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Suzuki T500 Carbs on a CB450 K0

So a bit perplexing. For some context. It seems to happen when it’s been sitting for some time. There is one issue I addressed though.

Some pics.

Plenty of clearance all around. There is no way it’s getting hung up on the gasket.

IMG_1843.jpeg


IMG_1844.jpeg

The float itself isn’t bent.

IMG_1846.jpeg

Here is one thing though. The fit between the posts was a little snug when the float was installed in the body. It would operate normally though. Seemingly. But when removing even a slight angle and it would catch.


IMG_1847.jpeg

So I used a small fine micro file to smooth it out and give it a tiny bit more room.
 
Jays100 said:
For due diligence, when the float level is measured, both sides are gauged?
Click to expand...
Yes. In fact I specifically try to make sure the floats themselves are even since sometimes they are slightly bent. If they are off it’s a tiny amount.

These aren’t the easiest to measure. Can’t get the caliper in there so I used the old style u-shaped. But it doesn’t extend over the float.

So it’s by eye.

I measuring from gasket surface, gasket removed, to top of float. Body held at angle.
 
More results. I suspect… I’m rich, but something is still awry on the left.

I put bike on center stand and start bike from cold, let it heat up and adjust idle mixture. Idles well. Never touch throttle. As a sanity check, I pull plugs. Decent color.

Took the bike out again. With one change.

I bumped main to 122.5 from 120. Figured it would make some difference better or worse. It did. My dead spot happens at lower rpm now.

But… something is going on with left. Lean.

I put bike in the bad range, which is about half throttle, and plug chopped. A bit over 6k.


IMG_1849.jpeg
IMG_1850.jpeg

Here is the other thing. When I get back home I let it idle for about 3 minutes. Left is still light. Is this just a bad test?
 
teebo said:
Pulls more or less fine until 7k. Starts stumbling. I’m not sure I can get it much above that. It was struggling so I didn’t really push it and took it back down to happy range.
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Usually the main is increased until the motor cannot reach WOT and then one drops back down a couple of sizes. If the motor was bogging down at 7k, the main may already be too large. This ignores other factors that could be at play in your specific case.

teebo said:
I bumped main to 122.5 from 120. Figured it would make some difference better or worse. It did. My dead spot happens at lower rpm now.
Click to expand...

Increasing the main jet would cause the motor to bog down at a lower engine speed, so this makes sense.
 
Would it be best to get an ultrasonic cleaner? I’ve just used carb cleaner, air, and carb soak.

I can’t help but wonder if some air jet is clogged on left. No?
 
One difference between my setup and Jays is around the needle. He was using a P4, and me a P5. We’re using the same jet needle though.

I ask because I haven’t even reached WOT yet. This is mostly needle range, right?

Of course, likely not the only difference once the rest of the bike is considered.
 
teebo said:
Would it be best to get an ultrasonic cleaner? I’ve just used carb cleaner, air, and carb soak.

I can’t help but wonder if some air jet is clogged on left. No?
Click to expand...
I don't have one, either, but I have a can of Berryman's for soaking. I also spray through air passages to see if they are clear.
 
stl360+450 said:
Can you give the full code for your needles (jet needles)? I was going to check the profiles.

You mean you're using the same needle jet that Jay used?
Click to expand...
Series 6. 6DH7.

However… when checking keep in mind that my needle jet is a different series. What was in there was a series 5, 5FP17. Which is 2 mm shorter. The 6DH7 had to be shortened so as not to hit the main jet.
 
Ok. Went back over left carb. Dropped needle one notch and put 120’s back in.

All around felt better. Was up to 8k and almost 3/4 throttle. Ran out of space. And, I wanted to see what was going on with the left.

Here is the plugs again same rpm/throttle.

Left still white.
IMG_1854.jpeg

Right

IMG_1852.jpeg
 
Is a slide tower leak considered unmetered air?

Was spraying around on the left looking for any leaks. On the left, a blast of starter fluid in a particular spot where the cap screws on causes a stall. The right will register a change of idle speed, but it takes more spray.

I know exhaust leaks can cause false leans. Is that just at the manifold, or where the muffler connects too?
 
All carbs do leak…
I think Crazypj noted boots still available? Still, I wouldn’t think there’s enough leaks/unmetered air to cause that big of a difference.
Question, is the left carb the one with the odd float bowl vent?
 
Jays100 said:
All carbs do leak…
I think Crazypj noted boots still available? Still, I wouldn’t think there’s enough leaks/unmetered air to cause that big of a difference.
Question, is the left carb the one with the odd float bowl vent?
Click to expand...
Interesting question.

