#4 cylinder rich

[Drumagician]

Went to do throttle chops today and checked plug colors. At every throttle position, #4 was rich and all three others looked a little lean but all the same. All carb parts are the same and I checked float levels dimensionally and fuel volume wise. I am just looking for suggestions as to what is causing this. The only two things I can think of is that there is some air restriction in the #4 carb or the compression on that cylinder became low since the last time I checked it. I don't think the mixture screw effects anything over half throttle right?

[natemoen]

Went to do throttle chops today and checked plug colors. At every throttle position, #4 was rich and all three others looked a little lean but all the same. All carb parts are the same and I checked float levels dimensionally and fuel volume wise. I am just looking for suggestions as to what is causing this. The only two things I can think of is that there is some air restriction in the #4 carb or the compression on that cylinder became low since the last time I checked it. I don't think the mixture screw effects anything over half throttle right?

The idle screw does effect through all ranges not a whole lot at WOT though cause the mains by far overtake it. Just as a question are all your needles at the same height?

[WMarshy]

The idle screw does effect through all ranges not a whole lot at WOT though cause the mains by far overtake it. Just as a question are all your needles at the same height?

Are all of your idle screws about the same amount of turns out? Did you check the diaphragm in #4 foe holes?

[bikerphil]

JAT, are you getting a hot spark at #4? Maybe try the ol' cut 1/4" off the wire and screw the cap back on trick.

[Drumagician]

In answer to all, all needle positions are the same; the idle screws are all different, they are #1=3.5, #2=1.75, #3=1.5, #4=2.0... not sure why #1 is so far out either but that is where it runs best; didn't notice any holes in the diaphram when I rebuilt them but it could be possible; just put new wires and caps on and they ohm'd out good but I will check.
Thanks for the ideas all.

[TADracer]

Try something other than throttle chops.

Another question...how are you doing your throttle chops? Are you using a clean set of plugs each time and are you getting the motor up to operating temp before you chop?

OK, that was 3 questions but IMHO throttle chops do not give a good picture of what is really going on. You might be getting ready to upset your carb tune when it is not necessary. Consider it takes a minimum of 15-20 miles riding to get up to operating temperature . So if you just are running the bike at full throttle for a short distance at WOT and cutting her off like most manuals say, you may not be getting a correct reading. I rarely do the throttle chop method because I feel it does not give you a real accurate look at what is happening, only a brief snapshot at WOT at best. What I am getting at is that the #4 plug might be showing rich before you started your testing, if it was not a clean plug and then given the time to color.

I know it sounds like a PIA to do because the motor is hot but before I check plugs I get all my carbs, timing, valves, etc. set and then take about a 20 mile ride. Then I pull over and change plugs for a clean set and read the ones I just took out. Since it takes about 20 or so miles for spark plugs to color up (or to change color) completely, I ride another 20 or so miles and read then read those those. Try it...you may be surprised at what you see.

BTW, a clean set of plugs does not mean they have to be a new set of plugs. Use an old set that you have cleaned well and gapped correctly.

[Drumagician]

It seems as though everybody has there own way to do throttle chops from what I have gathered on this sight and talking to old school bikers that I know. My bike was definately warm, my plugs were clean as I could get them. the color at the top of the plugs (above the threads) all seem to be the same (very hard to explain this color, it varies from front to back and is not realy tan nor white nor black but maybe a combo of all). If I look below the threads which is where I read is the best place to look, it is white with a little grey/tan on 1,2,and 3 and surely black on #4. Why is #4 black below the threads but like all the others abobove the thread??

[Larrym]

Dark Matter???

Why is #4 black below the threads but like all the others abobove the thread??

Drumagician,

I've encountered the same Blackened region when the cylinder was oil fouled and when the mixture (AFR) was WACK (for whatever reasons...). Not hard to tell when it's oil fouled cause the region is OILY and WET. When the AFR was way off the region was mostly DRY and SOOTY.

As far as the tips being different than the inner insulator, when the engine rpms increase the volume of fuel/air being put through increases and therefore may end up being ignited/burned at a rate which is closer (yet still OFF...) to what it should be. Less time for anything to make its way down into the inside of the plug.

But back to the original problem: #4 being rich.

I gotta ask whether or not it is rich 100% of the time and right now. If you went out and ran the engine would #4 be way off? What I'm getting at is that sometimes things happen temporarily like the floats getting stuck or FOD blocking a much needed air/fuel metering passage/jet.

