idle: achieved

[Guest]

so...

Bought a non-runner '79 GS550. PO says the engine failed (not seized) so he put in one from an '81 550 but couldn't get it to idle. He was a mechanic (triumph), so this worried me. Says the bike was his sons, if it was, good MM is not hereditary. The '79 has VM's and '81 CV's (BS32SS). '79 intake boots won't fit the '81 head so I'm using the CV's for now. I might bolt the '79 head on so I can use the VM's, or not. Going to rebuild the (failed?) '79 engine once I move the bike out the shed. Also, the '79 air filter boot box won't fit the CV's soooo, k&n rc-2382. Basically pods, but of the dual variety. Main jet on the CV's is 137.5. Haynes says it should be 97.5. Pilot was 40. Pistons are proper minging, carbon city. Might squirt in some seafoam (and some in the fuel) and see what they look like then.

So here's what I done so far (in no particular order) :

New starter relay , The oldun didn't work, I gather PO just kicked it, no kick on the '81. Tests concluded relay was at fault, replacement confirmed this.
Replaced the regulator and the rectifier (they're separate on the '79) with the electrex reg/rec. test's didn't show fault but from what I've read....one less worry
Carbs cleaned, twice. Okay once if were only counting a proper clean (as per described in your docs)
New plugs and gapped as per spec. Olduns looked fine, but again, one less worry.
Valves: exhaust within spec (.04-.07mm) Intake spec is 0.02-0.05mm. Two valves are 0.04 and two are smaller. New gauges in the post (current ones min0.04)
Good compression, don't remember now but I checked on here and found similar results.
New intake boot rings (boots themselves in good knick) and exhaust gaskets
choke cable and plunger up to handlebars
rejet to pilot 42.5 and main to 105. Idles great now, but a little sooty on the plugs. might try going back to #40 and fiddle with the pilot mix to see if I can get a good colour. Once I get it out the shed and on the road I'll run a chop to find out what's up with the main jet size. In the meantime can anyone tell me what is correct stock main jetting for '81 550, 97.5 as per Haynes or the 137.5 I found in there. Maybe the '81 gs550 my engine came from had performance exhaust and filter hence the massive up-jet. I have stock 4-1 with the aforementioned k&n 2382.
welded an angle iron across the tail and built a flat seat to go right to the back ,new tail-light/plate mount. Don't judge, I want this to be my new work horse and I need a flat tail to strap my tool-bag to. Going to weld up a pannier rack at some point too. I'd call it a street tracker if names like that didn't make me cringe.
Came with no side panels so I welded up a new battery box to sit right up under the seat along with the relays, fuses, reg/rec, etc.
Various other bits, clutch adjustments, paint, new speedo, controls, new oil (as recommended)....Just remembered I forget to change the filter, on it now.
after cleaning and rejetting the carbs I set the mix screws to where they were at before as the manual says these are 'preset' seems fine but there is quite a variation in how many turns out they are, stick with what works right?
I'm sure there's something I missed, I've been in the shed many hours this last month.

Sorry for the long post, I'm hoping this will save time with back and forth questions later.

I want to do as much as I can from my shed before I bring it round. It takes three men to coax this nag through the garden path to the front of the house so once she's out the stable, she's not coming back until next winter at the earliest.

I'd like to open up my exhaust to get the most out of the filters but don't want to spend a fortune. any suggestions? It's stock at the moment (4-1)
tyres are: front 19 x 3.25 rear 18 x 3.75 (according to Haynes). I can find the rear size anywhere and I'm on the tread limit now, will 18x 4.00 fit?
I'll put on the dyna coils at some point, I've ngk caps on the plug leads (PO replaced)
Aside from final tuning, which I can't do in the shed (please tell me I'm wrong) what else should I do?

I love this bike. As much as the manual is a must have, if I had to choose between my Haynes and GSresources I'd burn my manual immediately! You boys are the nuts!

I've read all the docs and welcome pack info. Very helpful, thanks.

More questions to come, just figured I'd get this out there first.

Thanks again!