But no. Right had the odd missing vent. But I added one because every other pic of the float bowls had a vent tube on each bowl.
 
Jays100 said:
All carbs do leak…
I think Crazypj noted boots still available? Still, I wouldn’t think there’s enough leaks/unmetered air to cause that big of a difference.
Question, is the left carb the one with the odd float bowl vent?
Click to expand...
Is the right carb rich, or the left lean? Which is wrong? How does one know?

Mind blown.
 
Jays100 said:
The really white one is the leaner of the two. The left one!
Click to expand...
Correct. I was saying I assumed the lean one is wrong. Perhaps the right one is? The right has the modified float bowl. And is the one over filling.

At any rate. The air entry on left wasn’t through the cable entry hole. It was something around the cap. I used some thread sealer which corrected that. But I don’t know impact yet. It was raining most of the day.

But ya. I don’t have a real explanation yet. This was never a symptom previous carbs.
 
Side question. Is there a darn alternative to the seat screw? Second one that has come off and they aren’t cheap. The peculiarities on this bike is maddening.
 
Progress. Good.

Recap: right was rich, lowered needles. Left of course still lean.

Change: Made a new gasket for the left slide cap since it was leaking. Made double sure my carbs were synced. At idle, full throttle, and off idle.

Left and right are now similar in color.

However, stutters slightly at 6k, and enters a flat zone. Also does it between half and 3/4 throttle. Somewhere around 7200 she really comes alive. Whoosh.

IMG_1870.jpeg

IMG_1868.jpeg
 
Jays100 said:
Was this the same problem you were chasing with the 14H’s?
Click to expand...
No. The problem with the 14’s was lean. The only time I had the plugs this color at around this range the rest of it ran like crap. That’s when I gave up with those.

The bike was pretty hard to start with the 14’s too. I’d complain about it. With these I’m shocked when I come out after it’s been sitting for a day and it fires right up. This makes me happy.
 
I’m rich though, right? I can smell it when I come to a stop. Always makes me look down to see if fuel is spilling out. It’s isn’t though.
 
Maybe when I get the gasket material I really wanted, the thicker buna-n material, I should replace both gaskets on the carb. I also have some new plunger caps coming. Then go back through the idle jet/tuning.
 
Update: Have it running pretty good as of yesterday.

I am literally at the same setup as Jays with jets/needle. Most of my problems so far have been related to a solid setup. Various leaks being a big culprit. The difference between left and right went away with a better slide cap gasket.

The big change was getting the P4 needle jet installed. I didn’t originally because it didn’t accept the same mains. Wrong thread pitch. So I decided WTH and tapped them to the correct pitch. Worked like a champ. Now pulls clean and strong to 8k & 3/4 throttle. It feels like it would go all the way though.

Next up: Rigging up a temporary kill switch and will scout out a better place to do some range of plug chops. Still haven’t tested WOT. I rather wanted to get some reasonable tune in the bands I do most of the riding in.
 
As a way to help myself track this or get comments, here is my first run.

Setup: jets 25/120, P4, 6DH7-middle position.

12 mile ride, chop near end. This is my most common rpm and throttle position on most rides.

~5500 @ 3/8+ throttle

Note: Used plugs. Perhaps I should put clean ones in?

IMG_1878.jpeg
IMG_1879.jpeg
 
Thoughts about this?

I suspect I’m a bit rich in the 1/8-1/4 range. Like when riding out of my neighborhood. Gears 1 & 2.

A bit “chuggy”, but after the bike is up to temp it’s not horrible.

This is cutaway range. I talked with Jay about it but I don’t think there was a firm conclusion. The 3.0 slide is what I was wondering about.

Here is the diagram from the VM32 manual from Mikuni.

IMG_1873.jpeg
 
Going to a 3.0 slide will lean the mixture in that throttle position by allowing more air into the mix.
My ambiguity/prevarication is not advising to expense $100 on a $10 problem. But apologies, that's your decision to make.
 
Jays100 said:
Going to a 3.0 slide will lean the mixture in that throttle position by allowing more air into the mix.
My ambiguity/prevarication is not advising to expense $100 on a $10 problem. But apologies, that's your decision to make.
Click to expand...
Valuable input. Actually I’m going to not do that unless there is a better reason. Mainly because what I read was changing the cutaway isn’t a simple matter because it just starts the jetting effort over.

