SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Aftermarket Carb Kits - A Case Study
/cgi-bin/YaBB.pl?num=1750728203

Message started by DragBikeMike on 06/23/25 at 18:23:23

Title: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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”.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:30:49

It should look like this. See the threads.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:33:24

Looking at the slide from the outlet side of the carb, it looks worn.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 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.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:36:38

Dead giveaway. Doesn’t take a keen eye to see this.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:37:38

The “white spacer” has been shaved down to .076”, which raises the needle .037” (more rich). A stock spacer is .113”. Shaving down the white spacer is a typical tuning mod on the LS650, so it’s not unusual to find a thinner spacer.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:38:29

The needle jet is brass in lieu of stainless steel. Always a bad sign. Checking the orifice with a pin gage shows the orifice is .127”. A stock needle jet has an orifice that is .121”. The needle jets are generally provided in .0002” increments. So, the brass needle jet is equivalent to 30 jet sizes larger than stock. Ya think we will get enough fuel? My goodness, that is a BIG needle jet. I’m thinkin someone may have hit it with a drill.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:39:56

The air-bleed jets in the top of the carb are correct. PJ1 is #45, PJ2 is #230. Both jets were checked with pin gages to verify that they weren’t drilled out.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:40:47

The main jet is a #152.5 (3 sizes over stock) and the pilot jet is a #52.5 (stock). Both were verified with pin gages to ensure they had not been drilled out. I personally don’t view the oversize main jet as a problem, but it doesn’t help. If the engine is stock or mildly modified, I recommend a #147.5 or #150. The #152.5 won’t cause the reported overly rich condition at 1/8 throttle, it will only make the performance a little soft or lazy at WOT.

The main air bleed system was clear, no obstruction, and the air bleed jet is the correct size. A .023” pin gage fits nicely. No problems with air correction.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:41:24

The float bowl was crusty rusty. Looks like water has been in here.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:42:15

The floats are a bit beat up, but they didn’t leak.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:42:59

When you remove the float pin, it’s best to support the post. I have broken a post. The little pin is a slight press fit, and it’s easy to break a post when you drive the pin out. I use a long piece of brass tubing to buck up the post before I drive the pin out.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:43:56

The floats looked pretty funky, so they took a quick dip to check for leaks. No bubbles observed.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:45:15

The float level was too low (33mm vs 28mm).

The spring-loaded pin in the needle was frozen. It was completely ineffective. That’s gotta go.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:46:03

It should look like this. The pin should go into the needle valve when you press on the pin, and spring back when you release the pin.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:46:58

The needle seat was not captured. The retainer plate and screw were missing.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:47:48

I tested the needle and seat for leakage. Using a burette and mineral spirits to simulate fuel (safety first), the assembly failed miserably. The burette was empty before I could blink. It was most certainly a fire hazard if gasoline had been used as a test medium.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:48:30

The mineral spirits puked out of the main air bleed and dribbled down the carb. This leaky needle & seat would certainly exacerbate an overly rich condition. Glad I didn’t try to run this thing as-is, fire hazard for sure.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:49:09

The transient enrichment valve diaphragm is deteriorated. This needs to be replaced. It is a vacuum leak waiting to happen, but it would not cause an over-rich condition.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 18:53:48

Looks to me like we have the Niagara Falls of fuel delivery. I think the way to fix this turkey is to:

-Install an OEM needle jet

-Install an OEM slide needle

-Replace the float needle & seat

-Install a float seat retainer and screw

-Adjust the float level

-Manufacture a custom idle mixture screw

-Machine the carb body to accept the custom idle mixture screw

We can do this. Best to start by fixing up the leaky float needle & seat, and installing a good OEM needle jet and slide needle. Let’s see how it works with those big problems fixed. Then we will know if it is salvageable.

I installed a new float needle and seat from an aftermarket overhaul kit. They are all yours ThumperLife, gratis. I readjusted the float level to 28mm. The subsequent mineral spirits test was satisfactory, 5 minutes, no leakage.

I temporarily installed my OEM needle jet and slide needle. Rather than fiddle around with the spacer, I left my .065” spacer on the needle. The OEM needle only has one groove, so no need to ponder which groove to put the eClip in. If the carb works good, we know that new OEM parts will fix the problem. I will take my parts out after the test.

I set the bogus mixture screw at 1.5 turns, and jacked the idle speed way up.

Let’s see how it works. This video is proof of life.

https://www.youtube.com/watch?v=MYQntw1ahBQ

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/23/25 at 19:02:19

So, now we know this jalopy carb can work. Time to put the project on hold and see what ThumperLife wants to do.

ThumperLife, do you authorize me to try and fix the idle mixture screw hole in your carburetor body? The stock threads are M6 x 0.5. I would machine the hole and re-thread to M7 x 0.5. I already procured the necessary tooling. There is a risk involved. I could screw it up and ruin the carb body, but I would do my best to do a good job. No guarantee, but I would do my best.

Before I start machining the carb body, I will make a custom mixture screw from brass. The screw will mirror the geometry of a stock OEM screw with the exception that the threaded portion will be M7 x 0.5, and the threads will be a bit longer. Machining the carb body will be dependent on successful completion of the custom mixture screw.

