HPN tank and fuel starvation

[sideshow_bill]

Since I have owned my R100GS, fitted with a 45L HPN tank I have had intermittent issues where it appears to run short of fuel. I have rebuilt the carbs, flushed the tank, replaced the hoses . . .
The fault may go away for many months. Has anyone else experienced this? And if so was a cause/remedy found?

Thanks

 

[(RIP) Proff]

Since I have owned my R100GS, fitted with a 45L HPN tank I have had intermittent issues where it appears to run short of fuel. I have rebuilt the carbs, flushed the tank, replaced the hoses . . .
The fault may go away for many months. Has anyone else experienced this? And if so was a cause/remedy found?

Thanks

Vent hole in the cap...
When it seems short of puff loosen cap if you hear sharp intake of breath, there's your problem, a vacuum

 

[sideshow_bill]

Vent hole in the cap...
When it seems short of puff loosen cap if you hear sharp intake of breath, there's your problem, a vacuum

I dont think its that, Its got a vent pipe from the cap.

 

[Kenny]

Take the cap off and blow/suck through the vent pipe...sounds like what Proff says

 

[BillN]

Definitely establish that you have a fuel starvation problem

Does it run short of fuel - i.e. check the float chamber when it happens

If fuel spews out then it is coming through

are the floats sticking

start at the petcocks and work down

take the petcock off and check them, if I remember correctly the HPN tank has it's own, (i.e. not the BM ones), petcocks - but anyway check that they are working OK

or does it just not run......which could be an other, (electrical problems)

 

[sideshow_bill]

Definitely establish that you have a fuel starvation problem
Does it run short of fuel - i.e. check the float chamber when it happens
If fuel spews out then it is coming through
are the floats sticking
start at the petcocks and work down
take the petcock off and check them, if I remember correctly the HPN tank has it's own, (i.e. not the BM ones), petcocks - but anyway check that they are working OK

or does it just not run......which could be an other, (electrical problems)

Usual manifestation: - Runs fine at moderate cruse, on A road. When I go for a fast run it will begin to missfire engine revs dropping no response to throttle. If I close throttle bike slows and then will catch again and run, as long as I dont try to go for a high throttle setting.
When I pull the float bowls off there is fuel in them. Floats seem free to move. Spews fuel when cocks opened etc.
Its like there is an airlock in the fuel pipes from the tank. As may only happen once a year, its possible that something may be fouling the vent pipe? It is a big tank and I would have thought a lot of vacuum would have been necessary to stop fuel getting out of the bottom. Are the floats prone to sticking with no obvious cause?

 

[(RIP) Proff]

Usual manifestation: - Runs fine at moderate cruse, on A road. When I go for a fast run it will begin to missfire engine revs dropping no response to throttle. If I close throttle bike slows and then will catch again and run, as long as I dont try to go for a high throttle setting.
When I pull the float bowls off there is fuel in them. Floats seem free to move. Spews fuel when cocks opened etc.
Its like there is an airlock in the fuel pipes from the tank. As may only happen once a year, its possible that something may be fouling the vent pipe? It is a big tank and I would have thought a lot of vacuum would have been necessary to stop fuel getting out of the bottom. Are the floats prone to sticking with no obvious cause?

Nope, not a lot of vacuum at all. in fact 2 up on my 80g/s going balls out for around 6 miles it will start to starve itself, thats why i got a 2 tap tank on
I hope you run with both taps on
BUT I digress, they need very little vacuum to starve themselves and by the time you've got off and took float bowls down enough petrol will have got through..

DAMHIK

 

[John Armstrong]

Just a thought, checked the float levels? My bike didn't like going above 70 mph or up long slow hills Adjusted the float level and now it goes faster and up long slow hills

And having both taps on didn't help, and it'll run almost flat out on one tap 88 R100GS with 24 litre (ish) tank and the fuel cap that isn't flush and has the breather pipe coming out of the front.

Sort of felt like running out of fuel, which in some respects it was

 

[Thunder]

Just a thought, are the fuel lines from the taps lower than the bottom of the tank?

Speaking from experience on this one.

 

[sideshow_bill]

Nope, not a lot of vacuum at all. in fact 2 up on my 80g/s going balls out for around 6 miles it will start to starve itself, thats why i got a 2 tap tank on
I hope you run with both taps on
BUT I digress, they need very little vacuum to starve themselves and by the time you've got off and took float bowls down enough petrol will have got through..

DAMHIK

This does sound like the most promising lead! When Max is happy he will run on one tap full throttle all day. When the lurgy strikes a couple of miles at fast motorway will have him coughing and spluttering. turning on the other side makes no difrence.
He has been in the garage for the last 5 years, and I am now getting him back to working condition. The problem was there on the last run before going into the garage but I can not find any cause, but (Just been out to the garage now) the cap breather hose does seem to have some resistance to being blown through. . . .

