'79 carbs on an '81?

[steve murdoch icoa #5322]

After referencing this post from 2007 i concluded that i can put '79 carbs on an '81 but it might be more of a struggle than usual.
viewtopic.php?f=20&t=2528&p=13171&hilit ... lds#p13171

So far i am having no luck. Semi-pliable rubbers, hairdryer heat, a lubricant and i sill cannot get the carbs to seat in the manifolds.
Tried lots of different angles, straight muscle, wood working clamps, a cargo ratcheting strap is next.
Over the years i have probably changed carbs 15 times with no major issues. Not so much this time.
Any thoughts?
Will the connection to the airbox manifolds be a major struggle as well?

[FalldownPhil]

That ratcheting strap is my tool of choice for carb installation. I don't even try anything else anymore. This method takes the pain out of carb installation.
Phil

[tevan]

Use heat gun and warm them boots till they are real warm and then they will go on with a little lube . For sure with ratchet strap.

[NobleHops]

What Tevan said - I was advised to heat my old hard ones til they stunk (and smoked) and then bear hug the engine from the header side. POP!, they were in in 10 seconds. Are you certain they are all 'clocked' correctly, and nothing is obstructing them, like a slipped clamp?

N.

[steve murdoch icoa #5322]

"Thunk"...now that is a lovely sound.
Apparently i had forgotten to invent new swear words while wrestling with the carbs. Took care of that.
A bit more muscle, heat and lube and they landed.
I understand the early carbs will work with the later engine, it was the different manifolds that i thought were hanging me up.

[EMS]

Steve: I am a little confused. The only difference between 79 and 81 carbs is internal in the jetting. As far as physical fit is concerned, they are identical. If you change the manifolds between carb and engine from the original 81s to 79 manifolds, you would have to change the airbox, because the carbs will angle upwards towards the back. If you did not do this, it should not matter what year carbs you install.

[steve murdoch icoa #5322]

MIke, i was having such a difficult time getting the '79 carbs mounted that i thought it may have had something to do with not changing the manifolds.
It is all a moot point as when i was connecting the cables to the throttle control the front cable unhooked from the carbs. Yuck.
Oh well, practice makes perfect.

[EMS]

It is all a moot point as when i was connecting the cables to the throttle control the front cable unhooked from the carbs. Yuck.
Oh well, practice makes perfect.

I guess you should consider yourself lucky. If that happened, the cable was probably not attached 100% correctly to the throttle lever and would have come off sooner or later during a ride.

[Mike Nixon]

I don't often comment, and Phil, you're a good friend, but for whatever this is worth I have to put in my vote strongly *against* any kind of straps, wood devices, et al. The choke system on these carbs is just too delicate to withstand that kind of treatment. The carbs are prone to get out of alignment and the chokes then hang up, when treated to that kind of force. In fact, i just got off the phone with a fella who was having that very problem with carbs I sent him. The heat gun trick is one on the other hand I heartily endorse. The angle of the manifolds and that of the carbs makes them natrually not easy to install, and add hardened manifolds and the situation is doubly difficult. A heat gun solves it all. Plop! They're in there. On the subject of different years, though the carbs are at a 5 degree different mounting pre- and post- Pro-Link, I have seen many interchanges where you couldn't tell the difference, including my own 81 that got 79 carbs almost the first week I had it (being at AHM I had access to carbs). With 56k on the clock, those carbs are still on there. The 79 carbs happen to be the best, in my opinion. Three-jet instead of two-jet, so they are more tunable and even if left stock simply work better. My $0.12 (inflation, you know...).

[FalldownPhil]

Thanks Mike,
I am so embarrassed !! I will save it for a last resort
Best,
Phil

[EMS]

On the subject of different years, though the carbs are at a 5 degree different mounting pre- and post- Pro-Link, I have seen many interchanges where you couldn't tell the difference, including my own 81 that got 79 carbs almost the first week I had it (being at AHM I had access to carbs.

Once again, I am confused. The different mounnting angle is in the carb-to-engine boots, not in the carbs. One should not see a difference in mounting 79 carbs to an 81, as long as the 81 boots are used.
Although it is only 5 degrees, the carbs will no longer fit the airbox properly with the wrong boots.
That is the main reason it is very hard, if not impossible to fit a late model airbox ( with the nice bolt-on sideplates) to a 79 or 80 CBX with stock boots and carbs.

[Mike Nixon]

Ah, see, you guys are way ahead of me! I didn't know folks were fitting all the different parts all around. I have only thought of swapping carbs, not airboxes or boots. Since it is only the carbs I have switched, I naturally would not observe any problems (that's me, master of the obvious!). My mention of the 5 degree thing has no relevance. :). (It does however explain why the twin-shock bike's carb tops are harder to remove in the frame than are those on the Pro-Link bikes.).

[Jeff Bennetts]

On the subject of different years, though the carbs are at a 5 degree different mounting pre- and post- Pro-Link, I have seen many interchanges where you couldn't tell the difference, including my own 81 that got 79 carbs almost the first week I had it (being at AHM I had access to carbs.

Once again, I am confused. The different mounnting angle is in the carb-to-engine boots, not in the carbs. One should not see a difference in mounting 79 carbs to an 81, as long as the 81 boots are used.
Although it is only 5 degrees, the carbs will no longer fit the airbox properly with the wrong boots.
That is the main reason it is very hard, if not impossible to fit a late model airbox ( with the nice bolt-on sideplates) to a 79 or 80 CBX with stock boots and carbs.

Mike I'm thinking it's no big deal to use the 81/82 airbox with 79/80 intake manifolds and or carbs if the 5 degree difference is in the 81/82 airbox intake horns (the manifolds in-between the carbs and airbox). The front portion of the airbox assembly comes apart by removing a few screws and the intake horns can then be removed and swapped out with the 79/80 intake horns thus allowing you to eliminate the 5 degree difference and now you can have the nice bolt-on side plates the 81/82 airbox offers on your early model CBX.

I have all the parts to do the swap, just need to get around to doing it.

[Mike Nixon]

Thanks Mike,
I am so embarrassed !! I will save it for a last resort
Best,
Phil

YOU'RE embarrassed? I am the one who should be embarrased. Butting in with nonsensical stuff nobody cares to hear about and stuff I know nothing about anyway. Of the heat gun trick though, I am an avid fan. On another note, Harry dropped by today. We had a great confab about folks we both know, engines, intakes, H-Ds vs. Hondas, etc. Like you said, a great guy. Got to read his promo in the Ultimate Motorcycling you thoughtfully sent along too. Just finished it. Neat!

[EMS]

Mike I'm thinking it's no big deal to use the 81/82 airbox with 79/80 intake manifolds and or carbs if the 5 degree difference is in the 81/82 airbox intake horns (the manifolds in-between the carbs and airbox). The front portion of the airbox assembly comes apart by removing a few screws and the intake horns can then be removed and swapped out with the 79/80 intake horns thus allowing you to eliminate the 5 degree difference and now you can have the nice bolt-on side plates the 81/82 airbox offers on your early model CBX.

I have all the parts to do the swap, just need to get around to doing it.

That would sure be another way to circumnavigate the issue, Jeff. I don't know if the difference in angle is compensated for at the airbox by the intake horns or if the whole airbox is different.
But in any case, the original point was that ANY carb can be installed on ANY bike and it does not make a difference. As long as you just change the carbs, no boots , no airbox.