CB 450 twin. I said I needed a project

cardinal

Been Around the Block
Thanks for the idea. When I was bleeding the brake I could see that both holes in the MC were not plugged, is there another hole that you are referring to?

I am pretty sure this is related to the amount of pressure needed to push the piston into the caliper though. I just pulled it off again and the seal looks ok, there are some tiny nicks in it, but I think it's fine. When I installed the piston I could stand on it and it wouldn't move into the caliper. Using blocks and my bench vise I got it to seat, but it takes a lot of pressure to move it past the seal. It looks like the piston should be able to be installed by hand, right?
 

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pidjones

Over 1,000 Posts
Yes, it should fit in by hand. Did you lubricate it and the seal with clean fluid on installation? The rubber needs the fluid to lubricate it some. Otherwise, sounds like the seal is too fat or piston to large OD. Does it fit in smoothly without the sealing ring?
 

cardinal

Been Around the Block
Yes, it should fit in by hand. Did you lubricate it and the seal with clean fluid on installation? The rubber needs the fluid to lubricate it some. Otherwise, sounds like the seal is too fat or piston to large OD. Does it fit in smoothly without the sealing ring?
Yes I did use DOT fluid on the seal, and after taking it off there was residual fluid on everything. The piston does slide freely in the caliper without the seal. I think I may just order a new seal and see if it’s any better.
 

pidjones

Over 1,000 Posts
Make sure nothing in the seal groove. On seriously gunked-up old cylinders I use a small brass brush wheel in a Dremel. Could also be that you just got the wrong thickness seal. Can you compare it to the old one?
 

cardinal

Been Around the Block
Good thought, unfortunately the old seal is still stuck in the rusty old caliper. It was so bad that I just bought a new caliper. The piston is new too. I ended up ordering a new seal just to make sure I've got the right one. Should be here in a few days and we'll see how it compares.
 

cardinal

Been Around the Block
After getting the bike to start and run, I could not get it to move without stalling. I was at the end of my abilities and decided to take it to a local shop. That was in October and after they struggled with it for a while it was determined that I needed to replace the carbs. They ordered up a pair of Mikunis and installed them. This took about three months to do and so when I heard that it was running and I could pick it up December 23rd (the last day they would be open until the new year) I immediately got down there to pick it up. The guys gave me a great deal on it due to it taking so long (I’m sure they were as sick of me calling every week as I was hearing “it’ll be done next week”). They had to delete the stock air box, which I wasn’t expecting, and they hadn’t been able to find replacement filters for it, so I rode home with no filters.

Having a “running” bike is great, but it lags so much in the lower RPM range that it can’t really get out of its own way. It isn’t fun to ride as-is. I’ve ordered some Uni pod filters that should be in next week. Will the new filters help? I have no idea how to tune these carbs, any one have a Mikuni conversion that can lend a hand?

The bike is close, but it definitely not the reliable, fun vehicle that I want it to be.
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teazer

Over 10,000 Posts
DTT BOTM WINNER
At the risk of rubbing salt into an open wound, the shop decided they had no idea what was wrong with the bikes, so they fitted new carbs and it isn't much better than before. That must be very frustrating.

Do you know what size the carbs are and what jets are in them and where they came from? 34's work well on a race motor but have little bottom end power/torque. Smaller is generally better for the street if you want a bike that's sweet to ride at lower revs around town.

Do you also know what the compression is on both sides?

How is the ignition? New or old, timed correctly or not?

In other words, before we all try to help you to jet it properly over the mighty interweb thing, do we know that everything else is perfect?
 
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pidjones

Over 1,000 Posts
"I was at the end of my abilities and decided to take it to a local shop." This is often the beginning of a long, expensive story. Deciding to throw new carbs at it is a familiar plot line, also. Wish I could male a helpful, non-cynical remark here but all that I have is to study and learn. Consider this bike your training academy. Here is something really helpful - avoid the urge to install pods and get your old airbox and carbs back. You will eventually need them.
 

cardinal

Been Around the Block
I appreciate the feedback as much as I hate to hear it. Originally my plan with this bike was to make it a reliable daily ride, and with that goal I wanted to keep the stock airbox, update the electronics including putting electronic ignition on it, replacing the reg/rec and in general just refine things to make it a solid bike to ride.The Mikunis do seem a lot easier to tune than the stock carbs, but losing the airbox feels like a step in the wrong direction from my ultimate goal.

To answer your questions Teazer: I didn't get any info from the shop on the carbs. Like I said I got in there the day before they left for a winter break and I haven't talked to them about the specifics yet. I believe the carbs are 32s? The inlet side is 57mm (2.25") but I haven't had them off the bike to measure the outlet size. I checked compression before all this and both sides were good (I don't remember the numbers, a friend helped me with that). The timing has been checked by multiple people and I am pretty sure it is set up correctly.

