Mech

The regulator's up front, on the right side near the steering head.

I'd take the cable off the engine end and see if the lever on the cases returns to center nicely.

I guarantee the workmanship.. But all my work is on used vehicles, and done in accordance with and after negotiation with the customer's needs and priorities. If the work is some compromise, and it nearly always is on some plane, then I advise them of the possibilities and implications.

Clear communication's the thing, making sure they understand what's being done and what might not be, and why. The whole crux of professionalism isn't this do it once and do it right bullshit, it's about your customer being able to have confidence in you.. Ask any lawyer or doctor or accountant..

If it's got a throttle cable you should check that's going right back when you throttle off. If the throttle's electrical you should check it moves properly, and goes right back of course, then check it's wiring. Check that it's not moving the handlebars that's causing it too.

Are you sure it's really going to full throttle.. like, if you have only given it half throttle, does it really move to full throttle by itself, or just stay at some revs.

Morning Chris. I'd think the oil would have to be really old before it effected the clutch badly. We've had wet clutches for a century and they are normally really good. I'd check the adjustment of the clutch. It sounds like it's dragging a little.

 If the adjustment is correct, it could be that the clutch is nearing the end of it's life. A common symptom of a worn clutch is that it drags a bit even when the adjustment's right.. But a worn clutch basket will also cause clutch drag(they get notches where the plates rub, and then the plates can't slide sideways in the basket like they need to as it engages and disengages).. or bent/buckled plates but that's unusual.

I grew up on two wheels. They say that when we ride quads, we have to apply our weight to the outside wheel on turns..We still lean in, but we put the weight on the peg/wheel that will drive us around the way we want to go. If you get more grip on the inside wheel it tries to push us straight ahead.. I've rolled off mine doing donuts in a big mud patch we have over the back.. My sons thought it was too easy doing donuts in two wheel drive so we started doing them in four wheel drive. Then they thought that was so easy.. so they started doing it with the front diff lock on..  We rolled a lot !

Well.. It depends whether I'm checking or wanting to grind.. I run cam covers and even in the old days carby faces over it. They say head's(on cars/trucks), should be ground to a fairly rough finish.. It would be about like grinding an aluminum bike head with 250 to 150. If you have a big surface though it makes a difference to the pressure you apply, and so to the finish you get. For big heads you flip them and rub the glass over the head. Generally I'd use 250 and apply pressure..

Haha.. My man. Way to go.

So if you are happy with doing donuts and rolling I figure you've ridden before.. and I'm not familiar with those models, so it's probably nothing useful, but.....

does it have a manual clutch or a centrifugal/automatic clutch. ? If it's like most quads and an auto clutch then I'd try adjusting it. If it's a manual clutch then I'd guess it's just a matter of getting used to the shifter and the right revs etc to change at. Lots of bikes are a bit hard to get into neutral once the bikes stopped rolling. It pays to slip them into neutral before you come to a stop, or sort of dump the clutch a little so it starts to lurch, then slip it into neutral as the revs and load comes off the gears.

I have seen two wheelers that have been dropped and pushed the gearchange shaft into the case buggering up the shifter till it's pulled apart and repaired, but I don't see how that would happen on a quad.

If the diaphram goes, it normally doesn't rip right to pieces and get through the small holes in the slide. Best fish whatever it is in there out though. Pull the slide and you can see down from the top. If it's not that blockage causing the problem then it sounds like a dirty carb or needle's come loose in the slide. First thing is pull the slide and check the blockage and needle(easy), then use the drain screw to check there's plenty of fuel getting through(easy), then pull the carby off and clean it(pretty simple). You could try a new plug first(cheap).

Yours is a K4.

If you pull it out it's a common size, but the genuine item has a superior outer seal to prevent dirt getting in..

https://www.mickhone.com.au/partFinder/fiche/suzuki/1991/lt-f4wd/secondary-gear-propeller-shaft#next

Good work.. The thing about things like this is that we have to be methodical, and really thorough.. we have to know absolutely that the first thing we checked really is right before we go doing any more steps.. otherwise we end up going around in circles..  Probably is a small split underneath somewhere you can't see. If you suck on that vacuum hose going to the pump it should build up vacuum and not keep flowing air.

After you've fixed the rest adjust the mixture to best lean and it should be right.

Good luck with the bolts on the manifold. Sometimes giving them a tap with a hammer and punch on top to spread the hex out a little works, and it lets the spray get down the threads.. and single hex sockets are good for rounded bolts. That manifold probably has an O ring between it and the head.. best change that too.

Sound's like a temp sensor problem to me.. no cold start enrichment. I'm not sure if these computers detect out of range readings like cars do to post a code. I'd use a gauge and check the temp sensor.

