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79 cb750 Dohc issue idling

Cafe Customs

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My uncle has a few cb750 cafe racers and we have been working on getting her at a steady idle and to rev appropriately it's running on choke and only for a limited time he has changed multiple carbs have tried different afr have good spark going to the plugs changed the cdis multiple times and it just won't budge any recommendations or tips
 
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Its even worse if you try to run with nothing on the carbs. these carbs are terrible with anything but stock air box. Some people say they have jetted them and they run perfect woth pods but I about 100% guarantee they are down on power compared to stock air box. These carbs are too touchy about incoming air flow into the carbs. You could search on here about the topic. AMC wrote about it many times because this topic comes up several times a week. Intake plenum box volume, shape, length all affect how these carbs run even at idle. The picture above is absolute worst case scenario for trying to get it to idle rev or run right.
 
Stock are box or at the very least look for one of the air filter setups that connect to all 4 carbs. People wrap the pods with tape or something similar to restrict airflow which does what you are basically doing with your hand. But that looks like sh*t and you are restricting airflow and power at the cost of drivabilty. Honda probably spent hundreds of thousands of dollars and hours in developement to make the bike and carb run right...with the stock air box and exhaust.
 
And hundreds of people have the exact same issue lol Everyone is too cheap to buy good Keihin CR or Mikuni RS carbs on their custom builds then complain about how shitty they run with pods on stock carbs. Not saying you are complaining just saying this question comes up every week and the answer is always the same.....
 
I understand we are new to the engine also I'm a gsxr guy but my uncle has a few projects and I'm getting into it to learn more on them
 
Run std airbox on mine....as stated this issue comes up often.

Another issue, for future reference.. common to late 70s/80s Honda bikes is that many pods obstruct some ports at the mouth of the carb, bikes wont idle/erratic....comes up on other forums like the CX500 forum.....

hope u get it sorted
 
We fixed the first issue which was the pods instead of tape we made restricted plates inside the filter to regulate the air to the bikes liking now we are trying to figure out is the amount of turns we need to put on the air ratio screws to set it better
 
These bikes were some of the earliest with "lean burn carbs"...finicky to get right..with perseverance youll probably get an acceptable outcome.


cheers.
 
As an aside if you cant get the carbs sorted with pods...
Consider Murrays Carbs(tuned Mikunis)...and just sell on the stockies.....youll recoup a good portion of your $$
 
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nail on the head there dirtdigger , those japs know there stuff. i commented a while ago about my 750 japan market FZ bogging out with 102 main jets. i put these in because the books i had said 102's. after weeks of study i found out the air intake on my air box was matched for the original 75 mains. i didn't want to take the carbs off again so left off the air filter rectangular cover so it pulls more air in around the side panel. i still need to do a plug chop at 5000 plus revs but up to now she has been great at tick over and all the way through the revs.
 
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