Topic: Fuel gauge for CB750

[evanphi]

Has anyone ever retrofit an electronic resistor-type fuel gauge to a CB750 tank?

My speedo has a wire for one, and I figured it would be nice to have if it is possible... because why the hell not, right?

[lucky]

Has anyone ever retrofit an electronic resistor-type fuel gauge to a CB750 tank?

My speedo has a wire for one, and I figured it would be nice to have if it is possible... because why the hell not, right?

Electric near fuel. Does not sound good.

[Garage_guy_chris]

Electric near fuel is fine if its done properly. Cars have electric fuel pumps in the gas tank and electric fuel level sensors.

I have thought about something similar except i was just going to add a low fuel light. From what i have seen alot of cars use a little sensor about the size of a "AA" battery to detect low fuel it would just be a matter of figuring out how to plumb some sort of dip tube into the tank and wire the sensor to a idiot light

[bjbuchanan]

On a kz they use a bobber that is on the bottom, opposite of the petcock. It is easy enough to do in theory but your tank obviously won't have threads there, or a hole for that matter.

Could integrate the bobber in to a cap and angle the bobber to the right and down. Would take some tweaking

[Nic]

My trip meter is my fuel gauge.

[Gordon]

I have a running graph in my head that has to do with the amount of free time on a sohc4 owner's hands as compared to the extent of non-essential modifications being made to said bike.  This one ranks pretty high up on the "Tons of free time" scale.

I used to be pretty high on that scale, too, before we had a couple of kids.  Now I'm lucky if I get a couple of hours to do a regular tune-up and oil change.

All kidding aside, my biggest concern with this mod would be the addition of another hole in the bottom of the gas tank.  If done correctly I'm sure it would be fine, but you're still adding another place where gas could potentially leak from. 

[seanbarney41]

There is/was an aftermarket one commercially available...I have seen them on ebay.  They are now rare and expensive.  It replaces the stock gas cap.  There are some old threads on this here somewhere.

[Stev-o]

There is/was an aftermarket one commercially available...I have seen them on ebay.  They are now rare and expensive.  It replaces the stock gas cap.  There are some old threads on this here somewhere.

Not so rare, Sean, but rather pricey....


http://www.ebay.com/itm/Honda-CB-750-Four-Asahi-Denso-Gas-Cap-Vintage-NOS-Fuel-Gauge-Cafe-Racer-CB750-/161096481570?pt=Motorcycles_Parts_Accessories&hash=item2582193b22&vxp=mtr

[70CB750]

I have one on my old sears lawn tractor,  it is waiting in the barn to become a sawmill - yeah, right, maybe in the next century 

Anyway, the screw on cap has a piece of metal and a floater to indicate the fuel level, very simple, works well. 

[evanphi]

I figured there would be little to no options. I'm happy to use my trip meter.

[70CB750]

This is what it looks like.  Simple and dependable, but not easily adaptable to motorcycle tank.

[Geeto67]

is it really so hard to open the cap and look in at a stoplight? I did it this morning like it was nothing. If you bike is maintained properly you have a reserve on the petcock - bike starts to stumble - switch it over and find a gas station, it isn't a hard concept.

There is something about motorcycles and getting into good habits - know your fuel level pre ride and your average fuel mileage to a tank is one of those things. Pilots have pre-flights, same kind of thing.

Here is the problem with a motorcycle fuel gauge. it is only accurate when you are stopped, on level ground. motorcycles tilt so no matter where you put it while you are in motion it isn't gonna read right.

You can try it but I just think you are being lazy.

[70CB750]

Agreed 

I keep records on fuel consumption in all my vehicles - OK, not on the diesel tractor:)  -  the motorcycle is no exception.  The fuel gauge interests me as a technical problem, that's all.

[evanphi]

is it really so hard to open the cap and look in at a stoplight? I did it this morning like it was nothing. If you bike is maintained properly you have a reserve on the petcock - bike starts to stumble - switch it over and find a gas station, it isn't a hard concept.

There is something about motorcycles and getting into good habits - know your fuel level pre ride and your average fuel mileage to a tank is one of those things. Pilots have pre-flights, same kind of thing.

Here is the problem with a motorcycle fuel gauge. it is only accurate when you are stopped, on level ground. motorcycles tilt so no matter where you put it while you are in motion it isn't gonna read right.

You can try it but I just think you are being lazy.

I'm not lazy, and I am fully capable of reading my gas tank and trip meter. I was simply embracing my DIY spirit.

[Geeto67]

my ducati has a fuel warning light because it is FI, does not have a gauge, and does not have a petcock. The thing begins to flash when there are 2.5 gallons left in the tank (more than half full). To a person who is hypersensitive to looking for idiot lights it is very distracting.

DIY spirit has nothing to do with whether it was a good idea or not - that just means you aren't going to farm it out. Good engineering would mean you were solving a problem on your own where the existing solution is inadiquate to address. Please enlighten me as to how a fuel gauge will solve the fuel problem better? 

There is a fuel gauge on the 1986 1000R ninja. The damn thing is only right when it is full or empty, in between it is slow to move and then moves really really fast. it also bounces in turns. Actually every bike I have ever owned that had a fuel gauge had pretty much the same behavior.

if you feel you need it go right ahead. some people feel like they need busas with streched swingarms. same kinda thing.

[evanphi]

my ducati has a fuel warning light because it is FI, does not have a gauge, and does not have a petcock. The thing begins to flash when there are 2.5 gallons left in the tank (more than half full). To a person who is hypersensitive to looking for idiot lights it is very distracting.

