Intake boots + GSXR-600 throttle bodies...

[jtolbert]

I have an '83 GS1100GL that I'm working on converting to EFI using a set of '01-'03 GSXR-600 throttle bodies and a Megasquirt ECU. I've accounted for the spacing difference in such a way that each throttle body intake center point is only offset 1.5mm from the center point of the intake boot. The catch is that the throttle body intake-side tubes are larger in diameter than the intake boot opening. If I stuff the throttle bodies on individually, I can get all four on the engine without issues. However, if I try to get all four on as an assembled rack (with the proper spacers added between the central throttle bodies) things don't cooperate. I've tried a bit of lubrication and I'm going to try heating the boots up a bit with a heat gun in a little bit, but has anyone ever tried anything like this? What worked for you? I'm not opposed to opening up the intake boots a bit with a dremel and a sanding wheel...What would you suggest? I'm betting the boots on the bike now are original; how much more pliable are new boots? Do they have quite a bit more stretch to them?

I've got a page up that documents the project if anyone's curious.

[80GS1000]

Interesting project for sure.

New boots are MUCH more pliable and flexible than the old ones, and they can stretch much more than the old, hardened ones.

What's the advantage of using a Megasquirt over say a GSXR 1000 or Hayabusa ECU?

[jtolbert]

The Megasquirt setup is very well-understood, openly-developed and the support community is huge (compared to the community to fit GSXR ECUs on to older bikes). The Megasquirt setup is much more flexible...I have lots of different ignition choices, etc. The sensors and other components I can use can all be incorporated more easily than if I tried to use a bike-specific ECU that required all of the bike sensors...For example, I can go anywhere in the country and find a GM three-bar MAP sensor, but a town that doesn't have a motorcycle shop most likely won't have any place that will stock a Suzuki MAP sensor.

There's no Power Commander or anything required for tuning the Megasquirt; a laptop with some (free) software is all you'll need.

Basically, the Megasquirt is more versatile and more open as far as access/development goes.

Also, there's no advantage to using the bike-specific ECU over the Megasquirt. I'd still have to jack around with throttle-body spacing, have a new fuel rail built and do all the other fun little bits I'll have to do with the Megasquirt, but them I'm stuck with that bike ECU. The Megasquirt is an evolving product that's not made just by one company...Chances are good I'll be able to get new Megasquirt ECUs long after Suzuki stops making whatever ECU I'd use for my bike conversion.

[RJ]

I know you already have the GSXR 600 throttle bodies, but if you wind up having to re-engineer the throttle shafts and all it may be worth it to find a set of GPz 1100 throttle bodies that will match up with the intake spacing perfectly and reduce the headache factor a good bit.

[t3rmin]

You can get varying sizes of Mikuni intake boots on bikebandit.com, or you might find a different brand (Kawasaki boots fit, I believe) that's more workable.

[jtolbert]

RJ: yeah, the GPz1100 throttle bodies would have been easier to start with...However, they're getting pretty scarce and the GSXR-600 TBs are all over the place.

t3rmin: interesting. I'll have to poke around on their site. A quick look only found me the one set of Mikuni boots; I must be looking in the wrong places.

[jtolbert]

So, I found the other Mikuni boots, but I need to find out more about the stock boots. First, why is there a left and right part? Do they have an angle to them or something? Second, does anyone know the distance between the studs, and is there any reason a universal Mikuni boot won't work?

[Ironriot]

Yes they do have a certain angle to them. Which stud would you be talking about?

[drhach]

Left and right boots

I think the angle that you 're referring to for the left and right boots is actually the placement of the vacuum tab in the boot. If I remember correctly, there is a screw tap in the boot where you can install a vaccum tube for syncing the carbs. If you put a left on a right and vice versa, you can't get at those taps. It would seem that for your case, those would not be necessary and it shouldn't matter what you use.

[jtolbert]

Studs...Sorry, the screws that hold the flanges on the head. The Mikuni boots call them studs and I was looking at them when I wrote the post. I could pull one of my bike's boots off and measure the screw spacing, but if someone's got a set of boots (or a de-booted head) laying around and could measure the spacing, it would be appreciated.

Vacuum ports...Interesting. Thanks.

[jtolbert]

So I took the #1 intake boot off. Bolts came loose without any trouble.

The center-to-center spacing looks to be something like 68mm...Hopefully I'd be able to get a 70mm generic boot to fit. Looks like Mikuni has the I-VM36-200-1 boot, which will accept things up to 43mm in diameter...The throttle bodies were just a hair under 44mm, and I was able to stuff them in the boots I have now. I think I might give these a try. Of course, BikeBandit carries on with a 70-75mm stud spacing in 36-40 (inside TB diameter) size, but they don't seem to have the 70mm-only version of the same thing. They have two "generic" ones without sizes listed, so I guess I'll have to call them tomorrow and find out.

There's another flange that's essentially the same as the one above, except the boot itself is 3mm longer. I may go with this one, just cause the 3mm longer boot may have a bit more "give" to it since the throttle bodies are offset a bit. Decisions, decisions...What do you guys think?

The generic Mikuni boots are also differently-designed...They don't use an O-ring; instead the entire thing is rubber. Think it'll hold up to an air-cooled engine's heat?

[Billy Ricks]

It's more about the port spacing you end up with by having left and right manifolds. You could try switching sides of either one of both of each pair to see if it helps alignment. You can flip them over to change the angle to the ports.

[jtolbert]

Billy Ricks: great idea. Thank you. That may have been the key I needed. I don't know why I didn't think of that. Since it looked like the left and right boots canted towards the center of the engine, I just swapped the two outer boots. That way the outer ones cant towards the outside and the inner boots cant towards the inside, which is pretty much exactly what I want.

I can successfully get one "side" of the throttle bodies installed right now, but it's cold in the garage. I figure I'll break out the heat gun and WD-40 tomorrow evening and see if I can get them to cooperate a bit more.

New boots would most likely help, too.

There are no vacuum taps or ports on these boots. I think the sidedness is just due to the cant.

[KoolKat]

This may sound rough..but it might help get those TB's into the manifolds.
Lube them up,place a length of 2x4 accross the inlets left to right,then use a ratchet strap from 1 front down tube looped around the cylinder head and back to the other front down tube.This way even pressure accross the rack could be applied safely,and hopefully they will pop in without to much effort on the ratchet.You could apply heat at the same time while keeping load on the strap.
I haven't tried this,but have come very close trying to fit the slingshot GSXR carbs into my GS1150 inlet rubbers...there really stiff.
Just an idea??

[jtolbert]

KoolKat: I had thought about using ratchet-straps around the downtubes before, but honestly if I have to work that hard at it, something's not right. I have yet to try the heat thing; hopefully that'll do the trick. Thanks for the idea; at least I'm not the only one that's thought of this.

I ordered new intake boots, O-rings and clamps, too. Hopefully they'll be a bit more forgiving.