Carb vent hoses for '77 750

[steveu812]

I have searched high and low, but can't seem to find a direct reference to a '77 so I apologize if '77's are the same as '78's and '79 or something like that.

Anyhow, most of what I find says that #2 & #4 carbs have vent hoses, but that #3 goes to the back of the petcock? When I removed the airbox I don't remember there being a hos on #3. There are 2 hoses on the petcock, one goes to the fuel filter, but the second disappears somewhere under the tank.

I found this pic somewhere on the web and I relabeled the ports I'm referring to.

Thanks

[Seana23]

Hi babes...
The vent holes stay open...
The ??? Hole is the fuel hole... Tube from there to your petrol tap...
Small vent hole at front ov carb #2 is the vacume tube, connected to the vacume hole.in fuel tap....
Hope that helps some.
Xxxx

[steveu812]

Hi babes...
The vent holes stay open...
The ??? Hole is the fuel hole... Tube from there to your petrol tap...
Small vent hole at front ov carb #2 is the vacume tube, connected to the vacume hole.in fuel tap....
Hope that helps some.
Xxxx

OK, in my pic, carb #1 is on the left #4 on the right - correct?

The nipples on #2,#4 are vents that remain open. That much seems to be consistent in most everything I read about this and jives with the way it was when I got it.

So are you telling me that #3 gets connected to the "petrol tap"? is that the fuel petcock here in the states?

You lose me after "...Small vent hole at front ov carb #2 is the vacume tube, connected to the vacume hole.in fuel tap...." That seems to contradict what you said about the vent holes in the first sentence.

[btbarb]

#3 is the vacuum port

... Anyhow, most of what I find says that #2 & #4 carbs have vent hoses, but that #3 goes to the back of the petcock? When I removed the airbox I don't remember there being a hos on #3. There are 2 hoses on the petcock, one goes to the fuel filter, but the second disappears somewhere under the tank.

Sitting on the bike from left to right, the #3 'vent' is for a vacuum line that will connect the #3 carb port with the vacuum tap on your petcock. If your petcock has two ports, the smaller one is the vacuum port. The vacuum that's created when the bike is running pulls on a diaphragm in the petcock that releases fuel. When the petcock is on PRIme, the vacuum mechanism is bypassed. Normally, the petcock should be on the ON position, 6 o'clock. If your bike is running, this must mean your petcock is staying on PRI. Keeping the petcock on PRI all the time is not good, do an advanced search to see why, search on Petcock (titles only) and then go to the last page and work forwards, looking for 77-79 models.

[allojohn]

FYI, The use of a fuel filter is well documented here and can cause fuel starvation and lean running.
If you have sh!te in your fuel from rust in the tank then fix it!

[Steve]

That picture is awfully tiny, but I was able to blow it up enough to see what you had labeled.

The vent hose labels are correct. The "????" label is for the vacuum port to the back side of the petcock. That is the one that will turn the fuel on when you start the engine. Your petcock needs to be in the RUN or ON position for this to happen. DO NOT leave the petcock in the PRIme position (lever pointing to rear of bike) for normal running of the bike.

Seana saw just a little off when saying that the "????" label was your fuel input. The fuel input is the "T" that is dead center, between carbs 2 and 3, your label appeared bo be pointing to the port that is actually on carb #3.

.

[steveu812]

Thanks. It all makes sense now. It appears the PO didn't have that hooked up and was running it on PRI....

I'll pull up the tank and locate the other end of the 2nd hose off the petcock.

Thanks all.

[steveu812]

FYI, The use of a fuel filter is well documented here and can cause fuel starvation and lean running.
If you have sh!te in your fuel from rust in the tank then fix it!

It does have a FF. When I pull the tank I'll check it out. This tank looks very clean inside though.

Thanks