Topic: Gas ran out, no reserve on my '76 CB750F

[sessna]

 I was wondering if anyone ever had this experience:

I was on a long ride and the '76 CB750F bogged down. I pulled over and switched it to reserve. It wouldn't start. The tank was near dry. I flagged down some guys doing lawn work and bummed some gas off them. I didn't put a lot of gas in, maybe a quart or more. I just wanted to get to the next gas station. There was enough gas that looking in the tank you could see it. I had a really hard time starting it and after I let it sit for 10 minutes it started. I rev'd it a bit and it bogged and died again with a few pops and backfires. I finally got it running and I got about a mile before it bogged again and died. Once again.. it would take a lot to start, then bog and die. A friend ran for gas and once I put an full gallon in it ran fine. I filled it up and did 100 miles strong.

I really don't know anything about tanks and petcocks. I was just riding out the tank to see how far I could get then, like everyone else, switch to reserve and ride to get gas. I don't know what's wrong. I'm guessing it's on reserve all the time and when the tank's dry it's BONE DRY. What now?

[WJL75]

The filter with the hoses may have broken off of the petcock.  They stick up into the tank a few inches, and once the gas level gets below that point, you need to switch to reserve.  If those broke, then there is no reserve.  Also, due to the petcocks position on the tank the gas obviously needs to be able to flow to the side with the petcock in order for it to feed the carbs.

When I was testing my tank for leaks, adding only a little bit of gas would not allow it to drain until I tipped the tank to get the gas over the hump and over to the side with petcock on it.

Not sure what your tank configuration is, but mine has an offset gas cap, and the petcock is on the opposite side. 

[sessna]

Ah, ok. Yea, I know nothing about these tanks or really ANY tanks with a reserve. My only bike before this was a scooter with a gas gauge. I now know how it works thanks to you.

Not sure what you mean by offset cap. is it off to the side of the center of the tanks? Mine's in the middle and my petcock is on the left side when you're on the bike. So I guess it's a lesson learned that there has to be a decent amount of gas in the tank or it'll run out depending on the tilt of the bike. I guess I assumed the bottom of the tank had some sort of drastic dip in the bottom so that wouldn't happen. NOW I KNOW!

So now I guess I have to look in there and see what's going on. THANKS!

[WJL75]

That's what I was talking about, my 550K tank has the cap offset to the right side a bit.  The petcock is on the left side, so if I only have a very small amount of gas in the tank, it cannot always flow over to the side by the petcock.  It is not a big deal if you just keep it topped off, but you can get parts to replace anything that is no longer working.  Others may be able to chime in on the nuances of the 750 petcock and its removal and repair.

[Bob Wessner]

Sessna, if you are temporarily without a reserve for whatever reason, your tank, if stock, has approx. 4.6 gal. capacity. If you have a handle on your gas mileage, peg it to the 4 gallons as your max before needing gas and use your odometer as a fuel gauge.

[sessna]

Yea... I see. Pretty poor design I guess... but I don't know if they still make tanks like that. i hope they don't!

I saw so fiches of the petcock and it looks like one tube sticking up... maybe with two holes in the side? Or am I looking at this wrong... is it actually two separate tubes? Like you said I hope someone with my era 750F chimes in. I don't know where the differences lie...

Once again.. thanks a lot. You provided some needed incite!

[sessna]

Yea... that's what I'm going to have to do. Eyes on the trip odometer...

I think the previous owner changed the sprocket and it's gear high as hell, so I may get a little less mpg on the highway then what's expected of the bike. I'll probably just fill up after 100 miles and play it super safe!

[super pasty white guy]

Just a datapoint for you- on my 76 F, I get just over 105 miles till I hit reserve.  Running 35-40 mpg.
My PO put on a 16" rear wheel so I'm running ~6k rpm on the freeway @ 70mph.

Dave

[Killer Canary]

Remove the petcock and see if the standpipe has been removed or is cracked. Also a good time to clean the screen.

[sessna]

WOW! IS your bike a 76 CB750F? It looks like one. Looks great! I painted mine all yellow as well. I painted the side covers black though.

I'm going to have to take the petcock apart like you said. Hopefully I can figure it out and get parts if they're needed. Thanks a lot!

[Killer Canary]

It's a '78 550K. I used a length of brass tubing from a hobby store. You can alter reserve capacity by changing the length of the tube.

[warreng22]

I have a 76' 750F that I am currently restoring. Yours should have two tubes extending from the petcock into the gas tank, one shorter than the other.

If you does not I would suggest getting a tube of brass as Killer Canary suggested, this is the easiest material to use, since it is very hard to find fuel resistant plastic at that small size. Or if you dont want to try to fix it yourself, you can get a new honda oem petcock at http://www.shawmuthills.com/fiche_section_detail.asp. It costs $56 for the entire assembly, just bolt it on, easy fix. Or you could try a bike parts store if anyone knows of one.

Hope this helps

[sessna]

This is all a huge help. Thanks everyone. It might be a week until I dig into it and see what's going on in there. I'll post back if I get stuck fixing it.