Hitchcocks Forum

Hi all. I think my Classic 350 may be suffering from fuel starvation. Mostly happens when I'm running a steady 45 ish on a motorway (indicating about 60mph) and every 15 miles or so the motor starts spluttering and popping - opening up the fuel cap seems to cure it, until the next 15 or so miles and the same happens again. On side roads this rarely occurs and so I'm thinking this could be fuel starvation. The fuel cap, the lockable type, doesn't look to have a vent hole. Strangely this hasn't happened in a long while, possibly a few years at least. I only run the bike during summer months (2003 with 15,000 miles). To test for this possibility I'm thinking of filling the petrol tank and draining a gallon direct from the fuel tap. Does anyone know the flow rate so that I could check the time it takes for a gallon to run through? Thanks.

Sounds familiar, not sure what you'd do to clear it if it's an old British style locking cap, but the round locking caps (Indian style at least) DO have vent holes and these can become blocked. Strip your filler cap down and you sell see there is a rubber disk inside with a circular groove between the inner and outer vent which ISTRC is somewhere around the lock mechanism.



A.

Hi Ogri------------- a Classic 350 on the Motorway ??.........that's Heroic Stuff and no mistake !!.....OK, if all is "normal" then your fuel tap will either be ( or based on ) a 1/4" BSP threaded body and look something like this -----------> --------------------> ---------->Find yourself some 1/4" hole pipe and allow some water to flow through it..............you can see it's not slow in coming out and neither should your petrol be either.............Note that there is usually a built-in filter and that might need cleaning............Try the following}--------- Go back to the Motorway and travel untill the spluttering starts again, undo the fuel cap but don't do it back up, continue driving............If the spluttering re-appears you have a partial blockage in the fuel tap assy..........If the spluttering DOESN'T re-appear then you have a fuel cap venting problem...

Morning Ogri
I have recently had the same problem on my 2004 bullet 65. After chasing round the houses as usual found it to be a swollen rubber washer in fuel tap blocking fuel outlet port. That's the filter bowl washer on Karcoma tap which I think you will have.
ATB MickH

Yes Alan R, that's my fuel tap all right. Also, during this recent episode of riding on the motorway (my fault, I suppose, for riding with a couple of guys on more modern bikes and trying to keep up) I did loosen off the cap to the point that this was just sitting there under it's own weight (with small splashes of fuel coming out around the collar of the tank) and this seemed to eradicate the problem hence my thoughts that it's a fuel starvation issue.

Problem for me is that I had an earlier issue with a small leak from around the tap and it took ages (and dowty washers) to resolve so I'm really reluctant to take out the tap again, unless there's no other option. That's why I was hoping there'd be an optimum flow rate so that I could make this initial check, before I attempted any surgery!

Ah-ha !!---------first you didn't have this problem, then you had a "leak" that was solved with Dowty washers etc------------ and now you do have this problem !!........ergo, something you have done ( or not done ) recently has caused this problem to appear............I think Mick H may well be in the same area of thinking...........I'm guessing that you don't have much experience or "spannering" skills so would advise that you remove the tap again and along with a mate or two for help and guidance give the tap a good old clean up..........You'd best get access to some compressed air for thorough cleansing...

I forgot to as}---- Did you check the tap in both "Main" and "Reserve"positions ????

Here's a Karcoma tap dismantled showing the rubber that Mick H referred to}-----------

It's easy to check the tap without stripping it, just unhook the fuel line from the carb and have it draining into a fuel canister, turn the tap on with the fuel tank cap removed, if all is well with the the flow from the tap WITHOUT the tank cap on you know it's the cap breather. If the petrol wont p*ss through the tap even without the cap fitted, you know the tap is the source of the problem, be it clogged filter, swollen rubber washer, etc.



A.

Thanks Adrian. But what should I expect in the way of flow? I have to be able to measure this to make a comparison. Otherwise it's just too subjective ( one says looks good to me, other says looks slow flow to me)

Bit like the prostrate for us gents??!!