Easy to determine if this is a permanent FAIL of something on carb 4 or just a temporary scare: Swap the plug from another cylinder into #4 and then go for a ride. Look at the #4 plug and see what it did to the "new" spark plug. (Throttle chop or just a ride down to the convenience store to buy a lottery ticket...you decide.) If the plug looks wack then you have a continual/ongoing problem versus an intermittent one.

As far as the next steps to take...well, you got three other carbs you can compare #4 with. Before you disassemble everything I would suggest that you do the slide test to see if your diaphragms are leaking. Lift each one up and then plug the vent hole at the airbox side of the carb inlets.

Which hole is the vent hole???

Not gonna rob ya of the sense of discovery on that one. Site here has good pics with all the labels with circles and arrows. Or you can just lift the slides and find out which one has to be blocked to keep the slides from falling. You decide.

Either way I'd say that eventually the carb bank will come off and you'll be carefully examining #4 disassembled along with one of the others for comparison purposes. Even if only to rule out carburation/fuel as the source of your blackened plug region.

It's what would happen behind closed doors if you took your bike to a shop, right?

[TADracer]

Drumagician,

As you can see, spark plugs and carbs are each an idividual science by themselves. But, no one has asked you, how is the bike running? Are you consuming any oil or are you satisfied with the performance and fuel milage? If so then, just ride for awhile and see how it all fairs out. Rich/lean spots come and go on these machines. I know I have had them before and have done absolutely nothing and next time I checked plugs, all were fine. Switch plugs like Larrym suggested and see what happens. All might just be fine.

BTW, the reason the tips of your plugs were different color on one side and not the other is because the colored side happens to face the intake valve when the plug is installed and it is being cooled somewhat by the incoming fuel charge when the valve opens. The varied color is completely normal IMO.

[Drumagician]

Well I switched the plugs and went for 20 minute ride and the #4 plug became black again. This is a chalky black, not a wet oily black. All other plugs look good. I will have to clean this carb again and reconnect my plug cap and see where I am at.

[DGXSER]

A couple things to look at. Try switching plug wires on #1 to #4. This will let you see for sure if it is electrical or carb related. If the problem moves to #1, then you know you have a bad high tension lead or plug cap.

If it does not move, then you know it is carb related. The only time I had this issue was when I messed up reassembling the slide and needle assy on my 81 carbs. Essentially, I moved the needle valve by putting the spring in the wrong spot. So perhaps your needle is not correct??

[Drumagician]

My plug wires are a part of the coil and cannot be disconnect. I am assuming that you don't mean to simply take #4 plug off and put it on #1 as this would cause the engine to not run correctly, right?

[dbeardslee]

I've found that the thing that seems to have the biggest impact on that black sooty ring is float height. I can make it appear and disappear with a couple mm's of float height. The last time I set mine (last week) I used a digital caliper to do the deed, and I got better accuracy that way. I was VERY careful to bring the caliper down on the float until it just barely touched it, but didn't push it down (harder than it sounds).

I always check both sides of the float, and also found a better way to set the 'other' float (the one I didn't set with the tab). What I used to do was grab the float cross piece and bend it up or down to adjust. Problem with doing it that way is the sides of the floats can get off vertical with more propensity to catch the side of the bowl or gasket. This last time I grabed the float across the pin and used a torquing motion to adjust the float. That kept the sides vertical and got me dead nuts on the proper setting.

The other thing about your setup is the brass floats. It's possible your #4 float could be leaking, which would make it run rich. It can take a while for the gas to enter a leaking float, and it will evaporate out if the float has been 'dry' for a while. Easiest way I know to tell is to pull the carbs, immediately remove the suspect float, and shake it. If you hear liquid inside, dry it out and heat up the soldering iron.

In answer to your coil question - it's a waste spark system, so switching the wires between 1 & 4 won't affect the way it runs but may cause the black ring to move from #4 to #1 - if the wire or cap is bad.

[Drumagician]

Excellent, I will check both items.

[cywelchjr]

My plug wires are a part of the coil and cannot be disconnect. I am assuming that you don't mean to simply take #4 plug off and put it on #1 as this would cause the engine to not run correctly, right?

Yes, he does mean that. Being that these bikes use a wasted spark system, 1 and 4 fire together and so can be swapped without any change, other than there being a problem with either the cap or the wire, and 2 and 3 are the same.