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CV carb rejetting on '80 GSL

  • Thread starter Thread starter tirebiter
  • Start date Start date
Oh my, WOW ! Apparently two of the Aluminum plugs have been missing the entire time I've been using the bike. Now all of them have been removed. I am currently running 120 mains and 42.5 pilot jets. Was planning to order a couple of more sets of pilot jets even larger.

The bowl gasket looks like it entirely seals the hole. I don't see that there can possibly be any air leak. I can certainly put the two aluminum plugs I have, back in and make something that will fit in the other two holes, to fill the void.

If it matters ... the bowl gaskets are not the right ones either and they do indeed cover the holes where these plugs go. I tell ya, I got a real mess here that actually runs pretty good.
 
I bought the metric feeler gauge. Once I'm happy that the jetting is good enough and the bike is driveable by my standards, then I will go into the valve clearances. For now, I'm aware that they are close to being at zero clearance - when cold - and am keeping a jaundiced ear on the exhaust note as I drive off in the morning.

I hope you will bear with me Steve, just a little longer. When I do make valve adustments maybe it will help others to see what difference the valve clearances can make in the jetting and driveability of these bikes.
 
Actually there is no point in doing any more jetting checks until you get the valves correct and get those plugs in the carbs.

If clearances are not correct, you might not be getting the proper amount of air past the carbs that needs to have gas added.

As an example, if you are approaching true ZERO clearance, the intake valves will be closing a bit later, allowing some air to blow back through the carbs. Since carb jets don't care very much which way the air is moving, some gas will be added, making that slug of air just a bit richer, since it already had a dose of gas added the first time around. To make things worse, the next time that valve opens, that super-rich slug of air will go past the jets a THIRD time. Guess what happens. Yep.

Get your valves adjusted while you are sorting out some sort of plug for those two carbs that are missing it. Your gasket will NOT seal it sufficiently, you need that plug.

.
 
tirebiter said:
I bought the metric feeler gauge. Once I'm happy that the jetting is good enough and the bike is driveable by my standards, then I will go into the valve clearances. For now, I'm aware that they are close to being at zero clearance - when cold - and am keeping a jaundiced ear on the exhaust note as I drive off in the morning.

I hope you will bear with me Steve, just a little longer. When I do make valve adustments maybe it will help others to see what difference the valve clearances can make in the jetting and driveability of these bikes.
Click to expand...

Valve adjustment is the VERY FIRST thing to be done when you start tuning a GS. Get the valves right, and only then start fiddling with any carburetion issues. Oh yeah... adjust the valves with the engine dead cold. It shouldn't have been fired up for 12 hours or so.
 
Believe it or not, I realize the risk involved in not adjusting the valves at this time. I also realize there will likely be some more carb tuning to do after I adjust the valves. It migth be a simple mixture adjustment. It might be more involved like a jet change or two. Time will tell and I will report what I experience with this 850 engine.

As far as those pesky little aluminum plugs that are missing fom the bottom of 2 of my carbs go, I'll take a MUCH closer look into that after the weekend. "Little Suzy" will be carting me all around for work in several - 1 hour away - places, this weekend. Once I receive my next jet order (by Monday supposedly) I'll have the carbs off to put in an even richer pilot jet. Running 120 mains and 42.7 pilot jets now.

Now for the good news. The special lifter tool is on it's way also and I plan to adjust the valves sometime late next week. Yes, the way I'm going about this is backwards but so far, the gasoline I'm saving by using her regularly, as I slowly go through the bike, is worth it in my world.
 
I made a couple of plugs from fibrous organic cellulose to put in where I was missing the two aluminum ones. It doesn't SEEM to make any difference in how she runs though. I studied the passages and saw how a vaccuum leak could occur if the float bowl gasket was not in good shape. It seemd prudent to follow your suggestion on this one, Steve.

Presently running 120 mains and 45 pilot jets. Mixture screws are at about 2 turns. The flat spot at 3000 RPM has all but dissappeared entirely. In fact it is difficult to reproduce the slight hessitation at all, when I try. Occasionally it still rears it's head. I believe it's happening only when the throttle plates just start to uncover the low speed orifices in the carb bores.

This is where the fine tuning begins. If I can 100 % eliminate the flat spot, and still get good fuel economy, I'll be happy. Seeing about 39 MPG tankful after tankful but doing more 75 MPH driving than before.

Will be thinking along the lines of moving the needle in the air piston/slide and/or an air corrector jet change. I'm interested in finding out how much the overall operation of these carbs will be altered by changing the air corrector jets.

Expecting to do more driving than working on her carbs all this week. Will report back when I have a chance to try some other carb/jet changes.
 
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