CV carb rejetting on '80 GSL

[tirebiter]

Took out the 115 mainjets and put in a set of 120 mainjets today. The full throttle bog has completely disappeared. Still had to turn the pilot screws out to 3 turns though. Still have some backfiring upon decel but only from above about 4,000 RPM.

Considering trying a set of richer pilot jets, since full throttle seems ok now. Will give it a tank or two to measure fuel usage.

Meanwhile I also did some bench-synchronizing. MUCH BETTER !!! More steady idle speed too.

Adjusted the throttle cable free-play down to almost nil. Now when I turn the handle bars all the way to the right, the RPMs rise up a thou or 2 and drop right back to idle when I straighten the steering. Nothing odd happens when I turn the handlebars fully to the left.

Do I need a new throttle cable or do I need to redo the cable routing ? Are these bikes that sensitive to cable routing ? I tried a couple of different routings but still, the cable somehow gets pulled and opens the throttles a little when I turn all the way to the right.

I really do not want to reintroduce freeplay in the throttle cable to alleviate this glitch. I like not having to find where the throttle grip begins to open the throttles, everytime I want to accelerate.

Anybody ever see this "turn-right-fully-and-increase-idle-RPM" before ? Anybody have a solution ?

 

[Spyderman]

most all GS's need
0.5 to 1.0 mm cable free play to allow for the bars to be turned you need to adjust the free play until the bars can be turned without affecting the RPM of the bike
if not then it is unsafe for you to ride and can cause you to put it down and this will more than likely be at the most inopportune time that can be chosen

 

[Steve]

I, also, appreciate the absolute minimum of free-play in the throttle cable, but you need to add some to yours. Add about 1/2 turn of the adjuster, then turn the bars to the right to check. When the idle speed stays steady, lock the adjuster in place.

Oh, virtually ALL of the bikes do that.

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[tirebiter]

UNACCEPTABLE ! But for now I guess I'll just have to grin and bear it. I will DEFINITELY be looking into how to make this problem non-existant ... if at all possible.

It certainly helps to know that this is not a singular problem on only my GS.

Steve, you are a wealth of good information.

 

[rudeman]

UNACCEPTABLE ! But for now I guess I'll just have to grin and bear it. I will DEFINITELY be looking into how to make this problem non-existant ... if at all possible.

It certainly helps to know that this is not a singular problem on only my GS.

Steve, you are a wealth of good information.

I don't know of any motorcycle that does NOT require some free play in the cables. Aside from the annoying idle speed change, the cables will last longer since you're not preloading them.

 

[Steve]

Personally, I don't understand why the speed changes when there is no clearance. After all, the cable sheath is anchored at both ends and does not change length. The cable is also anchored at both ends and does not change length. What changes to affect the relationship of the two cables that make the idle speed go up? :-k

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[rudeman]

Personally, I don't understand why the speed changes when there is no clearance. After all, the cable sheath is anchored at both ends and does not change length. The cable is also anchored at both ends and does not change length. What changes to affect the relationship of the two cables that make the idle speed go up? :-k

.

He might have a break in the helical sheathing. If he does then every time he puts tension on the cable sheath he could be pulling on the cable core. it might be remedied by proper routing. Nevertheless he needs to put some free play in there for durability.

 

[Steve]

Not sure I can buy into that "break in the sheathing" bit, as I have had that happen when I installed a brand new cable.

No disagreement on needing the free play, though.

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[tirebiter]

OK, not zero freeplay, not preloaded - but such a small amount of freeplay, that it is basically indescernable to my right hand - as I'm rattling through a bumpy intesection and trying to apply just the right amount of "barely opened" throttle at just the right time, to feel more in control and be smooth.

The stretched spiral-wrap or kinked cable concept will be thoroughly investigated over the weekend. I seem to remember this occuring on one other Motorcycle I had, years ago.

 

[tirebiter]

About the throttle cable and idle speed increase when putting the forks all the way over to the right. I tried securing the sheath/outer cable housing so it could not move along the frame tube and it did nothing. I found that by twisting the sheathing/nut slightly while securing the locknut on the throttle bracket at the carb, the RPM increase lessened !!!

Will investigate that further when I do the next jet change.

Put in 42.5 pilot jets today. I can't say the bike runs perfectly yet. Idle mixture screws stil lwant to be out more than 2.5 turns ! It still backfires upon decel. Still a slight flat spot (but less) just under 3000-3500 RPM when transitioning from level ground to going uphill. It also feels like there is less lean surge at all RPMs now. Acts like the carb diaphragms are doing a good job of maintaining RPM during elevation and pitch angle changes, without moving the throttle.

