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Carb tuning...for dummies please

12736 Views 281 Replies 23 Participants Last post by OddBird, 6 h ago

tboooe

Discussion Starter · 3 mo ago

Preface: I havent messed with carburetors in over 25 years, and even then I was not very good at it so please be gentle. Being a total carb newbie I want to take a methodical, stepwise approach to diagnosing the issue and ultimately identifying the correct fix, otherwise I will likely get overwhelmed making too many adjustments and probably end up making things worse.

I finally got one of my Superlights (#669) running. It is 100% stock. I adjusted the idle so it sits at 1100-1200 rpm. The issue now is that I think it is running incredibly rich. When I rev the bike it starts to pop through the exhaust at around 3500-4000 rpm. Additionally, the ends of the exhaust is covered in dark black soot. Plus based on the exhaust smell I think its rich.

First question, does this sound like the bike is running rich?

181 - 200 of 282 Posts

Nippy Zipper

· #181 · 2 mo ago

I was going to shut up be hey I'm allowed to change my mind, right.

With the choke closed ....

Remove both spark plugs, squirt a little bit of petrol directly into the cylinders via the plug holes. Replace plugs and try to start it. You will probably have to open the throttle a bit to get some air in and crank it over a bit. If it starts, runs briefly, then stops, your problem is 99% likely a fuel problem.

FCRs don't have a choke mechanism at all. The engine is started by using the throttle pump to inject fuel directly into the inlet manifolds, and blipping the throttle to squirt more fuel in to keep it running till it's warm enough to idle.

J.B.

· #182 · 2 mo ago

tboooe said:
PLEASE PLEASE remember!

I have not cleaned the carbs. The reason is that just 2 weeks ago the bike started and idled fine so I find it hard to believe that during that time the carbs ceased to work properly. Plus I verified I am getting fuel to the bowls and when the enricher is fully engaged, there is enough fuel to start the bike and have it rev to 3k consistently, before dying. Now, that isnt to say the pilots or jets or some other parts of the carbs dont need some cleaning or adjustment. But at this point, I am just trying to get the bike to keep running with the enricher engaged.

I really don't know what to tell you - I think you'd just want to remove the carbs and clean it up, so that you know that at least you can get the pilot jet circuit out of the equation. You could just get a small debris in there that could mess up some of the small pathways of the pilot jet and circuit. Assuming it's fine without knowing for sure that it is just complicates your troubleshooting.

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tboooe

Discussion Starter · #183 · 2 mo ago

SUCCESS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! (sort of). So at the recommendation of those on this site much smarter than me I bought an inductive timing gun so I can verify the spark plugs are working. I wanted to rule that out before tearing into my carbs. The first three times I started the bike with the enricher set on full, I had the timing gun connected to the vertical cylinder. Same behavior as before, bike would start, rev to 3k then die. I then put the clamp on the horizontal cylinder. Initially I was too lazy to remove the left side fairing so I connected the clamp a bit further away from the cylinder and spark plug, further up the spark plug wire. Tried to start the bike, same behavior but this time I saw that the horizontal spark plug was not firing. Hmmm...so I decided to remove the left side fairing and attach the clamp right where the spark plug wire meets the spark plug cap. Tried to start, the timing gun indicated I was getting spark and voila!! The bike started and continued to run as long as the enricher was on. Now I am not sure if the horizontal spark plug really was not firing this whole time and by attaching the clamp I somehow jostled something. Whats odd, is that I visually verified this past weekend that I was getting spark from the horizontal spark plug. So at this point, I am not sure if I was really not getting spark or by some magic my bike starts and runs now. I will check all the connections at the coils and ignitors. That being said, I think I must be getting intermittent spark because when I removed the spark plug a few days ago, I noticed that it looked relatively clean (see below).

Now I am back to where this thread initially started! The bike wont run with the enricher in the off position. I assume I just need to keep adjusting the idle speed screw. I cant do any damage if I wind it all the way in right? Worse that could happen is that my bike revs high right?

