Instructables

This is my first Instructable after using many ideas from the site, so go easy on me.

Having owned numerous Yamaha Motorcycles over the years, one thing they have in common is nasty Carb intake rubbers. Over the course of time they go hard, they shrink and the break up. This makes refitting the airbox inordinately difficult and it is usually found unattached the next time you take the tank off. Here is an instructable showing how I replaced the knackered rubbers with sexy Silicon hosing

Step 1: Step one, the size of the problem

First things first, check the diameter of the carb, this will decided the size of hose to order. The carbs on this FZ750 were 52mm, I ordered a length of 51mm hosing.
I then measured the depth of the lip on the original intake rubber, In this case it was 10mm (from the edge to the obvious ridge in the photo. I had a further 15mm to where it butted to the airbox. I then added 5mm to allow for shrinkage and to provide a "push" from the tank to hold things in place more securely

Step 2: The first cut is the deepest

Picture of the first cut is the deepest
carb8.jpg
carb6.jpg
I then set a pair of dividers and scored a line 30mm parallel to the end of the hosing. I went over the score with a Sharpie and proceeded to gouge out the line with the rotary tool. Once a succesful line was scored I went through the pipe with a junior hacksaw. A bandsaw would be a better option but I don't have one of those. It is  important to get this cut correct as it needs to firmly butt up and inconsistency in the first cut is amplified on succeeding cuts. I then faced the cuts on my bench grinder

Step 3: The second cut is just as deep

Picture of the second cut is just as deep
Now turning to the original rubber, I rotary tooled the old lip away just above the seam

Step 4:

I then trial fitted the silicon replacements to the airbox. Satisfied with the fit I then placed the new rubbers on the carbs and fastened them down. The airbox was then installed and If I had remembered to buy some more hose clamps I would have secured them to the airbox end.

There you have it, a cheap remedy for an annoying problem
 
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rnijland8 months ago
Have you glued the new hoses on the old one or something?
mikeasaurus3 years ago
I have a 1987 Yamaha FZX750, your manifold looks different than mine. What year is yours, and can you provide some more details on the removal of and re-installation of the carb. tubing starting from a completely assembled bike?
aideym (author) 3 years ago
I've only replaced the flexible lip. The full length of the stack remains intact. The silicon tubing is 5mm thick 5 times thicker than the original.
And as I mentioned earlier the original weren't sealing as they were mostly not there.
The bike won't be in a running state for a few weeks as I am just in the process of rebuilding but I'll be happy to update with the finished results
reptilehead3 years ago
Im more concerned that the FZ750 is a YICS motor which means that the carb boots are VITAL to synching the carbs. have you re-synched the carbs? hows the vacuum gage read?
if its solid.... then i think i know what im doing to my cafe racer!
aideym (author) 3 years ago
Indeed, ensure that everything is given a good clean, although any rubbish left can only be less damaging than the things flying in through the gaping holes betwixt carb and airbox
CementTruck3 years ago
Neat idea.

I worry about getting anything in the intake/carbs and so I just wanted to make sure the airbox was cleaned and free of fragments of rubber (from the sawing and "dremeling"). That could plug a jet right quick.