Topic: Keihin 649A Carb rebuild

[vulcan spoenik]

Hello,

I've seen some discussions about the Keihin 649A carbs. So it happens, that i'm just rebuilding a set of those carbs and thought i shared some pics with you all.

Some background first.

Honda Cb500 Four (Imported from Germany to Finland in 2009, history unknown..)

Frame: CB500-2047215
Motor: CB500E-2170859

According to those numbers, frame would be a -72 (k1) make and engine would be from the year -73 (K2)

Had few issues with the bike, so i decided to strip down the carbs and give them a good refurbishment. Problem was that the bike was running briskly on the rich side. Symptoms were sooty plugs, mild response to fast throttle action and a bit flat acceleration, smoke coming from the pipes (especially cyl #1). Also i didn´t have any problems starting this bike cold with choke off. As soons as i turned the choke on, the bike died.

Whaddye say?  Clearly matter of the bike getting too rich fuel mixture in to the system, eh?

The bike is completely stock, no 4-1 pipes, no cone filters. So my conclusion was that the carbs were dirty and/or the air filter was old/dirty which caused the bike to go on the richer side..

So, off the carbs from the engine and commenced the strip down. I removed the interiors (needles, jets, float bowls, venturi, air screws etc) and blasted the carb bodies with baking soda to clean them thoroughly. I payed special attention to the emulsion tubes and passages. Then i soaked the carbs in good solved for couple of days just to be shure i get all the gummed up dirt out of the carbs.

As the carbs were soaking, i examined the carbs, floats, jets and needles to see if they´d been tampered with. Since i have no knowledge of my CB´s history, i had to make shure that the PO didnt do anything peculiar fiddlings on them or something of that sort... The result:

ID 649A (Stampped on the rightside of the carbassembly)
Slow jet: 40
Main Jet: 78
Needle: 272304, 3rd groove

Everything had Keihin star stampped on them so there is a very good chance that carbs were in their original condition and un-tampered.

My plan is to replace the jets and needles with new ones (from Keyster rebuild kit). Since the bike is stock and a the intention is to keep it that way, im not going to mess with the jet sizes. #78 on the main and #40 on the slow will do just fine. However, since the bike was running on the richer side, i raised the needle clip one up (2nd g.f.t.). Then i´ll have to check the float levels. I washed all the small parts with ultra sonic cleaner. They came pretty aseptic so i think i will save them for later use (for spare parts maybe?)... But as i wait for my rebuild kit to arrive, here are some pics...

[vulcan spoenik]

More pics..  

[vulcan spoenik]

Few more...

[haggeo]

interesting to see a rebuild thread focused on carbs.

[brandEn]

I think its a great idea. I could have used some help last week on my PD carbs!

[vulcan spoenik]

Oi!

Thanks. During this summer i overhauled the engine but i dont have any decent photos of the process... my bad, cause was too lazy to fetch the camera... Reason for the overhauling was that i managed to break a sparkplug inside the engine. Cyl #3 went cold for some reason and i thought of changing the sparkplugs, since i didn't knew how old the plugs were.... To my suprise, swapping the plugs  wasn´t as easy operation as i thought..... While trying to open Cyl #4 sparkplug I somehow ended up only half a plug in my hand  The other half was still in the engine, it seemed to be welded there for good...  I managed to get rest of the plugs out and then i measured the compressions of the 3 cylinders.... long story short,  cyl#2 and #3  had worn piston rings.

As i started to dismantle the engine, i decided what the heck.... While opening the the cyl.head it was the same if i would tear down the whole engine and take a peek whats she´s eaten.... The bike had only 60 tkm on the gauge, so my assumption was that the guts should be in good condition.. and they were!

Anyway.... I browsed some discussion about the differences between 649A and 627B carbs... Somehow i happened to have a camera with me when i took the carbs out (well.... not right from the start because i didnt document the soda blasting...). I thought that someone could spot some differences (if any, except main jet size) between those two carb types via my photos..

I´ll post more photos of the progress when i get the rebuild kits....

Cheers!

[jack1980]

How do you like the ultrasonic cleaner?  What does a unit like that cost, if you don't mind?  Also what are you using for the cleaning solution?