The big question you ask is do I know that everything else is perfect?
The answer is an emphatic no. That is why I took it to a shop. I hear you pidjones, and I too am here to learn. This bike has proven to be a larger learning experience than I expected and I am grateful for the help of others that have helped me make progress in this training academy.

After the short ride the other day I pulled the plugs and it looks like it's running rich. The left side is richer than the right. The bike starts fine and once it gets up in the upper RPM range it seems like it wants to go, but the low and midrange are really bad, so I decided to move the needle up. It was in the middle clip position and I raised it one. It is still lagging, but it does seem to have improved things. When I was letting it warm up, I could hear and feel that the left exhaust was more sporadic than the right side. On the right I could feel consistent pulses of exhaust, but on the left side it was not as smooth feeling.

As far as going back to the stock carbs, I have all the stuff to do that, but with the Kehlins I was stuck in a dead-end with a bike that wouldn't run, and now at least it moves and has given me some hope that it will be able to improve to a useable state with some additional tuning. I'm willing to keep the Mikunis.
 

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cardinal

Been Around the Block
Another thing that kind of bums me out is that the manifold for the Mikunis uses an additional piece and three (!) hose clamps (or jubilee clamps) to hold everything in place. There must be a better way to mount these carbs to a CB 45o motor, right? This feels awfully hacky. Tell me I'm wrong.
 

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pidjones

Over 1,000 Posts
Unfamiliar with the motor, but just by your photo I suspect that your Mikunis are WAY too big for the motor. And this is the reason for poor low/mid range performance, also. But, not coming from experience. I think a lot of folks on here have experience with them, and given time will chime in. I would pull one carb and get the numbers/measure to give them something to go on.
 

benroloff

Been Around the Block
I also do not have experience with this motor, but it looks to me that the reason for the extra stuff used to mount the mikunis is needed because the stock boots are too small to fit the new carbs. This is not to say that you must go back to the keihins, but you may find that to be the easiest route in the end


Sent from my iPhone using DO THE TON
 

teazer

Over 10,000 Posts
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Plugs:
left in the picture is either extremely rich or burning oil or both. Right plug looks really clean and maybe lean if the bike wasn't running hard. Plugs are designed to self clean ie burn clean when they are run hard. when the bike runs less than flat out the plug temperature is much lower and that results in lots of black deposits. Stock were probably grade 8 back in the day but for gentle riding you could go to say a 7 grade at least until you get it dialed in. In CB77 racers we used to run D12. Our CB160s ran D10 on race gas and D8 on street gas with no sign of distress.

Carb mounts:
The OP is correct. The stubs/adapters are because the carb outlet spigot is too large to slip into stock carb mounts of because the carbs are hitting the rocker box. I have used that sort of set up in the past when testing different inlet lengths, but the better solution is appropriate sized inlet manifolds/mounts.

Jets
It would be a good idea to strip both carbs and write down all the jet and needle numbers so you have a frame of reference. It sounds like the pilot jets are too rich, but you can do simple testing yourself.

Gently screw in both air screws noting how many turns they take. Normal is about 1 1/2 turns out. Much more than say 2.5 turns suggests it needs smaller pilot jets and less than say 3/4 turn suggests it needs larger pilot jets. Once you get idle reasonably smooth and regular, the next step is as you rol the throttle open. You may find that perfect idle gives a stumble as you roll open the throttle. In that case it's OK to go slightly rich on idle to get a smooth transition.

Keihin CV carbs
Those old carbs are not well thought of but the same idea was used on CB750/CB900/CB1100 DOHC motors for years before emissions regulations made them obsolete. They work well but have to be set up correctly and if they are badly worn or slides are sticky that all makes it harder for modern mechanics to fix.

Mikunis:
What numbers are marked on the side of those carbs and do you know where the shop got them from or what changes if any they made to the jets? They are sold as 2 stroke carbs and are usually jetted all wrong for a 4 stroke. Doesn't mean they can't be made to work, but often harder than buyers expect.

You will get there.
 

cardinal

Been Around the Block
@teazer Thanks for the knowledge. I pulled the carbs and measured the engine side I.D. at 32mm. So these are VM 32 carbs. The main jet reads 185 and the pilot is a 35. I think the needle says 6DH4, and both needles were in the middle slot. but I've moved them up one spot to help with the midrange since the plugs were reading rich. I haven't talked to the guys at the shop about the carbs, but will reach out to them next week. The air screw is out 2 1/2 turns. I may try to raise the needles one more spot too to see if the low rpm range improves. Is the difference between right and left cylinders something to be concerned about? This engine has had a complete rebuild with new valves. I had another guy do the engine rebuild.

I have Uni pods but I still need to pick up some filter oil for them.
 

teazer

Over 10,000 Posts
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I worked with a guy in Canada with those carbs on a CB450 and he had 155 main jets in his and #30 pilot jets. With smaller pilot jets, the airscrew should be better closer to 1.5 turns out.

Those carbs typically come with #159 series needle jets in Q-6 size which is rich. They tend to work better with 176 series P-6 with a smaller air jet, say 0.5 to start. You can use the 159 series but they are designed for 2 strokes and go rich at higher revs compared to 176 series. You might check what's in there.

