Hitchcocks Forum

Yesterday I decided to go for a ride on my 1998 IC 500 She was very hard to start and needed the choke, which is unusual, she backfired alarmingly, both through airbox and exhaust. She was running perfectly the previous night, commuting from work.
I looked at the points, these looked ok, hmm.
I wiggled the carb about a bit and found too much movement, so, I removed the mounting rubber tube, it was split 1/3 of the way round, this must have gone through overnight, luckily I had a bit of silicone car radiator hose the correct i.d. All mended (bodged) for now, until I get the correct part.
Is it worth getting the modified one from our hosts? Or just the standard one? The one I removed could be 20 years old, or just leave the reinforced silicone hose on? she seems to run ok, I know it isn't exactly 'gas flowed', but then, neither is the original.

It's a big heavy carb on a very vibey engine so they do go. We then don't help by removing the air filters and fitting pod filters, thereby removing any support off the other end.

It's such a known issue on the 500s (either splitting rubbers or carbs falling off) that many owners make a support bracket to hold some of the weight. Often between the hose clamp on the air filter side and the rear fuel tank mount.

Not sure which type yours takes but if it's the rubber flange type, I'd get a genuine mikuni one, the quality of them is far superior to the Indian items.

Why not riding on with the silicone hose? If it works why bother changing it. I have been using a silicone hose for the last 7 year. First a blue one for the Mikcarb VM28 and now a black one for a Mikuni TM32. They are kind of indestructable. I never had any trouble with either one. The OEM rubber one was a pita so it's gone. regards Jacob

Silicone hose isn't fuel proof. It can go floppy and/or porous.

Quote: "It's a big heavy carb on a very vibey engine so they do go. We then don't help by removing the air filters and fitting pod filters, thereby removing any support off the other end."
Dead right it is. So when I did it I made a bracket to support the carb. It was easily done and works a treat. It is fastend to the frame at the tank mounting bolt and with a twist of the metal strip that is the bracket, slips in under the jubilee that holds the inlet rubber in place. This might give you an idea..

Thinking about the quality of the oem carb rubber, I wouldn't think worry about using silicone hose as a substitute. My experience is: they are almost indestructiable. In theory they might not live a long life submerged in petrol, but then again think about Samco silicone hoses used in the "racing" industri. If silicone were no good under the hood, it would not be used. They are sold by lenght in the ID you need. 1 ft. cost about 10 pound, that will serve your need for more than 20 years... regards Jacob ...PS and it's strong enough to hold the weight of the carb.

Samco hoses don't have petrol going through them though. They have air or coolant and can cope with high pressures and high temperatures. Sometimes the air will have traces of oil and exhaust gasses in which case they use a flurosilicone lining. Even that isn't petrol proof.

I'm not doubting the ones folks have been using are standing up to the fuel, but equally, I've seen the result of people using silicone hose in fuelling applications where it goes like jelly and the jubilee clips just cheesewire through it. It would be irresponsible to recommend it to others given how inherently unsuitable it is for the application.

Silicone hose would be ideal for the air intake side of the carb. Or if you fancied rigging up a supercharger powered off the distributor drive...

Butyl rubber, PCV or Teflon for fuel.

It is a bit of 'Samco' type hose I have used from my special car building pile.
My carb is supported by an air box now, but until recently it was fitted with a cone type filter and was un supported and a bit dangly, so the damage was probably already well underway.
The hose is black, so is invisible, I'll leave it on and keep an eye on it, but I will get a 'proper' one just in case.

Stinkwheel, I don't want to promote irresponsable solutions regarding our beloved bikes. I've told about my personal experience using a silicone hose as intake manifold. So far I have had no issues with the hose. One of them was on the bike for 5 years and it hasn't disintegrated, dissolved or changed in any way. It's dirty , but thats all. Maybe I have substituted it in due time? I don't know. I will keep an extra eye on the condition of the hose in the future. It's good that you can inform all of us in this forum about silicone and rubber in connection with petrol, so we can get wiser on the subject.

If it's any help, I have a VM34 fitted with a sizeable bell mouth, on my 612 and - in spite of Slo Poke being rigid framed and, thus, bouncing around a lot - the standard, Mikuni, rubber manifold readily supports its weight.