Thanks!

[TwoTired]

Do you also have the inlet snorkel over the air filter?  (I assume so)

Did you try replacing the air filter to help with the running rich issue?

We don't have the 649 carbs here is the states.
Could you measure the hole sizes in the emulsion tubes?
Could you measure the needle jet sizes in the end of the emulsion tubes?
Could you measure the pilot system air jet size?
Could you measure the main emulsion system air jet size?

What spark plug number are you using?

How is your engine breather tube routed?
Does your air filter have the breather element, drain hoses, etc?   What of the plenum air chamber drain hose?

FYI: The inner spark plugs need either the original tool kit's bell shaped spark plug tool or a very thin walled socket to clear the access tunnel obstruction.

Cheers,

[vulcan spoenik]

How do you like the ultrasonic cleaner?  What does a unit like that cost, if you don't mind?  Also what are you using for the cleaning solution?

Thanks!

If i remember correctly it, it was around 55 USD, and rhe capasity was about 0.26 gallons, which is not much but adequate to clear small things, like screw, bolts and carburator parts... I use different solvents for the cleaning.. for those carb parts i used Bräkleen. I know there are fancy liquids for those machines, but they are way overpriced imo. So i´ll stick with the normal stuff... Seems to work pretty fine to me. 

[vulcan spoenik]

Do you also have the inlet snorkel over the air filter?  (I assume so)

Did you try replacing the air filter to help with the running rich issue?

We don't have the 649 carbs here is the states.
Could you measure the hole sizes in the emulsion tubes?
Could you measure the needle jet sizes in the end of the emulsion tubes?
Could you measure the pilot system air jet size?
Could you measure the main emulsion system air jet size?

What spark plug number are you using?

How is your engine breather tube routed?
Does your air filter have the breather element, drain hoses, etc?   What of the plenum air chamber drain hose?

FYI: The inner spark plugs need either the original tool kit's bell shaped spark plug tool or a very thin walled socket to clear the access tunnel obstruction.

Cheers,

Ill get back to you during the weekend... I´ll measure those tubesizes and take few photos of the air cleaner unit.

[vulcan spoenik]

Oi,

Managed ttoday to put couple of hour on these carbs...

Do you also have the inlet snorkel over the air filter?  (I assume so)

Did you try replacing the air filter to help with the running rich issue?

Nope, i didnt have clean (new) filter at hand. However, i removed little bit the old airfilter and it got better, throttle response was more reactive. I also tested the method of  turning off the gasolene tap while the motor was running. Response to throttle action got more sensitive. Check the photos for the air box assembly. No snorkel, only a cover.

It funny because if you check out this http://images.cmsnl.com/img/partslists/air-cleaner-element-side-cover-cb500-four-k1-germany_bigma000083f13_8b50.gif, it different what it supposed to be...

Air breather hose from top of the engine goes behind the engine, and thats it. There are no entry point in the airbox the i could stick the other end of hose back in. There is a downtube in the cleaner chamber element, but the diameter of that downtube is way more than the breather tube can handle...

We don't have the 649 carbs here is the states.
Could you measure the hole sizes in the emulsion tubes?
Could you measure the needle jet sizes in the end of the emulsion tubes?
Could you measure the pilot system air jet size?
Could you measure the main emulsion system air jet size?

Check out the photos..

Main emulsiontube... l= 36,7 mm (+- something), sidehole w=1,0 mm (about), endhole w= 2,7 mm
Air jet l= 21,5 mm, sidehole w= 1,3 mm, endhole w= 1,5 mm
Mainjet D=6,0 mm, l= 9,5 mm, inner D₁=2,3 mm, inner D₂=0,1 mm

Couldnt get the needlejet dimensions cuz the i have already assembled the needles  back in the carbs...

What spark plug number are you using?

How is your engine breather tube routed?
Does your air filter have the breather element, drain hoses, etc?   What of the plenum air chamber drain hose?

Current sparky´s are NGK D7EA, previous one were (installed by PO i presumer) DR8EA and DR7EA. Yes, the engine was using different types of plugs.

FYI: The inner spark plugs need either the original tool kit's bell shaped spark plug tool or a very thin walled socket to clear the access tunnel obstruction.