[GSX1000E]

Welcome. I don't have Euro specs for that bike but in the U.S. the '81 came stock with: 92.5 mains, 40 pilots and 150 air jets. With your not stock 4-into-1 exhaust and those paired air filters,
It will probably run best with 102.5 or 105 main jets which you have currently. I would change the pilots to the 40's, keep the 105 mains installed, adjust the valves and install new clean plugs.

[78550GS]

It wasn't mentioned, so I will suggest using a manometer to sync the carbs. You should be able to get really close to final tuning this way.

[Anonymous]

Going to sync with my vacuum gauges (not mercury) once I can confirm my valve lash is within spec. I'm a bit concerned about the variation in my idle mix screws. As the manual says preset, after cleaning, I put them back to whereabouts I found them at (from 540-1080 degrees out from seated) --side note-- Is a 'turn' 360 or 180 degrees? Best to sort out the mix (and everything else) before a sync methinks.

So I guess my question is this: should all the idle mix screws be set to the same # of turns out?

Thanks again

[Anonymous]

Thanks, I'll plug in the 40's tomorrow. New clean plugs you say...considering the plugs haven't been used, aside from 3-5 minutes at idle, can't I just give em a clean?

[GateKeeper]

A full turn is 360 Deg.

[78550GS]

I always set them the same amount out to start and adjust from there. Not sure where yours should start at.

[GSX1000E]

Thanks, I'll plug in the 40's tomorrow. New clean plugs you say...considering the plugs haven't been used, aside from 3-5 minutes at idle, can't I just give em a clean?

Those plugs should be fine. Just clean them up with some carb cleaner or brake cleaner and gap them at .024-.026"
Turn the fuel/air screws in until LIGHTLY seated and then back them all out 3 full 360 degree turns. You will most likely have to turn them in up to a half turn or 180 degrees.

[Steve]

The "preset" setting for the mixture screws was done with the use of sophisticated equipment at the factory that could calibrate each carb/jet combination to optimum settings for meeting EPA standards. While most of them probably fell into a tight range of settings, I am reasonably certain that they were NOT all exactly the same.

The same thing will hold true today, but we are more concerned about rideability than meeting EPA standards, so the settings will be different. Do not be concerned if one carb ends up at 2 1/2 turns, two of them about 2 3/8 and one at 2 3/4. They need to be where they run the best, not just set to a number and left there.

The reason for starting with excess turns (usually 3, in my case) is to provide a slightly-rich mixture that helps with cold starting. The tuning process will lean out the excess, taking it down to where it should be.

.

[Anonymous]

Put the 40's back in and it wouldn't idle, even after warming it right up. Without the choke it would just stumble to a stop regardless of the throttle stop and idle mix screw's position. Turning them (idle mix) right out (5-6 turns) improved the idle sound but it still couldn't cope un-choked. Also, giving it more than 1/8 or so throttle, it'd bog down and die.

I should note at this point that I had been measuring my float height from the wrong spot and have since re-adjusted to 22.4 (where I thought I was before)
I had measured from float plate (thing the tang hags off) rather than what is shown on page 9 here: http://www.mtsac.edu/~cliff/storage/gs/BS32SS_Carbs.pdf
So what I thought was the proper height was really 2mm to low (or high? I get confused udside downy, either way, to much fuel in the bowl.)
My fuel level is now lower (and to spec) which explains the sooty plugs before.
Hoping that when I plug back in the 42.5's (today) I'll be back to a great idle but without black plugs.

Assuming this works, when adjusting my idle mix screws, should I keep adjusting them to get the fastest idle than lower it back with the throttle stop? This is how I would do it were the jets stock but with a size larger pilot I thought it might end up rich. Should I just set them all to wherever sounds best and leaves the plugs looking good?

Also, When I was going through the gears(with the ignition off) it stops at four. The bike is rather confined where it is now, so I can't roll it to see if it'll come into gear.
I shouldn't expect to be able to shift through the lot from a standstill should I?
I'd be devastated if I finally got it out on the road only to find out I need to strip it all down to replace 4th gear or a bent selector arm.
Need I worry?

Thank again.

[78550GS]

The lack of idle without choke would indicate a dirty pilot circuit to me. Did you run some fishing line through the pilot circuits? I would also grab another set of new plugs. I'm not sure about your carbs, but I do know some of the CV's need a supple pilot plug in order to idle correctly. You can get some of those from Z1.

