Split Carb Rubber

[Granty]

Guys -- 30mm open mouth dellorto -- MB Carb rubber split and fell off on the way back from Whitby, I think it might have been the fuel pipe that was adding pressure to the carb & pulling it down -- I want to try a reinforced "radiator" style rubber -- any ideas where to get the best ones or anyone have a solution?

Cheers G

[Donnie]

Ive cut my own before now from car rad hose. so basically any motorfactors.

[Donnie]

or this fella on fleabay http://www.ebay.co.uk/itm/dellorto-phbh ... xyVLNS7qST

[holty]

hi, ive got a silicone hose on my rb, the standard rubber was too short to clear my tank, i measured the carb stub diameter,mine is a 34 delly and bought some hose to suit, a couple of mm smaller gives a good fit, ebay is a good place to buy it, as for carb putting pressure on the hose, yes your right, some kind of rubber mounting fastened to the carb and manifold would be a good idea to support the carb and not rely on the hose to support the carb

[Nelly]

I have a lump of truck radiator hose I used to use as inlet hose for my Lammy before the reed conversion.
It came from a local hose supplier in metre lengths, if I remember right.
I think I have about half a metre left that's pretty useless to me now. I'll cut you a bit off and send it, where you at? PM me.

[Toddy]

If you think you have a fault causing the carb to push off the rubber I would sort that first as it may happen again

[Granty]

If you think you have a fault causing the carb to push off the rubber I would sort that first as it may happen again

On it too Toddy -- was in the garage last night looking to see what, if anything was putting stress on it -- interesting bit is both the jubilee clips were firmly in place and the rubber had split in the middle -- just like the carb had been "bent downwards" -- looking at the fuel pipe I move the banjo to point it down the way to stop the fuel pipe rubbing on the side of the panel -- I think that might have put the "downward" stress in it and with the vibration its split the rubber?

Onwards & upwards buddy -- what do you think? Possible?

[Scooterlam]

I had long running issues with my carb falling off, blamed a poorly cast inlet manifold, then rubber wrong way round, Apparently there are differences. hard to see with old man eyes.
turned out the screw on the jubilee clip when at the top will hit the engine mount on big bumps.
worth checking.
Also with rad hose be careful it doesn't ride over the thicker part of the manifold as this will also exert force and try and push the carb off.

[Storkfoot]

Rubber does perish and if undue pressure is being placed on the carb rubber, it'll fail quicker. How old is the carb rubber?

I use this carb rubber on both my engines. The ribs sit well in the grooves on the PHBH and both my manifolds. I'd much rather use one that was designed to fit (as long as it does) than radiator hose.

Given that rubber does perish, I replace the rubber every couple of years. Better than a seizure or hole in the piston.

[Granty]

Rubber does perish and if undue pressure is being placed on the carb rubber, it'll fail quicker. How old is the carb rubber?

I use this carb rubber on both my engines. The ribs sit well in the grooves on the PHBH and both my manifolds. I'd much rather use one that was designed to fit (as long as it does) than radiator hose.

Given that rubber does perish, I replace the rubber every couple of years. Better than a seizure or hole in the piston.

Rubber was new buddy -- just been here & there for MOT etc and it was on its 1st hop before it split -- only done c300 miles, something must be snagging it I guess -- as I said it didn't slip off it literally sheared in between the jubilee clips, didn't seize, hole the piston or conk out on the Stockton Flyover so not all bad -- G

[Storkfoot]

[steve t]

Be careful not all rubber hose is oil/fuel resistant. Nitrile rubber is. oil can soften rubber an turn it into a gooie mess . I paid 1.50 for a foot length from a local hose stockist

[Granty]

Might have found what's putting stress onto carb and rubber. Is it possible that the 90* throttle cable elbow is snagging on the frame when the bike is moving and I'm on it putting stress on the rubber by pushing the carb away from the inlet? Maybe a change to a 50* elbow will be enough to lift the cable clear off the frame? Thoughts and anyone had this before?

[Warkton Tornado No.1]

Might have found what's putting stress onto carb and rubber. Is it possible that the 90* throttle cable elbow is snagging on the frame when the bike is moving and I'm on it putting stress on the rubber by pushing the carb away from the inlet? Maybe a change to a 50* elbow will be enough to lift the cable clear off the frame? Thoughts and anyone had this before?

As a matter of routine with any carburettor, its best to fix it so that it is ‘upright’ as it can be with the rider sitting upon the bike.

Then, checks are advisable with the rear suspension fully extended & with the shock absorber removed completely.

Any ‘snagging’ issues will come to light following that easy procedure.

As you have requested advice, I’ll also suggest that you should persevere & research where you can buy a proper, moulded carburettor rubber to suit your application.

I say that because a tailor made item will have not only the central rib that is the abutment between the manifold & the carburettor, but it will also have the correct locating profiles to fit them both.

Additionally, there will be proper external shallow grooves for the worm drive hose clip to fit. People call them Jubilee clips but that’s like saying all cars are Fords. Use worm drive hose clips that fit the whole width of the grooves. The clips should be neither narrower nor wider & preferably with a hexagon drive, rather than a screwdriver slot.

