Topic: My story about carb cleaning and cylinder 1 not firing, and soda blasting.

[catsoup]

I just wanted to share a story about the work I've done on my bike over the past two days. Most of the frustration was caused by my own ignorance and/or error, so this ended up being a learning experience. Basically I was trying to fix a carb leak, and made the situation worse, though I eventually resolved all issues, and I'm back on the road.

background: 1978 CB750F, which I've owned for a few years now, it was my first motorcycle, and I learned everything bike-specific I know about maintenance by working on this bike. I try to keep it in good shape, and only really fail at this when I am introduced to something I was previously ignorant to.

So I parked it for a few weeks while I was traveling out west by car, leaving it in a heated shop, didn't think it would end up being as long as it was. Return and carb 2 and 3 are leaking a bit, so I figure, now is as good a time as any to clean/adjust. I take the carbs off, and they dont look terrible, but I notice my float heights aren't all that consistent, and there is definitely some gas gunk. proceed to strip them and soda blast / carb cleaner / rinse / compressed air everything. Put them back on the bike, and turn the gas on.

Gas pouring out of 2,3,4 carbs. problem has escalated. I remove carbs again and take the float bowls off. Find about a 1/4 teaspoon of baking soda sludge in each one. I must have done an absolutely pathetic job rinsing them, or neglected some area of them entirely. (I have soda blasted these, and other carbs, a number of times without ever messing it up, so I really don't know what I did here) So I strip them again and rinse them really, really well. Put them back on the bike, and they are okay, except now cylinder 1 is not firing.

I do the million steps of diagnostics that don't require taking the carbs off for the third time. Verified plugs, wires etc. The float bowl is filling with gas, but the plug comes out dry, so I figure it is probably the slow jet, which I have always been wary of. The slow jet on these carbs is pressed in, so it was not one of the pieces I removed when cleaning, removing that kind of thing makes me a little nervous of damaging it or never getting it back in. I try the guitar string through the jet from the carb bowl access, I try it through the air mixture screw, I try it through the air line at the filter side, I try it from the top after removing the slide. No go, so I take the carbs off again, and get up the nerve to pull the slow jet. Which was totally fine, and not hard at all. As expected, it was gross, covered in black gunk and some baking soda. (I didn't remove these the other times I have cleaned the carbs, so they had probably never been removed) I decided to take all four out, since the carbs were already off, and clean them all. They went back in nice and easy, and when I put them back on all four cylinders worked flawlessly. Adjusted the valves, cam tension, and synched them up and Im back on the road.

Morals of the story:
do not be afraid of removing pressed in jets
carbs require a level of cleaning that is higher than the eye can judge.
removing carbs does actually get easier every time.

Anyway I hope someone having this problem finds this thread and is saved some time and aggravation.

[Bru-tom]

thanks for that hahaha,sounds like you have had a fun few days! glad its sorted now!

im in the process of doing the exact same thing. tomorrow i soda blast. i have stripped everything off and out of them. the only thing i never removed was the needle channel that is pressed in.

 how far did you strip yours?

[TwoTired]

Very nice post.  And, very good morals!

Puts, in a nutshell, what several much longer threads encounter and their conclusion.  And, cudos for your methodical (if not thorough at the start) completion of the repair.

About the only thing missing is the accelerator pump operation and performance for the PD carbs of this era.
How's the response from idle to snap open throttle under load, any gear?

Cheers,

[TwoTired]

i have stripped everything off and out of them. the only thing i never removed was the needle channel that is pressed in.

If you are talking about the mains emulsion tube under the main jet, it is not pressed in (probably just stuck), and it is a mistake not to push them out and verify they are clean.  Just be careful not to damage the needle jet orifice shape. 
This would apply to the early CB500-550 carbs, not any of the CB750 Carbs, including the 78 F carbs that catsoup has.

[Bru-tom]

If you are talking about the mains emulsion tube under the main jet, it is not pressed in (probably just stuck), and it is a mistake not to push them out and verify they are clean.  Just be careful not to damage the needle jet orifice shape. 
This would apply to the early CB500-550 carbs, not any of the CB750 Carbs, including the 78 F carbs that catsoup has.

TT to the rescue once again  i read that they get pushed out from the bottom towards the top of the carb? do i need to remove them really, i mean, i can see very much clearly straight down its throat its so stripped.

