Author Topic: Carb Diagram and Cleaning  (Read 19645 times)

Offline Summit670

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Carb Diagram and Cleaning
« on: January 14, 2012, 09:50:02 AM »
I searched, couldn't easily find so forgive me for asking again...

I saw a diagram some had posted last year which showed routing of the air and fuel passages in the carb body and I can't find it.

Not that I need it, but I want to pull my carbs off and apart and make sure all those little passages are clear.

Which ones can only be cleaned by solvent and air and which ones should I be able to thread a thin line thru, like fishing line?

The thing I would like to know too is if carb cleaner is blown in one hole, I assume it should come out another but which exact holes exit where?  That is where I think the diagram would help.


Also - when I cleaned the carbs a few years go I didn't have new Pilot Screw o-rings so I re-used them though they were dryed out.  Do you suppose this could cause hard starting and backfiring while trying to start?

Thanks.
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Offline George R. Young

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Re: Carb Diagram and Cleaning
« Reply #1 on: January 14, 2012, 02:19:27 PM »
Diagram:
http://web.ncf.ca/ag136/cvCarb.jpg

Cleaning procedure in our own FAQ
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Offline Steve in Sunny Fla

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Re: Carb Diagram and Cleaning
« Reply #2 on: January 14, 2012, 07:32:25 PM »
heads up - that diagram isn't a keihin CVK. Also, whoever wrote the description of how it functions must have been guessing, because it's not even close. Try to follow either the diagram or the description and you'll be totally screwed up. Seriously - Steve

Offline George R. Young

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Re: Carb Diagram and Cleaning
« Reply #3 on: January 14, 2012, 07:46:16 PM »
Steve,

If you know of a better cutaway drawing and description, please let us know.

Personally, I've found this one useful.
65 CB160 (67-69), 69 350GTR (69-72), 72 R5, 73 RD350 (73-84), 82 XZ550 Vision (84-03), 01 Concours C10 (03-19), 89 EX250 (11-14), 00 SV650S (14-16), 03 SV650S (19-)

Offline Steve in Sunny Fla

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Re: Carb Diagram and Cleaning
« Reply #4 on: January 14, 2012, 08:22:38 PM »
I do know of one, but it's in my head, and nobody in thier right mind wants to look in there  :o

  Here's some particulars that are incorrect. There may be more, but these jumped right out.
1) the pilot air correction jet on the CVK isn't under the diaphram; it's at the back of the venturii next to the main air correction jet;
2) in the description of the pilot circuit, there's something about flow reversal - completely incorrect. He has a complete misunderstanding of the idle transfer holes. The pilot air screw sets the fuel flow at idle. The pilot jet feeds that circuit and the idle transfer holes.  the idle transfer holes are staggered and discharge sequentially as the throttle is slightly opened;this provides fuel that's needed between idle and when the fuel is discharging from the main well.
3) the description of slide function is completely incorrect. it states something about manifold vacuum raising the slide. Incorrect. The slide is raised by the air speed in the venturri area under the slide.  CV means constant velocity, and the idea is that the slide opens at a rate to feed ever increasing air volume at the same velocity to provide an optimised low pressure signal thereby providing consistent metering of fuel from the needle jet.
  HTH, Steve

Offline Summit670

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Re: Carb Diagram and Cleaning
« Reply #5 on: January 14, 2012, 10:04:33 PM »
Thanks guys.

Is it possible to thread some fishing line thru any of the holes or do just need to make sure air or carb cleaner comes out the other end?

Also, I bought the tygon fuel line and connector tube o-rings from Murphs but forgot about the old air screw o-rings I had reused last time until I was poking around looking for a carb diagram online.  Do you guys think the old o-rings on those would cause hard starting and backfire when trying to start?

Once bike is running, after a few minutes it runs great at all speeds.  It's just the cold start that has been becoming increasingly difficult over the years, the months of say July thru November the worst.  Actually, the backfires really began in November and then the weather got nasty the first week of December so I winterized it and haven't tried to start since.

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Offline Boomer343

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Re: Carb Diagram and Cleaning
« Reply #6 on: January 15, 2012, 12:36:18 AM »
Got to agree with Steve....that was interesting description of how a CV or any other carb works.....never heard of reverse flow in a transition port....LOL

Summit are you getting backfires through the carbs or through the exhaust?

