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More help with the 81 GS550

  • Thread starter Thread starter khardrunner14
  • Start date Start date
K

khardrunner14

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I finally got the bike to idle half way decently and it runs. The problem now is the top end is VERY weak. I rode my brother's 78 GS400 and it feels like a rocket compared to my bike! It seems to pull a ok to begin with but there is nothing at higher revs. I struggled getting it up to highway speeds and had to have it at WOT to keep them there. I had trouble keeping up with highway traffic. It almost seems to lurch a little at the higher speeds...like it goes for just a split second then weakens. It could be that I am looking too hard for something, but that is what it feels like.

Here is a quick recap of the major stuff I've done:
- carb rebuild
- new petcock on the way
- plugged vaccum line from #2 until I get the new petcock
- new battery

Any ideas??
 
I forgot to mention, the air screws are at 1.5 turns out. I have the origional main jets in. I was running 89oct fuel.
 
So if you blocked the vacuum line to petcock how are you getting fuel to the carbs? Is the original airbox and filter in place?
 
I thought someone would ask that...sorry I should have included that I have it running on "Prime".

Yes, the original airbox/filter are in place. I had removed them to clean the foam element. I oiled the element and put it all back together.
 
Sounds like the bike is not firing all cylinders. Do all the pipes get hot when you run the bike? What did you do when you say you "carb rebuild"? New plugs? Assuming the carbs are okay, sounds like an ignition problem.
 
Check fuel flow and slide diaphragms for proper installation and pinholes.
 
I followed the carb rebuild on the main page pretty much to the letter. I got rebuild kits from oldbikebarn.com (the most expensive ones).

I have new plugs, but I didn't use them. The old ones look ok accept they are a little ashen white. I will try new plugs next time.

All 4 pipes were warm (some hotter than others) and I didn't hear anything that suggested I was a cylinder down. I'm new at this though, so I will double check that as well. I will be able to give you a better description tomorrow.

I talked to a guy today who said I may need to adjust a clip in the slide. He said it is right underneath the spring that is under the top cover of the carbs. He said it would richen it up if I adjusted the clip up one notch since the needle would then be higher...what do you think? I never noticed a clip or any kind of adjustment in the slide.

I have fuel getting to the carbs. I can ride the bike just fine. The problem is that it is sluggish, especially at high revs and past 1/4 throttle (when it's not supposed to be!). I looked at the diaphrams when I had the carbs apart and they were supple with no cracks or holes. I will pull them tomorrow and look again.

I feel like it just won't go, like I'm driving a 50cc machine with a speed govenor set at 60. Throttle response is low under load, especially if the faster I am going.
 
81 GS550 has CV carbs which means no adjustable needles. Some people mess around with needle shims but that's a story for another day - your bikes problem has nothing to do with needle adjustment.

I really don't have any good suggestions. Poor high speed performance typically has something to do with fuel supply (float bowls not filling properly or clogged jets) or with ignition issues. First thing is to install those new plugs and make sure everything is firing properly. One other last thought relates to plugged exhaust pipes. Rust destroying the baffle which then blocks the outlet is a long shot but a possiability. Not sure how to check it though.

Good luck.
 
Do a search on plug chops. When you put the new plugs in you will want to start right off doing them. That will tell you whether it is ignition problem (plugs will be black from being too rich) or fuel issue (white plugs from too lean). Then you can actually find the problem instead of just throwing stuff at it hoping it helps.

Good Luck,

Torry
 
Thanks, I'll take a look. I did pull #1 and #4 already and they were light gray-white. I'll check out plug chops.
 
I bet your fuel float bowls aren't filling fast enough to keep up with the high demand for fuel... That's why your plugs are white, as you're running lean.
 
How do I fix that?

I pulled the carbs today and the other plugs (both of which were white). I am going to rip the carbs apart again and see what I can find. Any suggestions as to what/where to look?
 
Yeah I'm still waiting on the petcock from flatoutcycles. I'll hav ethat in as soon as I get it.
 
go back through the carbs, check the little screens on the float needles to make sure they are not blocked with crud, some applies to the rest of the carb parts.

did your rebuild kits come with replacement orings? did you replace the o rings in the air/fuel mix screws? are you intake boots old and cracked, the 550 ones love to leak if they are cracked. did you replace the orings behind the intake boots? is the #2 carb vacume port sealed to not allow air to be drawn in? air will get drawn in if your petcock is shot. are you float hieghts right?
 
I did everything you mentioned. The only question I have concerns measuring the float heights. I have significant (3-4mm) of play in my float between when it hits the tab and when it hits the needle. Which side of that play do I measure from? If I measure with the float hitting the needle I get one measurement and if I measure with the float hitting the tab I ge another measurement.

Here is another way to look at it. If I have the carbs right side up, the float touches the tab due to gravity and does not touch the needle. I get a large measurement to the gasket then. If the carbs are upside down (easier to access the floats since they are on top), The float rests on the needle and I get a smaller measurement to the gasket. Which do I use?

Also, where on the float do I measure to?

Finally, I found 2 of my air jets (as labled in the carb cleanup series) were not all the way screwed in. They are the jets on the air box side of the carb on the left of the intake. The cylinders were 1 and 2. How much of an effect would this have? Are they supposed to be all the way in?
 
If you have petcok problems, what about trying to ride in the pri position.
Regards
Otto
 
That is how I figured out that my bike had no top end...I was in "prime" and that i the only way the bike stays running right now. I rode it on the highway and it had nothing...I liken the acceleration to my 98 saturn! It topped out around 65-70 at WOT. My brother's 78 gs400 with 113000 miles on it makes my 81 gs550 with 50k on it look like it's standing still! All this was in the "prime" postition.
 
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