[TwoTired]

If you are talking about the mains emulsion tube under the main jet, it is not pressed in (probably just stuck), and it is a mistake not to push them out and verify they are clean.  Just be careful not to damage the needle jet orifice shape. 
This would apply to the early CB500-550 carbs, not any of the CB750 Carbs, including the 78 F carbs that catsoup has.

TT to the rescue once again  i read that they get pushed out from the bottom towards the top of the carb? do i need to remove them really, i mean, i can see very much clearly straight down its throat its so stripped.

They get pushed out TOWARD the bottom, where the main jet was.  When they get gunked up, it's where you can't see when assembled  It's a perforated brass tube.

Cheers,

[Bru-tom]

ah, so the chances are not great at getting them out without maybe damaging them. i almost broke the mains trying to get them out but i managed, will replace all orings and things once i get a chance to head down to industrial oring supplier

[Bru-tom]

no chance they are coming out. they are stuck stuck. i used a plastic rod not too hard to damage the needle entering section and there is no movement whatsoever. these carbs were full of old fuel varnish before i cleaned them, and i mean full

[catsoup]

Very nice post.  And, very good morals!

Puts, in a nutshell, what several much longer threads encounter and their conclusion.  And, cudos for your methodical (if not thorough at the start) completion of the repair.

About the only thing missing is the accelerator pump operation and performance for the PD carbs of this era.
How's the response from idle to snap open throttle under load, any gear?

Cheers,

The accelerator pump actually gave me some trouble initially as well. I took it apart and cleaned everything, but when I was reassembling, I put the spring above the diaphragm, rather than below (where it belongs). The way the piece is designed, it looks like the spring belongs above as it fits very nicely into the little metal ring. I noticed when it was assembled that the adjustment range was waaay out of whack, so i took another look at the diagram in the manual and realized my error.

The response is very good, very smooth, though it was running fairly rich on my initial test drive.

@Bru-tom
I stripped everything other than the slow jets initially. Without breaking them down from the rack into individual units.
floats/needles, main jet and aerator, air screw, slide and linkage and needle.

Removing the slides and needle is far less trouble than it seems at first glance, it opens up the carbs for cleaning, and understanding where each orifice/tube ends up.

My main jets have bolt heads and are very clearly threaded in. no problems removing them whatsoever.
Not sure what you are working with, but this page helps with the basics. http://www.salocal.com/sohc/tech/carb/dspg_mgs/rmvjts.htm

[TwoTired]

Bru,
The varnish is what is causing the sticking.  Are the slides removed?  This would get the needle out of the way, so you can use a plastic (delrin) or wood dowel to knock them loose.
Wouldn't hurt to spray/soak with carb cleaner beforehand.
Even heating the body with a heat gun would probably help.

Cheers,

[Bru-tom]

no chance they are coming out. they are stuck stuck. i used a plastic rod not too hard to damage the needle entering section and there is no movement whatsoever. these carbs were full of old fuel varnish before i cleaned them, and i mean full

i lied! i got them out!!! the little lip that acts as a stopper to not allow then to protrude too far into the carb throat was totally gummed up with sand, varnish and and and, they are pretty well blocked up! the little holes that is! stocked i got them out try and try again huh i shoved a piece of nylon in the carb throat and rested it on the top of the tube, from the needle side i put another piece of nylon on top of the other and whacked! dislodges them all, the one needed extra persuasion though

going to post some pics quick...

[Bru-tom]

@Bru-tom
I stripped everything other than the slow jets initially. Without breaking them down from the rack into individual units.
floats/needles, main jet and aerator, air screw, slide and linkage and needle.

Removing the slides and needle is far less trouble than it seems at first glance, it opens up the carbs for cleaning, and understanding where each orifice/tube ends up.

My main jets have bolt heads and are very clearly threaded in. no problems removing them whatsoever.
Not sure what you are working with, but this page helps with the basics.

yeah man, thanks for that. mine are the cr 550 jobbies. the slides and and are easy enough to remove once the carbs are split though

[Bru-tom]

i dont think my carbs could get anymore stripped:















@ catsoup...did you treat the newly blasted carbs with anything to prevent them from that white corrosion powder that forms?

[catsoup]

My cleaning process was a combination of the initial soda blasting, steel wool and elbow grease on the brass parts, and carb cleaner on almost everything. because I didn't separate the carbs, there was still a good deal of rubber hose and other parts preventing me from dipping the whole thing in the can of cleaner, so I used dental tools, q-tips and wire probes. Also lots of compressed air.

