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Author Topic: 627B Carbs rebuild  (Read 380 times)

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Offline scott jones

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627B Carbs rebuild
« on: July 22, 2019, 09:13:28 am »
Hi there, Scott here. I recently bought a 1973 cb500. Going through the carbs & had a question. The bike has a 4 into 1 exhaust & I am going to run pod filters. I bought #110 carb jets. My question is should I leave the needle setting at the stock setting # 4 position? I am at sea level if that makes any difference. Thanks for the help. PS 627B carbs.

Offline river

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Re: 627B Carbs rebuild
« Reply #1 on: July 23, 2019, 07:21:00 am »
I am assuming that you have done a very thorough inspection of the bike as well as a 3,000 mile tune up. If that is the case then my .02 is to make one change at a time and then go from there. My situation with carb tuning was a little different because I live at 9,000’ and can go to 12,000 or drop to 5,000 within 30 minutes from the house. It took a long time to get the tune dialed. Pretty sure I ended up at 38/100 with clips in the second position from the top. I have zero experience with pods but many here will suggest you use the stock box (and at least get things dialed there). Don’t forget to bench sync the carbs and know that moving those needle clips will require a vacuum sync each time. Good luck.

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #2 on: July 23, 2019, 07:49:10 am »
Thanks for responding. I have checked the bike over pretty closely & have done quite of work to it but I'm having trouble getting the engine to run right. I'm not a big fan of pod filters either but I have read that a lot of people run them. I really wasn't sure what effect the needle clip position has on the overall running of the engine.  I think I'll try the position #3 and see how that does. Thanks.

Offline Patrick

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Re: 627B Carbs rebuild
« Reply #3 on: July 23, 2019, 12:55:23 pm »
You really need to get the bike running to dial in the carbs, Scott. Pods and a 4-1 will probably run leaner, requiring bigger jets, but you won't know the right size until you can do plug chops at idle, mid-range and top end. The needles control the mid-range, which is where you will be running most of the time.

Do a bench synch and get it running well enough to idle. Then you can make adjustments using what you have as a base. Pods will be remarkably difficult to tune since air flow over the four carbs differs and changes as speed changes. A stock air box eliminates that by feeding all carbs from the same source.

Patrick

1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #4 on: July 24, 2019, 04:55:21 am »
Thanks Patrick. I'm going to bench sync the carbs and put them back on the bike & see where i'm at. I do have a question about the routing of the fuel lines. Do you think it makes any difference which side of the petcock I put the lines on. One line feeds #1 & 2 carbs. The other line feeds #3 & 4 carbs. It seems like it's easier to put #3 & 4 line to the left side of the petcock & #1 & 2 on the right side of the petcock. The lines seem to fit better that way. Like I ask, do you think it makes any difference? Scott.

Offline Patrick

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Re: 627B Carbs rebuild
« Reply #5 on: July 24, 2019, 06:18:44 am »
Fuel line routing is as much art as science. Just keep the line at a downward angle. If you leave the line flat or even make the fuel flow back upward for a while you may be subject to vapor locks.
1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #6 on: July 24, 2019, 07:34:34 am »
Ok thanks. I'll make sure of that. Scott

Offline Patrick

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Re: 627B Carbs rebuild
« Reply #7 on: July 24, 2019, 08:53:24 am »
One thing to consider when tuning with those pods. My Yamaha XS1100 actually has different jets and different emulsifiers on the two outside carbs to adjust for all the heat pouring off the big engine. You have need to do something like that with the jets or the needles to allow for the chaotic air flow into the carbs that pods will cause.

Patrick
1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #8 on: July 24, 2019, 09:21:57 am »
I don't know about these pods. I might just run with the stock air box. I see plenty of guys running pod filters. I've been watching a U-Tube channel hosted by Taylor. He is Classic Octane. All he does is change the jets to a #110 from a #100 and runs pod filters. Engine seems to run well. I'll get it right after time. I appreciate your responses. Thanks, Scott.

