Im going to replace my petcock/fuel valve and am wondering what to do with the negative pressure hose that runs from the carbs to the on/ off valve (membrane) Do I cap it off with a cap to seal the negative pressure or do I leave it open and let it suck it air? What Im trying to do is minimize as many hoses as possible. Basically one hose from fuel tank to fuel valve to carb T.
Vacuum line has to be capped off @ the carb if you're using an on/off style petcock. Else you're be sucking air into the mix and lean out like the dickens.
Cool.
Buddha.
I am in the process ( if like everything else on the bike , a LONG process) of removing the fuel petcocks all together and replacing with a low pressure electric fuel pump with auto shutoff. Simplifies plumbing considerably. Most modern bikes don't have a reserve anyway ( ie all my other bikes) so I won't miss it.
One pipe to the pump. One to the carbs. All vacuum lines removed ( the little air bypasses for the throttle slide have been removed).
I will post when ( if) it get it finished. Pump is off a Yamaha v650 so should flow about right. Biggest worries is if the fuell shutoff does completely shut off and if the needle/seats can handle the slight extra pressure. The plus besides the reduced plumbing , is the fuel bowl will be filled before the bike starts always.
Greg, why even bother with an electric pump?
I've just got a simple mechanical on/off petcock and it works fine. Talk about keeping things simple.
I only ride the bike once every 2-3 weeks, and it always starts up fine. If I forget to turn off the petcock and leave it open for days, then there is an occasional overflow of gas from the left float, but never a big deal.
The fuel pump has a auto shutoff whne not on. So only one line in and one out. The fast that it is pressure based ( low admittedly) means I can run smaller lines for most of the length and I don't have to turn tap on/off. Still have to make adapters for the fat ends though.
Having come from the days when every bike had to be turned off when you stopped, I am most aware of the pitfalls, like forgetting to turn the fuel on and riding off only to have the bike die when you really don't need to. But your comment is correct. You way IS the simplest.
Even simpler is to leave the stock petcock on there and cap the vacuum ports on both ends (petcock and carb). Then put it on PRI to run and RUN or RES is off. You can even remove the non-reserve fuel hose this way and cap both ends (tank and petcock).
This of course assumes the petcock doesn't leak fuel with no vacuum. Seems like the more common failure mode, but who knows.
The electric pump I had on mine was awesome. I felt like I actually had more power to play with. not much, but noticeable performance increase. I think I had it set at 4PSI. play w/ it its always easy to go back.
Interesting.
I can say my sense is that some of the imperfect cold starting behavior I see from time to time would probably be improved with a fuel pump. Always kind of wondered if there was fuel starvation issues at WOT/high-rpm. My guess is no, but maybe it depends on how long/hard you run those throttle/rpm conditions. ??
Quote from: mr72 on February 05, 2018, 12:06:57 PM
Interesting.
I can say my sense is that some of the imperfect cold starting behavior I see from time to time would probably be improved with a fuel pump. Always kind of wondered if there was fuel starvation issues at WOT/high-rpm. My guess is no, but maybe it depends on how long/hard you run those throttle/rpm conditions. ??
My startup has always been easy w/ or w/out pump. the issues I've noticed is leaning out at top RPMs with less than a half of tank of fuel left.. I'm sure its a pressure thing. but the fuel pump kinda fixed all that and gave me some grunt around 70-80mph that without it you can tell it's sorta choking for fuel. even properly jetted, I never figured out why it does that I mean sometimes at 80mph on the highway it starts chugging like when its running out of fuel, but if you let off the throttle to 65-70 and slowly pull back on it goes away.
but anyway, Used the fuel pump on a gokart and the GS got back its crappy petcock. that's forever stuck on RES. :thumb:
My thing is sometimes if the bike's been sitting for several days or maybe 2 weeks without being started, it doesn't want to start without being put on PRI. And sometimes even when it's been started/run within the past few days it'll still start first time cold and idle low for about 10 seconds and stall, have to restart it once or twice before it'll run like normal. I have chalked this all up to fuel in the bowls being low and insufficient vacuum to get the petcock open when cranking.
Re: the fuel starvation at high throttle openings. Once the slide are way open the vacuum is less in the manifold once at full flow , so possible the vacuum shut off is partially closing
Quote from: The Buddha on February 02, 2018, 12:08:02 AM
Vacuum line has to be capped off @ the carb if you're using an on/off style petcock. Else you're be sucking air into the mix and lean out like the dickens.
Cool.
Buddha.
Awesome, Thanks Budda!!
Quote from: mr72 on February 05, 2018, 07:25:19 AM
Even simpler is to leave the stock petcock on there and cap the vacuum ports on both ends (petcock and carb). Then put it on PRI to run and RUN or RES is off. You can even remove the non-reserve fuel hose this way and cap both ends (tank and petcock).
This of course assumes the petcock doesn't leak fuel with no vacuum. Seems like the more common failure mode, but who knows.
That does sounds like a good idea, I guess I want to minimize the hoses also but thanks for that
I've gotta say... what's the problem with the OEM vacuum petcock anyway. I've been having problems with the carbs but the petcock has worked flawlessly. If you want to simplify the vacuum lines then remove the solenoid and just leave a single vacuum line from the carb directly to the petcock.
I'm with Adidas Guy here (RIP), if the vacuum petcock breaks then buy a new one like you would any other part.
