Topic: I’m desperate, I can’t get this cb650 to idle good for nothing!

[TwoTired]

Anything I need to do besides make sure all 8 holes and clear and it's clear through the middle?

Yes, you must make sure the carb passageways are clear, too.  There are 4 exits to that passageway, the air jet, the slow jet, the Idle Mixture Screw, and the carb throat.  You must verify that the passageway is from each hole to every other hole.

I can put a thin wire (from a wire brush) through the holes, from one side to the other but the wire won't go through the jet lengh-wise.  Carb cleaner and air does go through

I can't see anything in the hole it came out of.  I assume I just need to make sure the walls are clean and the hole is clear.

Don't get too aggressive with that wire.  The jet tube has an internal restriction which is the actual jet orifice.  Damage that and you have other issues.  The orifice diameter is the jet number in mm.  A #38 is 0.38mm.

With the jet dried off you should see light through the jet.

Why they cheesed out and didn't make that part screw in for the '79 is beyond me.

It was to placate the EPA Nazi's.

Once the the regs for idle emissions were met, Honda had to make overtures that the carbs couldn't be easily tampered with, so the bike polluted more than as tested.

Honda didn't carry that jet as a replaceable item.  It was part of the entire carb body assembly.  All to discourage home mechanic tampering.


Cheers,

[Soos]

Honda didn't carry that jet as a replaceable item.  It was part of the entire carb body assembly.  All to discourage home mechanic tampering.


Cheers,

Mr. Honda obviously never met me.

 

l8r

[TwoTired]

Honda didn't carry that jet as a replaceable item.  It was part of the entire carb body assembly.  All to discourage home mechanic tampering.


Cheers,

Mr. Honda obviously never met me.

 

l8r

Mr. Honda wasn't trying to please you.   They were trying to get import permission from the EPA Bureaucrats.
Just your government serving your best interests.

[eurban]

I finally got one out!  Wah hoo!
Here's a picture of a low speed jet.

Anything I need to do besides make sure all 8 holes and clear and it's clear through the middle?

I can put a thin wire (from a wire brush) through the holes, from one side to the other but the wire won't go through the jet lengh-wise.  Carb cleaner and air does go through.

I can't see anything in the hole it came out of.  I assume I just need to make sure the walls are clean and the hole is clear.

Thanks,
Scott

Soak all 4 pilots in carb cleaner and you could even boil them in water for a bit.  Look for light thru the lengthwise hole.  Take a single strand from a COPPER wire and see if you can run that thru. Do not use a piece of steel wire.

[Cvillechopper]

Thats about it.

Be careful re-installing them though.
No need to trash your carbs after that much effort for that little part.


Why they cheesed out and didn't make that part screw in for the '79 is beyond me.
Has anyone ever replaced the pressed in slow jet with a screw in type?
If so, what were the results?

l8r

I did on the 78 750 carbs.  They will tap themselves into the carb body but you have to be VERY careful in doing this.  You risk screwing up your carbs if you slip or are too agressive.  If you don't have to, I wouldn't.  For me it was a matter of not being able to find press-in jets larger than stock to accommodate the open pipes and pods.  Local shop had some old screw-ins the size I needed so I went for it.  Worked like a charm.

[scott_cb650]

Well all appears to be good.
If it runs as good tomorrow as it did today, I'll be blessed!

I pulled the low speed jets and cleaned them last night.  Surprisingly they weren't very dirty, which actually concerned me.
I double checked the float height and blowed and sprayed(cleaned) everything on the carbs again.
I set the pilot jets to two turns out instead of the usual 1-5/8.
I assembled everything and did the float check with tubing off of the drain screws.  This required one minor float adjustment.
When I put the carbs back on the bike this morning, there wasn't much change so I was really worried.

I remembered the pilot screws were 2 turns out so I put them back to 1-5/8s.  No change.
Put them to 1 turn out, even worse. (This was progress)
So I put them 3 turn out.  Much improvement but a little too much.
Finally I put the pilot screws to 2-1/2 turns out and the moto runs better than it ever has in the last 3 years that I've owned.  Hallelujah!

I couldn't reach the #2 carb pilot screw without burning my hand so I expect that when I set it to 2-1/2 turns out like the rest, I should be set.

Thanks all for your help! As usual I learn a lot every time I read the information posted here.


Scott