The Smoke Pit: Stripping an 80's 2-stroke carb.

[Ducked]

Stripping a very gunged-up Mikuni carburettor, off a neglected 133cc Yahamaha RZR 2-stroke. Despite its sorry state, its a welcome relief from the concurrent issues with the "snakepit" 1986 Aisan on my Daihatsu car, because its comparatively SIMPLE.

One thing's bothering me though. I want to put the needle to soak in carb cleaner, but I can't get the rubber/plastic (?) depth stop (?) off, and I don't really want to expose it to carb cleaner long term.

I also can't offhand see how its supposed to work. There are rings on the top of the needle that a little C-washer locates in. I THINK they are supposed to provide an adjustable depth stop for tuning, BUT in fact the depth seems to be fixed by the rubber/plastic thing, which won't move, so it looks like they only affect the spring loading on the needle.

Pictures hopefully tell the story.

A : Dirty carburettor



B: Driving the float pin out. I embedded the carb (which is an awkward shape to hold) in potters clay in a plastic bag for hammering (my idea). I'd guess "silly putty", wet cornflour, (hippy mis-spent youth givaway) or concrete would also work, but it was still stubborn and I ended up using a spring loaded centre-punch (not my idea, and a good one).



C: Disassembled; Parts 1-5 L>R on the bottom row are the needle slider assembly.



D: The needle assembly



E Needle C-washer



I've removed the C-washer, but the rubber thing seems fixed on the needle.

Questions

(1) Is the rubber thing supposed to be removable? (I THINK it must be, because otherwise the depth isn't adjustable, but it does seem pretty firmly stuck.)

(2) If I can't remove it, is it likely to be OK if soaked in (3M) carb cleaner?

(3) Does the needle in fact have an adjustable depth stop?

PS. I had to empty a small whisky bottle to soak the parts in, so its possible things will be clearer after I sober up a bit.

 

[Smoky14]

1 It is removable, but I usually clean it by hand and leave it in place.
2 I would not, if I did I'd carefully measure the size as you will have to make a new one as the are un-obtainum.
3 Yes for mid range tuning

PS doubtful but possible

Smoky

 

[mk378]

My rule with carbs is do not take apart any more than is necessary to solve the problem. Routine "stripping" is likely to do more harm than good.

Usually if you have a no-start because fuel dried up in the carb during a period of non-use, the main and idle jets are simply clogged. All that is usually necessary is to remove the bowl and clean it out, and shoot spray through the jets.

 

[John_Conrad]

as mentioned you should be able to clean everything well enough to get it going without further tear down. i did one a couple summers ago on an early 80 4 stroke, similar but not quite....

you'll have to make sure the bike steers straight after the whiskey!

 

[Ducked]

Originally Posted By: mk378
My rule with carbs is do not take apart any more than is necessary to solve the problem. Routine "stripping" is likely to do more harm than good.

Usually if you have a no-start because fuel dried up in the carb during a period of non-use, the main and idle jets are simply clogged. All that is usually necessary is to remove the bowl and clean it out, and shoot spray through the jets.


You couldn't have shot anything through those jets, not even daylight. Have another look at the first picture.

After removal of the floats, I boiled the top and bottom with automatic washing powder, then cleaned them with a toothbrush and used brake fluid, then boiled them again.

Then I soaked them overnight with WD40

Then I removed the jets and they're now soaking in carb cleaner in a whisky bottle. Every now and then I rub the base of the whisky bottle on another one, which I've been told generates ultrasonics. Third go the float needle separated. It was firmly glued in earlier.

When the jets come out I'll clean them and the carb body some more with brake fluid and detergent, using a high pressure jet from a hypodermic syringe.

The above initial clean procedure is a bit drastic and could cause corrosion, but it does seem to work. I don't like spraying carb cleaner about, because it isn't very effective, and its unhealthy.

I've cleaned the tar off the needle using brake fluid, being careful to avoid getting it on the rubber stop (I hope). Don't like the look of the needle. Surface has some rough spots and I'm not convinced its perfectly straight. May try polishing it.

 

[Srt20]

I don't see the pilot jet anywhere. That needs to come out and be perfectly clean as well. Use a piece of metal wire or small drill bit to scrape the crud out.

 

[Ducked]

Originally Posted By: Smoky14
1 It is removable, but I usually clean it by hand and leave it in place.
2 I would not, if I did I'd carefully measure the size as you will have to make a new one as the are un-obtainum.
3 Yes for mid range tuning

PS doubtful but possible

Smoky


Thanks.

 

[Ducked]

Originally Posted By: Srt20
I don't see the pilot jet anywhere. That needs to come out and be perfectly clean as well. Use a piece of metal wire or small drill bit to scrape the crud out.


Fraid that's still in situ. Its VERY small and deeply recessed, (top hole in the first picture) so I've left it for now, though I can now see it. I may just try and blast it out rather than risk busting it by removal.

Scraping with a drillbit (I don't currently have any remotely small enough) would be an absolute last resort, but in extremis I might try a nylon bristle or very fine copper wire.

 

[mk378]

WD40 is ineffective to dissolve gasoline residue. You have to use something stronger.

