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Discussion Starter · #1 ·
My dad just bought a '75 GL1000. The reported problem was that it would start and run for 20 seconds before flooding.
Figuring it for a float/carb problem, I encouraged my dad to look into the bike and next thing I know he's bought it for himself!
The first thing I noticed while removing the carbs was that it had electric ignition and fuel pump "upgrades" :sobbing:
I went through the carbs with brake cleaner and compressed air to see that all passages were open; adjusted the floats while I was in there (which were - as I had guessed - very out of adjustment); and reinstalled the rack.
The bike still won't start (when I first installed the carbs again, it started for 30 seconds, but I couldn't get it to idle, and the first time it stalled was the last time it ran for me).
The two things that I'm thinking are the most likely culprits are the electric fuel pump having a bad flow rate (whether too much or too little I'm not sure), or the ignition timing. So thanks to the PO who thought those were good ideas :lash:.
This electronic mumbo jumbo is pretty outside of my experience. I feel competent in learning and executing the proper procedures, but I've gone to great lengths to avoid having to deal with these "improvements" that are pandemic to the modern automobile (I'm 23 buying 35+ year old bikes for chrissakes!), so if anyone has any advice for me I'm all ears.
 

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...if anyone has any advice for me I'm all ears.
Sell me the bike!

If not, I would go 100% factory stock and see how it does.

Remember you can run a gravity feed remote tank to eliminate or evaluate the pump.

I prefer the electric igintion over points, and I have had good luck fixing systems that were installed. Normally its just a bad or wrong connection from a prior owner or installer.


Bill
 

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Electronic ignition and electric fuel pump are popular upgrades and add value to the motorcycle.
If it will start and run for 20 or 30 seconds the timing must be reasonably close. If the tank is full or nearly so the fuel should flow by gravity. You could bypass the pump and confirm or eliminate it as a contributing problem.
The idle passages are very small in those carbs. You may have to boil or ultrasound them to get the idle passages free. Then maybe bench-test the carb rack with a suspended remote fuel source to see if the bowls fill up and identify any flooding issues.
At some point you may want to start with the basics. Good compression, good battery...?
 

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Details are needed.
What ignition is in it? What model by what manufacturer?
Which fuel pump?
What float height and how did you do it?

I'd rule-out the ignition (if set correctly) and the pump. Both generally need heat to fail and 30 seconds isn't enough.

Brake cleaner and compressed air alone may have actually worsened the problem.
Sorry to say, but a full disassembly of the rack is probably going to happen.
 

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Discussion Starter · #5 ·
Naw the carbs aren't the issue. This is actually the fourth GL1000 carb cleaning I've done this month, and the first three were all full Randakk directed and provided rebuilds. This time the carbs (and all the fuel and air jets) were clean. It seemed like someone had only recently rebuilt them, and had only really screwed up the float settings.
I have a tool, similar to the one Randakk sells on his website, which measures my float settings and I got them all correct.

My dad went out with me this afternoon and noticed that the fuel pump was being really loud, so we switched the petcock to reserve and suddenly the sound went away... the bike was basically out of gas! Didn't I feel silly.
The bike still didn't start once in reserve, after a little while of trying to get it going, there started to be a leak dripping from the header pipes. Couldn't really identify where the source was, but pulled the plugs and am gonna let the cylinders breathe tonight before I go back and do some flow and electric investigation tomorrow. Maybe fill that tank up too.
 

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It is not the flow rate you have to be concerned with on the pump, it is the pressure. If it pumps more than 3 or 4 PSI it will push the float valves open and flood the engine.
 

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Discussion Starter · #7 ·
If it pumps more than 3 or 4 PSI it will push the float valves open and flood the engine.
I think this is exactly what's going on!

So, I got the bike going today. Wasn't idling great, it would go between a 2500 rpm idle to a stall in 1/8 turn of the idle adjustment screw! And getting it to start again after a stall was impossible.

I eventually found that I was having some luck by turning the petcock off when I wanted to get it started.

Took it out for a 5 mile stretch. On the way out it was running very heavy, didn't want to accelerate quickly, made disgruntled noises when I tried to goose it, etc.
When I turned around for the return 5, it stalled.. I couldn't bump start it, I couldn't kickstart it. The battery got good and rundown. Finally a friendly face and I got it to jumpstart (again after a bunch of tries I finally just turned the petcock off and it started up after a few seconds).
On the way home I alternated the petcock between on and off. Switched it to on once it started feeling heavy, and similarly switched it to off when the same thing started happening on the other end. Doing this, I guess I was sort of regulating the fuel manually, and it ran very well (between the short patches of flooded and starved).

My conclusion, as Dave stated, is that my floats are being overpowered by the electric pump (which is also probably why my floats were so maladjusted, I bet the PO was trying to counter this issue). So that'll be my next evaluation. I'm also looking for an original '75 fuel pump if anyone has one kicking around.
 

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Again, what electric pump do have on the bike. How old does it appear to be? Tell us about the pump.
Anyone installing a electric fuel pump on that bike would know to put a low pressure pump on it. With all of the pumps out there, maybe you should tell us which one you have so to know, at least, what pressure it supposed to operate at.

