Jetting question

[Firehawk]

I have no idea, I've never messed with that, but I think the shop I took it to did last August/September when they looked at my valvetrain.

What should they be set at?

[xj11john]

Firehawk,

What are the mods? 4-1 exhaust, ind. filters? Or what.

It sounds like youve gone to rich, esp. with two sizes up on the pilots.

[motoman]

Pilot screw not accessable on 81 carbs unless plugs are removed. Will do better with stock pilot jets unless there is a real bad stumble transitioning into main circuit Unless your gonna nit-pic pefect plugs, perfect fuel economy, and a perfect world, leave pilot screw plugs alone on those 81 carbs. Make sure circuits are all clear internally, and especially the float levels, which should have a sea level setting of 23mm, which will work at a little higher elev. if your using other than stock airbox. Also make sure petcocks are in on position, not prime, and diaphrams are working properly in petcocks,(shutting off with no vacuum , and opening with a vacuum. The problems your having goes to basics, specially if they've been apart. Making sure it has Mikuni mains and pilots for starters, even with pods it should run off idle good, just lean up towards mid-range and up. Sorry guys, just my two-cents worth, as most of these carb problems are self inflicted with pods and the such which causes different rates of vacuum drops, which in turn causes these constant velocity carbs and there vacumm diaphrams to react adnormally. If you want these ole XS's to give you a general all round good ridability, reliability and performance, better left stock unless your strictly straight lining 1320's at WOT.

[Firehawk]

I've got pod filters and 4-into-1 exhaust without a baffle.

As for the pilot screws, the problem is this: I took the bike to a shop and they removed the plugs and possibly messed with the pilot screws. I have no real desire to mess with the pilot screws, but if I have to, I will.

The floats were all out of whack. Two floats were about 25-26mm, while one was 23 and one was 20. They are all now sitting around the 23 mark, +/- a milimeter at most. I'll be cleaning out the fuel enricher circuit now, and hopefully, be able to start it up soon.

[motoman]

Sounds like your headed in the right direction Firehawk. To bad a shop messed with things. Now you gotta go and start from square one, plus sort out all they messd with. Remember, pilot screws on front side of throttle flaps, as these are on these carbs, changes fuel at idle.........screws on back side changes air intake ratio at idle. So on my moto-cross two stroke, I always try to go up in elevation to races, and for every thousand ft., bout a 1/4 turn out, or untill there's no stumble from idle into main circuit. If you ride at 1000ft. or lower from where your normally jetted for.............better richen up a couple steps in main, or guarentee before the day's out the bike WILL chuck bottem-end. That's how jetting and settings affect a two stroke, as your depending on that 32:1 oil mix ratio to lube crank assembly. You won't have those drastic negative results with our four strokes, but rich or lean mixtures will give you visual tell-tale signs and run accordingly too.

[motoman]

Your float levels where my first suspect, and as you've stated, they were all whacked. If someone here has an initial setting for the pilot screws, use that for starters. Just don't make several changes at once, one change at a time, and go back to what it was before change if there's no difference before making another change in some other area.

[Firehawk]

T.C. has told me that the pilot screws are 1 & 1/2 turns from a "GENTLE" seating. I might return them to this setting. It seems like what the shop did was attempt to make up for the floats being at different heights by adjusting the pilot screws. Two are in the same spot, and the other two are at different spots, lined up directly with differences in my float heighths.

On one carb, the fuel enricher curcuit seems to fairly clean, spraying some carb cleaner through it had it spraying through the tube that sits in the bowl.

I have to go to work now, but I'll finish the cleaning tonight after work and possibly have it running tonight.

[Firehawk]

Ok, so I put it all back together: Floats are all at 23mm. All pilot screws are at 1 3/4 turns from a 'gentle' seat. The fuel enricher curcuit appears to be clean. I have 120 mains and 42.5 pilots (stock).

Bike is too rich at start now. It won't start because apparently there is now too much fuel. However, if I do a full throttle while cranking, and then return it to no throttle, it will start.

So I drove it around. It idles really odd. It'll idle at say 1500RPM, then drop to 1100RPM, then drop to 800RPM and sound like its going to die. It doesn't seem to want to idle down very much. As it got warmer, it started to stay around the 1100RPM range.

I just fueled up, got 22.5mpg for the past week of poor running.

Any ideas?

