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Throttle Restricter in Boulevard S40 (Australia) (Read 316 times)
IslandRoad
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Throttle Restricter in Boulevard S40 (Australia)
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:
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« Last Edit: 03/06/17 at 12:00:27 by Dave »  

Tube_in_Carb_001.jpg

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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #1 - 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.
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« Last Edit: 03/06/17 at 10:56:41 by IslandRoad »  

Lifter_Comparison_001.jpg

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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #2 - 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.
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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #3 - 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
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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #4 - 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.
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carb_top.jpg

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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #5 - 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.
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #6 - 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?
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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #7 - 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.
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« Last Edit: 03/06/17 at 10:59:50 by IslandRoad »  

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IslandRoad
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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #8 - 03/05/17 at 23:48:01
 
Here's the noise rating:
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IMG_20170306_185114.jpg

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Re: Throttle Restricter in Boulevard S40 (Australi
Reply #9 - 03/07/17 at 18:24:44
 
Must be an Aussie "thing". My bike doesn't have a noise compliance sticker.
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IslandRoad
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Re: Throttle Restricter in Boulevard S40 (Australi
Reply #10 - 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!


Kris01 wrote on 03/07/17 at 18:24:44:
Must be an Aussie "thing". My bike doesn't have a noise compliance sticker.

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Re: Throttle Restricter in Boulevard S40 (Australi
Reply #11 - 03/08/17 at 18:38:11
 
Probably just government regulations "just in case". They're just covering their butts!
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There's no problem that a full tank of gas and a sunny day can't fix!

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Re: Rev Limiter in the Boulevard S40 (Australia)
Reply #12 - 03/25/17 at 14:50:46
 
IslandRoad wrote 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.

That just ain't right!  Did the EPA sneak into your country?
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Re: Throttle Restricter in Boulevard S40 (Australi
Reply #13 - 10/16/18 at 03:39:00
 
got mine out and did spacer mod and rejetted, massive improvement!
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Re: Throttle Restricter in Boulevard S40 (Australi
Reply #14 - 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.
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