Carburetor

[Reaper87_imp]

Morning all so I need to rejet my 81 cb900f but don't know what jets to put into it it's got k&n pods and 4 into 4 straight through exhausts it gets stuck at around 3000-4000rpm when I twist the throttle and only goes down when I adjust the idle screw any help would be greatful as iv never done rejecting before thanks

[the Ferret]

Reaper this forum is based on the modern CB1100 from 2010 to present, which all have fuel injection, but there are many experienced members and maybe one can help you. I don't believe a sticking throttle would be jetting related though.

[Jfro5687_imp]

Hi Reaper. I get the impression you don't have much experience so if i am wrong i apologise. However, I would be very careful messing about with jets if you don't know what you are doing. Sounds like you have a' flat spot '. Setting up and balancing carbs is DIY do-able but you will need a decent set of gauges for a start and some means of getting the mixture right. Air cooled engines get hot real quick when you have them sat still and thats not good for them. Free filters and pipe will make it run lean. I would suggest asking around for a local mechanic who has a good reputation and take it there. If you do meddle make a note of where everything is before you start and then at least you can return it all to base if its a disaster!

[Rocky_imp]

Hi Reaper. I get the impression you don't have much experience so if i am wrong i apologise. However, I would be very careful messing about with jets if you don't know what you are doing. Sounds like you have a' flat spot '. Setting up and balancing carbs is DIY do-able but you will need a decent set of gauges for a start and some means of getting the mixture right. Air cooled engines get hot real quick when you have them sat still and thats not good for them. Free filters and pipe will make it run lean. I would suggest asking around for a local mechanic who has a good reputation and take it there. If you do meddle make a note of where everything is before you start and then at least you can return it all to base if its a disaster!

No disrespect intended too, but this is very good advice.
Bite the bullet and pay and experienced mechanic. It will be money well spent in the satisfaction of smooth running.

[SportsterDoc]

1. Is throttle return cable intact?

2. Is there some slack in the cable?

3. Is there any issue with cable routing?

4. Has cable ever been lubed?

5. Are each of the slide clean-no debris?

6. Are the slide springs stock?

7. Is there any binding in the linkage to the carbs?

I do not think this is a jetting discussion.

[teamvisegrip_imp]

There are those that are way more experienced at this than I am. But I have modified a few bikes in my life. If I want it perfect take it to the shop after you have modified it. Pipe and Pods will require rejetting.

Now what I do for modern bikes is get the Dyno-Jet or 6 Sigma jet kit. I hate to say it but I prefer the 6 Sigma as they will give you Idle Jets in their kit. My last Dyno-Jet kit only had the Main Jet and needle.

Anyhow These kits can get you right where you need to be. If it still is not right take it to the professional. Like I said some I was very lucky to get right with the kits others I took in and the results were well worth it.

[SportsterDoc]

There are those that are way more experienced at this than I am. But I have modified a few bikes in my life. If I want it perfect take it to the shop after you have modified it. Pipe and Pods will require rejetting.

Now what I do for modern bikes is get the Dyno-Jet or 6 Sigma jet kit. I hate to say it but I prefer the 6 Sigma as they will give you Idle Jets in their kit. My last Dyno-Jet kit only had the Main Jet and needle.

Anyhow These kits can get you right where you need to be. If it still is not right take it to the professional. Like I said some I was very lucky to get right with the kits others I took in and the results were well worth it.

For H-D there are two issues with Dynojet:
1. Main jet threads are not compatible with stock Keihin CV40 emulsion tube. Once changed, H-D/Keihin main jets are no longer compatible.

2. Jet orifice tolerances may not match size. For example a 165 main is supposed to be 1.65 mm. So, for H-D, best to use H-D, if available (last Sportster carb was 2006) or CV Performance.

Bottom line is ditto to concerns about Dynojet, if this is actually a jetting inquiry.

[the Ferret]

I dont think Reaper has been back since he posted the thread.

[Perry_imp]

Hey, Reaper. You may want to find your way over the the DOHC CB site - http://www.cb750c.com/index.php - That site is dedicated to the 1979 -1983 CB 750, 900, and 1000s. Lots and lots of people can help you there. They still know how to tune a carb! I will warn you, however, they are also going to tell you to pull the pods and put the air box back on. Those CV carbs cannot run with pods.

This site - http://www.dotheton.com/forum/index.php - is dedicated to bikes that are a bit more jazzed up.

Good luck!

By the way - I'm parting out a 900 that I bought to scavenge some parts from. Let me know if you need something.