Topic: Carb Question

[bkklett]

Please forgive me if this has been covered. I was unable to find what I have a question about.

I have a 1971 750F I have a 836 kit .I currently have 76 carbs on the bike. I wanted to go with 77-78 carbs. So here we go.
1. Will they work?
2. If they will, what will I need in addition to the carbs to make them work?
3. Is there another set of carbs form another bike that would work better? (I was once told CB900 carbs work also- Don't know if it is true or not.

thanks in advance.
brian

[mrrch]

71 F? First year was 75 for the F. The 77-78 carbs will work but you will need the intake manifolds to match. You will probably be doing some rejetting. Others will chime in with some recommendations. Are you using the stock airbox?

[flybox1]

YES, they fit easily and work well.  I have a K1 with K8 (PD42) carbs.
stock pipes, airbox, and jetting.
you'll need to pay particular attention to the accel pump unit on #2, and probably rejet if you have pods or a less restrictive exhaust.

[bkklett]

Sorry I was thinking F it is a K model. I am running an airbox. I have ported the head but no other mods. Will the throttle linkage work or do I need to change that also? flybox1- I know what the Pd stands for 42? Is there more than one type during 77-78? What about Super sport carbs 77-78 I have an opportunity to get my hands on a set of those.  Thanks again.
B

[lucky]

The 1978 CB750 K had slightly shorter intake boots.
Why do you want to change the carbs??

The 1977-78 carbs were the only CB750 carbs with the accelerator pump and spray nozzles. A real wild card when tuning.
All of the earlier carbs did not have that wild card to deal with.
Also if that accelerator pump bottom plate with the check ball wont work because of a corroded steel ball or seat you will have to buy another one and they cost $85.00!!

To me the 1969 KO carbs were the VERY BEST.
NO mechanical linkage. Just a cable and it pulls the slide up. SIMPLE
Just unscrew the top ring and the slide pops right out for needle adjustments.
Adjustable needles.
Simple air screw adjust just moves the slide up or down.Where you can get to them.
Clip on float bowls for easy access for changing jets.
Choke was a simple lever and linkage exposed- NO CABLE!!

[buca]

71 F? First year was 75 for the F. The 77-78 carbs will work but you will need the intake manifolds to match. You will probably be doing some rejetting. Others will chime in with some recommendations. Are you using the stock airbox?

Hello, need help.. Need to find replacement carbs for 1981 CB 650. What is the best , not necessery , stock ones, but some proven replacement for good reliable performance. And that can be fitted without modifications.   Thanks  Borivoje

[bkklett]

Maybe I am looking at the wrong thing. I have a Cb750 (836)that I hillclimb. It stumbles off the starting line slightly. I have to get the RPMs up so I can take off at a good pace. It is also stumbling every time I get off the throttle then directly back on. I have changed jetting and still no solution. Most of the hills I climb have multiple steps in them so I have to get on and off the throttle many times. It stumbles every time. I've done throttle chops and according to the plugs I am burning good. I have made sure they were synchronized. I have even checked temperature of the exhaust and they are all about the same. The reason I thought of getting the 77-78 carbs is reading, most people say it would be better for what I am experiencing. i have been trying everything I have read for over 2 years now and just frustrated. Any help would be appreciated. I really don't want to buy new ones just want to stop dealing with the problems I have.

[lucky]

Maybe I am looking at the wrong thing. I have a Cb750 (836)that I hillclimb. It stumbles off the starting line slightly. I have to get the RPMs up so I can take off at a good pace. It is also stumbling every time I get off the throttle then directly back on. I have changed jetting and still no solution. Most of the hills I climb have multiple steps in them so I have to get on and off the throttle many times. It stumbles every time. I've done throttle chops and according to the plugs I am burning good. I have made sure they were synchronized. I have even checked temperature of the exhaust and they are all about the same. The reason I thought of getting the 77-78 carbs is reading, most people say it would be better for what I am experiencing. i have been trying everything I have read for over 2 years now and just frustrated. Any help would be appreciated. I really don't want to buy new ones just want to stop dealing with the problems I have.

