80 GS550E jets

[geraldsmith822]

Hi Guys

I have an 1980 GS550E with a Mac 4 into 1 pipe (no baffle) and am going to put some K&N pods on it. What are the recommended jets that I need to change and where do I get them:?:

Thanks.

G

Any day the bike starts is a good day.

 

[Agemax]

dynojet kit, if they do one for your bike. if so.....ebay

 

[geraldsmith822]

I checked Dynojet's site and of course they dont have any kits listed for the 80 GS550 so I guess I'll just have to get a generic kit and experiment. UGH!

 

[Guest]

Get the kit for the 550. It will work.

 

[geraldsmith822]

Thanks Chef1366

I will try that. I was about to consider getting carbs from a different source (say a 650 or an newer 550 or something to that affect) and try.

Everyday the bike starts, is a good day.

 

[AJ]

If you can't find a custom jet kit to get you started, here are some rough guidelines to use to customize based on the air filter / exhaust combinations you may have (from motorcyclecarbs.com):

[FONT=verdana, arial, helvetica]Jetting Recommendations
by Denny Zander

Here is a simple set of jetting guidelines that have worked for me. For those considering jet changes, this might help select a starting point.

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

2 jet sizes for both single K&N and drilled airbox

2 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size)

Under a mismatch condition, like individual filters and stock exhaust or 4 into 1 header with stock filter and air box, subtract an additional 1 jet size.

Check plug color often, sync carbs after each jet change, make sure the floats are set correctly, and seriously consider purchasing a Colour Tune. (See "Colortuning Carburetors" in the Maintenance Section).

Make sure your carbs are in perfect working order before making jet changes.

Example from my '79 XS1100 F:
Stock main jets: 137.5

Stock pilot jets: 42.5

2 sizes for 4:1 exhaust (Jardine)

1 size for single K&N

1 size for drilled air box

4 (main sizes) - 1 = 3 or 137.5 + (2.5 * 3) = 145.0
1 (pilot jet size) or 42.5 + (2.5 * 1) = 45.0

With this jet configuration I get 32-38 mpg on the open road, Smooth idle, very strong exceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 65K mile on it, of which I have put 33K with this jet configuration.

I have applied this to the '78-'79 carb set with great success. These guidelines should work for the '80-'81 carbs also. The only part I have not tested is pilot jet changing on the second generation carbs.

Happy Jetting[/FONT]
[FONT=verdana, arial, helvetica]Additional info: decrease main jet size one step per 2000' above sea level.[/FONT]

Note: Even with a "jet kit" from a reputable company, there is a lot of variation between engines, pipes, etc. Even with a kit, you are probably going to be playing around for awhile before you settle on a "perfect" combination. Don't worry too much about damaging your engine, because if it's really bad, you'll know it (running crappy, fouling plugs, etc.) after a very short test ride. The best way to do this would be with a dynomometer and an air-fuel meter (AFM), but most of us do it by the seat of the pants and lots of trial and error. Good luck!!

 

[Agemax]

you dont need to sync carbs after every jet change. a different size jet fitted will not affect the mechanical set up of the carb slides

 

[geraldsmith822]

Thanks AJ & Agemax

Thats some pretty good info to start off with.. Now all I need is to figure out what size jets I already have and start meddling.

 

[AJ]

Gerald - I STRONGLY urge you to get a baffle in that Mac exhaust system. Besides keeping your bike from setting off car alarms as you go down the street (), it also adds a little backpressure that is essential for proper engine functioning. Without going into the mechanics of this, running a bike like yours without baffles will COMPLETELY kill the bottom end power and drastically reduce power everywhere but at redline. That's ok for drag racing, but it is miserable on the street. It also makes for extremely abrupt transitions in your carburetor circuits, from idle, to pilot (midrange), onto the needle, and finally to the main jet. This makes it very difficult to tune, and you can NEVER get the midrange power out of the engine.

You spend 98% of your riding somewhere between 2000 and 6500 rpm, and the other 2% from 6500 to redline. On a little 550, the baffle will barely decrease your peak horsepower at redline, but it will improve power everywhere else. Think about it.

 

[geraldsmith822]

AJ thats some good advice there.

I dont intend to drag race that bike and would like a decent sounding muffler on there as well. The Mac with the baffle sound like its has asthma and I dont know of anyone that still has pipes for that bike. And I also dont need Johnny Law on my back about the noise. I may try to modify the baffle itself and see.

 

[AJ]

The Mac with the baffle sound like its has asthma and I dont know of anyone that still has pipes for that bike. And I also dont need Johnny Law on my back about the noise. I may try to modify the baffle itself and see.

Ok, I didn't know you even had the original Mac baffle.

If you're trying to make your bike sound like "something" (anything! ), I understand. My son's 1985 550 sure doesn't sound like much either.

I'm wondering if you might be able to modify a straight-thru type of baffle like the Kerker to fit into your Mac megaphone.

Look at the baffles on this website: http://www.newmotorcycleparts.com/exhaust_parts/baffles.html
Does your baffle look like the top Mac baffle with the staggered tube at the top of the page? If so, measure the diameter of the inside end cap, the outside end cap, and the distance end-to-end of the baffle.

I can give you those same measurements for the Kerker style baffle ("MAC Products Replacement Baffle For KERKER"). I have that exact baffle on my 1100e and will say that it still has a hearty growl to it, even wrapped with stainless steel wool (instead of fiberglass).