Fastener Gas Household hardware Auto part Nickel

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duc96cr

· #184 · 2 mo ago

So, bad plug wire or plug cap, or maybe coil ? Intermittent spark on horizontal cylinder.

duc96cr

· #185 · 2 mo ago

You can swap coils , wires caps one at a time. When the problem moves to the other cylinder, you’ve found the culprit. If it’s still on horizontal cylinder no matter what you swap, the problem is before the coil. The Kokusan unit or something.

tboooe

Discussion Starter · #186 · 2 mo ago (Edited)

Good advice @duc96cr. But like I wrote I am not entirely sure there was no spark on the horizontal cylinder. I thought the bike can run only on 1 cylinder anyway.

Since I am not 100% sure it was a no spark issue on the horizontal I am going to refrain from making any changes. If and when this happens again I will know to check for spark and if I it is indeed the issue I will methodically swap out various components as recommended.

Now, how the heck do I get this bike to idle?? I will try adjusting the idle speed screw first.

BOTT

· #187 · 2 mo ago

10 going on 11.
1. When it jumps to 3 grand at idle, does it sound like both cylinders running? Wet finger, touch each exhaust header. Yes. Both are hot.

2. When you have the timing light going, do you see both cylinders spark? Yes.

3. So page 34, have you yet to clean the carbs? NO.

4. If I walk down the logic tree, of fuel/spark/compression, page 56 says, I have compression because it start every time. I have spark because it fire off every time. I have fuel but to use the choke to force fuel out, I choose NAPA the fuck out of it already!

5. Choke pulls out all 3 circuits along with the choke circuit [if applies], but you have a clogged circuit(s), where you shut off the choke, can no longer feed the fuel out of said jets.

6. Tonight is the learning curve of:
a. Compression: Can't be or it would not start each time.
b. Spark: If yes it runs on both cylinders at 3 grand, it's not spark.
c. Fuel: Yes, we have fuel that shows it runs at 3 grand till you flood it and stalls.

Cornclusion, Humor me, pull the drain screw out and photo the tip of the drain blow screw, and show it on your next post.

Signed,
WOThe Fuck Already, page 72

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tboooe

Discussion Starter · #188 · 2 mo ago

BOTT said:
Cornclusion, Humor me, pull the drain screw out and photo the tip of the drain blow screw, and show it on your next post.

What is a drain blow screw? You mean the float bowl drain screw?

BOTT

· #189 · 2 mo ago

Yes. I need a proof reader. Thank you.

Stillrollinalong

· #190 · 2 mo ago

BOTT said:
10 going on 11.
1. When it jumps to 3 grand at idle, does it sound like both cylinders running? Wet finger, touch each exhaust header. Yes. Both are hot.

2. When you have the timing light going, do you see both cylinders spark? Yes.

3. So page 34, have you yet to clean the carbs? NO.

4. If I walk down the logic tree, of fuel/spark/compression, page 56 says, I have compression because it start every time. I have spark because it fire off every time. I have fuel but to use the choke to force fuel out, I choose NAPA the fuck out of it already!

5. Choke pulls out all 3 circuits along with the choke circuit [if applies], but you have a clogged circuit(s), where you shut off the choke, can no longer feed the fuel out of said jets.

6. Tonight is the learning curve of:
a. Compression: Can't be or it would not start each time.
b. Spark: If yes it runs on both cylinders at 3 grand, it's not spark.
c. Fuel: Yes, we have fuel that shows it runs at 3 grand till you flood it and stalls.

Cornclusion, Humor me, pull the drain screw out and photo the tip of the drain blow screw, and show it on your next post.

Signed,
WOThe Fuck Already, page 72

Or BOTT he could go back to post #15
As for tuning there are so many overlapping varaiables. As shown below each part you are adjusting has a different amount of influence depending on how much throttle is being used. If its been 25 years maybe best left to an expert.

tboooe

Discussion Starter · #191 · 2 mo ago

Stillrollinalong said:
Or BOTT he could go back to post #15
As for tuning there are so many overlapping varaiables. As shown below each part you are adjusting has a different amount of influence depending on how much throttle is being used. If its been 25 years maybe best left to an expert.