I don't know if there is any real treatment you could do, I doubt it. Make sure you rinse, and then blow out anything you sodablast REALLY well. Also, Its good to have a _clean_ cloth with you for final reassembly to wipe everything down before it goes back in.

[Bru-tom]

yeah, it is a real pain to strip them all the way down as i did, but from the looks of things its a must, its not like my bike it together, its in pieces too

rinse them off with what? water? im thinking of blocking some holes to prevent any soda from entering, i mean, there are some places soda cant clean, so why allow the stuff to get in if you know what i mean...

do you have any pics?

[catsoup]

I didnt take any photos, I was expecting this to be a three hour job, not a three day job.

Rinse with water, lots of water and compressed air. Best way to get the soda out.

The only thing I would say about blocking holes off is that, say you block off the fuel line in one place but miss a connection in another place, you now have a dead end tunnel for the soda to get in, which will be significantly more difficult to rinse/blow out. I think this is what I did with the airscrew/slow jet, as they connect at right angles internally. Taking a look at http://forums.sohc4.net/index.php?topic=109258.0 might give you a better idea of areas you will have to pay particular attention to when cleaning. (hint, it's everywhere)

[Bru-tom]

thanks mate...
i cleaned my carbs off yesterday with thinners, i did a great job and there were no more rubber bits so i assumed it was fine.

now there is some very slight corrosion on the outside, like a fine white powder, id like to prevent this from happening after iv blasted them

[harisuluv]

That white residue can be dealt with. I experienced it before when I first started soda blasting.  First off, I learned you absolutely need the right type of soda. By this I mean you want to get the finer grade soda not the "XL" which is a large size particle and seems to be more prone to leaving white residue behind that is just tiny obliterated soda particles that break up. Get the small grit.

You need to have some kind of air filtration system.  That white residue you get after rinsing off comes from contact with water. If done properly you should never have to rinse off your carbs. This also means you need to be wary of blasting wet or oily carbs in the first place cause it will stick to it.  I use an air dryer and it was expensive (around 200 with an extra filter) and it was a total change in the blasting experience. Any little dinky cheap filter just isn't going to work and is going to cause you heartache. You need dry medium, period.



If your parts are clean enough for the parts to blast off without soda sticking and you have clean dry air, you will not get any residue. Do not rinse them off, you will only cause corrosion. Even brake clean will cause it. Use your dry air to blow out every passage and you're done.

[Bru-tom]

thank you very much for sharing!

i cleaned them off with petrol initially and read somewhere that someone used thinners, so i did that too. It did clean them off nicely. they are super clean now, inside and out, they just need that nice soda blasted finish now. so i shouldn't rinse them off in anything after blasting, as long as they were bone dry before is started?

woah, those are b-e-a-utiful!!!!

i am going to be using the compressor at work, and the cheap way of blasting:

http://www.aircooledtech.com/tools-on-the-cheap/soda_blaster/

so no special filter for me.

[harisuluv]

They don't have to be bone dry before blasting, it depends on what you are starting with.  Some things like caked on hardened stuff you can blast off, but if it is flexible it can bounce off or if it's grease like the soda will stick.  It's something you will have to get a feel for.  If I am dealing with a really really nasty set that I know is going to be more work blasting than usual I might try and hit them with a little brake clean first.  It will remove a lot of it and it dries fast so you don't have to worry about that.

Anyways, that's how I do all my carbs and it has worked for me, you have any other questions let me know.  You can check out some carbs I've done in my sig.

[Bru-tom]

thanks mate. i have been through your thread already fantastic work! iv got to settle with little old me to do mine! hahaha

well, mine are dry and clean, just worried about the slight corrosion in the airflow tube where the butterfly is.... in the big round hole here,



can i blast there?

[harisuluv]

I do, in fact I make sure to hit all the holes.  Even the little float bowl air vents.  The hole is really small on the float bowl side but once it is clean it will blast all the way through to the other end.  Like I said, just make sure you blow out all the passages afterwards, I usually feel with my hand to confirm that I'm getting out the other end.

I am not too familiar with that setup.  You might getting some residue from that powder.  I imagine it is more fine than specifically purposed baking soda for blasting.  Seems like it would kinda cake up, especially with moisture in the line.  You don't have more than a set to do so you might get by with it, I can't attest to the method though.  I would make sure I at least did it on a somewhat warmer day with no humidity.