Any Honda cb750 carburetor EXPERTS out there??

[bobrebos1]

I need a carburetor EXPERT for my 1972 Honda CB 750 chopper.  It was running fine a year ago, I took it to a shop that I won’t name for carb synching, fork seal replacement etc and it’s run like crap (no power under load) since.  It had 140 main jets in it (which were way too big and causing rich running and fouling of plugs). The carburetors needle positions were also set all the way up at the highest mark.   I have in turn set them at the midway marks and installed 120 main jets.  I had another mechanic work on it and he set the carb floats to the correct specs but it still diesent have good pickup/power under load.  Almost like it’s starved for fuel but I’m not sure.  Anyone know of an excellent cb 750 mechanic that I could trust or Il keep plodding along myself I guess???  Thanks for your help.  Oh I’m in Cleveland Tn. 37323

[guzzisteve]

You used to be able to buy a Dyna Jet kit & install and it just works. That was 40yrs ago though. I do know an expert though in Gainesville, GA

[aklawok]

 I don't claim expert, but have owned both an 81' cb750 and 900c. 2 things that can be an issue before beating the horse are: be sure that you have the proper valve adjustment, and the one that got me for a long time was bad coils! The symptom was intermittent especially when cold.
Better experts than I are waiting on the cb750/cb900c forum.

[bacongrease]

  Hondachoppers.....m ucho guys there who know the 750..

[Ncdan]

Carburetor kits for your carbs are readily available on line. A couple years ago I had the 4 carbs on my cb1000c rebuild with OEM carb rebuild kits.
Get an ole honda pro to rebuild your carbs.

[Mwether]

Bob, I know "f#$% all" (as the Irish say) about CB750 carbs, but I do know a varied stable when I see one!

That shot of the chopper next to the Burgman is great. It's like you made a point of having the least practical and most practical bikes! 

[Grabcon]

Go to this forum and create an account.   http://forums.sohc4.net. 

 The find a guy Hondaman. He is the CB750 SOHC guru.

[bobrebos1]

You used to be able to buy a Dyna Jet kit & install and it just works. That was 40yrs ago though. I do know an expert though in Gainesville, GA

Steve:  Would that Honda CB 750 carburetor expert in Gainesville Ga be YOU??

[Vagrant]

Not me for sure!
I would suspect Billy at Gainesville Motor Sports might be the best bet here, but he was just born then; I'd guess he has the knowledge needed.
I'll be up at TWO this am. If I see any of the guys with old bikes, I'll ask around. I know there is a group, I would guess on FB that keeps old Japanese bikes running, but I don't remember the name.

[bobrebos1]

Not me for sure!
I would suspect Billy at Gainesville Motor Sports might be the best bet here, but he was just born then; I'd guess he has the knowledge needed.
I'll be up at TWO this am. If I see any of the guys with old bikes, I'll ask around. I know there is a group, I would guess on FB that keeps old Japanese bikes running, but I don't remember the name.

Thank you Sir!  Have fun at TWO!

[MattP]

find or make a 4 into one manafold, but i wonder did it ever run well after being sodamized.

[bobrebos1]

find or make a 4 into one manafold, but i wonder did it ever run well after being sodamized.

Yes it used to run very well!  Until someone synched the carbs!!!  So much for that idea!!!!

[MattP]

I would look fot a used pair of two into ones,yhere were kits aparently worked  well. Infact  my plam was ,is to make a 2 into one fot mu  11oo  calie,s habe a few keine vavuem carbs off a tractor davidson.
 

[Vagrant]

It's not that big of a deal to sync them yourself. You can make your own gauges cheap. It was covered here 3-6 years back. Try a search. Drop the float bowls first, pull the jets and blast out every hole you can find and check the float levels.
Valve gap was mentioned. Have you checked them yourself?

[bobrebos1]

It's not that big of a deal to sync them yourself. You can make your own gauges cheap. It was covered here 3-6 years back. Try a search. Drop the float bowls first, pull the jets and blast out every hole you can find and check the float levels.
Valve gap was mentioned. Have you checked them yourself?

I will be removing the carbs from the bike for like the tenth time in a few weeks to double check the last mechanics work. 

[John A]

How’s the battery? I’ve ran across more the one Honda that ran like crap without a healthy battery .

[bobrebos1]

How’s the battery? I’ve ran across more the one Honda that ran like crap without a healthy battery .

Should be fine but Il double check it.  Thanks

[Ncdan]

I will be removing the carbs from the bike for like the tenth time in a few weeks to double check the last mechanics work.

Bob, if you want to work out a way to get the carbs to me I’ll get my ole Honda mechanic to rebuild them with an OEM rebuild kit. You can PM me if interested and I’ll give you my ph number.

[Grabcon]

Okay I wanted to stay out of this but here goes since you mentioned you were pulling the carbs again. I have owned a half a dozen or so of these CB750 SOHC bikes. Ethanol fuel and the pot metal of these carbs don't work well if sitting for long periods, the carbs will corrode.

First the number 1 carb always has issues if gas is left in the bowl. It is the left carb sitting on the bike. I would always run my carbs dry when I knew it was going to sit for any time.

