Topic: 1978 CB750 GAS TANK AND CARB CLEANOUT QUESTIONS

[TimK]

Hello All,
I'm working on a 78 CB750 that was parked with a full tank of gas ... about 25 years ago!!!

The tank and carbs were a mess. 

I filled the tank with 5 gal of white 5% vinegar (supermarket quality - 3 gal for $5.) for a couple days ... and flushed it and repeated; twice.  Its pretty clean.  But, its not clean.  So I was going POR it.  Is that what you guys use?  POR is an epoxy coating.  The kit comes with a can of degreaser, a can of metal prep which  I think is muriatic acid and the two part epoxy.  Its a nasty job.  What are you guys using?

I disassembled and cleaned the carbs with vinegar, toothbrush, carb cleaner and then a bit of muriatic acid ... which works pretty darn quick.  I have one passageway that is clogged pretty badly so just wondering if anyone what the purpose was of the passageway.  (I dont have the book).
Here is a photo which I downloaded from the site (thanks KB02) and marked up.
It looks like the passage way runs from this tube which sucks gas and moves it through the passageway to the carb body tube.

Any tips on cleaning?

Thanks much
Tim

[calj737]

EvapoRust works well too. Or "The Works" toilet bowl cleaner. Clean it thoroughly this time and never look back. If after you de-rust it, lining may no t be necessary, but many opt for it. And yes, POR-15 is a very good product.

[flybox1]

For the tank, I prefer to use Kleen strip prep-n-etch.
A few hours and it should be nicely coated with phosphorus.

Try some small dia. wire, carb cleaner spray, and compressed air to clear out the passageway.

[harisuluv]

The first picture is the slow jet.  You should remove them to clean them.  They are pressed in, no screwing in.  You need to grip them with something firmly and then gently remove them.  If you use vise grips something to buffer metal to metal contact is recommended.

The nozzles in the second picture are the accelerator pump nozzles.  The two are not related.  Each nozzle squirts gas immediately to give you more immediate throttle response.  It's easiest to clean them by shooting carb cleaner/compressed air from the nozzle hole (points inward and is hard to access).  Then to verify that it is clean, it is easiest to shoot carb cleaner from the reverse end (those 3 tubes with clips between each carb) and watch for it to come out the nozzle.

For carbs 2 and 3, there are double nipples where the tube attaches, so you will need to hold one closed with a finger.  In addition, $2 has a hole that leads to the float bowl/accel pump circuit so you would need to hold that closed also to test it.

[TimK]

Thank you guys ... for the ideas.

CalJ ... i never heard of evaporust or "the works".  When I get notice of a product like this no matter what, I always look at the national safety data sheet.  It lists the mixture - carb cleaner for example is just acetone.  Thanks I'll check them out.

Flybox ... that's exactly what I've been doing ... on my running bike, i could disassemble the carbs every spring ... and clean them with carb cleaner and blow them out and it was good to go.  This one was sitting with gas in it for 25 years and its like a cement.  I hammered the wire end a little to form an edge on it like a screwdriver and twisted it town to cut through ... and there is tan powder.  But, it ain't happening.  I can go down fairly far with the wire (photo1) but not to the bottom; and i can get in all the way from the tube on the intake side.  it seems like its clogged right in that area where it jogs.  I'm reluctant to pull that pin out.

harisuluv:  ... thanks.  that pin is a slow jet?  I thought it was just a tube going down to the low part of the fuel bowl so it could suck gas from the bottom.  Like I said above, I'm reluctant to pull that out because ... because nothing seems to go right the first time you do anything.  :-) 

I thought the two nozzels were independent.  I marked that photo #2 wrong.  The nozzel that is NOT centered (off to the side a bit) seems to run all the way back to the "jog" and then up the tube.  BUT, if i blow air into that nozzel, it blows out like you said to somewhere.  I didnt take those little short fuel lines that run between the carbs off.  But, It seems like it came out that hose.  The center nozzel ran somewhere and I guess that one goes to the accelerator pump.  That seems to be clear.

Thanks for the information guys. 

http://forums.sohc4.net/index.php?topic=106060.0
I searched and found this link ... thanks again for the "breadcrumbs".

Tim

[TimK]

OK, so this why it has to come out. 
Thank you.

[TimK]

Well, ... I soaked them in carb cleaner (acetone) for a couple days and then just blew them out.  I dont know what the diameter of the hole is but the tiny-est wire I had was way too huge ... hence the extended soak.

Thanks guys.

[calj737]

Many use a guitar E-string.

