Nero's Pods come to haunt him. GS550 Jetting help.

[Nerobro]

Here's the setup.

1980 GS550E:
550 L Exhaust, Nearly gutted
Emgo Pods
Stock 550 carb setup.

last year, with the gutted exhaust, I was running quite lean.

The bike WOULD start. A little choke, and it would actually jump to life pretty quickly.

The bike would not rev above 3500rpm. it would die as soon as the slides started to come up.

Using the chart at the motorcyclecarbs.com site, I decided going up three main jet sizes and one pilot jet would be a good plan.

I was able to buy the 100 main jets at the local honda dealer. They did not have the 42.5 pilots that the page suggested.

We installed the 100 main jets on the bike. The bike could then rev to 5500rpm. Before dieing.

When it dies, it's a bucking, stuttering death. And the engine drops below the critical rpm, and comes back again. On the road I can wack the throttle wide open, but it will sputter at a lower rpm. (engine making more power... sucking more air, opening the slides further....)

We then took the slides out, and removed the spacers on top of the needles. (these are non adjustable needles, but there was a spacer I could remove) With the spacers out, I could actually rev the engine to redline. However under load, it starts showing problems at 5500, and the engine will not continue past 6-7krpm

I "think" this is a needle issue. And I just can't get the needles rich enough.

now for the fun part. And I now get to admit the sneaky bit. I have GS650 carbs. (same bs32ss carbs) 110 jets, 42.5 pilots. Rich on the jets, and should be perfect on the pilots. The bike will not start with those carbs on it. it "could" be that the starter carb's are gummed up... because if I "manually" choke the carb by putting my hand over one of the bellmouths I can get it to start for a moment.

SO, what's the next direction to take?

Or should I just install the 650 pistons, barrels, and head and try to make that work with the 650 carbs? I'm persisting with the 550, becuase I will just need to do the same work again on one of my other 550's

 

[gspaul]

I would have gone 4-5 sizes up on the main jets,if you go to an electronics store you can get tiny washers and use those as spacers under the circlip on the needle.
We got the adjustable carbs here just like the UK.
I have a few spare sets of carbys on my bench at the moment, I would guess 1.5 notches from standard as a start,I can give you that in mm if you like as you have no way of nowing what that is.

 

[first timer]

if you try the 650 carbs, make sure they are clean other wise you are just wasting time,

next, try running th 550 carbs with out filters see how that works, next i don;t know what it's called at the moment but their is a hole on about halfway up on the carb mouth filter side, either on the left or right, i thinks it;s a air piolet jet? when i did my jet kit it came with a reduces that i needed to put in that hole and super glue in, it reduced the opening of that hole by 75% this was dynojets way of reducing the air mix into the carbs. keep on my but and i'll see about scanning my jet kit parts list maybe you can pull some inof off it that will help you not buy a jet kit.

-ryan

 

[Nerobro]

The pilot jet was my first guess as to why the 650 carbs wouldn't work on the 550. I will try exchanging those.

The 550 carbs without filters runs leaner. and dies off 500-1000rpm lower when under load.

Methinks I should just go ahead and order the canadian needles. Or try the adjustable needles that came with skreemers dynojet kit.

Can you measure the orafice in your restrictors?

I have this funny feeling the 650 carbs will just work when I throw them on the 650 barrels and pistons. Maybe I should get that done tonight. I just want a working bike for the crud run.

I'm gonna have to publish the results of all of this aren't I? ;-)

GSPaul, I guess I'll go and pick up some 105's. as it stands, I have 92.5, 100, and 110's. 40, and 42.5 pilots. And I don't recall the air pilots I have.

The largest american mikuni distributor is just down the road from me. I'm going to call them tomorow, and ask for reccomendations and to see if I can get OEM adjustable needles.

And yaknow... I can get my carbs in and out in less than 5 minutes now. *grins* I really.. really... enjoy that.

FirstTimer: What exactly are you running. Joe pointed me at a place where I can translate DJ jets into Mikuni sizes. it's not perfect, but it's a good start.

 

[Nerobro]

While I got in contact with fox distributing, they handle only comercial, not OEM carb parts. I did however find someone who could order the needles. http://www.randbmotorsports.com/ will get them for me. $10-15 a needle.

I'm buying 105's today.

 

[Nerobro]

I bought, and tried the 105's. The engine was even stronger. But it still died at high loads. We tried the 110's as well. And frustrated, we compared the 650 carbs to the 550. The springs in the 650 are heavier. Which will keep the slides down further. I'm not exactly interested in that.

We swapped in the dynojet needles from the later 550e. The needles are 2/3 the diameter of the stock needles. From just off idle, to 5500 rpm the engine is superich. But from 5500 to redline it pulls like it should.

We are going back to the stock needles, and going to try 140's. I called Factrory Pro today, and they suggested I go up 10-20 jet sizes from stock. The number that the owner pulled out was 130-140ish. And maybe going one pilot jet larger. Evidently, the 550 intake was very, very restrictive.

So, we have the bottom end jetted right. Just need to feed my hungery bike

 

[Nerobro]

So, today, I went back to the stock, raised needles. I visited the honda dealer, to pick up 140 mains. And... Failed. They didn't have 140s. But they did have 130's. So I bought those.

I installed them. And went for a run. Ilde to 5k, the bike runs strong. Dies off around 5500, and by 6500 it's back, running hard straight to redline. The plugs read a little lean. Much less lean than they ever have before for me. It's looking like 140's will be about ideal.

Not a bad guess for a number pulled out of a guys behind. I called the guy at factory pro again today. Told him how close he was to getting it right. He wasn't to suprized, and he went ahead and told me the rest of the steps of tuning the carbs.

he suggests tuning the carbs backwards. Getting the main jet right first, Then tweak the needles. Then work on the pilots.

He said the ideal would be to have custom needles... but this is the "old school" way of doing it, and is cool in it's own right.

 

[Nerobro]

Well, it turns out I was using the needles to help compensate for way to small jets. putting the needles to their stock location, blocking off half the air filter with tape, and going to 137.5's has the bike running like a scaleded cat. I want to pull the tape off... but there's no time to do real testing before the crud run tomorow. And Ireally want a working bike, versus the fastest bike.