Idle RPM Question

[motogrizzo]

Hi All,
I introduced myself a couple of weeks ago and appreciate all of the responses:
(http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1283088764)

I figured I would take my next question to the appropriate place. My turn signal switch broke the first time I had the bike out, so after a week or so, my new left switch gear arrived, I installed it (the simplicity of the bike so far is wonderful), and went for a longer ride around the local neighborhoods.

My inquiry: When the bike starts, it idles nicely, around 800 rpms, give or take. I take the choke off once it's warmed up and ride around, no problem, it idles nicely. I find if I then give the engine a real good rev, the idle then stays around 2k rpm. Only after a good twist of the throttle, not for an extended period of time. It seems to then start to get hot, especially if I'm sitting still and it's idling around 2k. This only seems to happen after the engine is warmed up. Until then, if I give it a good rev, it drops right back down to 800rpm.

I thought, ok, maybe I did something to the throttle cables when I routed my new switch wiring harness, but I played around with the cables and it didn't affect the idle. Perhaps it is carb related? If it were just one carb, wouldn't it run roughly?

This is my first boxer/airhead, so I'm learning the characteristics. I have the service manual and read the procedure to adjust idle. I also have the engine mounted choke and noticed the book reads the choke lever should be parallel with the ground when the engine is cold or the temp is below freezing. Normal operating temperatures, the choke lever should be pointing toward the ground. I read that about 5 times because it seemed counter-intuitive to me. Is that correct?

Anyway, I'm going to ride it to work tomorrow to see how it runs. Thanks for any help. :-?

Mike

[Bob_Roller]

Usually this is the result of synchronizing the carburetors on a cold engine .

One member here had a similar problem a week or so ago, and it turned out to be the old hardened rubber tubes that go between the carbs and the cylinder head   .

[mimmo66]

In my experience I would check  the valve setting first,  then the  carbs and/or eventually a sticky bean can.

All easily accomplished in your garage.

Procede in such order and you'll have it sorted out.

Domenico

[montmil]

+1 on checking the valve lash first. Surprisingly, the airhead idle is closely related to proper valve settings.

Use 0.004" intake and 0.008" exhaust clearances. Yes, that's larger gaps than the manuals may state, but these wider clearances are now accepted as better for the airhead's engine and valve train.

BMW music, anyone?

Monte

[Barry]

Given the valve clearances are Ok it's almost always carb settings.

With the choke off the engine should not idle at all from a cold start and will not reach your target idle speed until it's done maybe 10 miles.

Every day after my 4 mile commute I have maybe 800RPM at idle. After ten miles or it will reach my target speed of 1050 RPM. This means you can only set the idle speed after a decent run otherwise you may get the symptoms you have described.

There can be some more subtle things wrong with the carb assembly and adjustment but there is nothing easier or quicker you can try than just lowering the idle speed so I would do that first and only then worry about the more difficult stuff if it doesn't work.

The engine mounted choke lever on the early bikes is off when pointing backwards (parallel to the ground) and fully on when pointing down. There should be a detent at 45 Deg at the half way position but it can be hard to feel.

[Lucky_Lou]

Have a look at the thread in this section"Over Revving Resolved" it may help basicaly the problem had 3 issues but the main one was the rubbers to the  head which when hot were leaking badly.
Lou

[motogrizzo]

Thanks for your responses, much appreciated.

Well, today was really the maiden voyage out on the road and not around the neighborhood. I rode to work, about 15 miles each way.

I looked at the rubber between the carbs and head and they look new. The bike starts right up with the choke on and runs great. After about 10 miles, I removed the choke and the bike idled low like it should, but it ran rough with less power. It also felt like there was a surging effect. So, I imagine the carbs are going to need to be adjusted. I was wondering if one of the butterflies is sticking, is that possible?

In what order should I make the adjustments? Carbs, then valves?

