Topic: Length and diameter of CB750K fuel petcock standpipe

[willbird]

I bought this from Ebay, it was listed as Original part but I am just not a trusting person. Wondering if anybody knows the proper standpipe dia and length ?? My original to me Petcock apparently the standpipe went bye bye. The tank it was on my dad bought used after his original was stolen in the 70's. I never had any reserve and never knew it :-).

I have thought of modding my original to tale the common 1/4" translucent  fuel line by making new barbs and machining out the old ones. Then make two 1/4" nipple carb feeds if possible. To do things right I would make a new standpipe as well.

[Don R]

 I've seen different lengths of standpipe. Mine may have been modified, I can't say for sure.

[rotortiller]

Empty the tank and throw a gallon of fuel in it and have a look with a flashlight through the filler hole and see where the tube end is. Reserve is about 4 liters remaining.

[CycleRanger]

On one of those OEM petcocks I have I measure the pipe as 65mm long from the base where the pipe connects.
Diameter measures ~5.42-47mm. It's not perfectly round over its length.

Also, that one you show in that picture looks like genuine OEM to me.
The aftermarket repops are usually much more shiny.

[willbird]

On one of those OEM petcocks I have I measure the pipe as 65mm long from the base where the pipe connects.
Diameter measures ~5.42-47mm. It's not perfectly round over its length.

Thank you :-).

[HondaMan]

A little bit of interesting history of the standpipe (as shipped in new bikes back when):
In the sandcasts it is longer than in the K0.
In the K0 it was shortened because it was discovered that the bike ran lean while on Reserve, and Honda worried about burnt valves (which didn't happen but once that I ever heard about, details below).
In the new, taller K1 tank the length was the same as in the K0, resulting in less Reserve than in the sandcasts.
In the new (again) K2 tank, which is flatter and wider, it became the same as in the K0 again.
When the petcock moved to the other side (K4) it got taller again, for more Reserve and deeper float bowls from that increased head pressure.

I lost track of the changes after that...

There was just one bike, an early K0 diecast, in the Peoria shop where I worked that came in with 2 burned exhaust valves (the only 2 I have ever seen in these engines). I think they were on #2 and #3, don't remember for sure. The rider's story was: he had ridden to Arizona to see the Grand Canyon, with his sleeping bag tied to his instruments to be his "fairing", along with his friend on a (retired and rebuilt) Police Harley Glide. They rode at H-D throttle-peg speed across Kansas and Oklahoma, and most of New Mexico. The H-D indicated 90-100 MPH (it wasn't stock) the whole way. As they entered Arizona at 100+ degrees temperature, the 750 started slowing down, so when they pulled in to a gas station he removed the sleeping bag to get his cigarettes while the bike was idling and he noticed the Oil light was on. So, he checked the oil, which wasn't shown on the dipstick(!) and bought some Valvoline 30W (that's what the gas station had) and topped off the oil tank. That night he changed the oil (with more 30w) and they rode the rest of the trip without issues, except when he got back toward Illinois (somewhere in Missouri) the 750 would not idle anymore, so he had to 'hold it up'.

In the end, both exhaust valves were burned and the seats of all 4 exhausts had to be recut, and the crank bearings took enough of a beating that the oil PSI was only 40 with proper 20w50 oil aboard after that.

Oh - and the H-D was trailered home from somewhere in Kansas, didn't make the trip home on its own wheels.