fuel starved

[lou]

Hi all

After testing many other issuse which i thought was the problem, when i go below half tank bike splutters revs high, and can backfire, after when i fill up runs great, which has been the case every occasion, changed the fast flow tap for a new one, still the same totaly puzzled checked the flow all seems good !!, Standard Ts1 delly 30 vhsh , nk pipe..... any help welcome

Cheers

[mick1]

Blocked breather hole in fuel cap ?

[Adam_Winstone]

I've been suffering from the same on a slightly exotic motor and have been through all of the factors that I could to increase flow to my 30 VHSH, which has not cured it in my case because of the higher than standard position of my carb, meaning that my only option now is to fit a fuel pump. However, trying to sort mine has thrown up a number of issues that might help you:

1. Have you fitted a decent size float needle valve to yours, e.g. 300 or 350, with corresponding float needle? These are required on a high demand gravity system motor like your TS1.

2. Has the body of your carb been 'blue printed', as MB always used to go on about the VSHA and VHSB carbs requiring to avoid fuel starvation? He was 100% right then and this carries on to the VHSH range too. This involves taking out the filter on the fuel inlet passage and then drilling out the 'D' shaped passage so that it can supply the fuel flow that the new bigger float vale will need.

3. Float height, have you stripped your carb down and had it on a flat surface to check the float height is correct? This was the last thing that I went back to, having had a look at it once before in the early stages of my fuel starvation issues (cost me a piston and a replate!), and found it made a MASSIVE difference to the flow rate and went a long way to resolving my issue.

Addressing all of the above has improved my bike dramatically and means that I can now ride it long distance and hold it open for long stretches of M'way without too much concern. In my case, I will still need to look to fit a fuel pump to cure it 100% but that is because my carb is about an inch higher than it sits on a TS1. Have another look at the 3 points raised, if you have not done so already and good luck in getting it resolved.

Adam

[lou]

Breather hole all clear first port of call , Thanks adam seems a very in depth you say exoctic motor in your case, but for me standard TS, i did change the pipe to a nk from pm in winter.. which ive jetted to suit, i started to get the problem end of last season, but now so bad below half tank im screwed, i hope in my case dont want to be drilleing out carb etc thats out of my league.

Thanks

[Adam_Winstone]

Lou,

Some of the carbs are pre-modified by scooter dealers when you buy them, others are not. This is something that you'll have to watch out for as the VHS* range can suffer fuel starvation if not modified. You can check by taking the hex head cover/bolt off the side of the carb, next to the brass fuel inlet tube, removing the filter (you can leave this out to increase your fuel flow) and looking into the fuel passage. If you see a 'D' shaped fuel passage then it is unmodified. You may get away with the carb not needing modification or could send it off to a dealer (e.g. MB) to have it modified. If you want to see more about what I'm on about, I'll go and find you a very good link that I've seen before.

Certainly address the other issues that I've raised; float needle valve size and float height.

Adam

[Adam_Winstone]

http://www.scooterhelp.com/tuning/carbs.dellorto.html

[lou]

Adam

Thanks.. For help any links info be great help, its a real annoying problem !! i will take carb apart and get back,i had no idea it had a filter in carb (learn all the time !!), i have taken that bolt off before sure there was nothing in there ... bought it from AF with the TS kit.

[Adam_Winstone]

Is your fuel pipe being pinched/restricted when you sit on the bike?

[holty]

fuel pipe under the frame ?, check for kinks, have you done a flow test, if i remember right a pint of fuel in a minute is what af recomend, do you have an inline filter, how long is your fuel pipe, plus the carb modification that mb do, i am surprised you havent melted a piston, i hope you find the problem. i siezed my rb250 with fuel starvation, the fuel tap has a washer inside with 3 holes in it and the rubber broke up and blocked the outlet slightly causing it to run weak, i had no idea that i had a fuel issue, it ran fine, maybe too well, that might have been a clue! anyway good luck, im sure will sort it out,
holty

[lou]

Adam
The fliter inside carb, where the hex bolt was the problem , run it without all fine.

Cheers for all replys