Hot Rod Brian's 87 SX

[badasskfx]

200s or,if your going to rip I’ll take 250r

[fabiodriven]

Either will work, but both are going to be tough on your back! If you have a set of 2-ply 22's, put those on either machine and brace yourself, lol. We all run SX's and Big Red's now. The big poofy tires are key!

[badasskfx]

The big red and sx are crazy money right now.

[fabiodriven]

The 87 was a gigantic pain in the arse yesterday. Two weeks ago when we took it to the mountains, it ran "well enough" for a bike that had been parked for at least a decade, but it needed some love. It was idling high, it had a hanging idle, and it would spit and backfire when downshifting. At our first stop in the woods, we adjusted the air screw and that did seem to quiet the backfiring somewhat, almost completely actually.

We have been running this bike with a carburetor I had on the shelf here, not sure what year carb it is but probably 86. Yesterday I rebuilt the original 87 carburetor. This carburetor has been out of this bike and cleaned so many times it's embarrassing, but I am missing something. This time it was rebuilt, new parts were installed from the kit, but not every single piece comes in those kits as most of you are aware. I replaced everything I could and the carburetor had been soaking in carb cleaner for days. I spent the ridiculous amount of time it takes removing the current carburetor from the SX, then spent the ridiculous amount of time it takes to install the original 87 carburetor (again). This is what happened.

Once this carburetor was installed, it ran exactly the same as it was running with the other carburetor on it, much to my chagrin. Where I swapped out the carb and nothing changed, that tells me whatever I just changed is not the problem. I was pissed at first, but began trying to tune the carburetor in. It's rich at idle and will not dial in using the idle adjustment and air screws. At one point I stopped what I was doing and asked myself what the common denominator is here, because swapping the carburetor made no difference at all, so that's not the problem. What are the common denominators? One common denominator is the intake. The intake was removed, re-sealed, and actually replaced because I broke the intake that came off the 87 originally. Could the intake be the problem? It is feasible, but if there were an intake leak it would be lean at idle, not loading up with fuel (which is what it was doing). Oddly enough, the hanging idle is more of a symptom of a leaky intake, so it has symptoms of being both lean and fat at the same time. Figure that one out!!

An issue I caught which is highly suspect is a choke cable issue. The choke lever has never felt right on this bike, it doesn't pull right. I have a feeling someone may have stretched the choke cable sheath which is now causing the choke to hang open just a tad. This seems extremely likely to me. I wanted to test this theory, so I removed the choke and cable from the 87 carburetor (with the carburetor installed on the bike) and I installed a loose choke plunger in the hole and seated it all the way down in it's bore. I started the bike and it had never run better. I began setting the idle and adjusting the air screw and the bike was dialing right in, I thought I had figured it out. As I sat there with the screwdriver patting myself on the back for figuring this out, like a light switch the bike loaded up like crazy, I had to grab the throttle to keep it running. It was so fat it felt like someone had put the choke on full. It happened with no warning, like I said, it was like a switch was flipped. I grabbed a screwdriver and whacked the crap out of the carb a few times and it seemed to clear up a bit, but we went right back to the carb being un-tunable again. Now I was mad.

So that's where I left off yesterday. My next steps will be a new choke cable, and I realized something this morning. There is a black rubber plug that goes into the choke orifice inside the carburetor. This 87 carb never had one of those from the time I disassembled it. I know it needs one, I can see it on the fiche, so I'm going to take the one black plug that I do have and install it in the 87 carburetor. Another big difference with the 87 carburetor, the air screw setup is VERY DIFFERENT on the 87 carburetor. Some of the parts interchange between the 86 and 87 air screws but not all of them. I plan to order the correct respective OEM air screws for all of these carburetors to get them all sorted out.

Last thought I had which two others have suggested is the CDI. I have a spare out there (I think) which I can try out on there as well.

Anyhow, typical SX carburetors, this thing is a gigantic pain in the arse. These carbs absolutely suck to remove and install and it does not get any easier with time, it just sucks.

[Dirtcrasher]

Those are some confusing conflicting symptoms... If that's an 86/76 it will start with Keihin 08 (That's what I recall, but that was a long time ago).

When you take out your floats, the 86/87 carb should have a black rubber plug in the top of the oriface casting, and the starter jet itself will be on the of that casting.


On the 85's, they were either an 03 or 05 Keihin and they have no jet on the side, and a non removable starter jet (except to replace it). Thats the jet that caused the cold start issues and to fix that you just drill it out to .080 thousands, agaain, if I recall correctly.

One time I had an SX doing something similar, it seemed like a carb problem, but it was actually a few broken and exposed wires where the CDI is located at the battery box. In my case, when the suspension moved up and down, you could see how it ruined the harness and CDI plug once the electrical tape was removed.