DIY spirit has nothing to do with whether it was a good idea or not - that just means you aren't going to farm it out. Good engineering would mean you were solving a problem on your own where the existing solution is inadiquate to address. Please enlighten me as to how a fuel gauge will solve the fuel problem better? 

There is a fuel gauge on the 1986 1000R ninja. The damn thing is only right when it is full or empty, in between it is slow to move and then moves really really fast. it also bounces in turns. Actually every bike I have ever owned that had a fuel gauge had pretty much the same behavior.

if you feel you need it go right ahead. some people feel like they need busas with streched swingarms. same kinda thing.

I know they're generally crap, always have known that. No hurt in trying to make something, though. Never said I needed to, just wanted to "just because".

Now enjoy:
Jane's Addiction - Just Because

[750K]

For me the fuel gauge is the petcock, it tells me I need to switch to reserve and it has yet to lie to me. Unlike the gas gauge on my old 60's volvos, haha. I know roughly where I'm at with the trip odo as well, I'm not going to bother reinventing the wheel. I'm on Holliday in Greece at the moment and riding a pos Peugeot scooter around Santorini, the fuel guage doesn't work so I just look in the tank once a day, haha.

[evanphi]

For me the fuel gauge is the petcock, it tells me I need to switch to reserve and it has yet to lie to me. Unlike the gas gauge on my old 60's volvos, haha. I know roughly where I'm at with the trip odo as well, I'm not going to bother reinventing the wheel. I'm on Holliday in Greece at the moment and riding a pos Peugeot scooter around Santorini, the fuel guage doesn't work so I just look in the tank once a day, haha.

yeah petcock is it for me. In-traffic commuting can mean a lot of stop go, and if i'm cruising too... messes with my ODO calculating. When it stumbles, switch to reserve and get to the next gas station.

[bjbuchanan]

For me I usually notice when it starts to rev up on its own. You know you pull in the clutch and it stays at 4k rpm, and pulls with no throttle given. I switch it to reserve and hit a gas station eventually.

[bambuhiphop]

I will be putting the sending unit out of an 03' R6. Not a cheap venture and really isn't the most critical thing to do but I personally think it is kind of a cool thing to have and my gauge has a readout for it so why not!

[KRONUS0100]

i have seen a few with outside the tank plumbing for fuel level indicators.  the kind like you see on the side of in-the-bed tanks on farm trucks or volkswagon trikes.
I have thought about the outside the tank thing alot and still havent done the mod.  something about drilling 2 holes in the sides of the tank keeps me from doin it

[Stoli]

I start thinking about getting gas after 200 miles, but that isn't the point. I too am contemplating putting a fuel gauge in my second project bike because it will have a digital dash, so I figure it might be a cool addition. I was looking at this:

http://www.summitracing.com/parts/sun-cp7591/overview/




and was thinking about mounting it here:



It looks like that space on the 77-78 tanks was made for it. Need to look at the size of the sending unit and if the float arm can be positioned correctly inside the tank so it will swing between the bottom and the top, but at this point I can't think of any reason why it wouldn't work. As long as the tank is grounded, I don't think it will blow up.

[Geeto67]

have you ever seen one of those sending units in real life? It's like a foot long.

[madmtnmotors]

have you ever seen one of those sending units in real life? It's like a foot long.

You could probably reposition the rheostat further up, cut off the lower stem, and bend the float arm to reach down further into the tank. That impression on the 77/78K tanks is exactly where the fuel sender is located on the CB750A models. If you found a complete "A" tank you would have a tank with the sender. Don't know what aftermarket gauges would be compatible though. The "A" models had the fuel gauge, gear position, and turn indicators located where the tach belongs ("A" models did not use a tach).

[RSchaefer]

But, correct me if I'm wrong, you would have to stop take the key out and open the door covering the gas cap and guage?

[madmtnmotors]

But, correct me if I'm wrong, you would have to stop take the key out and open the door covering the gas cap and guage?

We are only talking about the sending unit here. The "A" tanks route the wire from the sender to the gauge (gauge is separate from the sending unit) down through the "tunnel".

[Stev-o]

But, correct me if I'm wrong, you would have to stop take the key out and open the door covering the gas cap and guage?

Unless the fuel door was removed

[Stoli]

I was thinking along the same lines as Wilbur. It looks like there are 3 possible positions for the rheostat. Pick the lowest one possible, cut off the rest of the post, adjust the float arm as necessary and route the wire down through the drain hole to the gauge. The sending unit will read 33 ohms at empty and 240 full. Piece of cake.

[seanbarney41]

I was thinking along the same lines as Wilbur. It looks like there are 3 possible positions for the rheostat. Pick the lowest one possible, cut off the rest of the post, adjust the float arm as necessary and route the wire down through the drain hole to the gauge. The sending unit will read 33 ohms at empty and 240 full. Piece of cake.

or just buy gas every 135 miles (or so)...bigger piece of cake

[Stoli]

or just buy gas every 135 miles (or so)...bigger piece of cake

I respectively disagree. You are right of course, but I see this as a $25 upgrade that will take less than an hour to install and probably another two hours of coding to add a low-pass filter into the software that will dampen out the faulty readings during acceleration and cornering. While Geeto is removing his gas cap at the stop light I'll be glancing down at a functioning fuel gauge and nodding at the girls (who are ignoring me).

The bike I am working on has an old rusty frame which works very well, but I think I'll powdercoat it even though it would be easier and much more practical to leave it as is. Call me crazy but I don't see the difference between that and trying to get a fuel gauge working. It's a long winter, and if I can't ride the bike I might as well tinker with it. 

[Killer Canary]

I wish that the fuel gauge in the old Mazda was as good as the one the GPz has.

[Stev-o]

There is a new one for sale in the for sale thread.....