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Correct jetting for GS550 with pipes and pods

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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I have a 1978 GS550E I got recently, and I'm doing a lot of work on it in preparation for a long trip I'll be taking soon (see this long thread for more info). Part of that is replacing the stock airbox (and missing filter) with pod filters, and replacing the rusting stock 4-2 pipes with a 4-1 header and muffler. I also took the carbs apart and cleaned them thoroughly, blew carb cleaner and compressed air through all the passageways and put them back together. The bike shop opens tomorrow after the holiday weekend, and I want to get a bunch of jets and start getting the jetting sorted out to get it right at all throttle ranges.

I've read a lot of info, and had some good recommendations given me about this, but right now I want to know what other GS550 owners with pipes and pods (or other airflow modifications) have done with jetting and how it has turned out. Mine has the stock size 80 mains and size 50 pilots (actually that's the size of the mini 2nd pilot underneath the first pilot which is size 15) and before I did anything, it had a slight hesitation off idle, decent midrange power, and very little top end power. So, what have you done to your 550 as far as airflow mods and what size jets and what settings on the mixture screw and fuel metering screw did you use, with what results?

Alex
 
I too have a 78 GS550E. I have K&N pods, Kerker 4-1 header with a universal megaphone muffler that I just removed the Baffle from. Prior to removing the baffle, I had mains of 90, and pilots of 20 & 50. With the needle set at the 2nd notch from the bottom. Well after removing the baffle I tuned the carbs and found that I have the best power band with 102.5 mains and 25 pilots. I left the needle alone, but after a ride last night I started noticing that the bike would bog slightly in mid range cruising speed. WOT it flies and idles better than it did before the changes. Later today I am going to pull the carbs and lower the needle one notch back to #3 see if that relieves the slight bog. It's not bad, just have to open or close the throttle slightly and its gone. But I figure it's just slightly too rich, so I'll try leaning it out.
 
Contrary to what you may be thinking it is probably lean.
I chopped the mufflers off of my bike and stitched on some punched out H-D mufflers. My bike was lean at idle after that so I adjusted the idle mix screws till I got a coffee brown burn at the plugs. Then I took it on the highway and the bike bogged down at 4.5k rpm. It would absolutely FLY when I gave it WOT so I knew at that point I wasn't getting enough fuel in the mid-range/needle-range. Just to be safe I did an extended run in the bog-rpm range and then performed an ignition chop and coasted to the side of the road. Pulled the outside pluts and sure enough.....lean. I buttoned it back up, went back home, took the diaphragms out and raised my needles one clip-position. I also replaced the o-ring on my float valve seat on the #1 carb.
Since then the bike pulls like a stuck bull in all rev ranges.

So try going a little richer instead of lean. Unless you have done a plug-chop at your bog-point and it shows rich.


EDIT: If you removed your baffle it is probably running leaner.
My setup: Mains = 122.5
Needle clip= 4th clip down from the top
mixture screws = 3/4 turn out.

This is with EMGO pods and a punched out set of H-D mufflers clamped onto the stock header pipes.


:)
Dm of mD
 
Detman101, these guys are trying to jet a 550 with VM carbs, not a 750 with CV's. :)
 
doh.gif
 
Well, I wasn't sure what to do about getting the right jets for my bike, I didn't know which ones would be right and didn't want to buy the wrong size and not be able to return them. I have a '78 GS750 in terrible shape as a parts bike, and it has 105 main jets, so although I was pretty sure they're too big, I pulled them and put them in my carbs just to see what it's like. The bike runs fairly well through all throttle ranges now, but still doesn't perform any better at WOT than at 3/4. My chain is so old and loose it's about to fall off so I don't want to ride very far or fast until my new chain and sprockets come in tomorrow, but just from riding around the block I can tell I'm at least close to the right jet size. I suspect it's too rich at WOT but didn't do a throttle chop test and pull the plugs to see. I did the throttle chop at 1/2 throttle where it feels like it's running well, and pulled the plugs which were a nice golden ashy brown color, so I think I have the needle set correctly (at the bottom notch, 2 notches below stock).

I also met another GS owner today who actually lives on the same small street in the same small town as I do. He has a '78 GS750 which he just bought a week or 2 ago, it's in very good shape and tricked out with cast aluminum wheels, dual front disc brakes, and air shocks from a later model bigger GS, and mufflers from a Harley (the kind it's rumored you can get for free). The previous owner was an older mechanic who kept it very clean and in good shape. He had a Corbin-style double-bucket touring seat which the new owner had swapped for a more stock-style seat, and didn't know what to do with the touring seat. I gladly accepted it as payment for hooking up the wiring for the lights on his boat trailer, so now I'm the proud owner of a rather nice comfortable touring seat, which will be nice after 10 hours in the saddle.

I'm still hoping to hear from other GS550 owners about what airflow mods and jetting they've done. I'm not satisfied with mine yet and would love to hear your recommendations.

Alex
 
Alex

I have the pods.. and a no-name 4-1.. To be honest, its been about a year since I rejetted.. but I'll be into the carbs soon and will let you know what I installed.. My bike has a slight stumble at 7/8 throttle, and I really need to do a idle, mid, and WOT plug inspection.. maybe this weekend....

My GS550 was ridden on a 28.5 hour straight ride through your area a year ago.. http://www.thegsresources.com/_forum/viewtopic.php?t=10260.. is the thread describing that.

Since that ride, the rider put a total of about 10,000 miles on it in the space of a year.. so you should feel confident in your engine.

I'd recommend the Dyna III to get rid of the points if you still have them. Just one less thing to worry about.

Good luck w/ your long ride

Cheers, Tim
 
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