Carb help for Honda CB 750

[Zorro]

I recently purchased a 1978 Honda CB 750. Engine turns over but never starts. I can get a sputter out of it. I'm 99% sure the carbs are f'ed up - the middle left carb leaks gas as soon as you open up the petcock.

I was going to have an expert clean/rebuild/tune these carbs but I haven't received the expert's contact info. Since it's "new to me", I've been anxious to get it running.

Do we have a resident OR carb expert who's willing to help? I read a few threads about cleaning carbs and what not...but I'm somewhat nervous when it comes to doing something I never done - it usually turns out bad or costs me more money.

Thanks in advance...

[Sidewinder600]

Here: http://www.cyclemaintenance.com/mechicscorner/cb750_carbs.htm

I'm guessing the hardest part is getting the carbs off the bike. Aside from that, you'll probably just need a screwdriver, some small sockets or adjustable wrench, and gasket kits, if that.

Your symptoms are (probably) standard dirty carb stuff. Non-starting is usually because there's dirt or gummed-up gas plugging up the idle jet. The leaking carb is probably just dirt or something holding open the float needle.

[yotaman88210]

If you cant figure it out, I know a good carb guy. I will have to look for his number. I think he charges 120 + parts

[Zorro]

  yotaman88210 said:

If you cant figure it out, I know a good carb guy. I will have to look for his number. I think he charges 120 + parts

Yeah...PM me his number. Thanks Yota.

[El capitan]

i just tore my carbs apart on my 88 hawk and i can say its not that daunting if you keep everything in front of you and separated. it all made sense to me once i tore into it. matter of fact they are soaking as we speak. as far as tuning a clean carb i'm clueless, but then again i haven't ever tried.

[Zorro]

  El capitan said:

i just tore my carbs apart on my 88 hawk and i can say its not that daunting if you keep everything in front of you and separated. it all made sense to me once i tore into it. matter of fact they are soaking as we speak. as far as tuning a clean carb i'm clueless, but then again i haven't ever tried.

Thanks for your opinion. what do you have these soaking in? as for tuning, if you just set everything back the way you had it...they should be tuned...right?

[El capitan]

  Zorro said:

Thanks for your opinion. what do you have these soaking in? as for tuning, if you just set everything back the way you had it...they should be tuned...right?

i asked around and it seemed everyone had the same opinion that yamaha made the best cleaner. so i went to a yamaha dealer and bought a quart. you mix it 2:1 in a bucket using hot water.

as far as tuning goes... yeah you should be good as long as you set it back the way it was. but like in my case, i think someone tuned the carbs with ripped diaphragms installed so mine might be way off. it sounds stupid but reading the manual is pretty key to getting a good base tune.

i just finished putting mine back together, now i'm just waiting on parts to finish it up.

[El capitan]

literally i have like 3 hours tops in it so far, and probably another hour to go, but i could now do it much quicker having already done it.

[Zorro]

  El capitan said:

literally i have like 3 hours tops in it so far, and probably another hour to go, but i could now do it much quicker having already done it.

Thanks for the info.

How'd yours turn out?

[El capitan]

  Zorro said:

Thanks for the info.

How'd yours turn out?

i'm waiting on the diaphragms that should be here hopefully this week..

i just spent another 1/2 hour hooking up throttle cables, choke, and some fuel lines. i also seated the carbs and cinched em' down. so basically i have another 15 mins worth of work waiting for me so i can get in a ride hopefully this weekend.

[imprez55]

Carbs really are not as bad as some people make them out to be, there are a lot harder diy's on a bike than that. I did 2 sets before I even owned my own bike and really knew what I was doing.

All you need is the manual for your bike, carb rebuild kit, various disassembly tools and some cleaners. When I was doing 1 and 2 carbs (eventually broken down into two sets of 1) I just popped them into a pot with some dawn and boiled them once disassembled, worked great. With the E, I didn't really want to take all the bodies apart so I didn't boil them, instead I just used some carb cleaner and a tooth brush with a brake cleaner rinse.

I was looking for a rebuild kit for you and I found this, its a carb guide to for the '69-'78 SOHC CB750. Personally, I used this guide because it was bike specific for me. Either way just read the guide and the shop manual over to familiarize yourself with all the parts and it should be a breeze.

The four things you really need to check

1) Diaphragms, are they torn or not and do you have to get new ones

2) Are the floats sunken, are they at the right height (second part is assembly only)

3) How many turns out is the pilot mixture screw, is it in spec (if its not, is that why it was running bad?)