MUCH less handful of twist grip needed to go 75 MPH now !!

I have larger mainjets and will try the next size up 127.5, as time allows. Won't know which ones are too rich until I put them in. Getting there.

 

[posplayr]

Personally, I don't understand why the speed changes when there is no clearance. After all, the cable sheath is anchored at both ends and does not change length. The cable is also anchored at both ends and does not change length. What changes to affect the relationship of the two cables that make the idle speed go up? :-k

.

It is interesting and especially as it only happens when you turn right and not left (iirc).

maybe that is a clue.
When turning right the sheith is pulled stretching more than the cable is rpm goes up.
When turning left the sheith is in compression and the cable slackens.
Checking the slack would be sufficent indirect evidence of this theory.

 

[Steve]

OK, let's back up a square or three, if you don't mind.

I am VERY surprised that nobody (including me) has noticed yet that we don't know what bike we are talking about.

You started the thread saying it's an " '80 GSL", but there are SEVERAL bikes that fit that description, and all have different jetting requirements.

Also conspicuously absent is a statement whether you have stock airbox or pods, or if you have stock exhaust or a header.

If you wouldn't mind sharing those (somewhat IMPORTANT) details with us, we can make better suggestions.

.

 

[tirebiter]

Steve, you make some very good points. I added a signature and avatar to help clear thigns up. Furthermore, I find it odd that I finally started reading the "newbie" thread ... DOH !

OK embarrasing moment over now. I've been chronicaling my endeavors in another thread here : http://www.thegsresources.com/_forum/showthread.php?225303-Just-bought-non-running-GS850&highlight=

I have a stock air cleaner except I made the inner filter element support myself from some 20 gauge mild steel, rivited into an oval shaped band, after drilling numerous 3.16" holes in it. The element itself, is an aftermarket foam type similar to stock, I believe.

The exhaust is non-stock 4-into-1. Maybe Kerker. No markings that I can see. If it helps I can photpgraph the exhaust and in particular the mountings and clamp where the headers join the megaphone. Maybe somebody can positivley ID it, then.

All I know for sure is, it is VERY quiet. About a 1" to maybe 1 1/4" hole at the exit. Guess I should measure it. End of exahust pipe is about 4" diameter, Again I should measure. Will do today when I put in yet another size up on the mains.

 

[GSX1000E]

With your current set up, I would recommend going back to the stock 40 pilot jets and installing 122.5 or possibly 125 main jets.
Adjust the fuel screws and report back. You have already replaced the intake manifold O-rings and the header to cylinder head seals well also, right?

 

[Steve]

Steve, you make some very good points. I added a signature and avatar to help clear thigns up.

Thanks for the updates. :clap: :clap:

Now that we know what bike we are playing with, Eric has it about spot-on with jetting suggestions.

When my #2 son had his 850, there was a header on it of unknown origin and also "very quiet" (it's quiet enough that I am putting it on my bike

). We were running a stock airbox with a K&N filter insert. Carbs have 125 main jets, everything els was stock. Bike ran like a champ. Before we sold the bike, I swapped exhaust systems and carb jets with my 850. Since my bike is still in the "rebuild from the wreck" phase, I have not had it running, but expect it will do about the same as his bike.

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[tirebiter]

I went nuts on her putting in the largest mains I had - 127.5. Runs great but the backfiing is moreso now but of the "too rich" ilk instead of the "too-lean" ilk. Occasional, splashy and louder now, instead of quieter and constant like popping corn.

Still has the 42.5 pilot jets and mixture screws seem happiest (lean-drop method) at 4 turns now !!! Needed to turn in the idle speed adjustment screw to raise idle speed. As the engine warmed up, the idle went down. After warmed up and a test drive of a couple miles, I had to increase the idle speed a little more again! Definitely seems too rich now but I'm not sure what's going on with the mixture screws and the idle quality except it is about 20 degrees cooler today than it was yesterday.

Maybe I should have taken Steve's (and everyone else's on here) advice and stripped the carbs to begin with and elimentate the guesswork surrounding the behavoir/backfiring, I'm experiencing now.