[Anonymous]

Put the 42.5's back in an it runs great, Checked all the pilot circuits (with petrol and compressed air) and all are equally unobstructed.

Should I adjust each mixture screw to produce the highest rpm than lower with the throttle stop? Would that then be providing the ideal mix?

I'm eager to get them synced but obviously need the mixture to be right first.

Plugs seem fine but I've got new ones coming in the post anyway.

Thanks

[Steve]

Put the 42.5's back in an it runs great, Checked all the pilot circuits (with petrol and compressed air) and all are equally unobstructed.

Should I adjust each mixture screw to produce the highest rpm than lower with the throttle stop? Would that then be providing the ideal mix?

Ideally, you should be running at, or near, idle speed, so basically in the 1000-1200 rpm range. If tuning a mixture screw starts taking you over 1300, back off on the idle speed screw to get it back down to about 1100.

Suggestion: do the mixture screws twice.
Treat the first go-round as the 'rough' setting, just to make sure they are all in the ballpark. I then go through them a second time, just to make sure that is the right setting.

I'm eager to get them synced but obviously need the mixture to be right first.

Personally, I would do a vacuum sync before tweaking the mixture screws.

Think about it this way: let's say that one carb (let's pick on #2) is closed more than the rest of them (which shows as a higher vacuum on the gauge). It's not really contributing to the power of the bike, so adjusting the mixture screw really won't have any affect at all. Get all the carbs pulling the same amount of vacuum, so you know that they are all contributing somewhat equally, then do your fine-tuning on the mixtures.

Another suggestion: leave the vacuum gauges connected while doing your mixture tuning.
You will find that, as the engine speed rises ever so slightly, the vacuum also rises. That is because the engine is running faster, but the throttles have not changed their openings, resulting in more vacuum. You will find a setting where the vacuum level is highest (engine speed, too), then lean it slightly until you find the point where the speed drops considerably. Richen the mixture about 1/8 turn to get just above that drop-off, then go to the next carb.

This works well because it is a visual thing. Some mechanics are tone-deaf and can't hear the engine change 50 rpm. The tach usually bounces too much to see the difference. The vacuum gauges will rise and fall, making it easy to see.

.

[Anonymous]

Personally, I would do a vacuum sync before tweaking the mixture screws.

Think about it this way: let's say that one carb (let's pick on #2) is closed more than the rest of them (which shows as a higher vacuum on the gauge). It's not really contributing to the power of the bike, so adjusting the mixture screw really won't have any affect at all. Get all the carbs pulling the same amount of vacuum, so you know that they are all contributing somewhat equally, then do your fine-tuning on the mixtures.

.

Good point! I suppose I figured that if one or some of the carb's idle mixtures were off it would effect the vacuum. I guess this might be tue, but more so the other way around as you pointed out. Thanks!

Another suggestion: leave the vacuum gauges connected while doing your mixture tuning.
You will find that, as the engine speed rises ever so slightly, the vacuum also rises. That is because the engine is running faster, but the throttles have not changed their openings, resulting in more vacuum. You will find a setting where the vacuum level is highest (engine speed, too), then lean it slightly until you find the point where the speed drops considerably. Richen the mixture about 1/8 turn to get just above that drop-off, then go to the next carb.

This works well because it is a visual thing. Some mechanics are tone-deaf and can't hear the engine change 50 rpm. The tach usually bounces too much to see the difference. The vacuum gauges will rise and fall, making it easy to see.

Well helpful! I've read loads on carb tuning (GSR and elswhere) and nobody has ever mentioned this. It seems so obvious now I think about it! I've managed to loose a damping screw from my gauges so I'm going to try and fabricate one tomorrow. If that fails I'll just have a go with a bouncing needle and swapping dampers every so often.

Thanks again!

[Steve]

Good point! I suppose I figured that if one or some of the carb's idle mixtures were off it would effect the vacuum. I guess this might be tue, but more so the other way around as you pointed out. Thanks!

Actually, a vacuum sync on the carbs is strictly a mechanical operation, it has nothing to do with combustion or the quaility thereof.

In fact, you could hook up a contraption to spin the crank (think 'racing external starter motor') and sync the carbs without ever turning on the ignition key.

.