[TimK]

Thanks Calj
I used to play guitar and as I recalled, there were several kinds of e-strings.
Maybe it doesn't mean a darn thing in a practical sense but ...

[70CB750]

My K0 tank had basically varnish in it when it came to me.  Same as yours, somebody let the gas in there completely evaporate.

I used gallon of Purple Power, it took some effort but the tank cleaned eventually.  I never bothered with inner coating, it can cause problems down the road.  The best way imho is just to keep the tank full and ride the bike year around.

[TimK]

Hello 70CB,
I googled purple power and every hit came up ... as a "degreaser".  I didnt see anything that said  de-ruster.  I searched for the NSDS (national safety data sheet) and I actually couldn't find a sheet that described the contents.  I dont know.

Question for you ... did you add some kind of a gas line filter. 

I flushed the tank at least 10 times and I still get a residue.  The pieces are getting smaller like this stuff in the bucket but based on that idle jet hole ... any kind of anything is going to clog that thing up.  I guess I have to find a filter that filters down to maybe what half the size of the idle jet hole.   

[70CB750]

I used it based on recommendation I found somewhere on the internet, it was before I joined this forum.  It helped with the honey like dried out gasoline in the tank, which was my biggest problem.

Some people use in line filters, I tried but I could never fit them in well enough between the tank and carburetors.  That said, from my experience the stock petcock with sediment bowl works well enough to filter the fuel.

The fuel filters I tried were from TSC meant for lawn mowers, you may want to look at those.

[calj737]

Tim - pick an E strong you like, 9/10 will work. Perhaps you have an old strand lying about?

As for the rust particles coming out of your tank, you need to rid your tank of that as it will find it's way into your carbs. Some, use EvapoRust, some vinegar solutions, others electrolysis setups to de-rust completely. You can install a liner from Caswell, POR-15 or RedKote to treat the tank and encapsulate the rust if you wish. But deal with the rust now or suffer always.

[Tews19]

What are you using to rinse the tank out? There is no need to use anything but vinegar when cleaning. I use my pressure washer to then "rinse" the tank out. This will remove all the gunk. Of course once all the debris is out you want to pour in baking soda in and fill with water to prevent flash rusting then "rinse" again until water is clear.

[TimK]

Thank you again for the replies ...

I filled that tank with vinegar for a couple days and then dumped it/strained it.  I flushed the tank with a garden hose meaning I filled the tank to the rim with water and put a 1/4" air hose in attached to a trigger attached to a 1/2" air hose connected to my compressor at 90psi.  I covered the filler with a rag and when I hit the trigger on the air hose ... that thing percolated like I cant even describe.  So, the hose was still running and I let it percolate with the airhose to create some kind of urgency in the tank.  After a minute or so, I turned the tank upside down and shook it and shook it and all kinds of scale came out.  Then I refilled and repeated a few times until I didnt get any scale out.  Then I put the vinegar back it ... and repeated the whole thing.  I didnt flush with baking soda because it still had some discoloration and yeah ... the scale started forming again.  It wipes off. 

The thing that I dont get is how to get all of it out.  I thought maybe I would fill the tank and turn it upside down and keep the hose pointed up into the tank and then maybe that stuff would flow over that big lip in the tank.  The 78 tank has a door and the cap is reset down into the tank.  So, its difficult to get all the stuff out.

So, I'm using a "poor man's pressure washer".  But that stuff doesnt flow over the lip of the tank and out the cap.

When you guys gave me that info on removing the idle jets, I was on that for a couple days.  I can reassemble the carbs now and then get back to the tank.

Thanks

[Tews19]

The yard hose won't get it all out. If you do not have access to a pressure washer I would go to a car wash and use theirs. Have someone there with you to hold the tank. Bring a mat or towel to place tank on when doing this.

The baking soda is actually the end process. Once all rust and gunk is clear you then add the baking soda and fill to brim. Let soak a bit then pressure wash again to clean out all remaining residue.

Then use an air compressor to get the remaining water out. Then fill with gas.

[TimK]

Thanks Tews
Yeah, I'll do that.  I thought the commercial car wash pressure washer would create a bunch of urgency inside the tank and break up all the scale.

But what I don't get is how to make sure all the particles flow out of the tank (because of that lip in the tank).  If I flip it upside down and shake ... it doesn't make it out.  Most of it came out but not all of it.  If I turn the tank upside down and pressure wash, maybe all that movement of water in the tank might get it to flow out.  Or maybe a water vac.

Thanks again for the reply.  It's nice to know somebody did it.  This tank was pretty bad - like I said it was parked 25 years ago with a full tank of gas.

