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Message started by IslandRoad on 02/21/17 at 03:13:31

Title: Throttle Restricter in Boulevard S40 (Australia)
Post by IslandRoad on 02/21/17 at 03:13:31

It seems the late model Suzuki Boulevard S40 sold in Australia has a throttle restrictor installed in the carburetor. I and one other member of the forum from Australia found it in our carbs. However, our friends on the forum from North America (some of them with 30 years’ experience working on the savage) have never seen it in the carb before.

It does not appear in any manuals, or parts catalogs, that I know of.

Another member mentioned he had seen a similar device in the carbs of scooters, used as a throttle restrictor.

The restrictor is basically a plastic tube that sits in the top of the carb. It slots into the large spring which sits between the top of the carb and the bottom of the lifter. It restricts how far the lifter can rise.

I don’t know if it serves any other purpose. And I don't know about the legalities, in Australia, of removing it, so what you do with this information is completely up to you.

This is what it looks like in place:

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 02/21/17 at 03:14:37

These two images show the effect of the tube.

With the carb out, I used a screwdriver to carefully raise the lifter.

Left image: tube in.
Right image: tube out.

You can see that the tube restricts how far the lifter can rise, limiting the airflow, and ultimately the fuel flow through the carb.

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 02/21/17 at 03:16:45

I tested my bike, a 2014 S40, with and without the device. Results were as follows.

Tube in: max rpm = 5500, top speed = 135 kph (84 mph)
Tube out: max rpm = 6000, top speed = 150 kph (93 mph)

I would imagine it limits the effect of the main jet because while it is installed you can never really hit full open throttle. The throttle control will still go all the way, but the lifter will not open the carb all the way up. I dare say, this also has implications if you are re-jetting and are trying to find the best main jet.

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 02/21/17 at 03:18:00

To check if you have one in your bike, you just take the top off the carb and it’s right there.

You can either take off the seat and the tank, then take the top off the carb while it’s still in the bike. Or you can pull the carb and then take the top off. I personally find the first option easier (although more complex) because the carb can be challenging to get back in again.

If you’ve never removed the seat and tank, the instructions are here:
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1487500580

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 02/21/17 at 03:19:11

Now we can see what we’re working with:

There’s a plug/connector with a rubber housing sitting right on top of the carb. It slides on and off a lug on the frame. Slide it off and move it out of the way. You can also pull those two vent tubes out from under the frame for easier access, leave them connected to the carb.

1. Undo the four screws (I swapped my screws out for stainless steel Allen Head screws, as suggested by many on this site).

2.Gently lift the cap off the carb and maneuver it out from under the frame.

3. The spring will be pushing upward from the inside (it’s not pushing hard but just be aware of it). You need to be careful not to damage the rubber diaphragm inside the carb while you do this (see first image in this thread).

It’s not difficult, but be careful all the same. As the cap comes off, the spring will pop up and bring the tube with it. You can simply lift the tube out and check it out.

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 02/21/17 at 03:22:18

When you’re done checking it out, reassemble everything in reverse order. Note, when you put the cap back on the carb:

1. make sure the spring is seated in the circular raised part in the cap.
2. make sure the rubber lip of the diaphragm is nicely seated into the groove around the top of the carb body as it makes a seal for the
diaphragm.

Apart from that, just put it all together and enjoy the ride.

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by jcstokes on 03/05/17 at 21:46:15

Can you check your vin plate to see if there's anything about complying with Canadian emission standards? Are the Aussie MOPP or MOOC going to know you did it?

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 03/05/17 at 23:40:39

I had a look at the VIN plate. Nothing about Californian standards.

There's a statement about complying with The Emissions Act (I assume Australian).

If someone decided to remove it and leave it out, I Can't see how anyone would know, other than testing the bike.

I've asked around and come up with three possibilities for why it's there.

1. LAMS approval - but forum member 'au de sauvage' did the math and the bike is way under the limit, even without the restrictor.

2. Emissions control

3. Noise control - this seems possible to me because the noise rating plate on the bike has some pretty conservative numbers on it.

I'll post a pick of the noise rating plate.

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by IslandRoad on 03/05/17 at 23:48:01

Here's the noise rating:

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by Kris01 on 03/07/17 at 18:24:44

Must be an Aussie "thing". My bike doesn't have a noise compliance sticker.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 03/07/17 at 23:03:47

That's really interesting. I reckon that must be the reason for it. I would never have thought the S40 with the stock muffler would be too noisy for anything!

625B405A1918290 wrote:

Must be an Aussie "thing". My bike doesn't have a noise compliance sticker.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by Kris01 on 03/08/17 at 18:38:11

Probably just government regulations "just in case". They're just covering their butts!

Title: Re: Rev Limiter in the Boulevard S40 (Australia)
Post by buster6315 on 03/25/17 at 14:50:46

665C434E414B7D404E4B2F0 wrote:

That just ain't right! Did the EPA sneak into your country?

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by chrischrischris on 10/16/18 at 03:39:00

got mine out and did spacer mod and rejetted, massive improvement!

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by bobert_FSO on 10/19/18 at 19:45:28

IslandRoad, does AU have motorcycle horsepower restrictions for learners or for young drivers? It seems that somewhere I have heard of such restrictions, maybe in Europe. Possibly the throttle restrictor is there to limit horsepower (as low as it is already) to allow young riders to legally operate a Savage/S40.

