Topic: Help with CB750K4 fuel line routing

[rangelov]

My old fuel lines were hard, cracked and leaking.  I replaced them with 1/4" lines.  They worked, but the right hand line made a tight turn to the petcock and would pinch off the fuel flow.  I removed these fuel lines about 6 years ago.  The bike has been apart since then.

I have new lines, both 3/16" and 5.5 mm available to install.  I am working to get the bike roadworthy.  I'm not sure how the fuel lines should be routed.

I think that the right hand fuel line comes off the tee (between carbs #3 & #4) and goes through the round hole directly forward in the carburetor holder, then makes a 90 deg. turn upward to the petcock nipple.

There is no obvious routing for the left hand fuel line.  The most direct routing seem to have obstructions or pinch points.

I searched the repair manuals and part listings without finding any useful illustrations.  I also searched the forum but couldn't find a good description or picture of the routing.

Would someone please help with the routing?  A photo would be really great.

Thanks.

[andy750]

If no one else comes forward first Ill take a photo of my routing on my K4 when I get home later. I have stock 5.5 mm fuel line routed through the two holes in the carb plate. No kinks that impede flow. Ill post pics later.

cheers
Andy

[Toxic]

the inlets for the gas between the carbs swivles foreword enough so that the line runs upward and through the two holes in the carb plate as mentioned above.

The left side follows along the top of the carb to engine rubbers.

What makes a big difference is the length of the hose. if it is too long by as little as 5mm it will kink.

Instal as above but with the lines extra long then trim them to fit.

I was trimming off 3-4mm at a time until I got the exact length and then the hose will not kink.

[wildcatmahone]

The Tygon fuel line from Motion Pro is awesome! Would recommend it remains very flexible and makes it easy pulling lines on or off. Think I got mine years back from Z1.

[andy750]

here are some pics...






Good luck
Andy

[rangelov]

Many thanks, Andy.

The pictures showed me that I never saw the hole that the right hand line goes thru.  Now I understand the fuel line routing.

Before Andy's post, I was playing with it again today.

I found that spraying WD-40 into the fuel line end allows it to slip easily onto to the carb tee, while holding the tee steady with a 8mm open end wrench.  I noticed after a few days that it will not come off easily.

Getting any line off the petcock is always a pain.  Andy, I see that your line didn't come off the petcock nipple.  Sometimes it is better to cut it off.  Did it break off or slip out of the petcock?  If it slipped out, You should be able to Loctitie it in place.  If it broke off, new petcock (Honda or Pingel?) or make a new nipple to replace old one after drilling out the remants?

I ran the left hand fuel line from the tee between carbs #1 & #2 back around carbs #2 & #3 above the air box to carb rubbers.  I then fed it thru the small round hole in the carb plate holder between carbs #3 & #4.

I ran the right fuel line from the tee between carbs #3 & #4 forward and thru the hole made by the carb mount plate and carb #4 choke lever to the right of the small round hole that the left line went thru.  This is where Andy's photo shows this is wrong and needs to go thru the plate using the lower round hole.

I wish my petcock was on the left side, just like my other motorcycles.

Tygon is fine.  But I heard it gets very hard after being in service for a while.  I had some sort of clear line on my CB125.  It worked well.  After many years, it also hardened up.  I called a manufacturer a few months ago.  They had a great product (NexGen).  But the product manager said any type of plastic used for a fuel line will have problems.

I have 4 feet of Goodyear 3/16 fuel line, which I paid less than 3 dollars.  I also have 5.5 mm rubber fuel hose that I bought from a local Suzuki dealer.  Both lines fit the fittings well and have a relatively tight bend radius.

[Alan F.]

if memory serves the two lengths of fuel line were 6" and 12"

[rangelov]

I looked up the fuel lines in old Honda microfiche.

It calls for:
5.5 mm x 190 mm and 5.5 mm x 350 mm fuel lines for the K3 & K4.  Which is 7.5 in. and 13.77 in. long, respectively.

My old fuel 1/4" lines measured out 6-3/4" and 17-1/4".  My old long 5.5 mm fuel line measured 15" long.  They may be longer to allow the tank to be lifted in aiding fuel line removal.

[andy750]

Andy, I see that your line didn't come off the petcock nipple.  Sometimes it is better to cut it off.  Did it break off or slip out of the petcock?  If it slipped out, You should be able to Loctitie it in place.  If it broke off, new petcock (Honda or Pingel?) or make a new nipple to replace old one after drilling out the remants?

The petcock was brand new. The nipples would occasionally slip out of the petcock and get stuck in the fuel line as the photo shows. I just press fit back in when reconnecting the fuel tank. No problems so far but I may loctite in the future as you suggest. Thanks.

Good info from you on the fuel line!

cheers
Andy

[rangelov]

Andy,

THANK YOU!

Without your photos, I wouldn't have been able to find what I was doing wrong.

[Big Cobra]

get an aftermarket fuel filter...they have some that bend at a 135 degrees or more sometimes...fit it where the fuel line kinks