Unless you've changed the air chamber seal your description fits a bad seal exactly.
Chances are that the pump has been running that engine fine. Float height cannot compensate for a fuel pump that runs at too high a pressure overpowering the float valve.

I say we need to know what pump you have before you go wasting money on bad assumption. IF the pump is low pressure meant for a carburetor then a simple bench test can verify that it works as it should.

I too run a electric fuel pump, but without failure of any kind.
 

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As someone above mentioned, they'll run on gravity if you have more than half a tank. You could bypass the fuel pump and see if it cures it. If it does you know you have too much pressure.
 

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As someone above mentioned, they'll run on gravity if you have more than half a tank. You could bypass the fuel pump and see if it cures it. If it does you know you have too much pressure.
No, he probably won't know that. Just bypassing the fuel pump and having whatever head pressure that is available from whatever fuel is left in the tank won't simulate the working pressure of the electric fuel pump or the stock mechanical pump. Trying to get 3 psi from gravity-feeding out of the in-bike fuel tank won't happen...

If his head pressure is below 1 psi and yet still enough to fill the float chambers AND the floats shut the valves down afterward, then how will he know if a air chamber seal is bad? He'll know once the rack is back under working pressure. With gravity from the bikes tank he'll know if his float valves are working as they should, but that's it.

He needs to simulate the actual working pressure.

I would leave the rack in the bike and remove the air filter cover and filter. Then I'd key-on the pump and watch that plenum seal... If nothing happens after a minute of the pump pressurizing the chamber, I'd start the bike and watch the outlets of the chamber to each carburetor for fuel pulsing back into the plenum telling me I have a float valve problem...
 

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Discussion Starter · #12 · (Edited)
Here is a top and bottom photo of the pump.

I didn't split these carbs, so no, haven't replaced the plenum seal.

I'm going to try to do the diagnostic test that Captain explained, but I'd like some clarification.
Then I'd key-on the pump and watch that plenum seal... If nothing happens after a minute of the pump pressurizing the chamber
What sort of observations should I be expecting here if the seal is bad/good? Are you saying that the fuel passages through the plenum gasket may be leaking into the plenum?
 

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The part number for that pump is on the mounting flange next to the mounting bolt. It looks like "106" (to the right of the bolt that has the ground going to it).
A 106 pressures up to 6 psi. That's a little high for my liking. Hard to say if it would overpower a float valve. I suppose it's possible @ 6 psi, but not likely.

The air chamber has two fuel transfer ports on the bottom edge of the castings. Looking down into the air chamber the flooding would be most noticeable a couple of inches in toward the center from the ends along the parting centerline. Fuel will pool and if noticed carefully as the bike is running, can be seen coming up through that centerline seam of the two halves.

Alternatively, fuel can pulse backward out of the carb and into the air chamber if a particular carburetor is trying to flood the engine because of a suspect float valve.
 

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Discussion Starter · #14 ·
Gas appears in a few seconds and is appreciable in less than a minute - it is coming in from behind the right side screen. The bike is not on flat ground, it is front-higher, and the right rear is where the gas shows first.
 

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...then that is the carb you'll look at first.
Did you clean the tip of the float needle?
 

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Not to horn in on the cap'n, but you can put a piece of dry paper in the bottom of the plenum to pinpoint where it's coming from. If it's the plenum seal, it's in the middle of the plenum. ( sounds like it's not.) Once you identify the carb, you can take the cap and slide out. Dry it off and watch where it comes from looking down through the hole for the piston. If it's the float, you'll see it come up through the jet or jets, if it comes from the plenum side of the carb, it's likely the oring for the fuel where the carb is mounted to the plenum. You can separate the carb from the plenum to replace it if it is. It's a thick oring. I chased the float thing for a long time before I figured that out.
 

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Discussion Starter · #17 ·
Good info guys!

I've got a mechanical pump on its way, it should be here tomorrow. My dad wants to restore this bike to stock anyway, so I guess I'll just cross my fingers that the switch will put all this behind us (we measured this pump at 6 psi today).

I did check all the float needles and the fuel inlets. They were clean, but I wasn't looking at em through a magnifier so MAYBE I missed something.

Will keep y'all updated.
 

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The rubber tips of the valves get hard with age and won't seal. You can clean the hard coating off with Brake cleaner or acetone.
 

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I went thru a similar thing with my friend '76. It appears that after 34 years ,the o-rings where the carbs mount to the plenum get old an leak. We fixed that problem,then the gasket that seals the plenum halfs together started leaking. When the pressure of the pump builds up , it starts flowing pretty good inside the plenum and will flood the motor. It may even cause some of the carbs to be dry as no gas will make it to them. Be carefull you don't have a cyl full of gas when trying to start it. His no.3 cyl was filling up with gas.,,
 

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It's most often a bad float or plenum gasket, but your description sounds more like the seals where the fuel enters the carb. They should stand a little proud of the carb to be able to seal. The round but thicker than an oring one.
 
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