DR posing as an SV - Fuel vacuum hose?

Hi all,

Got a techie question but it doesn't refer to my SV, rather my DR. If this is the wrong place then mods feel free to move, just thought this a better place than Bikes - Talk & Issues as it is a general tech question.

When removing my carb yesterday, it became apparent that the fuel vacuum hose is connected at the carb end but has a bolt and washer to seal it at the other end and is hanging loose. I believe the reason is that the petcock fitted to the aftermarket Acerbis tank has only spigot (right word?) rather than two. So the only one that can be attached is the fuel line.

Question 1: Should this have any effect (positive or negative) on the performance of the engine? I haven't noticed crap performance, fuel consumption is also good. In other words running seemed fine to me and I'm wondering how this could be.

Question 2: Is this because the stock tank is a vacuum type and the Acerbis is a gravity tank? This is something someone said at a guess at work today.

Any advice much appreciated

[Sid Squid]

If the new tap has no vacuum connection don't connect anything to it. Clearly the connection should be blocked off or the motor will run weak. The fuel delivery is by gravity in either case, neither tap incorporates a pump of any kind. The original tap is vacuum operated - when the engine is running the inlet vacuum operates the tap to allow fuel to flow, when the engine isn't running a spring shuts the tap so fuel can't leak.

Functionally there is no difference, of course the fuel isn't automatically turned off when the motor is off, but in normal use you won't notice any difference.

Thanks Sid Squid, very useful to know. Would your recommendation be to leave the full length hose plugged and dangling in case I need it at a later date (I'm overlanding on this bike)? Or cut it and plug it much closer to the carb to get rid of the 6 to 7 inch long flapping hose, just buying a new bit of hose if I ever need one?

Originally Posted by Sid Squid

The original tap is vacuum operated - when the engine is running the inlet vacuum operates the tap to allow fuel to flow, when the engine isn't running a spring shuts the tap so fuel can't leak.

So on this one I'm doing the same job in effect by turning the petcock to 'Off' when not using? That explains it all, I had thought the vacuum hose would 'suck' the fuel through at high speed rather than just flick a switch allowing it to drop by gravity. Makes sense then why performance hasn't suffered.

Nice one!

dr350?

One of my mates replaced his tank with a 17 litre one over the weekend I'll ask him if you want?

Apparently the carbs are a bit tricky.


btw: tank cost £180.

btw: thinking of using a dr350 for a 4 month world jolly next year

DR650 - and it's coming on my hopefully year+ world jolly in the spring

Came with a 15 litre (I think) Acerbis tank fitted by the previous owner, have just got info I need to fabricate brackets to make the 25 litre Acerbis one for the pre-96 model fit my '99. 330-mile tank range at the consumptions I've been getting.

Originally Posted by Kinvig

One of my mates replaced his tank with a 17 litre one over the weekend I'll ask him if you want?

Yeah that'd be very useful, would be particularly interested if he's gone for an Acerbis as opposed to IMS, Clarke or Aqualine. Because if so I'd like to know what petcock they supplied with it - 1 spigot or two? And does it say Acerbis on it? I'm trying to work out if my petcock is the supplied one or a separate aftermarket part. Says 'OMG' on it and appears to suit being fitted on the other side of the tank so it's had to be turned around to keep the spigot pointing backwards in the direction of the carb. As a result, I have to reach under to get to the tap, and the 'On', 'Off' and 'Res' engravings face the cylinder head - very useful

Originally Posted by Kinvig

Apparently the carbs are a bit tricky.

In what way? To service/dismantle or just to remove from the bike?

Originally Posted by MeridiaNx

Yeah that'd be very useful, would be particularly interested if he's gone for an Acerbis as opposed to IMS, Clarke or Aqualine. Because if so I'd like to know what petcock they supplied with it - 1 spigot or two? And does it say Acerbis on it? I'm trying to work out if my petcock is the supplied one or a separate aftermarket part. Says 'OMG' on it and appears to suit being fitted on the other side of the tank so it's had to be turned around to keep the spigot pointing backwards in the direction of the carb. As a result, I have to reach under to get to the tap, and the 'On', 'Off' and 'Res' engravings face the cylinder head - very useful



In what way? To service/dismantle or just to remove from the bike?

1. Will ask - think Acerbis
2. I read it on here somewhere: http://www.horizonsunlimited.com/hubb/ Attempting to plan a trip next year from March/April for 4-ish months & I've been trying to figure out the best bike etc to take for a short a&se & the routes I'm planning - so I've been spending a bit of time researching. Stuck between the bmw gs650 & the suzuki 350 for different reasons!!

"I think it depends a lot on what bike he has (350/600), and whether it's the Mikuni flatside carb or the CV carb.

But basically yes, the Acerbis tank *should* have 2 petcocks, not one, which join up at a y-piece and then go off to the carb. If he's running only one petcock but still has the hosing for 2, then one end of the hosing will need blocking up and no it will make no difference to the carburation.

His best place for techie q's is http://www.thumpertalk.com/forum/forumdisplay.php?f=41"

and also, your second part:

"The acerbis tank for my bike has 2 petcocks (AFAIK, the IMS and Clarke tanks only have one) and yes they have OMG written on them! Single spiggot. You get 2 specific taps, one left and one right, so that you don't have the wrong way round situation going on that your mate is talking about."

Hope this helps

[Sid Squid]

Originally Posted by MeridiaNx

Thanks Sid Squid, very useful to know. Would your recommendation be to leave the full length hose plugged and dangling in case I need it at a later date (I'm overlanding on this bike)? Or cut it and plug it much closer to the carb to get rid of the 6 to 7 inch long flapping hose, just buying a new bit of hose if I ever need one?

As long as it it's appropriately secured you could leave the hose, but it's probably better to cut it as short as possible and then there's a rather lesser chance of it getting damaged I suppose.

Originally Posted by MeridiaNx

So on this one I'm doing the same job in effect by turning the petcock to 'Off' when not using?

Exactly.

Originally Posted by MeridiaNx

That explains it all, I had thought the vacuum hose would 'suck' the fuel through at high speed rather than just flick a switch allowing it to drop by gravity. Makes sense then why performance hasn't suffered.

All true.