airbox with stage 3 filters, it doesn't matter which manifolds are used (I believe).

I just took the carbs off of my '81 engine. The collars between the head and carbs are different from the '79/'80. They are thicker at the top and the same thickness on the bottom as the early model collars (to get the downward angle George mentioned). This must have been done to angle the carbs to improve flow into the head??

I had already (accidentally) bought early model collars for this engine. I'm going to try to mount the carbs with these collars (the old ones are hard as a brick). As George had said, if you are using individual filters, this should work (I have individual filters). This arrangement won't work if you are planning on using the stock airbox. Stock airbox on a late model will require late model collars.

Mike Nixon · Post by **Mike Nixon** » Fri Mar 09, 2007 10:36 pm

The carbs are held at a slightly different angle on the later models, probably affecting the float level and evaporative emssions spec. It's enough different in fact that the carb tops are harder to get off in the frame on the earlier models. :)

EMS · Post by **EMS** » Tue Mar 13, 2007 9:00 am

In order to improve airflow, the carbs were mounted more horizontally on the Prolink models. To achieve this, the rubber manifolds were wedge-shaped- thinner on the bottom and thicker on top. They had a mark to ease orientation during installation. As a result, the rear end of the carbs drop down. This means, together with Prolink manifolds, you will need to use a Prolink airbox, if you run one, because the holes will not line up. However, there are plenty of guys who are able to use early manifolds with late airboxes and vise-versa. Same guys who can take the airbox off without tilting the engine.
Carbs as such will go into either manifold. I have found several sources for new early manifolds but not for Prolink ones. I think CBXMan sells them, though. Using 79 carbs on a Prolink model, you will lose the vacuum valve, unless you retrofit.

sixofsix · Post by **sixofsix** » Sun May 17, 2009 8:32 pm

...yes I see the 79 carbs will fit an 81/82 motor BUT will the jetting be correct? I think the 79 exhaust cams will need to be mounted to suit the 79 carb jets?

..I am thinking of plunking in a 81/82 motor with 79 carb boots and air box in my 79. But I think the 79 carb jetting will not work on a 81/82 motor?

Any ideas?

Thanks, Tony

PS I found this thread that is similar to what I want to do, hence this posting...thanks!

EMS · Post by **EMS** » Sun May 17, 2009 9:44 pm

Tony, I think you will be fine. The exhaust cams are the same on Prolinks and 79s anyway, and the difference in intake cams will not give you a problem with the carbs. At least not one you will recognize. The little differences between the years and the 79 being sooooo much better in performance is all a big exaggeration. If you think about it, the actual difference in horsepower is smaller than the common variation due to manufacturing tolerances. The reason the 79 feels like it performs bettert han the Prolinks is because it is much lighter. I have an 81 that runs quite well and I don't think a stock 79 will run away from it.

sixofsix · Post by **sixofsix** » Wed May 20, 2009 1:00 am

Thanks!

silversurfer1050 · Post by **silversurfer1050** » Wed May 20, 2009 11:02 pm

..my limited understanding the '79s had larger diameter carbs than the '80s....

daves79x · Post by **daves79x** » Thu May 21, 2009 8:02 pm

No - all CBX carbs are 28mm. All years' carbs will work fine on any other year, as long as the carbs being used are in good running order. The jetting configuration is different for different years, but the fine differences in cams makes virtually no difference.

Dave

Randakk · Post by **Randakk** » Sun May 31, 2009 7:56 pm

Corrrect information above from Mike Nixon and others.

The later models ('81-'82) have boots that are tilted slightly downward to the rear and are "indexed" to the cylinder head for proper orientation to the carbs.

The early models ('79 -'80) have no tilt or index.

Confusion results from the fact the the geometry of the mount "ridges" on the head and on the carbs is the same. So, they are semi-interchangeable....depending on whether or not you run the stock airbox and other details.

Best to stick to the correct version for your model.

I'm working on details with an aftermarket supplier who will enable me to provide both the early and late versions of the carb inlet boots.

Details soon.

EMS · Post by **EMS** » Mon Jun 01, 2009 7:22 am

The early ones are readily available. No need to find someone who makes a mold for them.