Float bowl gaskets for RC24 VFRs (and maybe RC36)

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mangocrazy
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Float bowl gaskets for RC24 VFRs (and maybe RC36)

#1 Post by mangocrazy » Fri Aug 18, 2017 9:34 pm

One of the issues of owning a bike that is approaching (or has passed) it's 30th birthday is replacing o-rings in the fuel system that have gone hard/cracked/disintegrated over time. The OE Honda items are prohibitively expensive (if you can even still get them), and even UK-sourced equivalents are decidedly expensive.

Probably the first intimation you will have that something is amiss is when you rouse the old girl from her winter slumber, turn on the fuel and go to start the bike. It's the smell of petrol and the widening damp spot on the drive that gives it away.. On closer inspection, fuel is pissing out of one or more of the float bowls and the first ride of the year is looking increasingly distant.

The problem is that the float bowl o-ring gaskets have either dried out or cracked, allowing fuel to pass unhindered. Ironically this is more likely to happen if you 'did the right thing' and drained the carbs (using the drain screws thoughtfully provided by Mr Honda for this purpose) prior to laying the bike up for winter. During that period the o-rings dried out, shrunk and lost their sealing properties. Sometimes a splash of new fuel will cause them to plump up and re-seal, but more often they never recover.

So what to do? Well, you can buy the off-the shelf, pre-formed orings - NRP in the UK do a set of four for the pricey but not unreasonable sum of around £30. Here is the link for the FJ/FK float bowl seals:

http://www.nrp-carbs.co.uk/shop/index.p ... word=honda vfr750&product_id=4654

However if you're on a budget, then it's possible to buy a standard circular o-ring of the right size and make it fit in the contours of the float bowl recess. You want Viton o-rings, as they will happily tolerate ethanol as well as petrol and also have increased temperature resistance over nitrile. I found this site www.polymax.co.uk and they do 76mm internal diameter (i/d), 1.78mm cross section o-rings (exactly the size we want) in Viton for 39 pence each...! For quantities of 50+ the price drops to 36p, 100+ its's 30p ea, 500+ it's 26p each...

Here's a link. Just enter the sizes above and the material you want (Viton) and off you go:

https://www.polymax.co.uk/o-rings/rubber-viton-oring/

This site also do packs of 10 Viton o-rings of the same size for £6:

http://www.turbonoz.co.uk/imperial-bs18 ... of-10.html

The size of o-ring you want is listed as BS041 - so British Standards have adopted the US 'Dash' standard it would appear, as Stateside this same 0-ring is always referred to as -041 size. The 'dash' standard is extensively used in the USA for racing and aviation fittings
Last edited by mangocrazy on Sun Jul 14, 2019 10:50 am, edited 1 time in total.

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#2 Post by mangocrazy » Wed May 29, 2019 8:49 pm

As an addendum to this, when replacing the float bowl gaskets also replace the o-rings on the fuel inlet t-pieces that join the 2 front carbs and the 2 rear carbs. These have an i/d of 9.25mm and a cross-section of 1.78mm, and you'll need 4, 2 for each t-piece. Get them in Viton, of course.

I found this out the hard way, with fuel pissing out when I went to prime the carbs by shorting out 2 connectors on the fuel pump relay. This was after having to swap a bank of carbs over as the original set were sticking and refusing to run below 2000rpm.

I am getting so sick of pissing about with VFR carbs - they're a nightmare in every way, from fitting on the stubs to lining up the dowels when re-fitting the plenum chamber while simultaneously making sure the rubber bellmouths are lined up correcty with the mating face on the carbs. I hate the fucking things with a passion and never want to see another set.

As a result of all this aggravation, the VFR is on a final warning. Amy more shit like this and it's going. My patience is just about exhausted.

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#3 Post by mangocrazy » Thu Jun 27, 2019 9:17 pm

Well, it seems like the warning has worked... I took it for its MoT today, and the old girl is back to full power. As it turned out, all the issues were self-inflicted (who'd a thunk it?) - the near side rear cylinder's plug lead was not properly clipped down onto the plug top and while fixing the o-rings I'd managed to misalign 2 out of 4 of the diaphragm slides. With all that lot fixed, normal service has been resumed.

Just as well, the bike's heading back down to France early in July and it would have been an extremely tedious ride down otherwise...

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#4 Post by mangocrazy » Sun Jul 14, 2019 11:09 am

Well, I'm writing this from the South of France, trying to make excuses as to why I don't need to ride the bike today (it's that hot).

The VFR made it all the way down here, although the last third of the distance was done with virtually no clutch disengagement at all. There must be a fluid leak somewhere as the reservoir was virtually empty when I checked. I've refilled it and bled it, but will be keeping a look out for pools of fluid on the floor.

I should really have put some serious miles on it before attempting a ride of this distance (850 miles door to door), but there's nothing like a long ride to bring any shortcomings into focus. Besides the clutch, I'm also pretty sure that the head bearings need tightening down a fraction, as I was getting a topping out clunk over rises, and minor judder on the brakes as I came to a halt.

The shock spring rate is still too high, (but I knew about that) and I'm getting a backfire on deceleration (but a very muted, genteel one - this is a VFR after all) so I'm pretty sure there is an air leak on the inlet or one or more of the exhaust clamps need tightening up.

What was surprising was the fuel economy (or lack of it). I was only getting a range of about 125 miles from full to reserve. I would normally have expected at least 150 miles range. Part of this is due to the centre stand being removed for previous maintenance and not being re-fitted. This means I can't use that last 2 or 3 litres of capacity when refilling. Hunting around for petrol stations in rural France when you're well into reserve is never a fun activity.

But we made it, and the aches and pains are slowly starting to recede...

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