That's no trouble, these things can be frustrating. Even mechanics get frustrated, and often it turns out to be the simplest thing. Sometimes we walk away and have a coffee and when we come back everything just falls into place. You sound experienced and competent, you'll get it.

I've been assuming that you've checked any vacuum hoses it has...

Well if both carbies did it, and you say it was going right for a bit till you refitted the throttle cable perhaps it's just the cable ? Frayed wire in there perhaps ? No free play, routed wrong so it gets pulled when the bars are turned .. If you leave the cable off, and the duct from the aircleaner, then you could use a small screwdriver to operate the slide from the back, to test it's dropping properly when there's vacuum on it.

Yeah that's right mate.. air getting in before the carby is just more air.. it gets all the air it needs anyway through the aircleaner so a bit more unfiltered air makes no difference.

Starter fluid is a good way of finding leaks. Try that around the manifold.

If you wind the idle speed screw right out the slide should go right down and clack on the carby body, if you then screw the screw in you should be able to hear a different sound as the slide lands on the screw. If you make sure the slide  is going right down every time that would be a good start. Then wind it back out till the slide's sitting on the carby body. Then, wind the idle mixture screw right in, gently so you don't damage the screw or seat, and it should not run at idle at all. Start it up with a bit of throttle and see whether it dies right back to stopped when you throttle right off. If it does die then, then wind the idle speed in a turn or two and wind the mixture screw out a couple of turns. After that you wind the speed up till it will idle, then adjust the mixture till it runs at the highest revs it will, then adjust the speed either up or down as needed, then the mixture in or out to give the highest revs it will do at that speed setting. Keep doing those two adjustments till you get it at the highest revs it will with the least amount of slide lift. If it will idle, wind the mixture screw in and out to find the highest revs, then wind it in slowly till the revs just start to drop.. That's called best lean mixture and is where it should be when hot.

If those adjustments don't work, then you must have done something wrong in the rebuild. Perhaps the slide needle is in the wrong place, or the float level's to high, or the choke mechanism isn't operating properly.. Is the choke a butterfly, or a plunger ? If it's a plunger, check it's going right in.

It all started since the carby work, so it's either a bad(very rich) mixture combined with an air leak, or something wrong with the carby work.

Try those checks and adjustments, especially the slide going right down, and for an air leak around the manifold, and let us know how it goes.

Perseverance always wins.. giving up never does..  You'll win.

https://www.manualslib.com/s/suzuki+atv.html

If it's sucking air in from anywhere before the carby, it will just mix that air with the air going through the air cleaner, and not do anything.. except let dust in ..haha.

If it had a big air leak after the carby, between the carby and the engine, it should just run lean, or not run at all.. It would only make it race if it was also getting more fuel than it's meant to.

I've seen them race when the idle mixture screw was set wrong. So... is the idle mixture screw near the engine or near the aircleaner end of the carby ?

They have manuals in here, under "downloads". In my collection of manuals your year doesn't show a hose routeing plan, but in the later model manuals(which have the same systems) it does, so perhaps get a later model manual.

Ok, so I'm presuming your throttle cable goes to the left side of the carby. On that model there's one hose fitting on the left rear, that's the fuel pipe. The fuel pipe comes from the fuel pump which is under the front fender on the left side. The fuel pump has three hoses, one at the rear comes from the fuel tap, the front feeds fuel to the carbies left rear, and on the flat side facing the center of the bike there's a vacuum hose. That vacuum hose goes to the carby on the right front, but since you have a vacuum operated fuel tap it goes to the carby via a three way junction. The third junction goes to the fuel tap.  On the carby at the right rear there is a hose fitting, that's the carby vent pipe and it goes up under the range selector panel. At the end of that pipe it quite often has a three way junction fitting.. but nothing goes on the other two branches. I think it's just so it can't get blocked so easily.

There are two other model carbies that I know of so if that doesn't sound right let me know and I'll run through the other models.

All the hoses need to be thick walled. If you go to an auto shop they may sell you thin walled vacuum hose.. It doesn't do, ask for fuel hose of the size you need.

The small component you describe, it's either the fuel pump, or part of an emission control, but, if I'm reading your model number right you are in Africa ? And I doubt it has emission controls. If it's not the fuel pump, post a picture and we will see if we can identify it.

So a mikuni without a diaphram .. the cable goes straight to the slide ?

Well... Is this a diaphragm carby or an old fashioned one with the throttle cable going straight onto the slide ?

