PCV System and idling - 2 topics in 1?

[Baileyman]

I just got my top end back together and have been riding Stella (as in Stella Blue, the song from that Hippie band that people used to follow around) around the past few days.  She runs fine, but the idle is whacky.  By whacky I mean at warm up idle is on the high side 1500-2000 rpms, then it settles down to about 1100-1200.  After running a bit, wants to die at stops, a little throttle keeps her happy.  A couple of times now I have increased the idle speed after getting it home when the engine is nice and warm.  I get the idle about right, but then again after some riding, the idle wants to drop again.  I've only done cursory searches of the board for idle issues.  I'm sure I need to check for vacuum leaks, worn out rubber, etc.  It would be great to adjust the pilot screws, but essentially impossible with those caps on them.  I don't know how much I like them.  The idea is nice, except when they need adjusting...

I have not adjusted the pilot screws, but I did set them all to 2 turns out, and tried to adjust them according to the manual with no noticeable changes in the RPM, although I didn't hook up a tach that reads in 50 rpm increments.  I have noticed that the PCV emmisions control thing they have on CA bikes is not present on my bike.  I'm guessing it's not necessarily present on models for the other states.

I don't really understand what the PCV emission thing does, how it works, and the effect of it being present or missing on idling.

I also think I need to replace the little rubber caps under the carb bodies.  Don't know what they're called, or what they do, but the rubber is def shot.

Thanks for listening and for your suggestions / lessons!

BaileyMan

[Brittles]

Maybe a weak spring on the idle adjustment screw allowing the idle to change due to vibration?

My bike is a California bike and I got rid of all that emissions stuff. Idle is fine.

[windrider]

As for your idle problem, check the choke operation on each carburetor.  Might also want to spray a little carb cleaner around where the carbs mount to the head, while the engine is running.  If the idle changes, you have a leak.  Might need to check mounting torque.  May have left one loose.

As for the PCV and California bike, you are confused.  The California bike had a Evaporation Canister that would vent the gas fumes from the tank through a charcoal canister.  PCV is Positive Crankcase Ventilation, which your bike does have.  It is the breather tube from the crankcase back to the air filter housing.  This allows crankcase fumes, (where the oils is), to be drawn back in the air inlet through the air filter and carburetors.  Excess oil collects in the drain tube and needs to be dumped occasionally, if the air filter box has a capped drain tube. Older bikes didn't have a capped tube, they just dumped going down the highway.   This is not meant to hurt, only educate.

[Baileyman]

This is not meant to hurt, only educate.

Didn't come across as insult.  I appreciate the information as I learn about all of this.

This should be the schematic of the canister with the PCV circuit, right?  I'm pretty sure all I've got is hose #12, going up to the gas tank.  I don't have any other hoses coming off the canister.
http://www.mrcycles.com/fiche_section_detail.asp?section=124027&category=MOTORCYCLES&make=HONDA&year=1984&fveh=2961

Where do hoses 13, 15, and 16 attach?

And what about this diagram of the carb assembly?
http://www.mrcycles.com/fiche_section_detail.asp?section=123990&category=MOTORCYCLES&make=HONDA&year=1984&fveh=2961

Where do the hoses 15, 18, 25 & 26 go?  I think I've only got hoses #30 coming off the carbs.

Anyone have a good pic of the those hoses attached?  I'll try to get pics of what I've got, and what's missing.

I couldn't figure out how to embed the actual diagrams, just the links...

[Bad Boy]

Your bike is not running right and the fuel tank evaporative system has been tampered with. 

Some owners remove this fuel tank evaporative system thinking all pollution control is bad, not true.  I don't think routing fuel tank fumes back into the carburetors reduces performance.  Owners messing with an engineered system they don't understand most likely will mess up the balance of things.  Plugging off and removing tubes feeding air to the carburetors is not good if those carburetors where designed to compensate for that extra air.  Also if the fuel tank vent hose is capped off the tank will not vent.  California bikes do not have vents in the fuel cap.  Bike may not run right if pressure or vacuum builds up in the tank.  If hoses are disconnected and not capped they could be sucking dirty air into the engine.

I don't know enough about what disconnecting this system will do.  I do know it can't help and it may be your problem.  You could try to restore the vent system.  You may have to find a source for used parts.  Ebay or wrecking yard and get a shop manual that lays this system out.

[Baileyman]

I'm pretty sure the vents etc. are capped where the PO removed hoses and such.  I'm def leaning towards getting this PCV system back the way it was engineered to be.  I wonder if there is a similar PCV on the newer 750's that will work for the 700s, as they're not available OEM for the 700s anymore.  One day I will have this running and riding great!  I'm too invested in it now not too...

Keep the comments / thoughts / tutorials coming!

Thanks,
BaileyMan

[Brittles]

My bike is a California bike and I got rid of all that emissions stuff. Idle is fine.

Forgot to say that I replaced my California carburetor with a 49 state carb.

[Brittles]

#13 attaches to the underside of the #3 carb
#15 attaches to the double t fitting (#17 in next diagram)
#16 goes to open air



#15,18,25, and 26 attach to the engine side of each carb.

Are you certain you have California carbs? Carb number should be VE77A.

I've got a spare California carb with the hoses still attached. Let me know if you need them.

[Baileyman]

Thanks for putting in those parts pics, and for the explanation, very helpful.

I do seem to have the CA carbs, VE77A.  Carb 3 does have a spot underneath to attach a hose.  It's capped off with a rubber cap at the moment.

I'm thinking about getting a bunch of hose and replacing all worn, cracking hoses.  I think there's a bunch, but they might not all be necessary to replace.  My bike has 41k miles on it, and has definitely seen better days, and definitely been worked on by a PO who did the minimum necessary to make it passable.  At this point it needs lots of little things done.  My goal is to do the work right, and get it running sweet.  Getting the top end done was just the start, now it's the little things to get it cherry.

@ Brittles, I don't need the carbs so much, but would love to have the hoses, and t-fittings, etc.

Are you willing to get rid of them separately?

PM me, we can figure something out offline.

[Baileyman]

I spoke to my mechanic today to learn a little more about the PCV system.  He say's it won't effect the idle as long as those vacuum ports are closed off.  It's mostly an emissions thing.  I just put some new vacuum caps on the carbs, some of them were cracked.  There may still be a vacuum leak, and now that I feel pretty confident that the lack of the PCV won't get in the way, I can start checking for leaks.

[Bad Boy]

The rubber tube that comes off of the fuel tank needs to be open to vent fumes or gas.

[Brittles]

@ Brittles, I don't need the carbs so much, but would love to have the hoses, and t-fittings, etc.

Are you willing to get rid of them separately?

The hoses and t-fitting are yours for the asking. If you think you still need them pm me your address and I'll get them out to you.