Yup, I am going to try adjusting the idle speed screw first. If that doesnt work I will then check and clean the pilot jets. After that I will see about the fuel idle adjusters.

tboooe

Discussion Starter · #192 · 2 mo ago

Hey guys, sanity check on my approach to adjusting the idle speed screw. Should I start over and back it all the way out so that the butterflies are fully closed. Then slowly (1/4 turn) start winding it back in until I get idle at around 1200-1300 rpm? My thinking is that I've been fiddling around a lot with the idle speed screw and want to start fresh with a known starting and ending point.

BOTT

· #193 · 2 mo ago

Tboooe, forget the idle. The throttle opening is more the second way to check idle. But throwing the choke off it stalls. So technically it's a waste knowing [in my internet back and forth 30 pages later], you have yet to understand 3 jet circuits feed idle to WOT.

So to touch the idle for any reason is not going to do anything but you winding up that screw and ruin the body of the carb, the taper of the needle... NAPA now.

BTW, where is that colored blow(sp) screw photo? LOL

duc96cr

· #194 · 2 mo ago

Hard to recommend a next step since we are not sure it’s firing all the time on both cylinders and you can’t get it to idle at all . You may have a cylinder that isn’t running all the time and the other cylinder is attempting to keep the engine running by itself. You still should be able to keep it running with the throttle. 1) If it’s not sparking on one cylinder, you need to figure that out and fix it. 2) If it’s sparking , then you have a fuel issue, but not necessarily a carb issue. Could be the restricor in the return line, until you figure out if it’s there, or a problem inside the tank not giving full flow ( I had a cracked line leaking inside the tank affecting flow output) 3) If you have spark, and sufficient flow, then you need to tear the carbs apart. We know you don’t want to, but this is where Jagger starts to sing “ You can’t always get what you want “.

tboooe

Discussion Starter · #195 · 2 mo ago (Edited)

duc96cr said:
Hard to recommend a next step since we are not sure it’s firing all the time on both cylinders and you can’t get it to idle at all . You may have a cylinder that isn’t running all the time and the other cylinder is attempting to keep the engine running by itself. You still should be able to keep it running with the throttle. 1) If it’s not sparking on one cylinder, you need to figure that out and fix it. 2) If it’s sparking , then you have a fuel issue, but not necessarily a carb issue. Could be the restricor in the return line, until you figure out if it’s there, or a problem inside the tank not giving full flow ( I had a cracked line leaking inside the tank affecting flow output) 3) If you have spark, and sufficient flow, then you need to tear the carbs apart. We know you don’t want to, but this is where Jagger starts to sing “ You can’t always get what you want “.

Good points. I started and ran the bike a few more times last night with the timing gun attached to the horizontal cylinder. It showed I was getting spark consistently. I am going to keep using the timing gun while I try to figure out the idle so that I will know right away if that is the issue. This way I can isolate and separate spark vs fuel issue. I dont want to unnecessarily tear into the carbs for no reason either so I want to make sure I exhaust all simple solutions first.

I am able to keep the bike running by giving it just a bit of throttle so that the rpm is at around 1200. When I blip the throttle the revs climb quickly. So while using the timing gun and verifying spark, I am going to adjust the idle speed screw. If I cannot get it to idle then I assume I have an issue with pilot jet or some other part it the carb and I will take Mick Jagger's advice.

duc96cr

· #196 · 2 mo ago

Make sure your mixture screws are the same before you start, mine are around 4 turns out. I see nothing wrong with having the bike idle at 1200, but it really is up to the bike , and your personal preference.

