Topic: 81 Cb650 revs in neutral, won't under load, shuts off after 10 mins of riding

[dfoxengr]

With CVs, the size is 120. This is what the manuals, both, state.

Yes.....but that only applies (per oem spec) in unison with the oem standard air-box/filter.....these carbs can work beautifully, if you set them up correctly and only depart from standard spec where absolutely necessary.

What's going on is that the PO had the wrong set of mains in there. That's what I've been explaining the whole time. I am getting them back to near the size they should be stock.

[grcamna2]

Do you're spark plugs look nice and Tan ?

[w1sa]

With CVs, the size is 120. This is what the manuals, both, state.

Yes.....but that only applies (per oem spec) in unison with the oem standard air-box/filter.....these carbs can work beautifully, if you set them up correctly and only depart from standard spec where absolutely necessary.

What's going on is that the PO had the wrong set of mains in there. That's what I've been explaining the whole time. I am getting them back to near the size they should be stock.

Ok....not wanting to labor the point.....what is also possibly (probably) going on, is that the k+n (pod) filters will allow a reduction in vacuum/draw thru the mouth and throat...that's usually typical with pods...as is re-jetting.  With CVs in the equation, the reduced vacuum at the mouth will most likely reduce the ability of the piston/main needle to lift to correct operating levels for the standard set-up (jetting).....This tends to limit the engine in the rev range and in its ability to work properly under load. 

Also, the abilty to draw fuel into the throat (at the right AF ratios) is no more important than is maintaining the correct working fuel level in the bowls, while running.

With a more correct main jet size your running should now be much improved.....if it was the dominant problem, you should be able to ride much further with better performance.....if it cuts out again, (or even after a decent half hour/50mph run) pull the plugs before it is restarted and post the pics and details.......

[dfoxengr]

Good point w1sa. I'll definitely do that.

Thanks.

[dfoxengr]

The final answer was not carb cleanliness, like I was saying.

What was happening was the following:
When I first posted, the previous owner had a super small 78 main jet in there, I then drilled it to 120 size. I had been running with a lot of choke to keep the 78 richer. When I changed to the 120 the choke was making it too rich at WOT, hence the bog. So first the bog was due to not enough fuel, lean causing the engine to run hot and then seize up. Then after jet change, it was too rich at WOT with choke, causing the bog again.

Now she runs great.
Rode the bike 150 miles so far and it's good. Now working on sorting other small issues.

[ThomasD883]

Sweet news! How about a few pics? Everybody loves pictures

[dfoxengr]

I'm probably going to put on a Mac exhaust and some superbike bars soon so I'll post some then. 

[grcamna2]

I'm glad it's running better for you  dfoxengr

[phil71]

new exhaust 'eh? How big does that drill index go?

[dfoxengr]

are you thinking I'll have to rejet again? I dont think so from what I've been reading.

Right now the size I chose is slightly larger than stock already.

[phil71]

really depends on how much less corked up it is .. but obviously try it as is first.

[dfoxengr]

yeah no big deal. drills are in small increments anyways.