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I've had carbureted bikes with fuel pumps in the past, they always shut themselves off( internally) at a fixed pressure . Anytime the engine was running they were powered. We're making this way too complicated here.
no return piping or anything. Make up a pressure gauge setup and power the pump up and see what it does. It's not that sophisticated I'm sure.
I used one on a bike with FCRs on a manual switch, no overheating of the pump or over pressurized carbs,
The pump stops pumping at a fixed pressure, low enough for the float needle to handle it.
This^^^^^^^

All low pressure fuel pumps work this way. I can only assume there is a relay there to stop the pump in case the fuel line ruptures or something like that. It's not necessary.

Just find a switchable power lead on the bike and wire the fuel pump directly in. Or ditch it if gravity feed works ok.
 

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I always assumed it ran off the spark unit to pump more fuel at higher rpms. Thanks for correcting me. That's why this forum is the best. Learn new things every day. Even though I've been working on bikes 25 years. After the bullshit you can really learn more than anywhere else
 

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This^^^^^^^

All low pressure fuel pumps work this way. I can only assume there is a relay there to stop the pump in case the fuel line ruptures or something like that. It's not necessary.

Just find a switchable power lead on the bike and wire the fuel pump directly in. Or ditch it if gravity feed works ok.
The relay is there so the pump stops pumping after you smash yourself into a guardrail and burst into flames. It's a safety thing and shouldn't be removed unless it's just for testing.

Bike falls over...your leg is under it....bike stalls....pump stops.. With no relay......pump keeps going ... leaks out the bowls and soaks your nether regions with fuel.....you are shitting yourself now and don't think to turn off the ignition..... or you rang you bell on the way down.....fuel is now dribbling on the hot exhaust.....
 

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I always assumed it ran off the spark unit to pump more fuel at higher rpms. Thanks for correcting me. That's why this forum is the best. Learn new things every day. Even though I've been working on bikes 25 years. After the bullshit you can really learn more than anywhere else
Actually after digging a little deeper, I think it's the other way around.... you taught me something.... I think. The spark unit supplies the ground to the relay when it fires a cylinder, so when running, it isn't constantly grounded. Trials needs to head over there with his scope and FP gauge and put this thing out of it's misery.

So is it the internal pressure switch in the pump that dictates pressure period, or does the intermittent ground (varying by rpm) create a difference? For now my money is on the pressure switch in the pump and the relay ends up being grounded long enough that it only controls on and off.
 

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The relay is there so the pump stops pumping after you smash yourself into a guardrail and burst into flames. It's a safety thing and shouldn't be removed unless it's just for testing.

Bike falls over...your leg is under it....bike stalls....pump stops.. With no relay......pump keeps going ... leaks out the bowls and soaks your nether regions with fuel.....you are shitting yourself now and don't think to turn off the ignition..... or you rang you bell on the way down.....fuel is now dribbling on the hot exhaust.....

Really? What about tank ruptures on any bike (EFI, fuel pump, gravity feed) and you just burst into flames anyway? I think if you smash the bike hard enough to allow the fuel pump safety relay to come into play you have bigger problems to worry about.

Sure it's a safety feature but so were vacuum fuel taps and twin throttle cables. Bikes work without them - and this bike doesn't seem to work with his.....
 

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I've had carbureted bikes with fuel pumps in the past, they always shut themselves off( internally) at a fixed pressure . Anytime the engine was running they were powered. We're making this way too complicated here.
no return piping or anything. Make up a pressure gauge setup and power the pump up and see what it does. It's not that sophisticated I'm sure.
I used one on a bike with FCRs on a manual switch, no overheating of the pump or over pressurized carbs,
The pump stops pumping at a fixed pressure, low enough for the float needle to handle it.
I do believe you are correct... at least it appears that this pump has a pressure switch built in. There are some pumps that just keep running (without a return) cause I have some.
 

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Really? What about tank ruptures on any bike (EFI, fuel pump, gravity feed) and you just burst into flames anyway? I think if you smash the bike hard enough to allow the fuel pump safety relay to come into play you have bigger problems to worry about.

Sure it's a safety feature but so were vacuum fuel taps and twin throttle cables. Bikes work without them - and this bike doesn't seem to work with his.....
Yes really.. Granted there are other ways to set yourself on fire, but the reason for the relay is to reduce the chance of fire. Any new vehicle with an electric pump won't be compliant without a fuel cut of some sort. He's a new kid, apparently trying to learn, so I don't think anyone should tell him a safety feature installed by the manufacturer and mandated by most governments is not necessary.
The increased risk of fire doesn't just apply to him,
 

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Yes really.. Granted there are other ways to set yourself on fire, but the reason for the relay is to reduce the chance of fire. Any new vehicle with an electric pump won't be compliant without a fuel cut of some sort. He's a new kid, apparently trying to learn, so I don't think anyone should tell him a safety feature installed by the manufacturer and mandated by most governments is not necessary.
The increased risk of fire doesn't just apply to him,
You're probably right - his bike is going to be heaps safer if it doesn't actually run.
 