When pulling the carbs apart lay the parts out in order for each carb.

Make sure you pull and clean the emulsion tubes. Welding tip cleaners work well but be careful as they are files and can remove matierial and make the holes larger.

Make sure all main jets are the same size. This is something I have found is that sometime folks get things mixed up.

If possible I would go back to standard OEM jetting, most likely 110 or 115. Also set the needles back to OEM original position. It is hard to chase a problem without a baseline.

If doing parts replacement only use keihin carb parts. No aftermarket stuff.

I know this is a custom bike but those types of air filters are known to be Performace inhibitors, the factory air box is best.

If you set the needles back to OEM spec you will need to sync the carbs and will need a 4 gauge setup. In those carbs there is no baseline carb so syncing takes time. Set all air screws the same number of turns out to factory spec. and then adjust the slides first. It is a therapy session.

And the comments about a single carb forget it. One would need a massive carb for the airflow requirements on that engine.

That is my 2 cents. You may want to do a valve check, points and timing check. If a aftermarket points plate was used there Amy not be enough movement to rotate for proper timing. A static timing setup is fine to get running, once running use a timing light.

Note: I was doing some digging and this was my carb setup for a CB750 with an 836cc big bore and a Web performance cam. (Set for 6500’ elevation 105 main jets, 38 slow jets and
needle valves set to second ring from top)

Best of luck

[bobrebos1]

Bob, if you want to work out a way to get the carbs to me I’ll get my ole Honda mechanic to rebuild them with an OEM rebuild kit. You can PM me if interested and I’ll give you my ph number.

Thanks for the offer.  It’s going to be a few weeks before I can get back to the Honda project but Il let you know when I know.  Thanks again!

[bobrebos1]

Okay I wanted to stay out of this but here goes since you mentioned you were pulling the carbs again. I have owned a half a dozen or so of these CB750 SOHC bikes. Ethanol fuel and the pot metal of these carbs don't work well if sitting for long periods, the carbs will corrode.

First the number 1 carb always has issues if gas is left in the bowl. It is the left carb sitting on the bike. I would always run my carbs dry when I knew it was going to sit for any time.

When pulling the carbs apart lay the parts out in order for each carb.

Make sure you pull and clean the emulsion tubes. Welding tip cleaners work well but be careful as they are files and can remove matierial and make the holes larger.

Make sure all main jets are the same size. This is something I have found is that sometime folks get things mixed up.

If possible I would go back to standard OEM jetting, most likely 110 or 115. Also set the needles back to OEM original position. It is hard to chase a problem without a baseline.

If doing parts replacement only use keihin carb parts. No aftermarket stuff.

I know this is a custom bike but those types of air filters are known to be Performace inhibitors, the factory air box is best.

If you set the needles back to OEM spec you will need to sync the carbs and will need a 4 gauge setup. In those carbs there is no baseline carb so syncing takes time. Set all air screws the same number of turns out to factory spec. and then adjust the slides first. It is a therapy session.

And the comments about a single carb forget it. One would need a massive carb for the airflow requirements on that engine.

That is my 2 cents. You may want to do a valve check, points and timing check. If a aftermarket points plate was used there Amy not be enough movement to rotate for proper timing. A static timing setup is fine to get running, once running use a timing light.

Note: I was doing some digging and this was my carb setup for a CB750 with an 836cc big bore and a Web performance cam. (Set for 6500’ elevation 105 main jets, 38 slow jets and
needle valves set to second ring from top)

Best of luck

Thank you!!!

[Grabcon]

A couple of other thoughts.

Between carbs 1 & 2 and 3 & 4 are the fuel supply fittings make sure they flow freely, Squirt some carb cleaner in them to make sure it comes out the needle jet.

Also there should be some breather tubes make sure those are clean as well. There should be rubber hoses make sure the hoses are clean.

Check for crud in the tank at the pet cock and make sure the fuel filter is clean.

[Kiwi_Roy]

I wouldn't even attempt to revive a CB750, I have enough trouble with simple Guzzis.

[aklawok]

I wouldn't even attempt to revive a CB750, I have enough trouble with simple Guzzis.

It really is not that bad. Honda 4's WANT to run....one of the reasons so popular for so long. The issues come along when one starts to stray from the beaten path: pods instead of air box, mod cams, big bore, etc. the quest for upgrade comes with a price!! Learning to sync is not the hardest part.

[Grabcon]

I wouldn't even attempt to revive a CB750, I have enough trouble with simple Guzzis.

The SOHC engines from Honda are simple machines just like a Guzzi. Very straight forward to work on until people start to modify things just like any other bike.

[MattP]

Go to a  store that sells music wire by some 6 in pices of dif diamatute  ok nice thin stiff to poke the crud out of your jets take the flote bole off one at a time remove jets  clear spray carb cleaner to make sure pasages are clear rhen do the next ect   i would leave the carbs fo geatherdont auger the jets out with welfing tip cleaners. Bend a loop on end of wire  helps to hold them put om a key chain for next  lawn morr ect