Fuel issue?

[speedy231278]

This may well get sorted when I swap my carbs over, there again it may not.... My RVF seems to have picked up an issue where it doesn't like running when the fuel level is getting low, either when it's close to running onto reserve, or close to running out completely. A good number of weeks ago, I'm sure the bike took ages to pick back up after running onto reserve. Normally as soon as you switch from main to reserve, it stops coughing after a couple of seconds, but it seemed to take quite a while in comparison. When I was about a month ago and got horribly lost, the same sort of thing happened when I went on to reserve. It was quite a way to the next petrol station, but I knew it was within range. However, the bike developed a soft but pronounced misfire about a mile from getting fuel. I've run out before now, and found the hard way that usually if you get a miss on reserve it's usually yards rather than miles before the bike stops. When I filled up, I got about 14.5 litres in, so it wasn't empty.

Last Saturday, I filled the tank to the brim. After I filled it, I did the tyre pressures, and due to dodgy tarmac the bike leaned over a very long way, and enough that it actually caused some petrol to flow out the tank overflow. So, I knew it was rammed full and I could expect a good big figure on the trip before it went onto reserve. Yesterday, the bike started spluttering at 170kms, at least 10-15 short of where it would normally do even if I hadn't spent ages squeezing every last drop it. I knew it couldn't be that short, as I'd not ridden that hard since filling, and there was a good load in the tank. I switched to reserve, and after another slightly extended period the bike picked up again. So I switched back to main and it was happy for another 10kms before doing the same again. At this point I gave up my ideas of getting back without filling, and stopped at the next place to fill up. I'm sure the bike did the same thing again before I got there. A run at 8-9K for a minute or so seemed to be enough to get it to do this, yet backing off to say 5K was enough to let it recover. With a full tank, it was back to running as happily as usual. Although, that means it's running a little crap which is why I'm changing the carbs for freshly serviced ones. Right now, I sometimes get a split second misfire when shifting at about 8-9K and getting back on the throttle. At other times it's fine. I got 12.45 litres in this time, so it wasn't on reserve. Normally after running onto reserve and picking a garage I get over 13 in. Doing the sums, when I got petrol, it had done just over 40mpg, which isn't wonderful but is what I usually get.

I'm guessing that there might be slightly restricted fuel flow and that when the fuel height in the tank is barely above the bottom of the fuel tap feed points for main or reserve there's not enough pressure to feed the carbs enough to meet the demand for fuel at higher revs. I'm going to check the fuel tap to make sure it's not got crap in it, or on the filter elements, and that it's flowing properly. It's been HRC modded, so I'll check that the diaphragm isn't slipping off the spacer and restricting the flow. I'll also check the fuel hose to make sure it's not been pinched by something, and that the tank overflow and breather points aren't blocked. However, if there are any other suggestions I'd be grateful to hear them!

[Cammo]

Must admit I've only skimmed over the long post, but -

It sounds as though it's working as it should. In every aspect. When you switch to reserve it fills the carb bowls back up which can supply the engine enough fuel for 5-15 km's depending on a several things.

I can get anywhere from 160 - 190 km's on a full tank - yours wasn't full.

I wouldn't be worried.

[speedy231278]

It was full... utterly, and I didn't manage to put enough fuel in after I stopped to get within half a litre of the main tank volume, never mind what would have been used if it truly was on reserve. Doing the sums, the fuel economy tallied with what I usually get, so I should have gone further than I did, and it never normally takes more than a few seconds to pick up after running onto reserve, but now the time taken to resume proper running seems exaggerated. I've had the bike 10 years and I can assure you it's suddenly behaving in a completely different manner to usual when it's low on fuel....

[RandomDan]

While your changing the carbs id check the fuel lines and filters on the tap to make sure there arnt any blockages.
Might be worth buying some more fuel line to be 100%?

[Baz]

See my thread "reserve not working?"
I am having a similar problem and have been advised it could be the vacuum hose.
I cant try this till I get home tonight but it sounds about right.
might be worth checking for nowt!!