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #9 on: July 24, 2019, 12:31:41 pm »
One more question for anyone. I want to adjust my floats properly. The manual says 22mm float height. I understand i have to push the float up until it barely starts to touch the little pin on the float needle. The pin is spring loaded. Do I push the float up enough to depress the little pin or just enough to touch the little pin? Thanks 627b carbs. 1973 cb500f.

Offline magnum56

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Re: 627B Carbs rebuild
« Reply #10 on: July 24, 2019, 02:22:10 pm »
Just touching the pin. 


Note: Most here will also recommend a final float level check, and adjustments using the "clear tube method".   
 
'74 CB750K

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #11 on: July 24, 2019, 02:39:07 pm »
I have not tried to check the float level using that method yet. I understand the principle behind it but how do you connect the clear tube to the carb? The only place I can see would be the bowl drain. Is there a special fitting to put there to connect the hose to? Thanks.

Offline Erny

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Re: 627B Carbs rebuild
« Reply #12 on: July 24, 2019, 06:58:35 pm »
No special fitting needed. Just cut 4 pieces of clear tube and "screw" it in drain thread
I did just few hours ago. Carbs are 022A, but the same princpile on yours

CB750K K7 USA model (1977)
CB550K1 USA model (1975)

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #13 on: July 25, 2019, 04:05:49 am »
That's cool. I'll try that. Thanks. I hadn't thought of that. Nice looking carbs!

Offline Erny

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Re: 627B Carbs rebuild
« Reply #14 on: July 25, 2019, 04:32:53 am »
Yes. They are after rebuild, unfortunately I still have issue with too rich mix on idle. So its 3rd time I had to take carbs off to perform check, change jets, float level, o rings...
CB750K K7 USA model (1977)
CB550K1 USA model (1975)

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #15 on: July 25, 2019, 05:26:41 am »
What position for the sir clip do you have the slide needle set at. Or does your carbs have slide needles? The stock position for my 627b carbs is #4 but I have moved it to #3 position. Any thoughts on this? Thanks.

Offline Erny

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Re: 627B Carbs rebuild
« Reply #16 on: July 25, 2019, 05:54:15 am »
I should have it at 4th (according to person who made carb rebuild). This is stock settings (I have all stock).

If you have all stock, keep stock settings
CB750K K7 USA model (1977)
CB550K1 USA model (1975)

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #17 on: July 25, 2019, 06:04:29 am »
I have pod filters & a 4 into 1 exhaust. Other than that the bike is stock. Haven't put the carbs back on the bike yet. Still waiting on jets. Putting larger jets in.

Offline TwoTired

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Re: 627B Carbs rebuild
« Reply #18 on: July 25, 2019, 09:23:53 am »
You are better off starting with the stock carb setting and adjust as needed after you get it running.  Unless you are prepared to replicate Honda engineering efforts.

FYI:  Pods and 4 into 1 are a style for looks, not a specification.  Air flow and pressure drop vary among manufacturers, and few pod designs make any effort to keep the air flow laminar going into the carb throat.  The stock set up does for good reason.  Its a high RPM high airflow design.  And air behaves oddly with obstructions and velocity, complicating air fule adjustments at different air flow velicities.

Same is true for the 4 into 1.  These were originally designed to improve flow in a high RPM band where neighbor cylinder exhaust flow helps scavenge other cylinders.  At lower RPM, the reflected pulses actually spoil any scavenge effect, and diminish engine efficiency.  Racers don't care, they spend more time at max engine output.  Street riders should, and is probably the reason why Honda did a 4 into 4 for a nice responsive street bike at any throttle setting.

Aftermarket exhaust makes are selling a look.  Most have no performance figures or design development to actually tune for this motor.  It is just lighter and cheaper than restoring to stock or making the motor perform better.