If you throttle on and then off quickly with the engine turned off, can you hear the throttle clack back against it's stopper ? What's the idle mixture problem, seized screw or damaged so the screwdriver doesn't engage ? If you are sure the throttle is closing right off, and it races, it might be just the idle mixture. The needle in the slide only effects from 1/8 throttle and up, so it shouldn't be the problem. The only place an air leak in would effect things is if it's between the carby and the engine, on that rubber manifold.. which can get old and cracked when you work on them.

The manuals do normally have a diagram showing the hose and cable routeing. Are you looking in a genuine suzuki manual or something like Clymer/haines ?

Failing that, does it have a manual fuel tap or an automatic one controlled by vacuum ? How many hose fittings does it have on the carby ? Does it have any emission control systems on it ? Does the carby have a diaphragm on top, or does the throttle cable go straight into the top of the carby ?

I liked the look of those two "wheelers'.. they looked like fun.

Here's what it's like over here.. My sons and their mate who runs adventure bike tours all over the world.. He's the one with the camera.

These are nine to twelve hour rides..

https://bit.ly/341yGMH

https://bit.ly/3IsN1Aw

I knew that snow was trouble !

Oh. that sounds like a good deal from Ebay.. I'd jump at that. Then it's just a quick swap job.. No wondering about worn things and hassling around finding parts..

I'd be inspecting all the rubber bits on it, like the rubber boots on the drive lines. Give them a bit of a twist and bend looking for cracks in the bottom of the corrugations. The carby has a rubber diaphragm in the top of it, I'd pull that out and give it a bit of a gentle stretch to see if it's got tears or is going to tear. There are rubber hoses to the fuel pump and tap that are probably getting old by now, and are pretty cheap to replace with fuel or vacuum hose from an engineering supply place.Those brake hoses at that age are probably suspect if they've never been changed, apart from the internal delamination and swelling they get cracks you can see on the outside. The front suspension bush bolts have a habit of seizing into the bushes, then turning in the chassis till they wear the bolt holes in the chassis, then they start hammering in there and really wear things up bad. It would be a good simplish job to take the bolts out and grease them. When you tighten them back up you do it with the weight on the wheels because the rubber bushes aren't meant to turn on the bolts, the rubber's meant to flex as the wheel goes up and down. It's important to tighten them up the last turn or two in their sitting position so they aren't preloaded with twist/flex. If you drive it up onto a couple of thick planks or hunks of wood to get a bit of ground clearance it makes that easy. In theory the rear suspension should be at risk of doing the same thing, but I've never seen it on the back.. but you could pull the bolts and grease them as well.. then they won't be seized if you ever have to do the bushes or take it apart.

You could check all the wheel bearings for play or noises. Grab the wheels top and bottom and try rocking them feeling for play, then give them a spin listening for noise, and turn them while twisting them top and bottom(to apply a load on the bearings) feeling for roughness.

You could adjust the valve clearance because that doesn't seem to get done ever..  Air cleaner element can be cleaned, oiled and reused. Oil the gear change and brake lever pivot.. I've seen a lot of those worn out. Cables are nylon lines these days and aren't meant to be lubed. Inspect the chassis for rust, especially on the bottom rails. Inspect the wiring looking for frayed insulation, tape it back up and secure it so it doesn't move if you find any. There are small struts under the front bodywork, from near your knees, they run into the bottom chassis, I've seen those two bottom bolts rust solid to the bit's of tube they go through, the tube's a part of the strut. The bolts go through about two inches of tube and when they seize, they really seize, a bit of grease on those bolts saves a real sh** of a job if they seize in and those two bottom bolts are the best place to undo if you want the front body work off. All the small bolts holding the plastics on are made soft so they can be drilled out if/when they seize up or get chewed screwdriver slots.

Hope that all helps.. I've been fixing and owned suzukis for ..err.. about forty years  haha.

The 1999-2004 suzuki manual has a detailed description of overhauling that diff. The special tools could be improvise with threaded rod and washers/plates, and feeler gauges instead of the DTI gauge.. There is a bit more back and forwarding than car diffs, but it's not really as complicated as they make it sound. Any competent/experienced mechanic should be able to do that.

And what about the brakes ? Do the pistons slide in the cylinder ?

Your bike looks tidy enough. It's probably worth repairing. The diff comes out easily. You could take the diff assembly to a bike shop or find someone to do the work on it, a mechanic that's familiar with diff assembly would be best. Perhaps take it apart yourself first to check it's not got too many broken bits. If you strip it you lay everything out on a bench in the pattern it is in the bike, left parts to the left, right to right, front to front. The good thing is it's not like a diff in a car where if you get the adjustments wrong it will whine bad and wear out early. That front diff only has any load on it when you're using the 4x4. And most of the time, if you  just fitting new bearings, nothing else needs adjusting. I dare say that even a new set of gears(OEM ones) and bearings will be ok with all the old adjustment shims.