Poor performance puzzling me..

[rustybronco]

The color down appears (as best I can see it) to be a light tan, but it is hard to see all the way down in there..

looks like the jetting is close.

he raised the needle and the stuttering moved lower, that's why I suggested lowering it to see what changes, if any, it makes.

We know the bike has the correct needle, but does the bike have the correct needle jet?

http://www.alpha-sports.com/spst/1981 GS550T/05.gif (#40 jet,needle)

 

[TheBigRed]

looks like the jetting is close.

he raised the needle and the stuttering moved lower, that's why I suggested lowering it to see what changes, if any, it makes.

We know the bike has the correct needle, but does the bike have the correct needle jet?

http://www.alpha-sports.com/spst/1981 GS550T/05.gif (#40 jet,needle)

Yes, the needle jet is correct, I verified this a week or two ago due to PM's with another forum member.

As for raising or lowering the needle from here, I'm not sure that will help any as at it's highest (with the spacer below the circlip) the dead spot comes on at 4k (and about half throttle) and it's lowest (spacer on top of the circlip) the dead spot comes on at 5k. By logic anywhere in between (ie using radioshack washers) will just vary where the dead spot appears.

I actually have another local shop that I want to see if they'll work with me on the jet purchases. They have been reasonable to work with in the past ($40 to rebuild forks that had the clips rusted in place!!). The question is whether they have the jets on hand to try out or not.

Duane's Carbs should also be here today or tomorrow to swap my jets etc into to see if it's a problem with the carb's themselves.

Amos

 

[TheBigRed]

I'm thinking a re-jet shouldn't be needed as the exhaust had these holes in it before I started the project, oh almost 8 years ago, and I did not have any issues with the performance of the bike then, except for the transmission problem.

I have a set of 110 mains (the 550T uses 92.5 mains) and 160 Pilot Air Jets (the 550T uses 150 and most other 550's use 120)

So, is that too much of a jump to try out?

Amos

Ok, THIS info is good..

110 main is pretty big jump.. that what 7? 8? sizes there? Thats drowning probably. What do your plugs look like?

Never let it be said that I was afraid to admit I was wrong.

At the behest of Duaneage I pulled the carbs tonight and dropped the 110 main's in.

Long story short my issue at 1/2 throttle is gone.

I still have some surging at above about 3/4 throttle, so I may have to go up another size or two, if adding a little bit of oil to the filter doesn't help (I've been wringing it out a bit off and on so it wouldn't be too oiled)

Anyway, just wanted to post an update.

Amos

 

[TheBigRed]

Ok, just wanted to follow up one LAST time!!!

WooHoo!!

Called a local tuner to see what his suggestions would be for jetting the way it was set up, and he said the 110s were too big. Said I should go up one, maybe two sizes, which would put me at 97.5's.

Ordered some on ebay from nichesupply (3.65/jet6 with $1.88 flat shipping for however many your order). Should have followed up with them sooner to get them sooner. (Ordered Friday afternoon, sent a message Tuesday morning asking if they had processed my order yet got two emails within an hour saying they processed my order and it was shipping.) All that to say, if you order from them you may want to follow up with a message so they get on it, other than that the price isn't too bad.

Anyway, put the jets in Sunday (finally) and got to ride in to work this morning. It's pulling strong the whole way through, and beyond where I was able to go (I was on back roads and through towns, didn't have a chance to get on the highway, but the one straight stretch I did have her up to beyond highway speeds)..


Amos

 

[Nessism]

In your first post you said the jetting was stock. How did you get to 110 mains?

 

[TheBigRed]

In your first post you said the jetting was stock. How did you get to 110 mains?

When I re-did these carbs for use on the 650 (when I had it) I had purchased K&L kits. After I finally got around to cleaning the 650's own carbs, I left the K&L kit in and kept the stock parts in case I would eventually decide to do a 6/550 project with all the engine bits I have sitting in the garage.

So, basically I dropped the 650's main 110 jet in to see if it got rid of the problem described in the first post. Which it did, but then created a problem above 3/4 throttle, which after some searching pointed to being too rich on the main. So at that point I knew I had to come out somewhere in between. I was about to drop the gun and purchase several sets of sized from nichesupply, but after talking to a local tuner it was suggested to go on the lower side of the middle ground, or 97.5's to be exact.

So, now I have a small supply of jets for myself, but from what I"ve seen, the 92.5's are the smallest anything uses, and usually (as seen in my case) are way to small once modifications take place, so their basically going to be junk jets.

(how is that for a long answer to a short question.)

Amos