I dropped the needle a notch. At the throttle position I was at (really closer to 1/2 than 3/8), it only had a minor effect. Going to retest at 3/4.
 
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teebo said:
Valuable input. Actually I’m going to not do that unless there is a better reason. Mainly because what I read was changing the cutaway isn’t a simple matter and just starts the jetting effort over.

I dropped the needle a notch. At the throttle position I was at (really closer to 1/2 than 3/8), it only had a minor effect. Going to retest at 3/4.
Click to expand...
Or another way to put it…

The bigger of the issues was in the 1/2-3/4 range. Which is impacted more by the needle. So that’s what I’m keeping my focus on. Then WOT.

We’ll see how my 1/8 - 1/4 shakes out later. It seems to be a minor issue.
 
It occurs to me that the 1/8 - 1/4 can be considered negligible if I just roll from 0 to 1/2 as fast as I can. Every. Single. Time. 😉
 
And the age old question: is it Rich or Lean? Doesn't look like a plug-chop will help you much at this point.

my intuit is the mix is still rich so look at the 6F5 and if still rich, go to a 6DP17. I'm looking at the D4/D5 comparisons.
 
The straight diameter on the 6DP17 is longer so the off-idle fuel delivery is less.

And yes, you will find yourself looking (again) at overall runability with the PJ and MJ.
 
Jays100 said:
And the age old question: is it Rich or Lean? Doesn't look like a plug-chop will help you much at this point.

my intuit is the mix is still rich so look at the 6F5 and if still rich, go to a 6DP17. I'm looking at the D4/D5 comparisons.
Click to expand...
Thanks. I have been reviewing different needle sizes. But mostly in relation to the 1/2 - 3/4.

Was waiting to see how that ends up.

My gut says rich. Just a smidge. That’s how it feels at least. Wouldn’t be the first time I was wrong. That’s an easy plug chop though. Don’t even need to leave the neighborhood.
 
Old carb woes.

The right slide would stick at above 3/4. Sometimes. I thought I’d fixed it. Multiple tries. Nope.

Here is what I did. Maybe others have a different way.

I have some hard wax polish. I use it to polish the aluminum pieces. Not very aggressive.

Put a thin layer on the slide cylinder, and worked the slide up and down until it moved easier.

Then looked for shiny spots.

The main offender may have been one edge of the groove on the slide. I could see a vertical line where it was rubbing.

At any rate, solved. I sure of it this time. 🤞🏻
 
Great!

Storms again tonight so likely no test runs. But I thought I’d play with the off-idle issue in my garage. If possible.

It idles fine. Plug color looks good. But it does not like rolling the throttle up to 1/8 when cold or even warm. Once hot it’s not too bad.

So I held it at 1/8 for a minute. And… plug colors looked the same as at idle.

I could test different mixture and just see which does best?
 
Hi Teebo,

How many miles did you do on your bike after the rebuild ? (the engine has to run in before you can really final adjust the carbs, compression goes up, bearings wear in, the engine has to set, this all takes hundreds of miles) As long as the carbs are not lean, I would suggest to put some miles on the bike. Did you ever ride a CB450 K0, other then your bike ? If yes, how do they compare ? Letting the bike run for a longer time, without cooling isn't good, keep an eye on the temperature of the cylinder head. Too hot will lead to premature wear, especially when the engine / parts are not broken in on each other....

Be careful that your focus not turn into OCD ;)
 
jensen said:
Hi Teebo,

How many miles did you do on your bike after the rebuild ? (the engine has to run in before you can really final adjust the carbs, compression goes up, bearings wear in, the engine has to set, this all takes hundreds of miles) As long as the carbs are not lean, I would suggest to put some miles on the bike. Did you ever ride a CB450 K0, other then your bike ? If yes, how do they compare ? Letting the bike run for a longer time, without cooling isn't good, keep an eye on the temperature of the cylinder head. Too hot will lead to premature wear, especially when the engine / parts are not broken in on each other....

Be careful that your focus not turn into OCD ;)
Click to expand...
So I was wondering about this too because you’ve mentioned this before.

360 miles. I’ve never ridden another CB450 or even heard another one.

I do keep a check on temperature. Typically at end of ride. Haven’t exceeded 15 miles and I always let it cool all the way back down.

Yes, likely a little OCD.

As it stands right now I think it feels pretty darn good really, though perhaps not its best. Since plugs don’t look egregious I can live with the various imperfections at the moment and get some miles on it. I’d love to take a ride and NOT have to plug chop. That would be awesome.
 
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