Is his gas cap venting okay?? I know, it seems like you're leaning more towards "rich", I'm just tossing out ideas... I have NOS and used intakes if you want to try one just to rule it out.

[jb2wheels]

On a side note, did you check valve adjustment?
Maybe exhaust clogged up some by rodent or insect?
Just throwing stuff out there.

Looks like you have some decent local riding.

[fabiodriven]

Very conflicting, yes Steve. You described the cold start circuit perfectly, and that's where part of my problem is. I don't think it's going to fix everything though.

So the bozo who put this carburetor together last (me) forgot to install that rubber plug in the cold start circuit. Now, I hadn't already mentioned it, but the machine flooded like crazy the first time I tried to fire it yesterday when I had just installed the correct 87 carburetor. I used the choke and it instantly flooded. Now I know why, because I forgot to install the black rubber plug. As I said though, I don't think that's why the bike won't run right. Here's a couple pictures.

On the left here we have the 85/86 air screw, and the one on the right is the 87 air screw. They cannot be interchanged between the the two different carburetor castings, but (to the best of my knowledge) they both use the same spring, O-rings, and washer. I'd like to confirm that part for certain myself.



85 air screw hole



87 air screw hole



85 orifices. Notice no rubber plug and no jet on the side of the orifice. Only 86 and 87 carburetors have the side orifice and those carbs require the black rubber plug.



This is the 87 carburetor.





An exciting new problem we have is the brand new float valve leaking. The old float valve did not leak so it is going back into the 87 carburetor. My next step will be to assemble the bike again with the black rubber plug in place this time, install a different choke cable, then see what we've got. I don't want to add too many variables at once so I'm not touching the CDI for now.

Also the gas cap is not an issue and the valves are likely not out of spec. I'm not positive but I think I may have checked the valves when we first got this machine. No issues with the exhaust either.

[Dirtcrasher]

It's just something simple we're all missing... If you pull off the gas line and turn it on, does it flow out freely and fill up a big bottle on run or res and with the cap on?

But, YUP!! That's the difference in the air screws. The early 85's seemed to have that screw on the left in your picture. The screw on the right, it seems they left the brass full size so the secondary o-ring could keep it from getting contaminated.

I can't imagine a finger slid choke has a stretched cable, damaged, sure. But, it just moves a tiny plunger.

I've been out of the SX (And the other type of S-X) for a looooong time now I remember one time when I had literally zero spare parts. And I had an SX but no choke cable. I thought at the time I had a 350X carb and the choke plunger was a possibility. But, don't let me screw you up with that thought, it was probably 2001 when I did that, can't recall if I even tried that... Sorry...

I also have a NOS 350X carb, you could change the pilot and main with the SX jets and see if it runs well. I know, you don't want to be a "parts changer", and I respect that. But, you may have to try a totally different part to eliminate one of the symptoms...

[danbur55]

Just a thought. How’s the throttle cable?and is main needle seated well. Probably just the angle of the pics but the floats appear to be a little high visually but you have most likely dealt with way more of these than I have

[fabiodriven]

The throttle cable was actually a concern of mine initially but was ruled out, so I completely understand why you would suggest that.

The floats probably look high because the carburetors are upside down in the pictures, so the weight of the floats is pushing the spring down in float valve. The float height is not adjustable on these carbs.

[fabiodriven]

I'm beyond irritated right now, beyond annoyed, I'm very angry and frustrated and ready to take the maul to this machine.

Intake was examined thoroughly, even though it was already replaced and resealed. No issues there. The original 87 carburetor has been soaked and cleaned and cleaned and soaked, there is nothing clogged in there. I haven't swapped the CDI yet but I really do not think that's the problem.

https://youtu.be/0k3yVoXxKgE

[fabiodriven]

I thought I was onto something with the cable. I took the choke cable from the 85 SX we have here and swapped it out with the 87 cable. When I compared the two cables, I thought for certain I'd found my problem. Oh I found my problem alright. My problem is this machine and it's becoming a really big problem.

You can see how much longer the 85 cable is. The choke feels correct now when you use it at least.

[fabiodriven]

Try and bring your R where I go. Oh it would be comical.

[fabiodriven]

CDI swapped and valves adjusted with no improvement.

[fabiodriven]

Alright it's fixed. I'm not positive what it was, but in my mind it seemed like the air circuit was clogged. I took the carburetor apart again and paid special attention to the air circuit, then went through everything else multiple times, and I also swapped out the new pilot jet from the rebuild kit for the original pilot. The float valve stopped leaking after I took out the new one and put the old one back in, so that gave me even more reason not to trust the aftermarket pilot jet.

In the end I don't know if the problem was the air circuit or that pilot jet. All I know is I was going haywire there for a while.