GS1000 Fuel Flow Problems

[zwilmes]

Hi, I just want to start off by saying I really appreciate the wealth of knowledge on this forum. I'm one of those people that lurks for quite some time before asking any questions of my own. I started fixing up my 79 GS1000L over the winter/early spring and I've gotten it running really well at this point.

I recently scored 3 motors and a pile of carburetors and ignition parts on facebook for $450 and lucked out that the set of vm carbs had the bigger jets I was needing for my current exhaust, an old dinged up v&h 4-1. Well after a myriad of false starts resulting in me limping home a few miles on the bike (first time starter clutch started rattling and whining, temporarily fixed with a rebuild kit and tig welding the broken chunks back into the hub, second time a coil went bad presumably due to the engine finally getting completely warmed up for the first time in maybe 15 years, put on the dyna III ignition I got in my recent goody box) the most recent issue is that when holding WOT for any length of time the bike runs out of gas and I have to let it coast for a while before it regains power.

The original petcock that was on the bike before I started restoring the completely rusted gas tank (a whole other crazy story) was a very strange one, indeed. It had ON and RESERVE but no tube inside the tank for reserve, just a metal mesh over both holes in the petcock (I'm assuming maybe since the bike has a fuel gauge it didn't need an actual reserve?) I did take the petcock apart and clean it and get it working but the lack of a Prime function was driving me crazy with the carb tuning I was doing so I bought an amazon vacuum petcock. The issue I immediately noticed with it is that any small leak on the vacuum line would cause it to run out of fuel even at idle, so I took to just running the bike on the prime setting. However, I suspect that even the prime setting is not flowing enough fuel for full load on the engine.

Does anyone have any suggestions for a petcock that will flow better? I was attracted to the amazon one as it had the plastic filter mesh in the tank which is great because try as a i might I cannot find a fuel filter that will fit between the tank and carbs without kinking up the line but I could already see a problem with it in that it doesn't pull fuel all the way to the bottom of the tank. I'll have to hunt around and find some more pics of some of the work I did on it so far but I did find a recent picture of what it looks like after I got it cleaned up a bit.

[alke46]

Hey, welcome to the site. I am sometimes a resident in the area of Millard West high school. 29 miles from Blair.

I put a Pingel fuel tap on my GS1000E and I think it's great-----so long as I remember to turn it off after riding. I have forgot it a couple of times but my float valves did their job and kept the fuel from overflowing.

We'll have to arrange a meet up one of these days and I can share what I know if it would be of any help.

Good luck with your project.

[zwilmes]

Thanks for the quick reply, Larry! Yeah I live out by the water tower south of Blair on 133. Small world.

I did look into the Pingel but I didn't like the price and even less so on their vacuum operated petcock. My other bikes have manual fuel valves and I guess it's not the end of the world to shut them off after every ride but being somewhat absent minded at times (ADHD and a touch of autism) I like the convenience of the vac one. If that's the only solution though I'll do what I have to to get this thing running right!

[oldGSfan]

I had a petcock (NOS one that must have been a defect) with prime that didn't work. It was a bit of a hassle but I put a T fitting on the vacuum line with a rubber cap I could remove, and when I needed to prime it - always in the garage, I used a little vacuum pump from Harbor Freight.

I ended up with an Amazon knockoff petcock which, luck of the draw, worked fine. Perhaps that would work, get back to the one that flowed OK? Sorry, I think it may have been OK with the flow - but you need some paragraph breaks. Not meaning to be pedantic but it's tough to read one long sentence.

I've been down the road many times with rusty tanks, and using a battery & tender charger with a bolt dangled down as the anode worked the best by far. I tried vinegar and phosphoric acid, and for light rust, they worked but for heavy rust the electrolysis method is the way.

[zwilmes]

Ha Tom, thanks for the reminder on spacing. It didn't look so bad on my PC but reading now on my phone it's a massive wall of text!

Thanks for the input, if I can find a filter that's short enough to fit between tank and carbs I may just put the original back in and try your suggestion with the t fitting.

I do have the fuel sender Gauge back in it (original was completely rusted so I modified one from a Suzuki sidekick) but I don't know but that I'd still like to have a reserve valve if I can find one that flows well enough, maybe I could add a brass tube back onto mine to bring back the reserve but not sure where I'd source that at.