BOTT

· #197 · 2 mo ago

"I am able to keep the bike running by giving it just a bit of throttle so that the rpm is at around 1200."
New info! So for the last pages, this was or was not mentioned? So this is with choke off, obviously, right? I come away with choke stalls it, you push choke in, can't catch it by instant start with the choke, close it and rev slightly to keep it running. No need for a photo op with a 'season screw', a debris screw, a water in the gas screw, a level out of each bowl screw. Get it? NAPA is when you let it go stale turns to green muck eating the brass, due to the seasons gone by with a wet bowl. The should listened to turtle screw, but I'm screwed now LOL

"When I blip the throttle the revs climb quickly."
You can't have a high climbing rev with just a blip. That says 3 circuits open. Make sense?

"I am going to adjust the idle speed screw."
Better known as fiddlefuck screws. The last thing if not ever screw with it, but too late.

"If I cannot get it to idle then I assume I have an issue with pilot jet"
Oh fuck no. You can get it to idle that low so there are no clogged jets. Idle circuit is open. Main jet is for sure open. Rev says mid is open. Get it?

Remember I said you'll fuck up that body if not knowing you don't even touch the body with the "initial" out turns.
So someone suggest 4 turns out from the "initial", and that's where the amateur meets the pro feel of a delicate screw sent home to the Initial> I would not go there. You didn't move it that much, yes?

No idle cable, right? To set idle on this needs the CO sniffer for idle?

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tboooe

Discussion Starter · #198 · 2 mo ago

duc96cr said:
Make sure your mixture screws are the same before you start, mine are around 4 turns out. I see nothing wrong with having the bike idle at 1200, but it really is up to the bike , and your personal preference.

So 4 full turns out from the adjust screw fully tightened? Is your bike totally stock? Mine is except for an aftermarket air filter and Termi slipons.

BOTT said:
"I am able to keep the bike running by giving it just a bit of throttle so that the rpm is at around 1200."
New info! So for the last pages, this was or was not mentioned? So this is with choke off, obviously, right? I come away with choke stalls it, you push choke in, can't catch it by instant start with the choke, close it and rev slightly to keep it running. No need for a photo op with a 'season screw', a debris screw, a water in the gas screw, a level out of each bowl screw. Get it? NAPA is when you let it go stale turns to green muck eating the brass, due to the seasons gone by with a wet bowl. The should listened to turtle screw, but I'm screwed now LOL

"When I blip the throttle the revs climb quickly."
You can't have a high climbing rev with just a blip. That says 3 circuits open. Make sense?

"I am going to adjust the idle speed screw."
Better known as fiddlefuck screws. The last thing if not ever screw with it, but too late.

"If I cannot get it to idle then I assume I have an issue with pilot jet"
Oh fuck no. You can get it to idle that low so there are no clogged jets. Idle circuit is open. Main jet is for sure open. Rev says mid is open. Get it?

Remember I said you'll fuck up that body if not knowing you don't even touch the body with the "initial" out turns.
So someone suggest 4 turns out from the "initial", and that's where the amateur meets the pro feel of a delicate screw sent home to the Initial> I would not go there. You didn't move it that much, yes?

No idle cable, right? To set idle on this needs the CO sniffer for idle?

I am sure this info got lost in all the post but yesterday I was able to get the bike to start and stay running with the enricher engaged. Once I turn off the enricher the bike will not idle but I am able to keep it running by applying just a bit of throttle.

As for blipping, maybe that was not the right term to use. I should have said my applying throttle I can get the bike to rev cleanly.

Not sure I understand your comment about the idle speed screw and not to mess with it.

No I have not messed with the mixture screw at all yet.

jdaniele

· #199 · 2 mo ago

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tboooe

Discussion Starter · #200 · 2 mo ago

jdaniele said:
View attachment 1062432

LOL! But on the bright side, it appears that your suspicions where right and that my starting issue was related to ignition. Now that we have hopefully identified that, the issue focuses on the part that makes my briain hurt...carb tuning. At this point I am just trying to do something simple and get my bike to idle. I havent even thought about optimizing the carbs with jetting, etc. I may just quite while I am ahead if and when I can get this bike to idle.

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