You'll have to decide for yourself whether it's more important the have the bike look good while parked or be a very enjoyable bike to ride on the street.  It's a lot of work to get the motor running right with intake and exhaust mods.  Can be done with time, energy, and perseverance.  But, only expect a small benefit at or around red line RPM.  Motor doesn't care about your mod intentions.  Only the physics applied it.

See also:
http://forums.sohc4.net/index.php/topic,5410.msg203462.html#msg203462

And the series beginning with:
http://forums.sohc4.net/index.php/topic,5410.msg741438.html#msg741438

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #19 on: July 25, 2019, 09:53:12 am »
Thanks Lloyd for the response. I would prefer the stock set up but the previous owner had the 4 into 1 exhaust put on the bike years ago. The pod filters provide more room for installing & removing the carbs & yes they look cool. I have the original air box & its in good shape. I'm changing the carb jets to a larger size because I was told I had to do to the 4 into 1 exhaust. I haven't been able to find a decent original exhaust system. I did see one guy had one on Ebay for $1500.00. It was prestine but very expensive. To rich for my blood. LOL. I wouldn't mind a 4 into 2 dual exhaust but haven't found that either. Thanks for the links.  :)

Offline Patrick

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Re: 627B Carbs rebuild
« Reply #20 on: July 25, 2019, 11:21:56 am »
The 4-1 may or may not have a big effect on your tuning, Scott. It's the pods that are going to mess everything up. My first 750 had a 4-1 exhaust, but the muffler was pretty restrictive, so that bike (with original airbag) ran best on original meeting and needle position. No one, even our brilliant curmudgeon friend Lloyd, can predict what you will need to do with the jets or needle until you get it running. Every pipe is different, even within pipe models. Every pod is bad, but bad to differing degrees.

I have a hard time getting a good tune on my dirt bikes, running pods. And those have only one cylinder.

Patrick
1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline LastChancer88

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Re: 627B Carbs rebuild
« Reply #21 on: July 25, 2019, 12:25:35 pm »
I have pod filters & a 4 into 1 exhaust. Other than that the bike is stock. Haven't put the carbs back on the bike yet. Still waiting on jets. Putting larger jets in.

I have basically the same bike '73 500four with 4into1 and pods and the best thing I did was up the pilot jets one size to 42 and the mains went up to 115.  I'm at about 3200 feet elevation.  I could be wrong but I believe the 3rd position is stock unless I've read wrong so 4 is slightly richer which is also what I run.  That helped my bike all run much nicer with those mods.  My $.02
1973 Honda CB500 Four
1973 Suzuki TC125

Offline scott jones

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Re: 627B Carbs rebuild
« Reply #22 on: July 25, 2019, 01:33:33 pm »
Thanks for all of your advise guys.
« Last Edit: July 26, 2019, 05:48:16 am by scott jones »

Offline scott jones

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pod filters
« Reply #23 on: September 18, 2019, 08:09:59 am »
Good morning all. I have put pod filters on my basically stock 627b carbs. 1973 cb500. Engine runs like crap. Add choke & the engine seem to run better. The only thing I changed from stock is the main jet. I put a 110 in. Anybody have any comments on the pod filters? Or should I be more happy with the stock air cleaner system.

Honda3

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Re: pod filters
« Reply #24 on: September 18, 2019, 08:38:57 am »
Good morning all. I have put pod filters on my basically stock 627b carbs. 1973 cb500. Engine runs like crap. Add choke & the engine seem to run better. The only thing I changed from stock is the main jet. I put a 110 in. Anybody have any comments on the pod filters? Or should I be more happy with the stock air cleaner system.

pods can be a nightmare but once you dial them in they are good (unless it rains and they get wet). If your bike runs when you add choke, the its running lean. You need to richen things up by changing the main jet, pilot jet or both.

Somewhere on the net a guy posted a definitive jetting procedure for ppl running pods. I will try and find it.

Stock is always better. This is my 73 cb500F stock air cleaner




 

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