Topic: 1979 CB650 carb jetting

[Alfred Reed]

Awhile ago some poster gave a response to a carb jetting question I had and I cannot find it or who responded. I'm hoping possibly he might respond again or someone else can provide similar help by reading this.

I am having the usual CB650 problems with having to use the choke for too long so the bike will warm up and accelerate smoothly from a stop.  The answer I got before was that the poster solved this by increasing his jets by two sizes.

I want to ask him about what environment he rides in and stuff to compare so I can figure out what I may need to do under my conditions i.e. no elevation extremes and only normal ambient temperature affects, but excessive choking needed anyway (takes six miles to warm up).

I read that this is normal for 650s but if I can improve it by jetting I will. I checked out Spanky's and other tech sites but really need input from someone with experience and success with this.

Any help would be appreciated. Thanks

Alfred Reed

[Pinhead]

IMHO, the cold-bloodedness of the CB650 can be better resolved by an ignition upgrade (GM HEI conversion). The worst thing about the '79 and '80 CB650's carbs, is they're almost impossible to tune; there aren't any adjustable needles available and the slow jets are pressed in. Also, any changes to the airbox will throw your jetting way off (even simply removing the air filter cover necessitates an increase from 90s to 100s).

With everything stock, the GM HEI conversion greatly reduces the cold blooded nature of the 650s especially when combined with a wider spark plug gap.

[Bankerdanny]

You can find every post you have ever made in your profile and track down who responded to you.  Mouse up to Profile then click "summary'. When the profile appears there will be an option to view posts.

[Alfred Reed]

Thanks to you both. It turns out the poster I was looking for is on another forum. When he gave an explanation of his jetting x 2, he was doing that for issues he was having at the high end of the tach rather than the warmup problem I am having.

Pinhead: The GM HEI conversion tactic looks excellent and promising and I will check that out as thoroughly as my brain will allow, and some interpretive help from local wizards. All I have to say about your work is: WOW!