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Aftermarket Carb Kits - A Case Study (Read 132 times)
DragBikeMike
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Aftermarket Carb Kits - A Case Study
06/23/25 at 18:23:23
 
In August of 2024, ThumperLife did a post asking for help with his carburetor.  The carb was super-rich, and he was out of ideas.  I offered to go through the carb and determine what was wrong with it.

This link provides background information.

https://suzukisavage.com/cgi-bin/YaBB.pl?num=1723039919/21#21

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Re: Aftermarket Carb Kits - A Case Study
Reply #1 - 06/23/25 at 18:24:39
 
On 6/10/25 the carb arrived at my doorstep.

I unboxed the beast and took a quick look.  She is a funky specimen, well-worn after years of faithful service.  Note the protruding idle mixture screw; a sure sign that something isn’t right.
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Mix_Screw_Sketchy.jpg

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Re: Aftermarket Carb Kits - A Case Study
Reply #2 - 06/23/25 at 18:25:35
 
There is lots of surface corrosion and the usual array of rounded out pan head screws.  The throttle plate screws are concerning, but best left undisturbed.  Too risky to tamper with.

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Re: Aftermarket Carb Kits - A Case Study
Reply #3 - 06/23/25 at 18:26:13
 
The enricher plunger is slightly bent, and the plastic detent is broken.  That’s a leave-as-is situation.  Easy enough to manually hold the plunger out, or rig up a Mickey Mouse get around.  These plungers cost about $50 bucks, and they are worth about 10% of that.  As John Lennon said, “Let it be, let it be”.
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Re: Aftermarket Carb Kits - A Case Study
Reply #4 - 06/23/25 at 18:27:57
 
It didn’t take long to figure out that this carburetor was the victim of a cheap, aftermarket overhaul kit. Puleeeeeze, stay away from these aftermarket overhaul kits.  They screw up every circuit in the carb; idle, transition, mid-range, & WOT.  It makes diagnostics almost impossible because you are chasing four or five problems all at once.   Use genuine Suzuki parts (i.e. OEM).

This old post gives the straight skinny on aftermarket carb kits.  They are, for the most part, JUNK.  Tabooo, Stay Away.  Metallic carb parts rarely wear out.  Just clean them.  Don’t resort to one of these kits.  If you must use an aftermarket kit, use the info contained in my old post to evaluate the suitability of the components.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1641171298
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Re: Aftermarket Carb Kits - A Case Study
Reply #5 - 06/23/25 at 18:29:19
 
From the initial look see, it was obvious that the idle mixture screw was suspect.  It was sticking out rather than sitting well down in the hole.  I checked the setting; it was 1-7/8 turns open.  No help there.  As expected, it turned out to be a bogus aftermarket mixture screw.  Complete junk.  Review the old post for specifics.
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Bogus_Idle_Mixture_Screw.jpg

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Re: Aftermarket Carb Kits - A Case Study
Reply #6 - 06/23/25 at 18:30:08
 
Of more concern, the carb body had been damaged by an unskilled attempt to drill out the original mixture screw.  Almost all the internal threads have been destroyed, and the seating surface for the o-ring is chewed up.  Hopefully, the critical seat for the mixture screw taper is not damaged.
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Re: Aftermarket Carb Kits - A Case Study
Reply #7 - 06/23/25 at 18:30:49
 
It should look like this.  See the threads.
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Re: Aftermarket Carb Kits - A Case Study
Reply #8 - 06/23/25 at 18:31:55
 
A quick check with a pin gage shows that pilot hole for the mixture screw is the correct size, but it’s hard to ascertain if the actual seat, which is much smaller, is OK.
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Mix_Screw_Seat__121.jpg

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Re: Aftermarket Carb Kits - A Case Study
Reply #9 - 06/23/25 at 18:32:39
 
The old-school “flashlight test” proves that there is in fact a small hole, and it appears to be round.  A .050” pin gage fits.  The base of the taper on the needle is .055”, so I think it’s probably OK.  If we install a mixture screw with the correct geometry, it should work ok, just need to deal with the internal threads.
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Re: Aftermarket Carb Kits - A Case Study
Reply #10 - 06/23/25 at 18:33:24
 
Looking at the slide from the outlet side of the carb, it looks worn.
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Re: Aftermarket Carb Kits - A Case Study
Reply #11 - 06/23/25 at 18:34:12
 
But once I removed the slide, it seemed ok, not perfect but ok.  It moves smoothly.  No tears, cracks, or holes in the diaphragm.  I think it will work.  But that gold-colored slide needle is suspect.
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Re: Aftermarket Carb Kits - A Case Study
Reply #12 - 06/23/25 at 18:35:22
 
As suspected, the slide needle was bogus.  It’s brass in lieu of anodized aluminum, and the basic diameter is too small (.1170 vs 1185” stock).  That’s only .0015”, but these needles generally come in .0003” increments, so a change of ,0015” is about 5 increments.  Since the taper starts at the basic diameter, 5 increments smaller is a lot richer.

To make matters worse, the needle clip was in the bottom groove (richest setting), but it can be moved to a higher groove.  Also, the washer between the spring and the e-clip is missing.
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Clip_in_Richest_Position.jpg

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Re: Aftermarket Carb Kits - A Case Study
Reply #13 - 06/23/25 at 18:35:57
 
The slide needle is also bent.  It has .075” runout.  I have no idea how you bend a slide needle, but I doubt it will improve performance.
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_075_Runout.jpg

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Re: Aftermarket Carb Kits - A Case Study
Reply #14 - 06/23/25 at 18:36:38
 
Dead giveaway.  Doesn’t take a keen eye to see this.
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Needle_Bent.jpg

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