Topic: Air Box and Carbs Don’t Line Up

[jmelche2]

My 74 750 had pods when I bought it. I purchased the correct Airbox but as you can see from the photo, they don’t line up very well. I can’t be the first one to come across this. Appreciate any comments as to what’s going on here. Thanks, Jim

[carnivorous chicken]

Without support in the back (from the airbox and boots), perhaps the rubber boots that join the carbs and engine have sagged a bit under the weight of the carbs.

[fizzlebottom]

I believe you're missing what Honda called the 'air cleaning connecting tubes'.

P/N 17253-341-300

My bet is that you'd be able to angle the carbs up to line up with the tubes once they're in place.

[pjlogue]

What Fizzlebottom said, you need the carb to airbox tubes first.  Then make sure the airbox pivoted all the way back at the bottom.  Then make sure the carb to cylinder head rubbers are positioned properly.  The carb cylinder head rubbers have only two part # for them.  One for no's 1 &4 and one for no's 2&3.  There are numbers stamped on top and bottom of these rubbers and depending on which cylinder position the rubber is installed on determines what number is on the top side.  This takes a bit of fiddling to get them to line up and what I do is use a board placed across the carb side of the rubbers and rotate each rubber so each rubber sits flat against the board.  I use Dow Silicone vacuum grease  to lightly lube the mouth of each rubber to make pushing the carbs back on easier.  A ratchet strap around the carbs and head greatly helps!

The carb to airbox rubbers origionally had glue to seal the rubber to the airbox.  I used silicone seal for this.  airbox needs to be removed while adjusting the carb to cylinder head rubbers and removal/installing the carbs.

-P.

[BenelliSEI]

All of the above. I also open up the holes on the frame tabs a little bit to make it all a bit less critical. When I use new rubber stacks in the airbox they are soft enough, I don’t bother glueing them in…..

[MauiK3]

They are also called velocity stacks and serve that purpose, maybe one of the most critical items in the stock breathing setup.

[jmelche2]

I have the boots - just soaking them to soften up.

[Don R]

 I soaked a set of those once, I forgot for a few days and when they came out, the hard spots didn't swell but the soft areas did. You should have seen them, they looked like modern art!

[M 750K6]

I use a heat gun on its lowest setting to warm the rubbers through. It massively increases their flexibility, until they cool. I used the flat piece of wood test, to make sure the inlet rubbers are mounted correctly on the head, properly aligned, then tighten their clips up. Carbs onto the inlet manifold rubbers next, then the airbox with the rubbers pre-installed is slid onto the back of the carbs, then tighten up the carb rubber to carb mounting clips, inlet side first, then airbox side. Keep checking all are nicely seated, more heat if useful. Finally I tighten the airbox to frame mounts.

I found the holes in the frame's airbox mounts were a couple of mm too far rearwards, causing a rearward tension on the rubbers, so I filed a slight oval in the bracket holes, to reduce that. I don't know what caused it. Might be replacement rubbers, or shrinkage in the rubbers over time.

[HondaMan]

I might add: there are numbers on the tops of the hoses between carbs & engine. Make sure they are 'upright' when looking at them from the carb side. If they are the other way, then the carbs end up sitting at an angle that prevents them meeting the air hoses from the airbox.

If their angle is wrong, the fuel level inside the carbs also comes out wrong, and makes the engine run richer, all else being equal. This is due to the fuel level in the bowls then being a little higher than normal.

Chopper builders in the 1970s used to do this on purpose so the carbs would not ever weep fuel upon their creations while in bike shows. The bikes had to run to qualify for awards, which they did, but they didn't run right.