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jets and idle and stuff

wgeorge68

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so i just finished putting together my 79 750f brat trying to get my carbs tuned right this is what ive got.
pod filters
kerker 4 into 1
110 main jet
75 pilot jets
2.5 turns on the a/f screw
4 washers on the needle
the bike has good throttle response now when its warmed up but the idle is very low and wants to die when i mess with the idle screw it will be fixed for a minute then it will randomly want to idle really high untill i turn the idle screw back out then it will go back to wanting to die do these carbs have no happy medium?
thanks for the help
 
I've never messed with the CV carbs. That being said, I've read a lot. No one I've ever come across got those carbs to run good with just pods. But that doesn't mean you couldn't.. I suppose.
 
I've got the stock air box and have the same idle issue.

When i cleaned my carbs, the cleaner ate the already deteriorating diaphrams, replaced them and it ran great at >2500 RPM, but runs ruff and tries to die when the idle is lower.

Changing the Accelerator pump diaphram now.

nickel dime, nickel dime
 
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Okay... I have the stock air box and also have the same issue. Hoping this is the forum that can help. Have spent maaany hours now trying to figure this out. Purchased the bike and started assessing the issues.
-Does not idle.
-#4 exaust was blowing cold - #4 carb was not sealed into boot - Fixed it and now it fires.

Still won't idle.

-Turned in idle screw in - once it gets to the point where it will idle it will then stick up at a higher RPM when given throttle (4,000rpm)... turn it back down then it won't idle (no happy medium) this made me think the pilot jet hole (2 little holes right under throttle flaps in carb). was clogged since it seemed like pistons were not getting fuel until the idle screw was turned in far enough that the valves opened allowing the fuel from behind the valces to get through
-Took off carbs and cleaned with compresed air and carb cleaner twice. Blew out all holes.
-blew carb cleaner and compressed air in the pilot jet (this is the pressed in non-adjustable jet) - air would blow through each but definetly not easily. Still would like to press guitar string through this hole to make sure it is clear.
-Noticed all the jets were on wrong - fixed to 102main, 68pre-main, factory set pilot jet (non adjustable)
-adjusted air fuel screws to stock spec and would try to tweak from there (no real noticable change in idle when adjusting)

Still won't idle. (Should say will idle but has hanging idle when idle screw is in and won't idle when out but no hanging idle (no happy medium))
Other info...
-Does this in neutral and when clutch is in.
-Timing is good.
-New plugs
-No air leaks (at least in the carb to boot connections)
-Tail light disconnected (didnt know if this could cause electrical issue)
-Floats all set to factory spec (non adjustable but had to bend one slightly)
-needle valves not hanging up
-IDLES FINE ON CHOKE (which i would think allows it to suck harder on the small pilot jet holes pulling a more sufficient amount of gas out?)

Things to check/try next...
-check compression
-bypass Air Cutoff Valve or atleast check
-recheck timing

Has anyone had this issue and what was your fix?! Please help!!!
 
The only real permanent fix is aftermarket carbs. The stock cv carbs are junk, you will never get them right.
 
What dirtdigger wrote. But if it idles well on choke, it's running lean. Get those pilot jets 100% clean first.
I had to ultra sonic wash my carbs to get them clean from sitting for 20+ yrs. Cost me about $50 but well worth it. Now I KNOW they are clean in every passage. Might be something for you to consider as well? Or maybe add some more $ to the cost of washing your set and get some other non stock cv carbs instead..
 
Haven't got the carbs back on to try yet but I think I found the culprit. The Air Cut Off valve on carb #1 is wore through and the O-ring is missing. From checking other threads this ACV is to provide the cylinders with gas when you let off the throttle while driving so the bike doesnt strain for gas and pop and sputter. However, if they are wore through the bike will not idle right at all. I checked the #3 as well and it was fine. I'm hoping #1 is the only one that is back because if I need to check #2 and #4 it will mean splitting the carbs apart completely which looks terrible and like it could cause more issues for me. People have said they just block off this passage but I have heard that increases the popping and sputtering while driving so I am going to try to replace it. I will get these carbs right if it's the last thing I do..! then I'm going to kick the shit out of them and get after markets. :thumbsup: photo.JPG
 
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