I dunno, I seem to be having starvation issues on mine and I always thought the petcock can drain the tank in 10 mins or less, so it should flow fine @ WOT cos even @ 100 mph the bike cant use more than 4 gal in an hr .... except ... except .... @ WOT you have pathetic vaccum, so while you're using 4 gal in less than an hr you're also trying to pull through that complicated plumbing with poor vacuum ... Of course put it in prime and the problem still persists. So Stumped.
Cool.
Buddha.
@thebuddha I've got larger fuel lines on my GS too. still full throttle chokes for fuel this way. and ive had a petcock piss fuel down my leg before, I don't think its the petcock, I think its that T fitting that connects both carbs.
Pulled my carbs went to check my diaphragms again to make sure they weren't ripped [currently struggling at 80mph+ wont go full throttle without bogging again] opened white caps.. DOH! SOMEONE TOOK OUT THE SPRING IN ONE OF THEM. PUT THE LITTLE WHITE PLASTIC DISK BEHIND THE DIAPHRAGM. I SWEAR IT WASNT ME! I've forgotten to screw all the way in jets before. [lol] but I've never touched the white caps until now on this GS... searching through my pile-o-springs. but can't find anything suitable, gonna try ace later.
edit: that seemed to fix it! had to make my own spring from an existing spring - heated it up a little to take away some of its strength but revving the shaZam! out of it in 3rd gear can't get it to starve for fuel like it was.. still a lot of popping in the exhaust but I think there's something jacked up with the head or valves [hence the extreme smoking on startup only - valve guides probably.]
Quote from: J_Walker on February 07, 2018, 09:15:33 AM
@thebuddha I've got larger fuel lines on my GS too. still full throttle chokes for fuel this way. and ive had a petcock piss fuel down my leg before, I don't think its the petcock, I think its that T fitting that connects both carbs.
Pulled my carbs went to check my diaphragms again to make sure they weren't ripped [currently struggling at 80mph+ wont go full throttle without bogging again] opened white caps.. DOH! SOMEONE TOOK OUT THE SPRING IN ONE OF THEM. PUT THE LITTLE WHITE PLASTIC DISK BEHIND THE DIAPHRAGM. I SWEAR IT WASNT ME! I've forgotten to screw all the way in jets before. [lol] but I've never touched the white caps until now on this GS... searching through my pile-o-springs. but can't find anything suitable, gonna try ace later.
edit: that seemed to fix it! had to make my own spring from an existing spring - heated it up a little to take away some of its strength but revving the shaZam! out of it in 3rd gear can't get it to starve for fuel like it was.. still a lot of popping in the exhaust but I think there's something jacked up with the head or valves [hence the extreme smoking on startup only - valve guides probably.]
You had starving issues @ WOT ? Mine don't have the white cap though, I got 01-02 carbs on my 95.
Maybe it is something related to that thing they slapped on the 01-02 before they went whole hog on the 04. I'll look into it, also I should have 89-00 carbs here shortly, I will cross check with that and let you know.
Cool.
Buddha.
Quote from: The Buddha on February 09, 2018, 04:54:38 AM
Quote from: J_Walker on February 07, 2018, 09:15:33 AM
@thebuddha I've got larger fuel lines on my GS too. still full throttle chokes for fuel this way. and ive had a petcock piss fuel down my leg before, I don't think its the petcock, I think its that T fitting that connects both carbs.
Pulled my carbs went to check my diaphragms again to make sure they weren't ripped [currently struggling at 80mph+ wont go full throttle without bogging again] opened white caps.. DOH! SOMEONE TOOK OUT THE SPRING IN ONE OF THEM. PUT THE LITTLE WHITE PLASTIC DISK BEHIND THE DIAPHRAGM. I SWEAR IT WASNT ME! I've forgotten to screw all the way in jets before. [lol] but I've never touched the white caps until now on this GS... searching through my pile-o-springs. but can't find anything suitable, gonna try ace later.
edit: that seemed to fix it! had to make my own spring from an existing spring - heated it up a little to take away some of its strength but revving the shaZam! out of it in 3rd gear can't get it to starve for fuel like it was.. still a lot of popping in the exhaust but I think there's something jacked up with the head or valves [hence the extreme smoking on startup only - valve guides probably.]
You had starving issues @ WOT ? Mine don't have the white cap though, I got 01-02 carbs on my 95.
Maybe it is something related to that thing they slapped on the 01-02 before they went whole hog on the 04. I'll look into it, also I should have 89-00 carbs here shortly, I will cross check with that and let you know.
Cool.
Buddha.
yeah at WOT it would chug like it does right before it dies when you run out of gas, is the best way to explain it, but if you dropped off the throttle 2/3rds or lower, it would chug a little an then be perfectly fine, but as soon as I went WOT again it would chug. I got so desperate thinking it was a vacuum leak I just took a hose and sprayed water all up in the carbs general location, but nothing changed.. so I figured its the diaphragms/near them, and that I missed something.
Quote from: user11235813 on February 07, 2018, 01:40:26 AM
I've gotta say... what's the problem with the OEM vacuum petcock anyway. I've been having problems with the carbs but the petcock has worked flawlessly. If you want to simplify the vacuum lines then remove the solenoid and just leave a single vacuum line from the carb directly to the petcock.
I'm with Adidas Guy here (RIP), if the vacuum petcock breaks then buy a new one like you would any other part.
Adidas Guy has taught me a lot, he even sold me a custom chain guard. Very great guy.
Ive been having problems with it for a while when its on and prime.. Just want to replace it all together. http://gstwin.com/racers_corner.htm is exactly what Im looking for.