I am sorry you have had so much trouble getting the help you need.

To really help you I would need to know all of the facts first.


CB750F
1971
Year of the carbs?same?
Type of intake?
Type of exhaust?
Muffler??
idle jet size? (I think stock size on the F model was #38mm.)
Main jet size? #105 was stock.
Needle clip position?
mixture screw turns?

[TwoTired]

I have a 1971 750F I have a 836 kit .I currently have 76 carbs on the bike. I wanted to go with 77-78 carbs. So here we go.
1. Will they work?

Yes.  They can with some work.

2. If they will, what will I need in addition to the carbs to make them work?

Possibly carb couplers fore and aft of the carbs, and the throttle cables are likely different.  You'll also need a choke cable.
Internal jetting changes to accommodate the air filter and exhaust choices fr or the bike.

3. Is there another set of carbs form another bike that would work better? (I was once told CB900 carbs work also- Don't know if it is true or not.

I don't know the inlet and exhaust diameters for the CB900 couplers.  However CB900 carbs are CV type rather than mechanical slides.  With the correct jetting, they should cure throttle change stumble.  Probably need custom throttle cables, and other things, I'm not aware of.

I know what the Pd stands for 42? Is there more than one type during 77-78? What about Super sport carbs 77-78 I have an opportunity to get my hands on a set of those. 

There are PD41 A and B as well as PD42 A and B.  All these carbs have accelerator pumps, which is what you are after to cure the stumbles.
The PD 41 a or b  have adjustable slide needles which are handy for midrange mixture adjustments.
http://www.motorcycleproject.com/motorcycle/text/specs.html

Cheers,

[bkklett]

Maybe I am looking at the wrong thing. I have a Cb750 (836)that I hillclimb. It stumbles off the starting line slightly. I have to get the RPMs up so I can take off at a good pace. It is also stumbling every time I get off the throttle then directly back on. I have changed jetting and still no solution. Most of the hills I climb have multiple steps in them so I have to get on and off the throttle many times. It stumbles every time. I've done throttle chops and according to the plugs I am burning good. I have made sure they were synchronized. I have even checked temperature of the exhaust and they are all about the same. The reason I thought of getting the 77-78 carbs is reading, most people say it would be better for what I am experiencing. i have been trying everything I have read for over 2 years now and just frustrated. Any help would be appreciated. I really don't want to buy new ones just want to stop dealing with the problems I have.

I am sorry you have had so much trouble getting the help you need.

To really help you I would need to know all of the facts first.


CB750F
1971
Year of the carbs? they ARE 76 CARBS  same?
Type of intake?  I have stock Air Box. I could not get Pods to work.
Type of exhaust? Straight Pipes with slight restrictives for back pressure.
Muffler?? No!
idle jet size? (I think stock size on the F model was #38mm.) I think I am at 120's (I changed so many times I Can not remember.
Main jet size? #105 was stock. Stock setting On Idle
Needle clip position? I am in the middle
mixture screw turns? 1 1/2 turns.

The bike runs great, starts very fast, idles great, just have problem with stumbling.

[lucky]

OK just need to fill in the gaps.

CB750F
1971
Year of the carbs 1976
Type of intake  stock Air Box.
Type of exhaust, Straight Pipes with slight restrictives for back pressure.
idle jet size?
Main jet size #120mm
Needle clip position, middle position.
mixture screw turns? 1 1/2 turns.

#120's would be the main jets Bkklett.
When you say the exhaust has restrictives does that mean metal baffles that go inside the exhaust tubes?
Need to know the idle jet SIZE.
The carbs are very similar.
When you check the idle jet size make sure your floats are set correctly.
Here is a link for that http://www.salocal.com/sohc/tech/carb/asmpg_mgs/flthgt.htm