Bristles from a wire brush can work to rod out clogged jets. Copper is too soft.

 

[Srt20]

Originally Posted By: Ducked
Originally Posted By: Srt20
I don't see the pilot jet anywhere. That needs to come out and be perfectly clean as well. Use a piece of metal wire or small drill bit to scrape the crud out.


Fraid that's still in situ. Its VERY small and deeply recessed, (top hole in the first picture) so I've left it for now, though I can now see it. I may just try and blast it out rather than risk busting it by removal.

Scraping with a drillbit (I don't currently have any remotely small enough) would be an absolute last resort, but in extremis I might try a nylon bristle or very fine copper wire.


The pilot jet has a hole through the center, but it also has holes on the sides. As dirty as the carb was, there is no doubt those side holes are plugged. If you want the engine to run properly, it really has to come out and be through cleaned.

Clean the top as best as you can, and use a good flat blade screwdriver. I have never seen a pilot jet I couldn't get out. It will come out.

A paperclip can be used to clean the pilot jet.

 

[Ducked]

Originally Posted By: mk378
WD40 is ineffective to dissolve gasoline residue. You have to use something stronger.

Bristles from a wire brush can work to rod out clogged jets. Copper is too soft.


The WD40 was deployed in its traditional role as a penetrant to lubricate threads before removing the main and float jets (pilot still to come).

For cleaning I use boiling laundry detergent, brake fluid, and carb cleaner, as above, the latter usually in small quantities for soaking in a sealed container. I might also try brake cleaner since I don't find it very useful for cleaning brakes.

Its a few years since I've done one of these, but in the past I've found gasoline residues are only part of the problem. There are usually also mineral (?) corrosion products (?) that carb cleaner won't touch. These require water-based cleaning.

For really badly clogged jets I've used an insulin syringe as a last-ish resort. These have a very fine needle.

 

[Ducked]

Originally Posted By: Srt20
Originally Posted By: Ducked
Originally Posted By: Srt20
I don't see the pilot jet anywhere. That needs to come out and be perfectly clean as well. Use a piece of metal wire or small drill bit to scrape the crud out.


Fraid that's still in situ. Its VERY small and deeply recessed, (top hole in the first picture) so I've left it for now, though I can now see it. I may just try and blast it out rather than risk busting it by removal.

Scraping with a drillbit (I don't currently have any remotely small enough) would be an absolute last resort, but in extremis I might try a nylon bristle or very fine copper wire.


The pilot jet has a hole through the center, but it also has holes on the sides. As dirty as the carb was, there is no doubt those side holes are plugged. If you want the engine to run properly, it really has to come out and be through cleaned.

Clean the top as best as you can, and use a good flat blade screwdriver. I have never seen a pilot jet I couldn't get out. It will come out.

A paperclip can be used to clean the pilot jet.


Yeh, think you're right (Except maybe about the paper clip. For this one it'd have to be a bloody small paper clip.) That bullet will have to be bitten.

I'll give it a bit more heat cycling first, though.

 

[Ducked]

Pilot (I assume that's what it is) is out. Picture shows it on removal. Still couldn't see daylight through it but its joined the others for a soak in the whisky bottle, so there are some hopes for an improvement.

There appears to be only one central hole.

The brass has a little square stamped on the side with a "thar she blows" symbol inside it, which I suppose means "jet". Next to it the number 17.5 is stamped.

 

[eljefino]

I use a bit set like this one on carbs. Mostly to open jets up "a touch" but also to clean them out. $6, you could find something locally or online.

 

[John_Conrad]

http://www.homedepot.com/p/Lincoln-Electric-Oxygen-Acetylene-Torch-Tip-Cleaner-Kit-KH575/100341101

 

[Ducked]

Originally Posted By: John_Conrad
http://www.homedepot.com/p/Lincoln-Electric-Oxygen-Acetylene-Torch-Tip-Cleaner-Kit-KH575/100341101


That's a good idea, and since its a specific industrial application, I might be able to find it here.

I still like the insulin syringe, though, because it combines a fine stainless steel needle with a pressure wash effect.

 

[Ducked]

Insulin syringe



I use these for small jets, since they have a very fine needle.

 

[Ducked]

A bigger syringe gives you more pressure though. I generally use a 10 ml with a screw-on needle, since otherwise they can blow off and spray alcohol/brake fluid/etc (and needles) about.

I generally use them with a sawn-off needle cover, so you can squirt with it but are less likely to inject yourself with brake fluid, which would be bad.



Variation on the theme this time: small jet cuts its own thread into the end of the needle cover for pressure washing.



I couldn't get the depth stop of the fuel metering needle so its still in the richest position. Didn't clean up very nice.

 

[andyd]

Is spray bomb carb cleaner available? Or go to a paint store and get a little toluene.

 

[Ducked]

Originally Posted By: andyd
Is spray bomb carb cleaner available? Or go to a paint store and get a little toluene.


You mean in an aerosol can? Sure, I have some 3M stuff.

It has its place, but I use it sparingly (usually in a whisky bottle, see above) because its ineffective on mineral/corrosion products, I don't like breathing it, and it can attack rubber components.

You can't use it with a hypodermic because it attacks the piston gasket.