Many, many people (including loads of experienced racers) over tighten the clips so that the rubber is so compressed it stops doing its principle task of absorbing vibration & then that very vibration starts to go somewhere else & shakes the carburettor off.

If you do all of the above, your carburettor will stay in place.

[Granty]

Might have found what's putting stress onto carb and rubber. Is it possible that the 90* throttle cable elbow is snagging on the frame when the bike is moving and I'm on it putting stress on the rubber by pushing the carb away from the inlet? Maybe a change to a 50* elbow will be enough to lift the cable clear off the frame? Thoughts and anyone had this before?

As a matter of routine with any carburettor, its best to fix it so that it is ‘upright’ as it can be with the rider sitting upon the bike.

Then, checks are advisable with the rear suspension fully extended & with the shock absorber removed completely.

Any ‘snagging’ issues will come to light following that easy procedure.

As you have requested advice, I’ll also suggest that you should persevere & research where you can buy a proper, moulded carburettor rubber to suit your application.

I say that because a tailor made item will have not only the central rib that is the abutment between the manifold & the carburettor, but it will also have the correct locating profiles to fit them both.

Additionally, there will be proper external shallow grooves for the worm drive hose clip to fit. People call them Jubilee clips but that’s like saying all cars are Fords. Use worm drive hose clips that fit the whole width of the grooves. The clips should be neither narrower nor wider & preferably with a hexagon drive, rather than a screwdriver slot.

Many, many people (including loads of experienced racers) over tighten the clips so that the rubber is so compressed it stops doing its principle task of absorbing vibration & then that very vibration starts to go somewhere else & shakes the carburettor off.

If you do all of the above, your carburettor will stay in place.

Great feedback & thanks for that -- on another inspection today
- The carb sits at an angle upwards off the inlet
- The carb throttle elbow is 90*
- When I was sitting on the bike, with the weekend gear & with the road movement the top of the throttle elbow was hitting the top of the frame
- The fuel tap has also moved and the fuel lever had snagged the back of the carb
- This caused the carb rubber to be stressed & pushed forward – the clips held but the rubber eventually split

Solutions

- Moved the fuel tap & lever round to stop the snagging & tighten
- Ordered reinforced rubber for inlet & carb (along with other options volunteered - Thanks Nelly)
- Ordered a 50* elbow to lift the throttle cable & fitting well over the frame

Hopefully between us all I'll find a solution. -- Thanks again - G

[Warkton Tornado No.1]

I had meant to also say that the fuel tap rod may often need additional joints to make sure it doesn’t foul the carburettor in any way. Often, owners move it to the front of the carb but that’s not the most elegant solution…

[nickw]

It might be worth switching to a LTH manifold with the different rubber mount. Not yet done it myself but probably will do when finances allow.
Here is the one I mean
http://www.ekmpowershop12.com/ekmps/sho ... 2395-p.asp

[Granty]

Thanks Nick -- another good solution -- one wee step at a time I guess -- g

[Granty]

Think I've found the problem -- took the top end of last week to do some investigations

I think I've found the reason the carb rubber kept popping off and then split where & how it did.

- The inlet that was on the bike was a Mugello inlet
- The distance between the end of the spigot & groove makes it impossible for the rib on the carb rubber to marry with the groove on the inlet.
- The "sound" I was hearing thinking that the rib had found the groove was the end of the spigot hitting the end of the rubber, not the marrying of the groove & rib
- When the jubilee clip was less tight the rubber just slipped off the spigot
- When the jubilee clip was mega tight the end of the spigot just worked its way through the carb rubber & caused the split.
- I now have an AF inlet & the groove is much closer to the end of the spigot
- I put the rubber on the AF inlet & lined it up with the Mugello inlet that was on it previously--there's no way that the rubber could have lined up with the internal rib on the rubber.

If anyone else is having a pop off problem -- check the distance between the groove and the end of the spigot -- the solution I guess is radiator hose.

[Warkton Tornado No.1]

If anyone else is having a pop off problem -- check the distance between the groove and the end of the spigot -- the solution I guess

If you'd have left of the last few words as I've re-quoted you above, I would have agreed.

Unfortunately, only in my opinion, you spoilt it with:

radiator hose

which does not have the built in central rib (oooer!) which acts as abutment to carb & manifold. Obviously, it does not have any annular ribs to locate in the grooves, which you have found by your own experience to be so important.

You have been very methodical in working through the problem & sharing the experience & proved that with the correct 'isolation sleeve' matched to both carburettor & manifold, the set up should work well.

Any of this is not anybody's fault, so to speak. Unless knowledge is shared in this way, others will continue to mismatch carb, manifold & sleeves whilst, frustratingly, there is probably the ideal solution 'out there' given the opportunity for informed selection.

Unfortunately, can you imagine many traders declining the sale of the sleeves they have in stock despite it being 'not quite right' for purpose & telling the buyer to try elsewhere?

I have a feeling that somewhere on t'internet there is a record of carburettor spigot variations & sleeves available for them & if I ever find it, will post on here. It may be a site ascociated with karting or even a two stroke forum. Whatever, it would be bl##dy useful to us.

I hope you don't mind my additional comments......