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'86 450 Carb to engine hoses

11K views 17 replies 13 participants last post by  JGarrison 
#1 ·
So I have recently inherited an '86 450 from my step-mom when she passed away. The bike had sat for about 6-7 years due to a flat tire and laziness rather than mechanical issues. After a few hours into coating the leaky gas tank, a new battery, and [possible unnecessary] rebuilding the carbs, it started up like a champ and runs pretty solid. I personally never saw this bike run until recently.

My issue right now aside from getting the lights working properly and speedometer cable replaced is the hoses are not quite correct. I have them leading from the right carb to the right cylinder, but the entry to the left cylinder is plugged with no hose leading to it. Like I said, the bike runs decent but I imagine it would be better with those hooked up properly.

My question here is if anyone would be able to supply pictures or a diagram of how the hoses should be connected? My boyfriend and I are college students who don't have the funds to get the manual at the time being. We're trying to get this running to cut down cost of gas, while also doing most of the work ourselves.

Thanks in advance.
 
#2 ·
I recently acquired a 450 too. I'm still learning about it, brand new animal for me. I took pictures of my carb, it seems like it's stock. I compared it against the maintenance manual and they seem to correspond.
 

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#3 ·
Zombiijins, you may want to check your local library or the university system for a service manual that you can check out. It maybe in paper or ebook form. They are available in my state. If you can't find it, ask a librarian for help in getting one requested. I hope you enjoy the new ride.
 
#5 ·
There is a vacuum line (hose) from the top of the places where the fuel-air mix enters the engine. It's a 1/4 inch black hose. The one on the right side feeds into 2 lines and each then goes to the right side of each carburetor. The one on the left is very short and goes to a vacuum shut off on the fuel valve (petcock). That petcock can leak and is often replaced with one that does not have a vacuum shut-off, so the small tube sticking up on the left air-fuel intake point is plugged or capped, as it is not needed and may leak. That sounds like your situation. If it is, you have nothing to worry about.

Look at the photos posted by Guba. The first picture is the left carb, and the small hose I'm talking about is at the upper left of the photo. Just above and to the right of that hose is the bottom of the fuel petcock. If that hose is gone and the metal tube there is plugged, then someone has replaced the petcock with one that does not need the vacuum to operate. It's all good.
 
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#8 ·
Hi,

I ordered a CMX250 petcock to replace the original on my 450.

While the internal fuel filter and the mounting nut are the same as the original for the 450, the fuel line barb is SIGNIFICANTLY smaller in diameter to where a 1/4 I.D. Fuel line will not compress to give a leak free seal.

WTH?

I am running 5/16 fuel line (the barb at the T for the carbs is sized for a 5/16, not a 1/4 in, I am using an additional fuel filter that fits either 1/4 or 5/16 fuel line, and the original petcock fuel barb will fit either 1/4 or 5/16.

But a new 250 petcock, or at least the one I got off of eBay, has too small a fuel barb for a CMX450.

Anyone here that has actually purchased a CMX 250 petcock and compared it to the original 450 petcock?

Thanks,

Joe
 
#10 ·
Yes I have a 250 petcock on my 450 , I used a 5/16 hose with good fuel line camp to secure it to the petcock
 
#11 ·
wjmrty,

These are the I.D. measurements of the CMX450 and the supposed CMX250 petcock fuel outlets. Just over half of the 450 petcock outlet.

Would you or could you measure yours to see if it the same as the 450 or if it is the same as the 250 one that I just purchased?

In addition to fuel leaking because of a loose hose, I am also leary of there not being enough fuel flow for highway speed driving.

Thanks, Joe
 
#13 ·
In addition to fuel leaking because of a loose hose, I am also leary of there not being enough fuel flow for highway speed driving.

Thanks, Joe
I find it interesting that the standard measure of vehicle efficiency (mpg) simplifies to a 2 dimensional measure. Miles is length, gallons is volume or length*length*length, so the units are length divided by length^3 = 1/length^2. If you take the inverse of that it's gallons per mile, a small number. The interesting part is that the units simplify to length^2 (a 2 dimensional measure).

To put some numbers to it, say a CMX450 gets 60 mpg. That's also 0.0167 gallons / mile. A gallon is 0.133681 ft3. A mile is 5280 feet.


If my math is correct, 0.0167 gallons / mile = 0.039 mm^2


Why does that matter?

If you visualize the amount of gas you are burning as you drive down the road, in this case it would be a continuous squirt of gas 0.22 mm in diameter flowing at a velocity equal to the speed of the bike.

Of course, the mpg is an average and the size of the squirt will vary - but even if you were getting 10 mpg, the squirt would be 1 mm in diameter roughly.

So Joe, I don't think you need to worry about the size of the fuel line too much.
 
#15 ·
I use the 250 too.

You need a hose clamp, the kind that tightens and loosens via screw to secure the larger line to the petcock. They make hose clamps small enough.

As you see there are a lot of factors that go into suffficient fuel flow, but you will have enough to power the 450 through any situation.

Clamp it up (cap that open cylinder too) and get rolling!
 
#16 ·
Or you can switch to 1/4" fuel line to fit from the 250 petcock to the 1/4" inlet of your inline fuel filter. Then everything fits correctly with no leaks.

And before you ask, yes the 1/4" fuel line will supply way more gas than you can burn, by at least an order of magnitude.
 
#17 ·
I tried using a 1/4" fuel line from the petcock to the inline filter, it is the 1/4" line that is too big for the new petcock fuel barb.

I wanted to use the original fuel clamp but it just cannot clamp tight enough to securely seal the connection.

I have the screw type clamp, I will try it and see if it will provide a secure leak-free connection.

It may also be the type of 1/4 fuel line I just purchased, as it has a shiny outer coating, is very thick and not very flexible.

I am currently letting the tank air out after washing it out with acetone prior to using Caswell Epoxy.

I did get the magnet that came loose from my retrieval claw while cleaning rust out of the tank.

I used a compass to find the location of the magnet, then used a hard drive magnet (very strong) and with that magnet wrapped in a paper towel, I used the exterior magnet to move the interior magnet into a position where I could then use a magnetic retrieval tool to pull the lost magnet out of the tank.


Thanks for the help with volumetrics, once I get it running I will see what the plugs look like after a couple of 85mph stretches.

Joe
 
#18 ·
Ding dong darn

Yep screw/band clamp with a normal diameter 1/4 ID fuel line does seal.

Fueled 'er up, cranked until it started and it runs.

Unfortunately I installed the throttle cables backwards, so yes the tank comes back off and the carbs have to be partially removed.

Doggone it.
 
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