Author Topic: Repair method for cracked mainjet casting on carb.  (Read 1550 times)

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Offline Gonzowerke

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Repair method for cracked mainjet casting on carb.
« on: April 13, 2011, 04:19:22 pm »

Here is a list of the parts you will need:

   1. .45 cal spent casing
   2. old style carb, with splitting at main jet holder
   3. metal cutting tool (hacksaw)
   4. small, fine round file
   5. a tube with about 3/8" ID and 1/2" OD thats about an inch long, used as a shell driver.
Step 1: clean the carb on the tower where the main jet holder goes in.
Step 2: retrieve the spent casing and take it in your shop/garage
Step 3: cut the primer section off the casing leaving about 9/16".
Step 4: pinch all the cracked pieces down on the tip of the main jet tower and gently get your main jet holder nut started.
Step 5: slide and then gently tap the shell casing down onto the main jet holder tower with the spacer tube until it is tight.
Step 6: tighten main jet holder, reinstall main  jet, reassemble carb.
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Offline lucky

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Re: Repair method for cracked mainjet casting on carb.
« Reply #1 on: March 24, 2012, 12:16:04 pm »
Needs a photo or two.
I like the method but I would not use a brass tube because of the great corrosion potential of brass and aluminum together. I would use a small piece of aluminum tubing.

Good idea though!
« Last Edit: April 04, 2012, 10:17:23 am by lucky »

Offline dave500

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Re: Repair method for cracked mainjet casting on carb.
« Reply #2 on: April 05, 2012, 11:29:26 pm »
all the jets/float hinge are brass anyway?

Offline mono

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Re: Repair method for cracked mainjet casting on carb.
« Reply #3 on: April 24, 2012, 12:06:41 pm »
not trying to split hairs since it is better to be safe than sorry, but brass is quite a bit harder than aluminum.  i'd worry about transfer of aluminum --> brass, but not the other way.

however, that being said, doing everything you can to prevent cross-contamination on metals is a VERY good practice to be in anyways, especially when it comes to your sanding/polishing wheels.

I'll shut up now.

Offline Cvalero

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Re: Repair method for cracked mainjet casting on carb.
« Reply #4 on: April 24, 2012, 01:38:14 pm »
The amount of corrosion for dissimilar methods is based upon the electropotential of the metal.  These is some flow of electrons between any two different metals (anode and cathode).  The smaller the difference the better.  The electropotential difference between aluminum and brass is between 400 and 500 mV.  Anything under 300 is considered essentially neutral.
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Offline mono

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Re: Repair method for cracked mainjet casting on carb.
« Reply #5 on: April 25, 2012, 07:38:58 am »
SCIENCE!  :)

Offline lucky

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Re: Repair method for cracked mainjet casting on carb.
« Reply #6 on: June 08, 2012, 12:10:23 pm »
all the jets/float hinge are brass anyway?

Yes that is true.
 That is why when you see carbs with all brass floats many of them have extensive corrosion. Honda went to the plastic floats to keep the weight down.
But ethanol fuels are new to the game and the moisture absorbing properties of the ethanol fuel do not help as far as the corrosion.

On my 1969  Honda CB750 carbs the screws for the vacuum ports were aluminum.
The mixture screws were steel NOT brass. Aluminum has less corrosion potential with steel than with brass.

As the production increased, the brass was was easier to machine than steel.

But the bass pin in the float and the float tab is brass. That is good because those parts are subject to dry and wet cycles. Steel would have corroded badly  like those steel spring clips that held some of the jets on some models.