SuzukiSavage.com - Idle mixture screw strangeness

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Idle mixture screw strangeness
09/07/26 at 11:31:38

I went looking for the infamous 'EPA plug', and found that it had already been removed. It may be hard to see in this photo, but the idle mixture screw actually stands slightly proud of the hole, such that it looks like no plug could ever have been there. I wondered if this meant that my bike was running scandalously rich, so I counted the turns it took to fully seat the screw. I expected 4-5 turns, but it was only 1 3/4 turns! I then backed the screw back out to the original position and went further to 2 full turns out. This seems to have cleared up the tendency of the bike to die when I close the throttle abruptly. So, was she actually running a bit lean? Has anyone seen an idle mixture screw like this before?

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DragBikeMike

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Re: Idle mixture screw strangeness
Reply #1 - 09/07/26 at 14:10:01

"Has anyone seen an idle mixture screw like this before?"

Yes, you might have a bogus aftermarket mixture screw. These bogus screws make it close to impossible to correctly adjust the idle mixture. The tapered tip of the screw is too small so that it doesn't control fuel flow until the screw is almost completely seated. This old post will give you all the specifics.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1641171298

If you can't achieve satisfactory idle mixture, you can correct the issue by installing a genuine Suzuki mixture screw. Another option is the PUDA carb kit (if available). This old post provides the specifics on the PUDA kit. As I recall, the mixture screw in the PUDA kit also sits proud in the hole, but the geometry of the tapered tip is correct. It works good.

https://suzukisavage.com/cgi-bin/YaBB.pl?num=1750728203

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LikeTheSoup

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Re: Idle mixture screw strangeness
Reply #2 - 09/13/26 at 09:56:39

As expected, DragBikeMike was right. That's my idle mixture screw, with the 'cheap rebuild kit' geometry.

I see a PUDA rebuild kit on Amazon for $18. The idle mixture screw is the long one, but the geometry of the business end looks a LOT better than what I have now. Would such a kit be worthwhile, or should I pony up and get the real Mikuni kit for $80?

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DragBikeMike

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Re: Idle mixture screw strangeness
Reply #3 - 09/13/26 at 11:23:09

Not sure what you mean by “real Mikuni kit”. Have you been able to find a genuine Suzuki carb kit, or does the $80 get you several individual parts? I can see that Suzuki Parts House sells the individual mixture screw for about $12 bucks.

The safest approach is to always use genuine parts, but as you can see from my old posts, the PUDA kits work good. If you have decent mechanical skills and an understanding of how the carb functions, try the PUDA kit. The learning experience is worth the $18.

If the only carburetion issue you have is a rough idle, just use the mixture screw from the kit. If you have other carb problems like heavy after-fire, surging, hard starting, overflow, leaks, etc., the rest of the parts in the kit should help to get things working right. If you use the kit, don’t throw your old parts out, and don’t intermingle the existing parts with the PUDA parts. For instance, don’t use the PUDA slide needle with the existing needle Jet.

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LikeTheSoup

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Re: Idle mixture screw strangeness
Reply #4 - 09/13/26 at 12:18:26

Hi Mike,

Thanks for weighing in on this for me. I've only owned this bike for a few weeks and the guy I bought it from did say he'd been over the carburetor.

https://shop.mikuni.com/product/mikuni-carburetor-rebuild-kit-for-suzuki-motorcy
cles/

That's the 'real' kit I was referring to.

As for carburetion issues, I have a few:

Sometimes the bike will hang on a high idle. I can get it to settle down if I blip the throttle a few times. I've checked that the throttle linkage is tight against the throttle stop when this happens, so I don't think the problem is in the cable or anything like that.

When the engine is cold, there's a tendency to surge or stutter at medium RPMs. This seems to go away when the engine is nice and warm

The engine sometimes just dies when I roll off the throttle. If I'm coming up to a stop sign or something and I roll off the throttle abruptly, the RPMs drop and the bike sometimes just stalls. Backing the fuel mixture screw off a bit seems to be improving this.

I'm going to order the PUDA kit and swap out the junk idle mixture screw for the PUDA screw right away. Then, when the weather cools off a bit, I'll make time to rebuild the carb with the rest of the PUDA parts. It's been a while since I've rebuilt and tuned a carburetor. Any advice for a bone-stock 1998 Savage in Orlando? Any jetting choices I could make that would get my bike running its best in warm, sea-level air? Should I stick with the #52.5 pilot and bump up to a @150 main jet? Keep the white spacer or swap in something a bit thinner?

I'll re-read the carb tuning threads, but any advice you have would be much appreciated.

thanks,
David

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DragBikeMike

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Re: Idle mixture screw strangeness
Reply #5 - Today at 02:42:39

Thanks for the link to that genuine Mikuni carb kit. That looks like some valuable info. If you blow up the picture you can see that the tip of the idle mixture screw in that kit does not agree with the idle mixture screw that the LS650 comes with from the factory. Both steps are tapered on the screw in the Mikuni kit. Not sure what's up with that. I do know for a fact that the screw the LS650 is delivered with looks like the screw I show in my posts. Only the tip is tapered. I guess the most important factor would be the tapered tip that should comply with the sketch I provided.

Your surging and stuttering when the engine is cold is typical. It can be improved dramatically by raising the slide needle a bit (1.0mm to 1.5mm). But since it clears up completely once the engine is warm you could probably leave as-is.

The engine dying on hard stop is probably related to float level. The fuel sloshes around when you stop hard. If the float level is too high, it floods the engine. If the level is too low, the slosh uncovers the pilot jet.

The 52.5/150 jet combo sounds fine. You will probably end up with a main jet somewhere around 145 to 150. Just depends on your setup and preference.

If you install the PUDA needle jet and slide needle (remember, don't try to mix the PUDA parts with the existing parts, PUDA needle jet must be used with PUDA slide needle), I'm pretty sure you will end up leaving out the white spacer altogether. Review the post I did on Thumperlife's carb. It provides the details.

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