Needle jet question

Hello all. I have an ongoing problem with my csr750 twin. I have a bog in the throttle at low range rpms. Namely from a stop when taking off and trying to give it more throttle and also when cruising along at a low range rpm and rolling on the throttle. It feels like it's choking out and bogging then picks itself back up. I have cleaned the carbs twice and payed particular attention to the pilot jet and circuit with no luck fixing the issue. I've also removed, cleaned and lubricated the timing advancer and it appears to be functioning well. That also did not help. The only part of the carburetors I have never removed is the emulsion tube/needle jet because I have no idea how. Does this sound like a symptom of a clogged emulsion tube/needle jet? I have used up all of my knowledge on carburetor repair and tuning and am in dire need of assistance if anyone could chime in with advice on if this sounds like a needle jet/emulsion tube issue and if so how to remove and re install it would be oh so very greatly appreciated. 

Needle and mains don't affect low revs. Pilot solely does zero to approx one third revs, then main joins in to about two thirds, then the needle joins in up to full throttle.
There is a trick which has worked for a similar sounding issue on 900's and 1000's where you connect together with some tubing the vacuum ports for carbs 1 and 4 and then another piece connecting 2 and 3.
Its non invasive and cheap to try so not much lost if it doesn't work for your issue. 

Presuming you are running the stock airbox it is most likely a Pilot jet /off idle fueling issue.. Not needle, mains or emulsion tube ( unless the air metering holes are blocked )
Can be over or under fueling giving the same symptoms for different reasons.
To find out which you should feather the choke at the point of bogging.
If the issue clears you are lean. If it worsens or no effect you are rich.
You may be able to tune it out on the mixture screw , just a 1/4 turn in the right direction may be all it needs.

 

Thanks for the replies. Mine is a twin cylinder so I can't do that trick with the vacuum tubes. Yeah everyone said last time I re cleaned the carbs that it was the pilot jet. Not sure what to say. It's clean. I mean I really cleaned the hell out of both of them. It must not be a carburetor issue then...

wrote:

It must not be a carburetor issue then...

Have you tried the choke test to confirm ?
Also make sure the air passage from the carb mouth to the pilot jet is clear and that the choke plunger seats are not worn and leaking.
 

Reread Zed1015’s post. He is saying to fine tune the adjustments on the carburetors. 

Have you checked the fuel level in each carb using the clear tube method? Setting float heights dry will only get you close, but not exactly where it needs to be. The fuel level needs to be spot on before proceeding with other adjustments.

Then carefully fine tune the pilot screws. A small adjustment can make a big difference, and it is likely that each carburetor will need a slightly different setting.

After these adjustments are done, then synchronize the carburetors.

Readjust the idle speed as needed after each other adjustment.

These steps have to be done in this order. If you cannot get a step dialed in properly, do not move to the next step thinking it will fix things. It will not. As Zed also wrote, there are many possibilities, so if these adjustments do not solve the problem, these other possibilities will need to be checked. Yes, it would have been easier to check them while the carburetors were off, but as long as they are on, it seems reasonable to try the adjustments.

Edit: I am referring to his post before last.

It does seem to be better while using the choke. I will have to check these things out and report back. 

Hello everyone. I've got an update. So no offense to everyone's opinions but while I had the carbs off and torn apart, I tool the needle jets out. Sure enough the cavity that they sit in had some buildup in it and the tiny little holes of the needle jets you could barely see light through. So hosed em out with carb cleaner and got em all nice and clean, tossed everything back together and it's running way way better. Throttle response from low to mid range has improved significantly. When rolling onto the throttle while cruising along at about 3000-3500 rpm you could feel the motor kind of shake and bog down then it would pick up. I'm happy to report thats pretty much completely gone. Taking off from a stop has improved to be smooth and without hesitation. The worst was if you were on an incline and had to pull away from a dead stop say at a stop sign at the bottom of a hill. You go to give it increasingly more throttle and it would buck and bog and almost stall out. That has been remedied and now pulls away just fine. I do notice if I blip the throttle when down shifting to Rev match my downshift, it does pop so I think im going to play around with the adjustments but all in all, the needle jet was in fact the main culprit. 

What kind of carbs are they? VM or CV's?
Steve

I am 93.8% sure all the 750 twins came with cv carbs.

wrote:

Hello everyone. I've got an update. So no offense to everyone's opinions but while I had the carbs off and torn apart, I tool the needle jets out. Sure enough the cavity that they sit in had some buildup in it and the tiny little holes of the needle jets you could barely see light through.  

No offence taken.
Those tiny holes are the air bleeds in the Needle jet tube/emulsion tube that i suggested may be blocked and causeing rich running in my previous posts.
Those tubes are not the actual needle jet.
The needle jet is in fact the lightly pressed in brass insert in the floor of the venturi ( or the main opening in the top of the tube if it is the one piece type) ) that combined with the jet needle meters the emulsified fuel from the needle jet tube/emulsion tube to be atomised in the venturi ready for combustion .

TexasKZ post=869391I am 93.8% sure all the 750 twins came with cv carbs.

The reason I asked the diaphragms  may be hard or leaking.
Steve