79' cb650 carbs

[scott84]

Hey I just wanted to let everyone know that the mid 90s cbr600 carbs will line up with the heads one these cb650. I personally have a 1980 cb650 that has cbr600 carbs on it. My friend has a 1981 cb650 with cbr 900 carbs. so there are more options out there than the pd50 carbs.

[my79650]

I did the solder job to my pd50a's and got the floats set to mark on all 4 finally. But i got the gas smell when stopped. i pulled the plugs and 1 and 2 are slight brown, a little dirty but good. 3 and 4 were black as soot; too rich on that side; air screws at 1 1/2 turns this time. A pig on gas maybe 25mpg! I had my fill of this so i got some small bits to drill out the solder and replace the cutoffs with a good set out of a 79 cb750k cv rack. they fit the pd50s. a little loose in the holder for the pin on the backside but they're the same round at the cover. Drilling the solder on the air box side as i had filled the entire channel when i did this. I couldn't get it hot enough to melt the solder out of the holes so i'm drilling.

[my79650]

Scott84; what year was the cbr600 carburetors from? I just googled some pictures and diagrams and so far they show cooling lines for antifreeze and an electrical plug for something. Did you block or bypass this somehow?

[Volker_P]

I couldn't get it hot enough to melt the solder out of the holes so i'm drilling.

If you have a large heat sink (like large alumina parts) supporting the soldering rod with a hot air gun is a proven proceeding.
Also disassemble as much as you can.

[my79650]

Sorry no hot air gun.

[scott84]

The carbs on my bike are from a 97 cbr 600 I did not hook any of the lines up on the carbs. The only problem is they leak gas from the back of the carbs.

[Pinhead]

The carbs on my bike are from a 97 cbr 600 I did not hook any of the lines up on the carbs. The only problem is they leak gas from the back of the carbs.

Do those carbs line up directly with the intake ports on the head or did you have to perform some shenanigans to get them to line up?

[scott84]

The carbs line up almost perfect they are probably 1 mm off so I used some radiator hose to use as intake tubes.

[Volker_P]

Sorry no hot air gun.

Quite advisable tool if you care for old stuff.
For me of a similar importance like the big hammer.

[my79650]

Always have the hammer; yesterday i picked up a complete set of pd50s, including the plastic choke piece! Disassembling now. And i am not blocking the air cutoffs in this set. It has 4 good diaphrams. Just have to clean as they sat with gas in them; and i can swap over all the good used bits to make one running set!

[jude0007]

How big of a deal are those diaphragms? Mine are ok but not great. Does it just affect back firing? Any advice?

[my79650]

Underneath the diaphram itself is a small channel that goes directly to the slow jet. Before i did the block job i had no idle. Did that and i can idle but it was riching out, could smell the gas when stopped but when driving it pulled great. Plus my gas mileage went to hell too! With the set i'm rebuilding using all the good stuff from the now parts carbs. Don't forget to count the turns on the air screws so you don't do a half assed job getting it right. i am using the floats in these with my good needles; replacement carb floats were set proper, just needed a bath. Swapping over the float covers, acc. pump, fuel pipes, vent lines and needle valves; also all jets and emulsion tubes. Using the rest that was already on this set. Personally i feel that the diaphrams do more than just stop eshaust popping; i believe they also keep everything in tune as the channel goes to the slow jet; upper channel fromn air box side towards front ties into the actual vent area. The other from diaphram cover to the throat. Equalizes the air pressure; thats my opiniom on them. If you have good extras on hand save them; very expensive.

[my79650]

The replacement rack i am using now is getting bout 40 mpg. But i have a hesitation if i crack the throttle to quickly. If i let it gradually pick up speed it performs fine and lets me add more when i have to climb a small hill or go to pass a car. I knew i would have to pull and clean them a few times to get them properly cleaned. I may not have got all the crud out in my initial cleaning, but running them for a week may have loosened up any other dirt or varnish from setting for years on a shelf with gas in them. I knew this would happen as i don't have a sonic cleaner or fancy set up for this; but other than the hesitation i am quite pleased with the performance so far.

[jagans]

I have a nearly complete set of carbs for a 1980 CB650c that are disassembled and cleaned. PD50A's, but I do not understand your logic in not replacing the rubber in yours. If you think about it, all of the old sets of carbs are going to have old rubber which needs to be replaced after 30 some years.

What they charge for these parts is simply hyway robbery, I grant you that, but short of injection molding your own, I don't see any alternative to biting the bullet and buying the parts.

[my79650]

A lot of the carbs out there even to day still use the same size of cutoff diaphram..... if you get a set that has good cutoffs in them save them after you check them for size. 250 rebel/custom fiom the 80s til now; 78-83 cb750 DOHC's all use the same size cutoff as the pd50's series just to name a few....over $30/Cdn for me; that's overkill for a chunk of rubber!