I looked carefully and cannot see or hear any signs of exhaust leakage anywhere from the cylinder heads to the exhaust outlet. "O"-rings are in very good condition as are the mount rubbers even if they are the wrobng ones. I think the wrong carb mounts are on the bike. These are 2mm too small, but I am certain there are no intake leaks. At least not as far as I can tell by listening through a tube all around where leaks can occur. Spraying WD-40 near the cylinder head intake ports yields no change in the idle.

Backfiring had been almost non-existant the past day, running 122 mains, 42.5 pilot jets and mixture screws afjusted to 3- 3.5 turns (lean-drop method).

Will try Eric's suggestion with 125 mains and 140 pilot screws now and report back in a couple of hours or so.

Thanks everyone for all the help !

 

[Steve]

Maybe I should have taken Steve's (and everyone else's on here) advice and stripped the carbs to begin with and elimentate the guesswork surrounding the behavoir/backfiring, I'm experiencing now.

Every shortcut you take is just one more opportunity to do it over.

Please trust us when we make these suggestions and recommendations. We are not just trying to keep you busy doing "stuff", we are offering what will work to get your bike going. But, ... it also depends on having the correct information, such as year/model of bike and any modifications that have been done.

Not sure if I should ask, but somebody has to do it, ... have you adjusted the valves yet? :-k

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[tirebiter]

At the risk of sounding terrible I am leaving out a couple of aluminum pieces, when I go for this test drive.

They were in the bottom of the carbs loosely. They have a large diameter and a small diameter so they cannot get sucked into the carb bore. The hole they go in leads directly to the carb bore. The hole they go in also has a large diameter and a small diameter. The fuel bowl gasket covers the bottom of the hole. I can see no port, inside the hole.

Parts diagrams calls it a gasket - #34 on Carburetor diagram.

At a standstill, I seem to detect a bit of the flat spot I experience when going up at slight incline. Happens right aoound 3,000 RPM.

Steve, valve clearances are greater than zero and less than 0.002" cold. Checked, did not adjust any. Around 40 MPG on every tankful and firing on all 4 even when I first start it up from cold - on the choke - in the morning.

 

[tirebiter]

Mainjets 125, pilot jets back to the stock 40, idle mixture screws about 3-3.5 turns. Good, solid idle. Flat spot/lean surge around 3,000 RPM is back, especially when transitioning to a slight uphill. Lean backfire is as bad as it was before I tried the 42.5 pilot jets, previously.

I'm done for the day. Will be ordering a couple of more sets (45 and 47.5) of pilot jets, this week. "Little Suzy" liked the 42.5 pilots a lot. They will go back in as soon as I have time, until the larger ones arrive. Like I said, only way I know it's too rich is to make it too rich and come back from there. Maybe someday I'll get a wideband exhaust Oxygen sensor setup but for now, I have to go by feel and experience.

The 120 and the 122 mainjets I've tried already both seemed to work pretty well. Until I get the backfiring and the 3,000 RPM lean surge 100% eradicated, I won't worry too much about which mainjet is optimum.

So far she has run best with 42.5 pilot jets and 120 or 122 mainjets.

 

[Steve]

At the risk of sounding terrible I am leaving out a couple of aluminum pieces, when I go for this test drive.

They were in the bottom of the carbs loosely. They have a large diameter and a small diameter so they cannot get sucked into the carb bore. The hole they go in leads directly to the carb bore. The hole they go in also has a large diameter and a small diameter. The fuel bowl gasket covers the bottom of the hole.

If you have been leaving those aluminum pieces out on previous test runs, I am surprised the bike ran at all, let alone as well as it did. YOU MUST HAVE THEM INSTALLED for the carbs to work properly.

When you install them, give them a gentle tap to seat them. There should be a square-section o-ring that goes between the aluminum plug and the bowl gasket to keep them in place.

Please put ALL the parts back in the carbs, you may find that all of a sudden you are now running too rich, because you have been compensating for a MASSIVE air leak with those missing plugs.

Steve, valve clearances are greater than zero and less than 0.002" cold. Checked, did not adjust any.

Well, at least you checked them. "Greater than zero" still leaves a LOT to be desired, though. Keep in mind that tighter valves don't spend as much time on the valve seats to cool off, so will run hotter. As clearance approaches ZERO (and it always gets smaller on these engines), you stand a good chance of burning the valves.

Apparently you are using INCH feeler gauges, that is no problem. The thinnest feeler is usually 0.0015". If that does not fit, change the shim. Yes, it might take it just over the recommended clearance, but that is far less of a problem than running too small of a clearance.

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