Cheers,

Yeah noticed.... I used Honda´s own tool

[vulcan spoenik]

Couple more photos... Upper scale on the tool are inches and lower are mm.

[Niels Bojesen]

Nice to see another 649 A carb. I have the same carbs and the bike run badly when i got it, but that was because the carbs was installed with #100 main jets and that is what you read in the Clymer handbook   
So i took a look in the the big box of spareparts that came with the bike, and there they where #78 
But because the original Marshall 4 in 1 exhaust i had to find some bigger jets and my luck was in Canada...... #85 main jets and the engine came to life right away 
Now i just found out that the life of the primary chain is over, so now its time for the big engine overhaul and that will start in about 2 weeks.
I just planed to unscrew each carb from the bracket and then they go down my ultra sonic cleaner one by one, before polish in a vibratory tumbler... I will post some pics when the project starts.

[DaytonGuy]

Quick (and probably dumb) question.

Can you remove the needle and change the clip positon without diconnecting the four carbs from each other?  If so, how?  It looked to me that you have to remove the slides from the connecting rod to bet down int there enought to get ot the two little screws...?

thanks.

[brandEn]

on my carbs I remove the screw that holds the arm to the shaft, then undo the small spring inside the slide, then you can remove the slide. does that make sense?

[vulcan spoenik]

Heya,

on my carbs I remove the screw that holds the arm to the shaft, then undo the small spring inside the slide, then you can remove the slide. does that make sense?

Exactamundo.  Check this link http://images.cmsnl.com/img/partslists/carburetor-cb500-four-k1-germany_bigma000083e22_5894.gif

[vulcan spoenik]

Oi!

Some updates... Finally received my carb rebuild kits...... Note that 01600-KEY-1050N includes both #78 and #100 main jets.

I took couple of photos while putting the pieces together...

[vulcan spoenik]

Emulsion tube and main jet were quite tight fit... Had to apply some force before they glided into place..


I had some minor problems fitting the new carb bowl gaskets into the groove. Slippery bastards kept slipping from the groove from one end or the another.. I'll return to this issue prolly on sundae. I´ll use some sort of sealant to make them stay in the grooves..

[vulcan spoenik]

Oi!

Had the chance to put 1+ hour on these carbz today. They´re pretty much ready to be assembled onto the engine... I installed new inlets, rubbers and gasfilters. So far so good! 

Oh... I also replace all phillips screws with stainless allen screws.... Makes the future rebuild/maintenance runs alot
easier! 

[vulcan spoenik]

Couple more pics..

[OLDHEAD]

can some1 do that with a rack of 44b's

[vulcan spoenik]

Dear Members,

I had the luxury of putting few hours on this project furing the weekend.

I mounted the carb assembly back on the engine. Connected all the hoses, opened the fuel tap to fill the carbs with fresh fuel. All good so far.

Then i fired the ennige, and i must say..... Carb cleaning made wonders to my bike !  I made, the bike fired right away and it idled with the choke on smoothly!  After few minutes of choked idling i closed the choke and it still sounded good. I would very much liked to go out for a spinn but its about -3 degrees celcius outside n snowing so it wasnt possible. So i have to stick with the engine running on idle (atleast the following few months, sheesh.....  ). But  I am quite happy with the result.

What i yet have to do is adjust properly the idle screws ( i preadjusted them about 1 - 1 1/2 turns open before first start) and do a carb sync. The idling is good but it isnt perfect yet.

One potential problem, which i havent yet addressed is the smoke coming out out cyl#1. I tried to adjust the idle screw on carb no.1 1-2 turns but it didnt seem to help. Too many possibilities atm to speculate here but i am planning first doing the sync and then start shooting the problemas one by one.

[Franky]

I know this thread is old, but which jets did you end up using? 78 or 100?

Anybody know, which bikes use the 78 and which use the 100 ?

[vulcan spoenik]

Hey,

Still here 

I ended up putting #100 size mains.

[Restoration Fan]

Glad someone resurrected this thread.  I'm working on a set of those carbs right now and the pictures give me just one more frame of reference.  Glad you put this together back in the day.