[bazill13]

A bit long winded but here we go.
I have recently acquired a '90 across, and am trying to solve some idling issues.
Firstly some info on the issues:
To start from cold, full choke is needed then as soon as it starts (usually first time), I have to turn the choke off immediately or it dies, and to keep it idling I need to give it a little throttle until it is warmed up, and then it keeps idling at around 1700 rpm.
Giving it any choke (even after it's warmed up) increases the revs for a few seconds and then the revs die until stalling.
Occasionally, when idling, the revs will increase automatically (up to around 3000rpm, but sometimes more). This mostly seems to happen after revving and letting the revs drop back, they drop back to around 2000rpm then start to automatically increase, then I have to back off the throttle idle knob (black knob on LHS) to bring the revs back down

I have recently (over the last month) replaced spark plugs, oil & oil filter, throttle slide holders, coolant, battery and alternator/stator (I think thats what its called) cover gasket that was leaking oil.

After replacing the spark plugs, I have inspected the new ones occasionally and they have a dry black sooty residue on them (running rich?)
The plugs from cylinder 1 & 2 also had what appeared to be a 'white spot' on one side of the tip.

When testing the spark against the frame, it seems to be weak, not a strong bue spark that I've read about, but not knowing what a 'strong' spark is meant to look like, I don't really know if it is weak or not

Now for the questions:

1. I am planning on pulling the carbs out and giving them a good check & clean, is there anything I should look for while I'm in there?

2. I removed a couple of the idle mixture screws (the 4 screws on the carbs that are meant to 1 & 1/2 turns out) to check the o-ring, but the didn't appear to be anything there. From the diagram in the workshop manual and from reading some other threads, there appears there should be an o-ring & a spring, but when I removed the screw I could see anything. Should the spring and/or o-ring have come out with the screw, or will they sit in the hole and have to be removed separately. I looked into the hole with a torch & didn't see anything that appeared to be a spring sitting there. Do I need to put something down the screw hole to try & 'hook' them out or if they are there should they be obvious and easy to remove?

3. The spark plug leads seem to just pull out from/push into the spark plug 'cap'. Is this normal or should the leads be 'fixed' inside the cap?

4. There's a bit of white smoke coming from the exhaust, that comes and goes after the bike has warmed up (usually most apparent when idling). It doesn't start until after the bike has been running for around a minute, so I am assuming/hoping it's only condensation.
I am hoping that it's not the head gasket, there was no water in the oil when I changed it, but when I changed the coolant it was a dark 'dirty' green colour, but wasn't milky. If there was oil in the coolant, would it separate out from the coolant in a distinct layer, or would it mix in to give the coolant a dark colour?

5. When checking that that the fuel pump was pumping fuel correctly, the fuel had a black tinge to it. Is this a dirty/clogged filter (assuming there is one)? Does anyone know what type of new filter is needed (if I need to replace it)

Any insights appreciated

[bazill13]

Okay, I've removed and cleaned the carbies & now have a few more questions:

1. When checking the throttle slide holders (the white clip thingies) that I repaced recently, two seem to be snug, but two seem to have a bit of play back & forth inside the black cylindet that they sit in (piston valve?)
They don't seem to want to push any further in, but the play back & forth is noticable (maybe 1mm), and when its pulled back there is also play from side to side, but not when it is pushed all the way in. Is this a problem with the piston valve, or something to do with the jet needle?

2. When checking the float height, is this the correct way to do it:
- turn the carbs upside down so floats are at top
- move the float so that it just starts to pull (put tension) on the needle valve
- measure the height from the flat surface of the carb body (that the gasket sits on) to the top of the black float

this is how I interpret how the manual is saying to measure, but its a bit unclear and I would like to clarify if I'm reading it right

3. When I did a compression test, two cyliners on LHS (1 & 2?) where 150psi & 145psi, but the other two on RHS (3 & 4?) were both 120psi. Is this a sign the head gasket is leaking, or would the compression be lower?. There is no sign of milky coolant or water in the oil. Is there a way to tell whether the head gasket is dodgy, would the bike be running rough? The bike seems to run alright, but doesn't idle very well, it's a bit al over the place, will idle at 1700rpm, give it some revs and will drop down to around 3000 to 2500prm then after a little while sink back down to below 2000rpm. Would a head gasket iisue or worn rings cause idling issues?

Cheers

[Siddy]

I know this post is old but I can across it when google searching so I guess others will and might benefit from a reply to your questions.

The ruff idle (if your slide clips/holders are new and working properly) is due to the carbies not being balanced, you balance them by screwing the 4 adjustment screws all the way in, then backing off 1.5 turns and then use a carby syncornizer (you can make one from tubing an bottles of water) for the final adjustment (yes this part is necessary). Sync carby throat 1 with 4 and 2 with 3.

Compression should be 190-200 for this motor. 120-150 is terrible to be honest and I would not spend money on that bike. It's not only the low compression but also the fact that it is so varied, 30psi is a big difference. Even if you get it tuned and running it will always vibrate and have a significant power loss. The crazy idle is because of the carbies not the compression, even worn motors can idle stead-ish.

The carby slides should not have any play, nor should the holders, take them out and use steel wool (not the stuff you wash up with, the stuff that looks like a ball of wool but is steel) to scrub the bores in the carbies until they are smooth and shinny. Fit new clips again, if necessary.

Yes the leads just pull in/out of the spark plug, that's how they work. The other method is little caps screw onto the spark plugs and then the leads clip into them, that is generally for cars and the other generally for bikes.

White smoke: what matters is when you accelerate does it blow smoke? Have someone watch you when you take off cause its not really possible to see when your riding and its not the same when its just being rev'ed in neutral.
If it blows smoke under load, well thats pretty bad.

Blown headgaskets do not always lead to water in the oil or oil in the water, it depends on where the headgasket breach is. You can still buy headgaskets from Suzuki, but if you have evidence you need a new headgasket first take the head off and instect it to see if it is even worth getting a new one or if too much damage has been done.

As for the smoke and really low compression, either its cylinder wear or valve/valve seat damage. If I had to bet, I'd put my money on valve/valve seat cause the cylinders are not common to wear much on these motors but the valves will be easily damaged if the shims are not done regularly. They are supposed to be done every 20,000kms. Check the cam clearance, if it is a lot smaller than the specs (0.20-0.30mm intake, 0.17 - 0.26mm for exhaust) it is likely a lot of damage has already been done, consider swapping the motor or the bike. Cam clearance gets smaller over time, btw, cause the valve seat shrinks into the head - something I learned recently ;P