Backfire and slow RPM drop

[faber]

Hey guys,

So I've gone through the carbs top to bottom, cleaned rebuilt, and everything should be back to factory spec.

What I'm seeing now is when I rev the engine the RPM drop is very slow, like engine rev, then a few seconds to come back to idle. I'm also seeing back fires at slow idle.

So I'm wondering what I should check next. The pistons in the carbs appear to actuate correctly, ideas?

 

[faber]

Nevermind about the backfiring, I forgot to plug the vacuum line for the petcock. Still having problems with slow return to idle though.

 

[faber]

So, I'm thinking the contacts are probably in need of service. How the heck do you get the cover off? Mine has a single screw on one side and nothing on the other (unlike the manual).

I think it's just a friction pin holding it in but it seems pretty solid and I don't want to go prying on it until I'm sure.

 

[TimmyT]

What kind of bike?
your bike may run a little better if you modify a few factory specs.
How many revs is idle running at on your bike at the moment?
How many seconds does your bike take to idle down from say 5k.
Does it happen when in gear or neutral as well?

What air filters are you running and have you adjusted the jets at all from factory?

Sorry to try and anwser questions with questions but its hard to get there when we dont know where we are leaving from!

 

[faber]

Well it is screwed in behind that brass plug. Drilling it out left me access to the screw. The timing control looks fine.

 

[faber]

this is an 82 with 27k miles. ~1000 or so at idle, 3 to 5 seconds. Seems to happen under load.

 

[faber]

So I just balanced the carbs with the manometer, they were close but not right. This fixed part of the idle down problem, but I've noticed rev'ing up to 7K then letting it drop, it falls at a consistent rate until it hits 3K then hangs for just a second, then falls the rest of the way down.

Is this due to pilot / main lag

 

[ThePsuedoMonkey]

Sounds like the throttle cable is bad; give that cable some lube and if it gets any better than that's the problem.

 

[faber]

Yeah already lubed it up, you can clearly see the actuator assemble close, after the balance it's gotten a lot better, but still not prefect.

 

[HoughMade]

Sounds lean. What is your idle mixture set at? or are the factory plugs still in place?

 

[faber]

Pilot: 42.5
Main: 135

Idle set and balanced at 1200 rpms

It flutters a bit as well, I know the thing needs and oil change, I'll take care of that tomorrow and it's not running on great gas (from a feeder bottle).

If jetting is an issue I can of course, go up and down (I have lots of jets) but it seems to be running a bit rich if anything.

 

[HoughMade]

Have you adjusted the idle mixture screws? They are on the carbs, but on '82s, they are covered by aluminum plugs. Most bikes act better when these are richened up.

 

[faber]

thanks I'll drill them and play with it.

 

[faber]

So I pulled the brass plugs and adjusted the idle mix to 2 and 3/4 turns from all the way in (after some messing around with it).

Changed the oil, put the oil filter housing back on correctly (idiot that had the bike before me had it upside down)

Warmed it up, adjusted the idle and ran it around the block a few times. It still had a few instances of sticking at 3K RPM's didn't seem to matter if it was under load or not.

When I got back I pulled the plugs and checked them, They look good, not too lean or rich.

Any other ideas?

 

[ThePsuedoMonkey]

This seems to randomly happen fairly often, mine had this same issue once. I was idling at an RR crossing for a few minutes about 15min into my ride. Then I stopped for fuel and checked the cable action and found nothing. Has not happened since.

I do know that if you leave the choke on while riding it can idle around that high, after it has had plenty of time to warm up. That is my best guess at this point. Can you tell if the choke is working or not?

 

[faber]

Yeah the choke is working great. Both half and full choke work as they should. I would expect that as the carbs were sonic cleaned. I'm going to try and re-balance again, as I read on the 1100 forums that after pilot mix adjustment on bs34 carbs you have to rebalance. Hopefully that solves it.

I can say that the power was good, quick response and snappy feel.

 

[faber]

Well all balanced and checked out. The bike is running well, except for this slow to idle problem. Here's a video of what I'm running into.

 

[domains]

What did you do to balance out? float hight?

mine does the same thing, might be cable sticking or your issues.

 

[faber]

DIY manometer, sock float height. I'm starting to wonder if it's the ignition unit.

 

[domains]

back down needles maybe... i was at 3 1/2 turns and today i turned them 3 turns with little to no difference. if my throttle cable is not binding i'm going to try 2 1/2 turns