[rphillips]

Sounds strange, I'd Verify pet cock is problem. First check PRI. side of pet cock. Petcock to off, disconnect fuel line from petcock, install a piece of fuel line from petcock to bucket or jug, turn fuel to PRI. to verify petcock is problem. If no full stream, find what is restricting flow. Also easy to verify if vacuum side of pet cock is working, with fuel line still in bucket install a piece if hose from pet cock vacuum outlet, long enough you can reach your mouth. Turn to "ON" gently suck on hose, it takes very little vacuum, you can easily feel the vacuum valve opening and closing. Just as on PRI, should be a full flow from pet cock... But that's just me.... Oh yeah, Welcome

[alke46]

Also, it is NOT recommended to use a fuel filter in line. But if you do, you can get one for a garden tractor maybe at Bomgaars or Tractor supply.

[GregT]

I'd pull the tank cap apart and check the vent hole isn't blocked. No air in = no fuel out. Running out at WOT is a known symptom of a blocked or partially blocked vent.

[zwilmes]

I'd pull the tank cap apart and check the vent hole isn't blocked. No air in = no fuel out. Running out at WOT is a known symptom of a blocked or partially blocked vent.

I'm thinking about getting some new gas cap innards. The cap I had was badly corroded and I completely disassembled and cleaned/ oiled it a couple months ago but i'm not convinced it's working right still now that you mention it.

[unfocused]

If you're using an inline filter you MUST use a gravity style filter and not a pressure style - think lawn mower. Also, if you open up your fuel vents to the atmosphere I always recommend you install 2-cycle weedeater style filters as this prevents debris from entering your float bowls/carbs. We've done this for years in the small engine industry. Lawn mowers are dirty...

OP - Check your gas cap vent - this is the biggest problem with gravity feed systems. It will start to slow fuel down because of vacuum and eventually stall out because fuel won't move fast enough to refill the float bowls...

My carb vents after adding filters. These are the CV carbs on my GSX750 engine as I don't run an air box. The VM carbs have this vent in the inlet throat. This scoot is not a daily driver but these filters are tucked under the fuel tank and would not have any issues in the rain.

Resized_20240413_110546.jpg

[alke46]

Can the OP check for blocked cap vent by simply removing the cap and running it?

[zwilmes]

Ok. Update here. I did a flow test on my petcock. On RESERVE and on PRIME it flows nearly 1/2 gallon per minute, while on ON it is barely a trickle. I think the petcock is defective. This test was with the fuel cap on and the tank filled to the brim with gas.

Then for kicks I started the bike with the fuel in the carbs and did a flow test from the tank. No flow in reserve or ON and when checking the vacuum line there was a good suction to my finger even at idle.

[zed1015]

Sounds like a faulty tap diaphragm.

[zwilmes]

If you're using an inline filter you MUST use a gravity style filter and not a pressure style - think lawn mower. Also, if you open up your fuel vents to the atmosphere I always recommend you install 2-cycle weedeater style filters as this prevents debris from entering your float bowls/carbs. We've done this for years in the small engine industry. Lawn mowers are dirty...

OP - Check your gas cap vent - this is the biggest problem with gravity feed systems. It will start to slow fuel down because of vacuum and eventually stall out because fuel won't move fast enough to refill the float bowls...

My carb vents after adding filters. These are the CV carbs on my GSX750 engine as I don't run an air box. The VM carbs have this vent in the inlet throat. This scoot is not a daily driver but these filters are tucked under the fuel tank and would not have any issues in the rain.

Resized_20240413_110546.jpg

The filter I was wanting to use is a k&n reusable glass filter which are very high flow and designed for gravity feed. I've used them on other carbureted motors with good success. However, I cannot seem to find a spot to fit the length of it in there without looping the fuel line around to give extra length. So I may just not worry about running a filter. The tank is lined so there shouldn't be anything in the gas anyways.

[rphillips]

No clue what's going on with the petcock...Good flow on "RES" and not on "ON" doesn't make sense, it should be using the same diaphragm and vacuum for both "ON' & "RES"? Well, know you want it fixed, but you said were accustomed to manual valves, ride with it on 'PRI' then just remember to turn it to "ON" or "RES" when you turn it off... Same as your other bikes only different.