Engine stuttering when accelerating

3rdGen-73

CB750 New member
Messages
1
Reaction score
0
Points
1
Location
United States
Hey all,
I searched for a while and couldn't find anything on here that matches what's going on with my bike.

I have a '77cb750 with a weisco 836cc kit in it. I bought this bike about 6 months ago and it had an issue that I knew about. When accelerating, the engine stutters. It idles great, if I blip the throttle it is very responsive. But when I accelerate, it's almost like a REALLY bad misfire. I'm fairly new to the SOHC's and don't really know what to do.


Side note: it does not have the stock airbox. A guy at work told me my issue is that, but I have a hard time believing that.


Any help is much appreciated
 

dirtdigger

Moderator
Staff member
Messages
3,503
Reaction score
112
Points
63
Location
Black Hawk SD
Checked spark plugs? Check ignition timing?, check points? gap? dwell? Compression? Carbs clean? Has it been jetted for non stock air filter? Start with the basics and do all the tune up items them move to checking jetting onces carbs are clean and you rule out spark issue and making sure the engine itself is mechanically healthy.
 

Biebs

CB750 Enthusiast
Messages
71
Reaction score
15
Points
8
Location
Phoenix AZ
Pod bike?? individual pods on each carb??

Stock air box gives the 4 carbs a plenum chamber.

A plenum chamber is a pressurised housing containing a fluid (typically air) at positive pressure. One of its functions is to equalise pressure for more even distribution, compensating for irregular supply or demand. It is typically relatively large in volume and thus has relatively low velocity compared to the system's other components. In wind tunnels, rockets, and many flow applications, it is a chamber upstream on the fluid flow where the fluid initially resides (approximately at rest). It can also work as an acoustic silencer.

In conclusion you will be able to fix the Sutter problem when accelerating by messing with the jetting but you will induce new problems.

Best route is to try some sort of plenum chamber. Maybe the stock Air Box.
 

dirtdigger

Moderator
Staff member
Messages
3,503
Reaction score
112
Points
63
Location
Black Hawk SD
Pod bike?? individual pods on each carb??

Stock air box gives the 4 carbs a plenum chamber.

A plenum chamber is a pressurised housing containing a fluid (typically air) at positive pressure. One of its functions is to equalise pressure for more even distribution, compensating for irregular supply or demand. It is typically relatively large in volume and thus has relatively low velocity compared to the system's other components. In wind tunnels, rockets, and many flow applications, it is a chamber upstream on the fluid flow where the fluid initially resides (approximately at rest). It can also work as an acoustic silencer.

In conclusion you will be able to fix the Sutter problem when accelerating by messing with the jetting but you will induce new problems.

Best route is to try some sort of plenum chamber. Maybe the stock Air Box.
The sohc carbs work fine with no air box, they are not CV carbs. If the original posters problem ends up being carb related all he needs is to take some time and figure out the jetting.....although I am leaning toward an ignition issue. I have run pod sohc carbs on big bore motors no issue.....from 836cc through 1030cc.....these carbs easily work fine with correct jetting. You are correct for CV carbs though....they do need an air box to function properly.
 
Top