 

[brassmonkey001]

I have a similar problem. HPN 43l tank with both taps open, R100 pots, 32mm carbs IIRC which have been cleaned very recently, airbox breather mod done but still when I get it up to 90 (on the track, of course) it presents exactly the same symptoms you describe - starts spluttering and dying. I have to close the throttle and wait until my speed has dropped to around 70 before I can open the throttle again. it then pulls like a train again until it gets to 90 and then repeats.
The answer is of course not to go that fast but it would be nice to get it sorted.
I have the side-vented cap and blew through it - it does seem somewhat restricted.
Oh, and the other day I tried taking the cap off while it died but put it back on again quickly - probably before the carbs had managed to refill.
I might take it out for a spin with no cap to see what happens.

 

[John Armstrong]

I get it up to 90 (on the track, of course) it presents exactly the same symptoms you describe - starts spluttering and dying. I have to close the throttle and wait until my speed has dropped to around 70 before I can open the throttle again. it then pulls like a train again until it gets to 90 and then repeats.

Checked your float levels aren't too low?

 

[SJRoome]

Have you tried the fuel filters?

Hi

I would second the ideas of checking that the tank is adequately vented and that the float levels are set correctly.

However when something similar happened to me it was due to the fuel filters being blocked. I have a 1989 R100GS with the standard tank and I have added in-line fuel filters in each fuel line. The tank has two taps and each can be set to normal or reserve. On normal the fuel is taken from several inches above the botom of the tank. When you switch to reserve fuel is taken from the bottom.

Modern petrol decomposes fairly quickly and you get fine particules in it that settle to the bottom of the tank. When you switch to reserve any of this that gets through the filter built into the fuel tap will be swept into your fuel filter.

Try cleaning the filters inside the fuel taps and changing the fuel filters. I always buy fuel filters with transparent cases now.

In my case when I switched to reserve one day I suddenly found I had a bike that wouldnt go above 50 mph for any length of time and was only happy at 30.

 

[John Armstrong]

However when something similar happened to me it was due to the fuel filters being blocked. I have a 1989 R100GS with the standard tank and I have added in-line fuel filters in each fuel line. The tank has two taps and each can be set to normal or reserve. On normal the fuel is taken from several inches above the botom of the tank. When you switch to reserve fuel is taken from the bottom.

That's why when I fill up I use the LH tap in it's reserve position on its own. Usually run the RH for "normal" and occasionally use reserve early, for a few miles, too on this side. So far, so good

 

[sideshow_bill]

I have a similar problem. HPN 43l tank with both taps open, R100 pots, 32mm carbs IIRC which have been cleaned very recently, airbox breather mod done but still when I get it up to 90 (on the track, of course) it presents exactly the same symptoms you describe - starts spluttering and dying. I have to close the throttle and wait until my speed has dropped to around 70 before I can open the throttle again. it then pulls like a train again until it gets to 90 and then repeats.

This sounds similar to my issue, other than most of the time it will pull like a train untill I cant hang on any longer. I used to do the run from Bristol to West Wales early in the morning at full throttle with no issues. It does seem to happen more when I have a passenger, but I always put that down to Max wanting to embarass me! He pulled such a stunt at the Plume of Feathers meet up, when the battery died requiring a push start to get going in the morning. Im sure its not float settings as they wouldnt change themselves im sure? ? ?

 

[brassmonkey001]

Checked your float levels aren't too low?

I'll check them again but they were bang on last time I checked.
I put inlinr filters in but they didn't make it any better or worse.

My problem seems to differ to yours slightly Bill, as yours seems to be intermittent whereas mine happens every time I wind it up to 90.

I'll get to the bottom of it eventually.

 

[Voyager]

I'll check them again but they were bang on last time I checked.
I put inlinr filters in but they didn't make it any better or worse.

My problem seems to differ to yours slightly Bill, as yours seems to be intermittent whereas mine happens every time I wind it up to 90.

I'll get to the bottom of it eventually.

Are your carb mounts OK ?

As the problem seems to happen whenever you are 'giving it the berries' it could be fuel frothing in the float bowls due to vibration.

Just another thought.

Bob.

 

[brassmonkey001]

Are your carb mounts OK ?

As the problem seems to happen whenever you are 'giving it the berries' it could be fuel frothing in the float bowls due to vibration.

Just another thought.

Bob.

I think so. They seem solid enough.

 

[Redboots]

whereas mine happens every time I wind it up to 90.

Does it do that in each gear at the same rev range?

John

 

[brassmonkey001]

Does it do that in each gear at the same rev range?

John

Yeah, 90 in 1st, 90 in 2nd, etc.

I must admit I haven't wound it right up in the lower gears, I can't imagine why I haven't tried it as it did occur to me .

Today I took it out and tried it with the fuel cap removed. If I had been on a track I'm sure it would have reached 98/99 before starting to splutter, but as it happened I didn't exceed any posted limits.
A marginal improvement but obviously that is not the cause of the problem.

I also notice it sometimes has a high tickover when hot but it can slow down after a while.

Needles need adjustment do you think?

Or maybe I need bigger carbs? The engine is, AFAIK, a R80GS engine with 1000cc pots but the carbs are 32mm. Perhaps they're just not up to the job and I should fit some 40's?