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OP I looked in a Honda Common Service Manual from 1988, although it covers many topics, unfortunately It does not cover fuel pumps. You should track down a copy anyway. That way you can read and learn (a lot) without risk of being kicked in the nuts for saying something completely stupid about someone's mother.
There are also Honda Construction and Function manuals which are even more detailed, but they are hard to come by and I'm not positive ... actually I doubt they made one for VTs. They did make them for the likes of the CX500 Turbo which is in a slightly different dimension.. I believe there is a copy of that floating around the net. Get it as well if you can. Although nothing in the Turbo manual will apply to that thing you are working on, it is good reading.
 

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Discussion Starter #251
I'm liking that concept.
Just theorizing here but; if the pump motor only powers up for the duration of a spark, then it now has a way to speed up or slow down dependant on the engine revs. Pressure would not need to be controlled or even significant, the pump would simply keep the fuel moving along the line. Like a little stepper motor.

I think he's is on to something here and if the pump was always full on I just can't see that working well unless it was plumbed like a fuel injection system where the fuel constantly travels in a loop, constantly recirculating through the tank. ;) seems to me that might lead to the pump heating up, your carburetor bowl over filling and the bike running like crap after a few moments.
Oh wait :| is that what it's doing?
it sounds like that is what is happening. Although I will say that the pump it self isn't overheating, something it overheating the relay which is shutting off the pump, and starving the carbs for fuel

there is a domino effect here, "something">heating up relay>shutting off pump.
 

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Discussion Starter #252 (Edited)
Update.....You're going to love this!

I made it gravity fed!!!! Just got rid of the pump, relay, and plugged the tank to filter, filter to carbs! Im sure i sacrificed some amount of usable fuel from the gas tank due to positioning (not looking forward to finding out limit here, hopefully it doesn't die on me on the road.) but this is only a temporary solution anyway. I will track down the Honda Common Service Manual, CX500 Turbo, thanks for the reading recommendations. if anyone had other suggestions for reading material on the fuel pump system I'm all ears. thx

What's left:
-next ill be getting some proper tires
-"DOT" brake light
-changing license plate mount
-relocating new foot controls
-Proper seat mount
-tach repair
-another oil change
-paint
 

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Did you fuck up the back of your seat on the maiden voyage? Looks like it got kissed a few times by the tire......
 

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eh what can i say i got a fat ass!

no, actually the seat and light are fine.

Actually, they are not. They were hitting the tire before you left the driveway. While at speed, that will be a big problem. Not to mention the wear on your rear tire that is sure to happen. Bear in mind that stir will actually grow a bit at higher speed.
 

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Discussion Starter #256
Actually, they are not. They were hitting the tire before you left the driveway. While at speed, that will be a big problem. Not to mention the wear on your rear tire that is sure to happen. Bear in mind that stir will actually grow a bit at higher speed.
NONONO I meant they're fine as in they didn't get damaged on the test run.
I have a whole frame for the seat that i'm making. all said and done the seat will sit high enough that the suspension can travel as far as it will go without hitting the seat. :D

You missed my list of shit to do before i ride again...

What's left:
-next ill be getting some proper tires
-"DOT" brake light
-changing license plate mount
-relocating new foot controls
-Proper seat mount
-tach repair
-another oil change
-paint
 

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Discussion Starter #258 (Edited)
If you really think that seat is Ok, you have absolutely no clue.

Engineering student or not, this thread continues to be a huge fail. And an embarassment to the site.

Lets make caferacer great again.


I don't think so, I feel like I learned quite a bit. at the very least i have a little thicker skin thanks to all you old farts, CEOs, and Engineers shitting on me and my project left and right.
I mean every once and awhile I get a useful suggestion or direction so i mean it's not a total loss. Plus now this the forum has a perfect example of what not to do.
So actually you are all very welcome.

maybe I'll come back in another couple years with a new bike, or share the progress on this one.
But honestly I'm probably going to build a project car next :D
Cheers m̶a̶t̶e̶s̶ old farts!
 

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Yes it's a bit of a gong show... I include myself in that, but I learned a bit about how a fuel pump relay works on a VT700. Not sure what I'm going to do with that little pearl. I'm reasonably confident there isn't a VT anything in my future.
 

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oh wait he left? i was rather enjoying him 'blossom" and "learn" and "transform" from his first post till now.
 
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