[calj737]

Flush it thru the petcock, but remove the petcock first and any internal filter. If it's that bad, you may prefer to line it using Caswell or equivalent that will cover and seal the rust behind it.

[Tews19]

Remove the petcock when you use the pressure washer. Let it drain from the bottom. You will never get everything but you should get just about all of it. I think I posted a video of the before and after using this method.

[TimK]

I shook the tank upside over the towel to see what would come out.
When I say scale, those big chips is what I'm talking about.
The tank is light years better than it was when I started but its not nearly good.
And the top of tank, you can that the gas cap is down under the lid.  Thats the lip.

[TimK]

I didn't think you could get that filter out.  Yeah, I took off the petcock but the filter is pressed in I thought.  Like I said, I don't have a book yet.  But, if the filter can be popped out, yeah, that would do the trick.

I really appreciate you taking the time to reply.

What's the catch phrase for Honda?  I know that Kawasaki used to be "let the good times roll".  Honda in the 60's used to be "you meet the nicest people on a Honda".  That works for me.

Thanks again.

[Stev-o]

If it's that bad, you may prefer to line it using Caswell or equivalent that will cover and seal the rust behind it.

Tank sounds like it is very rusty, consider lining it with the Caswell sealer to prevent future issues. 

[Tews19]

You filled up a bucket with rust? Wow that is really bad. Was there a liner in there already? I've had some really bad tanks and never that much rust .

[TimK]

Actually, I couldnt the other photo.  There was 2 of those white containers ... AND all that stuff on the towel.

I'm not sure what that stuff is.  I thought a lot of it was a residue from the gas.  It was crusty and oily and flakey.  the tank seems sturdy.

But, yeah ... there sure was a ton of it in there.

[Stev-o]

You pulled 2 quarts out of that tank? That's an incredible amount!

[TimK]

Here are couple more photos; float bowl varnish, gas tank (first peek), master cylinder (it was like an oily sawdust).

It was gummed up pretty good.  I dropped the master cyl into a container of vinegar and it cleaned up to some degree.  I need to find c-clip pliars and pull the clip and check the piston, seals and bore.  Maybe it will be serviceable.

[Vinhead1957]

You have your work cut out for you. May consider a new tank

[lucky]

Thank you guys ... for the ideas.

CalJ ... i never heard of evaporust or "the works".  When I get notice of a product like this no matter what, I always look at the national safety data sheet.  It lists the mixture - carb cleaner for example is just acetone.  Thanks I'll check them out.

Flybox ... that's exactly what I've been doing ... on my running bike, i could disassemble the carbs every spring ... and clean them with carb cleaner and blow them out and it was good to go.  This one was sitting with gas in it for 25 years and its like a cement.  I hammered the wire end a little to form an edge on it like a screwdriver and twisted it town to cut through ... and there is tan powder.  But, it ain't happening.  I can go down fairly far with the wire (photo1) but not to the bottom; and i can get in all the way from the tube on the intake side.  it seems like its clogged right in that area where it jogs.  I'm reluctant to pull that pin out.

harisuluv:  ... thanks.  that pin is a slow jet?  I thought it was just a tube going down to the low part of the fuel bowl so it could suck gas from the bottom.  Like I said above, I'm reluctant to pull that out because ... because nothing seems to go right the first time you do anything.  :-) 

I thought the two nozzels were independent.  I marked that photo #2 wrong.  The nozzel that is NOT centered (off to the side a bit) seems to run all the way back to the "jog" and then up the tube.  BUT, if i blow air into that nozzel, it blows out like you said to somewhere.  I didnt take those little short fuel lines that run between the carbs off.  But, It seems like it came out that hose.  The center nozzel ran somewhere and I guess that one goes to the accelerator pump.  That seems to be clear.

Thanks for the information guys. 

http://forums.sohc4.net/index.php?topic=106060.0
I searched and found this link ... thanks again for the "breadcrumbs".

Tim

The stock idle jet is only .013 thousandths. A paper clip will not work. It will damage the jet.
You can use a #10(.010) electric guitar string and those can be purchased separately at a music store. Then use carb spray and compressed air. Make sure that you can hold them up to the daylight and wee the hole is open.

[TimK]

Thanks Lucky for the number.  I was looking for that and couldn't find it anywhere.  Yeah, I posted a photo of cleaned jet (above on page 1).

I pulled the filter using a 3/8-16 tap.  I only had to grip it with a pair of needle nose pliers so it didn't take a lot to get it out.  Just rocked it a liitle and it came right out.