4) Are the needles still good, do you need more

If you have all the parts on hand, 4 hours is the most you would probably spend on them your first time like El capitan said. If they are off your bike, even better.

Where in ohio are you?

[Zorro]

  imprez55 said:

Carbs really are not as bad as some people make them out to be, there are a lot harder diy's on a bike than that. I did 2 sets before I even owned my own bike and really knew what I was doing.

All you need is the manual for your bike, carb rebuild kit, various disassembly tools and some cleaners. When I was doing 1 and 2 carbs (eventually broken down into two sets of 1) I just popped them into a pot with some dawn and boiled them once disassembled, worked great. With the E, I didn't really want to take all the bodies apart so I didn't boil them, instead I just used some carb cleaner and a tooth brush with a brake cleaner rinse.

I was looking for a rebuild kit for you and I found this, its a carb guide to for the '69-'78 SOHC CB750. Personally, I used this guide because it was bike specific for me. Either way just read the guide and the shop manual over to familiarize yourself with all the parts and it should be a breeze.

The four things you really need to check

1) Diaphragms, are they torn or not and do you have to get new ones

2) Are the floats sunken, are they at the right height (second part is assembly only)

3) How many turns out is the pilot mixture screw, is it in spec (if its not, is that why it was running bad?)

4) Are the needles still good, do you need more

If you have all the parts on hand, 4 hours is the most you would probably spend on them your first time like El capitan said. If they are off your bike, even better.

Where in ohio are you?

Wow, nice info here! I was thinking of buying a carb gasket kit before I did anything. At a minimum, I would need this. As for diaphragms...i'm not sure...they're still on the bike.

Anyway, I'm in Dublin...North West side of columbus.

Thanks for the time/effort on this post!

[flounder]

I told you 50 times.. Tear into the damn things yourself and try and learn. If you cant figure out how to do it, then take it to someone. Whats the harm in trying to fix something thats already broke before paying someone else??????

[Zorro]

  flounder said:

I told you 50 times.. Tear into the damn things yourself and try and learn. If you cant figure out how to do it, then take it to someone. Whats the harm in trying to fix something thats already broke before paying someone else??????

See where i stripped the drain plug on my r6

I'm gonna start soon...just purchased this...

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230514135357&viewitem=&sspagename=STRK%3AMEWNX%3AIT

[starrz057]

Recomend Wes @ R.M.P 614-475-1245

[starrz057]

unless you decide to work on it your self

[Zorro]

Update!

I pulled the carbs off and dissembled them by removing the tops (official name?) and the bowls. I didn't remove the linkage so they're still together and hopefully synched still. I was surprised at how f'ed up they were - didn't realize gasoline can cause so much damage. Anyway, the two carbs on the left were most f'd. I guess this is because the bike is leaning that way while on kickstand. One of the floats, cant remember, was stuck. Some the the internal, non-removable, non-replaceable parts were starting to erode. I believe it's the main jet canal. I'm thinking I should be good still. I took pics...i'll try to post later. One carb was so bad that after removing the drain bolt...nothing would drain! The pilot screw??? The one on the main jet with all the super small holes, was completely clogged up.

I've been dipping all the removable parts in the carb bath solution and shining them up with steel wool. I'm waiting on a gasket kit...should be here this week. I dipped the set of 4 carbs in and was glad to see that my throttle response, which was super slow previously, is snapping back to closed. Hopefully all this work pays off and this bike starts.

[Zorro]

Update...

Carbs were cleaned and rebuilt. I installed them on the bike tonight. After troubleshooting a stupid problem (which inlet does the fuel line attach to?) I got the bike running!!!

Unfortunately it doesn't run like my r1/r6...but what should I expect from a 32 year old bike? Anyway, the engine is smoking a little. Not sure where it's coming from but maybe the headers or a gasket?

I took it for a ride around the hood for its maiden voyage

[El capitan]

  Zorro said:

Update...

Carbs were cleaned and rebuilt. I installed them on the bike tonight. After troubleshooting a stupid problem (which inlet does the fuel line attach to?) I got the bike running!!!

Unfortunately it doesn't run like my r1/r6...but what should I expect from a 32 year old bike? Anyway, the engine is smoking a little. Not sure where it's coming from but maybe the headers or a gasket?

I took it for a ride around the hood for its maiden voyage

feels good don't it.

[Zorro]

  El capitan said:

feels good don't it.

Yes it does!

[Zorro]

Updates with pics...

http://forums.sohc4.net/index.php?topic=76854.0