Usually it is lean mixtures that cause intake/carb backfires and rich mixtures cause the exhaust backfires.

I noticed a reduction/elimination when I removed the  anti smog equipment, did a valve adjust and put in Tony's stick coils. Mine were the typical decel burps.

I'd be checking plug wires and end caps, oil in the plug wells, replacing plugs, valve clearances and eliminating the possibility of air leaks before I ripped into the carbs.

From playing with old Honda carbs any O ring that is not pliable is going to cause problems.

As always your experience may vary......

Offline George R. Young

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Re: Carb Diagram and Cleaning
« Reply #7 on: January 15, 2012, 09:54:44 AM »
Temerity in this case is defined as debating carb stuff with a carb expert. But it's winter in Ottawa and much too cold and grotty to ride, so here goes:

I do know of one, but it's in my head, and nobody in thier right mind wants to look in there  :o

  Here's some particulars that are incorrect. There may be more, but these jumped right out.
1) the pilot air correction jet on the CVK isn't under the diaphram; it's at the back of the venturii next to the main air correction jet;

Yep, quite so, on our carbs, the pilot air jet (16) is located next to the main air jet (19).

2) in the description of the pilot circuit, there's something about flow reversal - completely incorrect. He has a complete misunderstanding of the idle transfer holes. The pilot air screw sets the fuel flow at idle. The pilot jet feeds that circuit and the idle transfer holes.  the idle transfer holes are staggered and discharge sequentially as the throttle is slightly opened;this provides fuel that's needed between idle and when the fuel is discharging from the main well.

Here's what I understand from the diagram. When the butterfly is closed, the bottom of the butterfly rests between the idle mixture hole (13) and the transition mixture holes (14). Fuel flows through the pilot jet (11) and mixes with air from the pilot air jet (16 at its correct location) and air from the transition mixture holes (14). When the butterfly opens enough that the bottom is between the transition mixture holes (14), fuel will also flow out the downstream transition mixture hole while air will continue to flow in the upstream transition mixture hole. When the butterfly opens more, such that the bottom is upstream of both transition mixture holes, fuel flows out both of them.

The reversal he's talking about is that sometimes air flows in while other times fuel flows out of the mixture transtion holes, depending on the position of the butterfly.

Here's a reference http://www.modelgasboats.com/Carburetor_Maintenance/ see "At idle"

3) the description of slide function is completely incorrect. it states something about manifold vacuum raising the slide. Incorrect. The slide is raised by the air speed in the venturri area under the slide.  CV means constant velocity, and the idea is that the slide opens at a rate to feed ever increasing air volume at the same velocity to provide an optimised low pressure signal thereby providing consistent metering of fuel from the needle jet.
  HTH, Steve

Here's what I get from the diagram. When the butterfly (1) is significantly open (e.g. 1/3), flow increases under the slide (2). Pressure drops due to the Bernoulli effect.
Reference: http://www.physicsforums.com/showthread.php?t=59877 see "carburetor"
Air gets sucked out of the vacuum chamber (3) through the slide vacuum passage (6) until the pressure in the vacuum chamber is the same as under the slide, lower than atmospheric.

The pressure in the the atmospheric chamber (18) is (surprisingly) atsmospheric, because air can get in through the airbox vent (15). The pressure below the membrane (5) is higher than the pressure above, so the slide rises to a new position determined by the spring.
Another reference for this blather: http://www.drpiston.com/Cvcarbs.html see "CV (Costant Velocity) CARBS"

----------------------------
In my opinion, this diagram covers the concepts and functionality of a CV carb. It names the bits and provides reference numbers on the graphic. Some bits may be in different places on specific CV carbs, like our CVK, and the wording in the explanation may be a bit fuzzy. Moreover, when the fellow prepared it, he forgot (5) Membrane - I added it in, you can see the different font.

It has helped me and maybe it will help others. If not, feel free to ignore it.

Edit: removed cursed commas from links
« Last Edit: January 16, 2012, 07:40:55 AM by George R. Young »
65 CB160 (67-69), 69 350GTR (69-72), 72 R5, 73 RD350 (73-84), 82 XZ550 Vision (84-03), 01 Concours C10 (03-19), 89 EX250 (11-14), 00 SV650S (14-16), 03 SV650S (19-)

Offline Summit670

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Re: Carb Diagram and Cleaning
« Reply #8 on: January 15, 2012, 08:07:42 PM »
Boomer - I've had this bike for 22 years, since new, 1987 bike though.