I will also take a look at the other thread regarding fast idle. Thanks again for all of your help. It's fun tinkering with this bike, a good experience so far.....

[mimmo66]

Valves always first.

You mentioned you rode for about ten miles with the choke on.

My bike is fully tuned and it will not take the choke at all other than  starting it from a cold sleep.
If I try to run it with the choke on it will actually sputter and choke!

Wonder if this is just me, my last carb rebuild was done three years ago and never had any problem since.

Domenico

[Barry]

After about 10 miles,I removed the choke

Sorry I didn't mean you should ride 10 miles with the choke on. Only that the engine should reach it's proper idle speed after a decent warm up like 10 miles. It's not a precise figure and I'm sure it will vary according to circumstances but for me 4 miles is not enough.

Like folgore my bike won't run at all with the choke on I only use it for starting the engine then it goes straight off before I pull away.  

I know others do ride on the choke but definitely not for 10 miles.

[motogrizzo]

Thanks for the clarifications. I only need to ride to the end of my street with my other bike before I need to remove the choke when it's cold. I thought it seemed strange that it should take such a long time to warm up. I misunderstood, but this is my first airhead, so I thought it's a much different animal.

It's interesting that the bike should run rough and sputter and choke when the choke is on, it's the opposite for me. So, when my choke lever on the engine is pointing down, it runs poorly.

I just have to roll up my sleeves and start going through each system to make sure everything is adjusted correctly.

Thanks!

[nhmaf]

On chilly mornings, I might need the choke for a full 60 seconds before turning it off, but if I leave it for longer than that, I'll just be fouling the plugs.   One can usually start riding out the driveway&along low speed roads shortly after starting up, and turn off the choke along the way - usually in the first 1/4 mile or so.

Make sure that your plugs are clean&properly gapped, and valves adjusted, BEFURE diving into carb adjustments.

[wxp]

How long had the bike been sitting before you got it? When I got mine over 2 yrs ago it had not been ridden much & it basically did the same thing.  The valves had to be re-adjusted & the float on one side needed to be replaced.  

Since then I hve rebuilt the carbs & until you get the carbs balanced & the air gas mixture adjusted properly your liable to continue having problems & it can be most aggreviating

I'd suggest cleaning the carbs @ the least & getting them adjusted...

my 2 cents

[motogrizzo]

I think the bike sat for a while, maybe a couple of years. The previous owner took it out and really cleaned it up and put new tires on it this summer but didn't ride it much or at all. He took great care of it, though.

I think the other problem is that I don't have the owner's manual, only the Clymer service manual. The Clymer manual says the choke is OFF when it is pointing down and ON when it is pointing to the back, or parallel to the ground. I have the engine mounted choke. Barry posted above that the choke is OFF when it is pointing toward the back of the bike.  This makes sense to me and the bike runs well when the choke is in this position and warmed up. For a day or two, I listened to the Clymer manual and was frustrated because the bike ran badly when I thought the choke was off.

Regarding the RPMs, I did the simplest thing first and looked at the rubber boots, they looked like new, but they were a little loose, so I tightened the clamps. The idle speed has lowered to about 1200.

I still want to check the valves and adjust the carbs, but I feel better knowing I was using the choke backwards. Like I said in my original post, the Clymer manual seemed counter-intuitive but I blindly listened to it.

[Justin B.]

If that is what the Clymers says then they are wrong - SURPRISE!!    Choke on is with the lever flipped down...

[motogrizzo]

So here's a new discovery......I arrive home from work last night and park the bike. I hear a hissing sound coming from the right jug. I get down on my hands and knees and move my head around trying not to burn my ear to locate the source of the hiss. It sounded like it was coming from the spark plug area. I guess I shut the bike off on the compression stroke before spark? I waited until the bike was cool and tightened the spark plug. I won't say it was loose but it wasn't tight, either. Do you think that could contribute to a high idle if air is being sucked in through the spark plug hole? It's rainy today, so I'm going to wait to test it out.