Topic: Carb issues - engine will only idle with choke on

[Squidmarks]

I bought a '80 CB-650 a couple years ago for $200.  I'm building a couple off-road karts, and the CB-650 engine looked like a good fit.  Plus, the guy had a spare engine kicking around, so I got one engine for each kart.

I've been building the karts for ~3 yrs on and off, and finally focused on one this summer and got it completed.  Now I've turned to getting the engine going.  I cleaned up the CB-650 engine, took the carbs off and apart, soaked them and re-assembled them.  After a cleanup, all the carb parts looked pretty good.  Re-assy went fine.  Once I installed and wired up the engine in the kart, I was astounded that after a few cranks it started right up!  One of the float valves was stuck as it began to piss gas out the bottom nipple.  I stopped the engine, took off the carbs, replaced the offending float valve and re-assembled.  Once again, started up fine and idled relatively nicely.  As it warmed it was very sensitve to the choke position.  Once it was fully warm, I could let up on the choke a bit, but if I opened the choke up more that a little, the engine would die.  I tried to take it for a spin, but it had very low power.  It seemed to idle relatively cleanly, but with bit a rolling surge to it.

The Clymer manual suggets that idle screws should be turned 2 1/4 turns out on the '80 CB-650.  Once the float bowls are screwed in place, you can only idle adj screws ~1/2 turn as they have a lever type head on them.  I haven't experimented with much different idle screw positions because of this, but that was my next guess.

Oh, one more thing.  I'm not using the airbox, but pods instead.  I have a 4-to-1 exhaust header (stock, I think).

Any ideas?

Thanks.

Geoff

[Gordon]

Oh, one more thing.  I'm not using the airbox, but pods instead.  I have a 4-to-1 exhaust header (stock, I think).

Any ideas?

Thanks.

Geoff

The problem is your "one more thing".  Using the pods instead of the stock airbox configuration will cause your engine to run lean because the pods allow more air flow than the airbox.  You either need to use the stock airbox or re-jet to compensate for the increased airflow. 

[Squidmarks]

I agree that I may need to re-jet to get optimal performance, but I would not expect that replacing the airbox with pods would create such a drastic problem at idle where air flow is very low.  I will re-fit the airbox on and see if that makes a difference, tho.

Thanks.

Geoff

[eldar]

It can lean things out but which side are the air screws on? If they are on the filter side, turning them in will usually richen the low speed mix as it lessens the amount of air going in to the carb low speed.  If they are on the engine side, then out will richen the mix. This is how they USUALLY work.

[MetalHead550]

So lets see a pic of this cart!

[Squidmarks]

Ok, airbox back on and things are much better.  Carbs still need syncing, but it runs pretty good.  I'll post a picture of the kart this weekend.

Thanks.

Geoff

[pmpski_1]

I was thinking that the problem was that you had 2 extra wheels. Shows how much I know