Two years ago started having higher rpm miss.  Ended up being bad coil so replaced with Stic coils but not before I went thru the carbs (though not as thorough as I should have since the jets looks clean) and all was well.

Last year I replace the pickup coils because one had a bad wire.

I believe the backfires have been thru the exhaust, especially one of the last ones because it was very loud.

The last valve adjust was done 5,600 miles ago.  I've been doing these around 10,000 intervals.  The bike has 73,000 miles.

I have not removed the smog fittings yet.

I will look it over real good, spray WD40 around the intake boots to try and find any air leaks.
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Offline Boomer343

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Re: Carb Diagram and Cleaning
« Reply #9 on: January 15, 2012, 11:26:12 PM »
Summit you've got enough variables happening to keep you busy for the winter.

But....if it runs good after warm up then you have to look at what is happening to the bike while it is not running.

If it backfires through the exhaust then does it do it worse when the enrichening system is used? Is it possible the floats are set high? Hot bike, turn off, heat soak, fuel in carbs flows into cylinders, not enough for hydrolock but enough to cause backfire. Petcock leaking....fear the hydrolock....

I would replace the sparkplugs, cheap and easy, make sure the air filter is clean and isn't over oiled.

For airleaks look at the mating surfaces of the carb to engine boots, when cold possible gap then no gap when parts expand. Given the age of the bike if the intake boots and mounts haven't been replaced then they should be done. Normally airleaks will cause acceleration backfires, have seen timing issues cause starting backfires through carbs and exhaust, things like stuck or sticking mechanical advance can be a real pain but again if it runs good when warm it probably isn't that.

Will be interesting to see what it turns out to be.....

Offline Steve in Sunny Fla

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Re: Carb Diagram and Cleaning
« Reply #10 on: January 16, 2012, 06:03:16 AM »
 George - both the links were broken.

  Your description of how the slide lifts is correct. The description about the Idle tranfer ports, hmmm... I gotta think about that. I don't believe air flows in a port behind the butterfly, then discharges out the port on the manifold side. Since air is easier to move than fuel, that would cause no fuel to discharge on the manifold side, and that's incorrect. At idle, the airflow provided to the engine comes from the throttle valve (I'm calling it butterfly). there would be a bernouli effect (vacuum signal) going across the transfer ports as they are uncovered, and a somewhat lesser signal to the more rearward ports. Since the pilot air correction jet is at atmospheric, it would push air toward the vacuum and provide the air for the mixture. This is borne out by the presence of emulsion holes in the actual pilot jet. In my mind, if the transition holes provided air, there would be no impulse to draw fuel, and the transition would go dead lean. JMO,

  Summit - check your airbox for a split seam on the front bottom edge. HTH, steve

Offline George R. Young

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Re: Carb Diagram and Cleaning
« Reply #11 on: January 16, 2012, 08:09:02 AM »
Fixed links, cursed commas were included.

Here's the one again about flow through transition holes:
http://www.modelgasboats.com/Carburetor_Maintenance/ see "At idle"

When the butterfly is closed, there's atmospheric pressure at the transition holes (14) and reasonably high vacuum (I measure around 10" Hg at idle) at the idle mixture hole (13). Looks to me like air would flow from (14) to (13), just as it flows through the pilot air jet (16) to (13).

BTW, the drawing originated here:
Carburetor-Theory
Seems to be course material for SUNY

Edited to add 2nd reference
65 CB160 (67-69), 69 350GTR (69-72), 72 R5, 73 RD350 (73-84), 82 XZ550 Vision (84-03), 01 Concours C10 (03-19), 89 EX250 (11-14), 00 SV650S (14-16), 03 SV650S (19-)

Offline dbethel

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Re: Carb Diagram and Cleaning
« Reply #12 on: January 16, 2012, 01:43:09 PM »
Thanks guys.

It's just the cold start that has been becoming increasingly difficult over the years, the months of say July thru November the worst.  Actually, the backfires really began in November and then the weather got nasty the first week of December so I winterized it and haven't tried to start since.