6DH4 is OK to start with but may need to be changed to get mid range clean after the jet changes, especially if you go smaller on the needle jet.

As a point of reference, smaller pilot jet will clean up idle and just as you crack open the throttle but won't make a lot of difference once the throttle is opened up.

Needle and needle jet cover 1/4 to 3/4 throttle and that's where most of us ride most of the time.

Main jet has an effect from about 1/2 or 3/4 to full throttle.

Air jet effects the main jet at full throttle as revs rise. On a 2 stroke or with #159 needle jets, teh air jet is huge or not even fitted because it has so little effect, but with #176 (bleed type) needle jets, the air is mixed in the jet which is why people call them emulsion tubes and too big makes a mess.

The idea behind a Bleed type needle jet is that raw et fuel doesn't burn well. What burns is the vapor surrounding each droplet. On a 2 stroke, the fuel goes down into the crankcase and then rushes up the transfer ports and the two streams collide, so there's lots of kinetic energy braking those fuel droplets up to burn.

In a 4 stroke the large droplets go straight into the head and don't burn well. The smaller the droplets, the greater the surface area to vaporize and burn. That's why modern fuel injectors have lots of small outlets rather than one larger one. It's all about getting more power and less unburned fuel in the exhaust. That's different to a rich mixture BTW.

So for a 4 stroke to run well, a bleed needle jet is preferred. For sure many people have used 159 series (Primary or 2 stroke) needle jets but 4 strokes do run cleaner with the right type needle jets.

Please push the needle jets out of your carbs and see what they are and check the inlet side of the carbs to see what air jet is fitted.
 

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cardinal

Been Around the Block
OK, I am completely in the dark about jet sizes. I pulled my needle jet and it does say 159 P5. The air jet says 2.0

I am having a helluva time reading these things. I have 50yr old eyeballs and the stamps are tiny!
 

teazer

Over 10,000 Posts
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So far so good. Someone got reasonably close and stayed on teh rich side of safe. #159 and 2.0 air jets are perfect for a 2 stroke and might work with your setup. They won't be perfect but we should be able to get a little closer.

Your eyes are 20 years younger than mine, so I use a magnifying glass. easiest is a 10x loupe. This is the cheapest I saw when I just searched https://www.zoro.com/aven-eye-loupe-10x-40d-self-mount-26034/i/G2104761/

Start with smaller pilot jets and see if that cleans up the idle and off idle and then fit smaller mains. Start rich - say 165 and work down. Then try dropping the needles one more slot (raising the clip) and let us know how that works.

Jetting is simple to understand but not so easy to isolate because so many factors overlap. Read the Mikuni manual I posted. It takes a while to digest and understand, but it all helps.

Those bikes are not exactly torque monsters but should be able to run OK. Lack of low end could be a number of things from ignition timing being off to low compression if the rings are not seating properly. It would be good to know where the timing is set and what the compression is after half a dozen or so kicks. All it takes is one valve to not seat properly to cause the side to side variation.
 
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cardinal

Been Around the Block
@teazer your explanation of the different needle jet type makes a lot of sense. I found 179 P4 or P6, but I haven't been able to find the P5. I am going to order P4 in the spirit of erring on the lean side. I'm also getting 30 pilot jets and 165,155, and 150 mains. I'll have to call my buddy over that helped me check the compression last time to see if he can have another look. The ignition is a Dynatek electronic unit that I timed months ago. I can have another look at it, but that is another thing that I am not 100% clear on how to dial it in. We did use a timing light to check it before, but I've heard that these may need to be clocked a little off from what the timing light suggests (again, I hear things and some make sense and some don't, so this may just be one mechanic's tale of how to time a CB450- I'm not claiming to be anything other than a student here to learn).

And you have been SO helpful with this I can't thank you enough. A lot of this experience has been just feeling around in the dark, but the shared knowledge that I get from DTT always gets me pointed in the right direction. Thank you!
 

teazer

Over 10,000 Posts
DTT BOTM WINNER
179? it has 159s and would be better with 176 but I would hold off on those until the low speed and high speed jetting is closer.

And just to complicate things, it will need a richer 176 than the 159 series because in a 176, it's a mix of air and fuel that passes through the orifice where on a 159 it's just fuel so you would have to go with say a P-6 or P-8 but get the low speed closer first before you invest too much in brass.

With the ignition timing, I would use a strobe and see how close it is at idle and also at say 3-4k revs. The Dyna is probably fitted on the stock Auto Advance Unit, and timing should increase as revs rise. It's a fairly basic system that uses weights to move outwards as revs rise. Just be careful when you time it because some oil will spray out of the alternator /timing cover and it gets everywhere.

It should spark at the small mark just before TDC at idle and should move to the other mark by about 3 or 4,000 revs.

For the compression test: wide open throttle both plugs out and let it turn over enough times until it stops rising.
 
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