I really can't see how it would be part of an emissions system.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by bobert_FSO on 10/19/18 at 19:53:30

There are engine size restrictions and power/weight restrictions for learners.

https://www.qld.gov.au/transport/licensing/motorcycles/licence-types

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 10/20/18 at 01:06:22

464B46415650240 wrote:

Yes we have restrictions. For the first three years of riding we cannot ride a bike larger than 660cc. The bike must also comply with a certain weight to power ratio. Bikes in this category are labelled as Learner Approved Motorcycles (LAMS).

Another Australian member on the forum (who rides a Savage) did the math, and the S40 is well within the ratio - even with the restrictor removed.

All I can think of is that it has something to do with noise control - given that our bikes do sport a noise compliance sticker.

Incidentally, I believe it's actually illegal here to adjust the carb or play with the air intake and exhaust ... It's 'technically' illegal, but common. I know of at least one insurance company that will accept re-jetting and a slip-on exhaust without affecting premiums etc.

I can't think of any other reason for it apart from the noise issue.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 10/20/18 at 01:07:47

676C766D77676C766D77676C766D77040 wrote:

got mine out and did spacer mod and rejetted, massive improvement!

Glad to hear you got her tuned up nice. I was stoked with the results when I tuned mine properly. For me, it was also a great introduction to working on my bike.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by MotoSamoa on 01/03/19 at 12:32:17

What jets were required after removing the restrictor? I live in Samoa, where it is always about 30C and quite humid. I feel that it may be a bit lean standard, as it tends to pop and backfire like when it is running out of fuel.

I ask, as I will have to order them online and wat a month or so for them to get here, so I need to be prepared before doing anything

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by Hiko on 01/05/19 at 00:56:21

It is helpful to know where you are at before you can figure out where to go
My bike was stock and was fitted with 145 main jet 52.5 pilot jet the pilot screw was 3/4 turn open I am at sea level in New Zealand and the bike backfired on closing the throttle and surged on opening the throttle .
I fitted a 150 main jet kept the 52.5 pilot jet, opened the pilot screw to 2 turns open and trimmed the white spacer down to 2.2mm from 2.8mm original
[ Not all at once that is what I finished up with]
Very happy with results Bike runs much better thanks to advice from the guys on this forum
There was no restrictor in my carburettor
Good instructions on how to do all this on this forum

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 01/07/19 at 12:33:11

103229320E3C30323C5D0 wrote:

Hi MotoSamoa,

If you have a restrictor, removing it will not really affect which jets are right for the bike. I'm running a Dyna muffler (which apparently has very similar airflow to the stock muffler). I'm also running the stock air-box and filter.

You are correct, the bike is set up very 'lean' from the factory.

My adjustments are similar to Hiko's except I went a bit richer on the main jet, and if I recall correctly, a bit richer on the spacer mod. My spacer is between 0.3 and 0.4 of the original thickness (I used washers so I could tweak the thickness). My bike is probably just a touch on the rich side. I tried it a bit leaner. This gave slightly snappier performance but the engine ran a bit hotter and it introduced a slight 'lean surge' at low throttle. So I opted to tune out the surge and accept a slightly rich running condition. I get the occasional small backfire from the muffler when I change gears in the low range. However the weather (temperature, air pressure, humidity etc) affects the tuning, so the ride varies with the weather (we're talking tiny differences at this stage).

As for ordering jets - I ordered two steps below stock, and two steps above, for the pilot and main jets, so I could experiment with the setup. I ordered them here in Australia from these guys https://www.mikunioz.com. They were only a few dollars each. The guy there was really helpful on the phone, after he told me the best way to get the most out of the stock carb was to tie it to a fishing line and use it as a sinker! hahaha

As for idle-speed, I have mine set to about 1400 rpm. I found that if I go any lower, the engine will cut out if I rev the bike and suddenly drop the throttle back (as in an emergency stop).

If you haven't already, I highly recommend this excellent thread on carb tuning - http://suzukisavage.com/cgi-bin/YaBB.pl?num=1309246277

Good luck, and let us know how you go.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by Psydton3 on 01/17/20 at 03:23:58

Islandroad, I have a 2016 s40 and I'm looking to up the main jet to a 150. I contacted Mikunioz and guy knows his stuff. So much so I'm confused as. Are you able to advise me what was the exact main jet you purchased as per their website?...

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 01/17/20 at 11:32:50

Psydton3,

Main jet (choose the size from the drop down list on the page):

https://www.mikunioz.com/shop/n100-604-main-jet-large-round/?v=6cc98ba2045f

Pilot jet (choose the size from the drop down list on the page):

https://www.mikunioz.com/shop/n151-067-pilot-jet-non-bleed-type/?v=6cc98ba2045f

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by Psydton3 on 01/26/20 at 17:24:16

Rejetted mine this weekend to a 152.5 main. Opened up the top to do the spacer mod Sure enough the nylon throttle restrictor was present and yep an aussie 2016 s40. I've removed this. I got the bike started and it idles... now to tune the thing. I'm a noob to the carby tuning game so any hints would be awesome :)

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 01/26/20 at 19:54:19

I think the best thing to know is that the jets overlap. So, start with the pilot jet. Get that right, then go to the spacer on the needle jet (that affects acceleration through the mid range). Then focus on the main jet (WOT).

I reckon everything you need to know is in the tutorial I linked to a couple of posts back in this thread.

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by DanJa on 06/17/21 at 02:26:08

Awesome! this info is all great, I have a 2017 S40, and about to get ready to tune things up a little :)

Title: Re: Throttle Restricter in Boulevard S40 (Australi
Post by IslandRoad on 06/17/21 at 23:43:45

25000F2B00610 wrote:

Awesome! this info is all great, I have a 2017 S40, and about to get ready to tune things up a little :)

That's awesome! Good luck with it. let us know how you go.