[speedy231278]

No, reserve does work, it's just that the bike has suddenly become very funny about running when the fuel is close to the reserve level, or close to running out, ie when it gets within about half a litre of running onto reserve or running out, it suffers a partial misfire and takes ages to recover. Usually when running onto reserve, it picks back up within a couple of seconds, not 20 or 30, and when I was reasonably close to running out the other week it coughed for about a mile and a half, yet still had over half a litre left when I filled it up. I'm convinced there's an issue fuel fuel delivery being slightly restricted. Normally it has a more pronounced misfire when hitting reserve, and picks back up almost instantly....

Dan - I'm going to check the fuel tap and everything else this weekend for crap in the system. I guess almost running out probably didn't help make the situation any better. I'll put the fuel line on from the spare carbs, the current one is motheaten and every now and then I have to cut it back a little more when the fuel tap spigot tears it when taking it off!

[Neosophist]

No, reserve does work, it's just that the bike has suddenly become very funny about running when the fuel is close to the reserve level, or close to running out, ie when it gets within about half a litre of running onto reserve or running out, it suffers a partial misfire and takes ages to recover. Usually when running onto reserve, it picks back up within a couple of seconds, not 20 or 30, and when I was reasonably close to running out the other week it coughed for about a mile and a half, yet still had over half a litre left when I filled it up. I'm convinced there's an issue fuel fuel delivery being slightly restricted. Normally it has a more pronounced misfire when hitting reserve, and picks back up almost instantly....

Dan - I'm going to check the fuel tap and everything else this weekend for crap in the system. I guess almost running out probably didn't help make the situation any better. I'll put the fuel line on from the spare carbs, the current one is motheaten and every now and then I have to cut it back a little more when the fuel tap spigot tears it when taking it off!

It will start missfiring when it gets to the reserve area? Your running out of fuel.. chances are one carb or more carbs are running out and jiggling the bike about allows the fuel to get into the carbs when near the limit of reserve.

IF swtitching to reserve fixes the issue then sounds liek that is the problem.

However, do you have a fuel filter or anything else attached?

With my 24 I installed a fuel filter as there was some crap in the tank... the bike suddently started to 'run out of fuel' feeling way before the usualy miles but switching to reserve cured it.

Since it is gravity fed, the extra fuel hose and place of the filter altered the fuellnig.

[speedy231278]

Sorry if I'm not being clear. The point I'm trying to make is that the last time I was getting near reserve, I got the usual misfire *before* I'd actually used enough fuel to get there, and the bike took longer to recover to normal running, plus when I was almost out of reserve fuel, it also did the same thing. In both cases I was at least half a litre away from actually being at the limit. The weekend just gone, it supposedly ran onto reserve, yet 15kms later, I squeezed in half a litre short of the reserve mark. After running onto reserve plus 10 mins to get to the next petrol station, I usually get about 13 1/2 litres in the tank. This time I got less than 12 1/2, which indicates to me that for some reason the bike is unable to cleanly draw the last half litre or so of petrol from the tank and it's running lean enough to cause a partial misfire.

I've got no extra filters attached to the tap, just the in tank ones. As previously stated, the diaphragm has been modded using the HRC method. I've not fiddled with the fuel hose, nor had the tank off for a good while, so I can't think of any reason why I might have disturbed it. I would guess if for some reason the tank wasn't sat straight it might alter the fuel height above the tap, but I'm sure it's bang on. I'll have the lot off at the weekend to see if anything is blocked or skew-whiff.....

[Neosophist]

Hmm.

Well there is always the possibilty of the blocked breather hose on the top of the tank.

How many times has this happened?

1/2 a litre isnt really here nor there.. depending on air temp, gears, even the pump that dispensed the petrol there could be some slight tolerance.

My bike usually stutters around reserve, but often riding of the bike will let it ride longer.

By all means investigate but it might be nothing..

[speedy231278]

It might be nothing, but then I've had the bike 10 years and it's seemingly now behaving differently. If I'd only done 170 and the pump had stuck 13 1/2 litres in, I'd not be concerned, other than the fact that the bike usually manages better than that. I don't usually take the trouble to squeeze every last drop in the tank, and I wasn't riding particularly hard since filling. The sums suggest the fuel economy was reasonably OK, so I'm convincing myself something is up as usual!