The cold weather (air) and winter fuel blends contribute a lot to poor cold start/idle during cooler months.
 

Offline hankgood

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Re: Carb Diagram and Cleaning
« Reply #13 on: January 16, 2012, 04:00:34 PM »
I found this helpful. Very similar to Connie carbs:

http://faq.ninja250.org/wiki/Cleaning_the_carbs_2

Offline Summit670

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Re: Carb Diagram and Cleaning
« Reply #14 on: January 16, 2012, 04:28:43 PM »
Steve - I don't see any split in that seam just looking at it.

Hank - thanks for that info. 

It will probably be a week or two before I tear into it, assuming I don't see or find any other probable causes when looking closer this weekend (the weather is supposed to be 53, so warmer than the 34 now.
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Offline Steve in Sunny Fla

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Re: Carb Diagram and Cleaning
« Reply #15 on: January 16, 2012, 04:48:36 PM »
george,  I've been doing carbs for about 35 years. all kinds of automotive carbs, Mc carbs, I have several books on hotrodding various carbs and I've never seen reference to the pilot transition holes feeding air until they don't. I personally am very suspect of that theory, and previously outlined why. Maybe I'm wrong, but you have links to back it up - and we all know that if you find it on the internet it must be true... so on this one we'll agree to disagree. Steve

Offline George R. Young

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Offline Steve in Sunny Fla

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Re: Carb Diagram and Cleaning
« Reply #17 on: January 16, 2012, 06:43:55 PM »
that link shows a carb w/o provision for an air correction jet, and it's supposedly using the transition holes as the air correction jet. The cvk's have such a jet, and it is sized selectively just as the fuel jets are. If this theory of transition ports providing air, then why even have air correct jets; why have emulsion tubes? they would be totally redundant. CVK's use different emulsion tubes depending on the application, with various placements of the holes. How does that work with the air being provided by the transition port and the needle jet, as that last link demonstrated? Steve

Offline MAN OF BLUES

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Re: Carb Diagram and Cleaning
« Reply #18 on: January 19, 2012, 11:17:42 AM »
that link shows a carb w/o provision for an air correction jet, and it's supposedly using the transition holes as the air correction jet. The cvk's have such a jet, and it is sized selectively just as the fuel jets are. If this theory of transition ports providing air, then why even have air correct jets; why have emulsion tubes? they would be totally redundant. CVK's use different emulsion tubes depending on the application, with various placements of the holes. How does that work with the air being provided by the transition port and the needle jet, as that last link demonstrated? Steve

Steve, there is a flaw in that diagram....
the actual proprty of the pilot air needle is to "throttle" air from the intake bell of the rear (bottom fixed orifice, iirc) up to in front of the 4 orifices in the throat near/behind the buttrfly, and as the circuit is directly tied to the orifices fuel curcuit, it causes a "siphon" to pull fuel there, and fuel exits the orifices as they consecutively are uncovered during the butterfly opening. The "suction" is modulated by the pilot air screw, not actual fuel delivery as shown in that mower diagram.... this is why idle/off idle fuel milage can be greatly effected, and performance off idle also, by that particular screw/needle.
But I may be all wrong.....I only been doing these for 40 years (between the 2 of us, we got damn near a century). ???
I did sleep in a Holiday Inn Express once though. :D

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Offline Steve in Sunny Fla

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Re: Carb Diagram and Cleaning
« Reply #19 on: January 19, 2012, 12:54:59 PM »
Rich, that's my contention also. Showing the transition ports being the method of providing air for the pilot circuit is something I've never seen before. George has sent me several links showing that, but I respond by pointing out that IF that were the case then 1) why is there a pilot air corrector ; 2) why are there emulsion holes in the pilot jet; and 3) since the engine could more easily pull air from behind the throttle plate to the manifold side of the plate rather that pull fuel from the pilot well, I feel that the holes behind the plate would do nothing but kill fuel delivery to the holes on the front of the throttle plate. My personal contention is that the airspeed across the area under the throttle is very high, and is, if anything pulling fuel toward the throttle and getting it ready to discharge as soon as the throttle passes a given hole and exposes it to manifold vacuum - but then what do I know, I only tune them. steve
« Last Edit: January 19, 2012, 04:51:42 PM by Steve in Sunny Fla »