[motoman]

My first suspition is your tank petcocks aren't sealing when bike isn't running, causing float bowls to over fuel, which means float needles aren't sealing either. Carbs are outa sync., causing various rpms. If you set float levels with carbs upside down instead of on there side, float weight WILL cause a false setting, which will be too high, (trust me on this one). Set carb asembly on its side just allowing floats to lightly seat, and you'll see what I'm talking about. With petcocks in on position, engine not running, pull fuel line off petcock. If gas runs or drips, remove tank, stand on end, remove petcocks, take petcock body apart, lightly stretch spring that holds diaphram seat in place. This should make diaphram seat tighter. Lightly smear a little dialetic grease(silicone) on O-rings and gasket portion of diaphram, reassemble, install, hold tank level with fuel in it and turn petcocks on........no fuel....fixed.................fuel still leaks, buy petcock rebuild kits for that model and year. If that's an 81, it'll take two kits..................If fuel isn't leaking............some others here surely can help. (Myself, would go to stock jetting with stock airbox using a Uni-filter).....just my 2cents worth, and that's not worth much.

[Firehawk]

The petcocks don't leak, thankfully. I guess I'll pull the carbs off again and work on getting the floats adjusted again.

I thought that as long as you didn't mess with the screws inbetween the throttles or seperate the carbs from one another, that the carbs would stay synced? I didn't touch that, and they were synced by that shop a while back.

[motoman]

Double check those float levels Firehawk, laying carb assembly on side, slightly tilted so floats just flop back allowing needle to seat. I don't have anything measuring in MM, so I use my 2 piece slide gauge that I use on auto carbs when rebuilding them. It's in 32nds, so that translates to 23mm=.98=31/32.......and so on. If this gives you some idea: I'm at 5000ft., and float level settings on all carbs whether automotive or otherwise are sea level settings, so I'll drop that level 1/16"or more. Bowl capacities in volume on these carbs are much smaller so the drop is in relationship to the capacity. End result has same effect tho. For example: At my known elev. of 5000ft, stock intake cept for the Uni-filter, 110mains, 42.whatever pilots, stock heat range NGK plugs(BP6ES), they constantly show a little black around thread base, which tells me a tad rich, which is better than to lean for sure. At 33,000K, I will have valves adjusted first, then have carbs synced as they have never been done. Don't think there too far off as it is smooth in all rpm ranges, and idles with no ups or downs at 1100rpm where I have it set. Idea is to eliminate any mechanical variables before looking at re-jetting, which in this case could very well end up with 107.5 mains and pilots left alone. Your individual air filters are somewhat simulating a sea level enviroment by pulling in more volume, which in turn= more oxygen molecule by volume= ability for more fuel to be added. My personnel choice with your set-up initially would be to leave the stock pilots(42.5) in , which is for idle circuit and slightly above transitioning into main circuit, set float levels at a 24MM, making sure all other orfices are clear, 115mains and test it out for any improvement, fine tune pilot screws at idle, with quick throttle blips, making sure you have no stumble transferring into main circuit. Not being there makes it kinda hard to diagnose the whole sinereo, so hope some of this helps.

[Firehawk]

Well, it still has issues, as I've pretty much plastered all over the boards.

Floats are properly set. Everything is supposedly mechanically sound in it.

And yet it is still quite rich, and I have to have the idle screw nearly all the way up just to get it to idle. And then it idles fairly choppy.

I think that it is 'de-revving' much slower because the idle screw is opening up the throttle bodies so much.

Basically, it's still running really rich throughout the powerband.

I'm not sure why it is doing this. The last time I had the carbs apart, it seemed quite clean, and they've been cleaned out several times in the past 6 months.

The shop I took it too seemed to not know why it is doing it either.

[Ken Talbot]

You say that your floats are now set correctly, but you also say it is running too rich. The correct setting for the floats is not a number printed in a manual, it is the actual setting for your engine's particular circumstances considering altitude, jet size, type of air filter, engine condition, etc , etc. If you take your floats up to 25mm, they will sit lower in the bowls, which means they will shutt off the fuel flow a bit earlier, keeping a lower level in the bowls. This will lean things out. Are you up to giving it a try?

[Firehawk]

Yeah, I'm up for it. Although I get antsy bending that tang, as it doesn't seem to like being bent at all. and I'm afraid I'll break something.

Two of the floats were at 26mm and that was causing some golding on the pipe. I think anyway, as I try to mentally orient the carbs to which pipes they were on.

It would be great if the starting issue was this as well, but I don't think the bike is gonna let me off that easy. I guess I will also need to buy another set of spark plugs. :P

And by the way, thanks for all the replies and insight. I really appreciate all your help.

[mro]

starting issue

My 80G will not start period... if you twist the throttle at all before it fires.

Don't know if this is an issue for you or not.



mro