If the mixture screw and carb body come out well, I will reassemble the carb with my needle jet and needle and run it again to verify that it works correctly. If it works correctly, you must then purchase a good, genuine Suzuki, OEM needle jet and needle. No aftermarket stuff, Genuine Suzuki parts only. It would be best if you had the new parts delivered here so that I can install them in the carb and test.

Piece 11 Needle Jet 09494-00861 (Babbitts lists for $41)
Piece 10 Needle 13383-24C40 (Babbitts lists for $15)

To address the TEV diaphragm, I ordered an aftermarket carb kit from Amazon. I’m not buying this kit for you, I’m buying it for me. I’m curious about the kit. It’s cheap and I want to see what I can learn. If the TEV diaphragm turns out to be a good part, I will install it in your carb (gratis, my gift to you). Then I will report on the kit. Hopefully it will have some useable components. Either way, we will know if the vendor is a good source.

I will wait for your response.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by LANCER on 06/23/25 at 19:43:33

I suggest genuine Mikuni parts, instead of Suzuki parts, it is a Mikuni carb.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by ThumperLife on 06/23/25 at 20:10:29

Looks like you've been busy Mike!

YES. See if you can machine the carb for the mixture screw. I trust it will be fine, and if not, the carb was already not working well last time I had it.

Let me know how that goes, and I will get those other parts ordered.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by Dave on 06/24/25 at 09:10:47

Working on carbs can bring lots of surprises - especially if the carb has been worked on previously.

I just did some work on 2 carbs from a fellow who sent them to me. On one carb the float was badly bent - when it was attached it held the needle closed so no fuel would flow.

The other one had an amazing amount of crap above the screen that is attached to the seat for the float needle. Heaven only knows what the fuel tank looked like! It also has a #125 main jet installed - but a jet gauge showed it has been drilled out to a #160 size hole.

Both carbs needed some replacement parts and cleaned up well, and should work just fine.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by Dave on 06/24/25 at 09:11:37

Another shot of the junk above the needle seat.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by Dave on 06/24/25 at 09:12:40

Trashy!

Title: Re: Aftermarket Carb Kits - A Case Study
Post by LANCER on 06/24/25 at 19:33:32

Years ago I was sent a carb to fix, and when opened up the entire bowl area looked like a slimy green Forrest of sorts…the worst I’d ever seen.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:15:22

The mixture screw was easy to manufacture. I used a chunk of 3/8” brass stock. First, I turned it down to the anticipated major diameter of the 7mm threads, and then turned a section to the minor diameter of the threads (essentially the tap drill size) to serve as a guide for the thread die.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:16:05

Used a thread die in the tail stock to cut M7 x 0.5 threads.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:17:19

Then started nibbling away at the smallest diameters first. That way, the work piece will remain as rigid as reasonably achievable as I cut away at the thing. Can’t use a live center or a steady rest on this microscopic piece. The needle portion (taper) was cut to a 10° included angle until the point was right about .035”. Best I could figure using a stock mix screw as a guide. We’re only lookin at about 1/8” length with a change in diameter from .035” at the tip to .055” at the base.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:18:14

I ended up with this. Not too shabby. Hopefully I don’t wreck it when I part-off.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:19:12

When I was all finished with it, I did a visual comparison to the OEM screw. I think that’s pretty close. The OEM item might have a bit steeper taper (maybe 12°).

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:20:09

Here’s a sketch of the new oversize screw. For some of you it might come in handy.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:22:00

The carb body was a bit tougher. Sorry, no pics of that machining operation. It took me forever to get the thing aligned properly. You can’t dial it in off the existing threaded hole because the hole was egg shaped (result of the prior drilling operation). Without a drill press and a lot of patience, it would be very hard to drill one of these out correctly. I spent a lot of time getting the drill rig centered on the lower .121” pilot hole. Ultimately, I ended up with this. I am very satisfied with the results. The tap drill size for M7 x 0.5 is .256”, and a ¼ end mill gave me a hole right on .256”. Talk about luck.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:23:04

The new screw fits nicely, and the action is smooth. To verify that the screw was seating, I coated the tip with black ink from a Sharpie, then inserted it and ran it all the way home. ThumperLife, refer to this picture in the future. It should give you a good idea what the fully seated position looks like.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:23:51

A quick look-see showed a nice contact line on the taper. Not perfect, but you can’t expect more given what the carb body has been subjected to. I got no way to clean up the seat in the body.

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:25:02

The bottom of the hole doesn’t look too bad. I think it will be ok. Look at the surface texture of the body. I think this baby has been in some of that old-school Gunk. Man, that stuff was good. Those days are LG (long gone).

Title: Re: Aftermarket Carb Kits - A Case Study
Post by DragBikeMike on 06/27/25 at 20:28:47

After thorough cleaning and blow-out, I put it back together and installed it on the bike. The carb runs fine. Note that the mixture screw can control the idle mixture smoothly. I suspect that it was more like an on/off switch with the bogus screw since the tapered tip was so small that it couldn’t throttle flow.

https://www.youtube.com/watch?v=fKIl_bczY24

ThumperLife, go ahead and order the new needle jet and slide needle. For these two parts, no aftermarket stuff, OEM parts are mandatory. Use the information I previously provided.

The aftermarket carb kit should be here in a week or two. Amazon already shipped it. If we are lucky, the TEV diaphragm will be a keeper. If not, no big deal. It seems to be working ok as-is.