Engine Runs Away

[Crossrodes]

This in my '79 which I tore down and rebuilt.  A couple of days ago I attempted to start it for the first time couldn't get it started so I replaced the points and condenser and set the point gap.  Last fall I had rebuilt the carbs with all Bing parts.  I set the throttle and choke cables up by eyeball.  They will need to be fine tuned once I get the bike running and the timing set properly.  I set the timing as well as I could statically.

At first when I started it with full choke it started almost immediately and was idling fine. After a couple of minutes it started to run rough so I set the choke down to half choke.  After it started to hic-cup again I turned the choke off and revved it with the throttle.  Then the engine started to run away.  I had to switch it off to get the revs under control.  I checked the cables (throttle & choke) to see if they were working and not sticking...seemed OK.  Tried starting it again and it ran away again.  So I changed the timing again by twisting the bean can.  I got the same result again.

I have no clue as to what could be causing the engine to run away like this.  One thing however...I did change the timing chain and in the process the mark the I put on the cogs were erased so I had to set the timing where I thought it should be by lining up the timing marks on the flywheel and ensuring that there was no valve/piston interference.  I think I have the mechanical timing correct but can't be sure...who knows if I'm off by one cog.  Could this cause the engine to race if my mechanical timing is off by a cog?

Any other ideas as to what could be causing it to run away like this???    

[Bob_Roller]

You need to perform a carb synchronization .

[Crossrodes]

Bob, I'll check/adjust the carb initial adjustments tomorrow (I thought I had done this when I rebuilt and installed the carbs).  Hopefully this will bring the idling down (right now it goes upward of 5,000 RPM).  If that works I'll be able to ride it and get the balance adjusted afterwards.  Meanwhile I'll keep my fingers crossed.

[montmil]

Mike, Suggest you slack off on the throttle cables at the carb adjuster and try starting the bike again. Sounds like a cable or carb idle stop or idle air setting to me.

Monte

[nhmaf]

Or perhaps when you revved up the bike, the needles didn't slid back down in the jet - perhaps stuck, slightly bent, diaphragm issue..

[Crossrodes]

I checked the idle mixture and it seems OK.  I turned it in again and out one turn.  I didn't check to see if the cables were OK but I'm pretty sure they are.  I'll double check them tomorrow.  I really don't wan to take the carbs apart again....but if I have to I will.

Thanks for the feedback.

[suecanada]

I installed a brand new throttle cable and it was defective right off the bat as it was hard to push and pull even manually off the bike. Also, had my throttle stick open luckily in the garage. Broken strands on the cable. Suspicion often lies in that splitter/distributor 'bullet' under the tank for either choke or throttle. Assume nothing even if brand new!

[Crossrodes]

Thanks for the feedback Sue.  

On my '79 there are no cable splitters.  Both the throttle and choke run separate cables from the controls.  The controls and the cables are working well.  They are not new but were lubed and checked when I had the bike apart.  

I'm thinking that I will take the carbs apart.  It makes sense that there is an issue with either the diaphragm (new) or the needle.  I probably will not get at that today because something has come up but hopefully I will be able to post what the problem is/was tomorrow.

[wilcom]

I'm thinking that I will take the carbs apart

Any other ideas as to what could be causing it to run away like this???  

Before you rip the carbs apart, check the butterflies and make sure they are closed with the cables attached. Take off the outter horns and lift the slides and peek in there with a light

 For the motor to rev up to 5K RPM, it has to be getting AIR from somewhere. Either a butterfly that is not closing or a leak after the butterflies maybe.

 Did you change your O rings on the throttle shaft? Could you have gotten one butterfly turned backward?   I'm betting AIR is the culprit with that much RPM.

Hope it turns out to something easy!  

good luck

[Tony_T]

I'm with Joe on this one.
I tend to think that it has an air leak somewhere.
Maybe look at the intake manifolds too.

[Julio A.]

I experience the same problem if there is something off between the carbs; could be one is running lean or the carbs are un-sync-ed that much.

Don't forget the vacuum tube where the syncronizers are connected, the rubber seals on mine failed me more than once on different bikes.

[montmil]

...I turned it in again and out one turn...

Mike,  I've found that just the smallest change in the idle mixture can create bigger engine speed issues. May I suggest you try a three-quarter turn out on the idle screws and see what happens?

I know there is a "factory recommendation" as to the initial setting, but it will only take you a couple minutes to try a little less. My 1981 R65 idles so much nicer once I went beyond what the manuals say and pinched down the screws a wee bit.

Monte

[Crossrodes]

Yahoo!

Problem Solved!

I should have had a lottery on who gave me the solution to the problem.  
Here's what I did:

1. I took the input & output plastic feed "tubes" off the carb and checked that the butterfly's were working...they were.

2. I checked the piston/needle and one of them seemed a little sticky but after moving it around a bit it was loose and working properly.  May have been a little sticky because the carbs had been unused for about 8 months after I rebuilt them.  Put everything back together and tried again...no joy.  Took the feed tubes off the carbs again and there was no piston/needle sticking....scratch that being the problem.

3. I checked for rubber seals on my connection for my vacuum tube.  There aren't any, but I don't believe there are supposed to be any on the '79.  I made sure the screws were nice and snug and all seemed well there.

4. I backed the mixture screw off to 3/4 of a turn....seemed to help a little but was still revving way too much.

And the prize goes to....

Monte and Sue...

The throttle cables were not sticking, however it was a cable issue.  I thought I had these set properly when I installed the carbs last fall but I thought I would just check them before I took the carbs off to tear them apart again.  I backed them off significantly and tried to start the bike.  It was hard to start and I had to give it throttle to start it and it would not idle unless I kept giving it throttle and of course it did not rev up unless I gave it sufficient throttle.

So thanks everyone for you input.  It really is appreciated.  

Now I will start the tuning process.  The valves are set so I will adjust the carbs and use a timing light to get the timing set up.

[montmil]

Mike,  This article, by ABC member Hugh Kenny, is my bible for Bing carb tweaking.

Read through it a couple times before starting the work. Follow his sequence. Get off the path -frustration and failure will be the result. Written in a break-it-down Barney-style that was simple for me to understand, and therefor, learn.

After the valves are set, then do the timing before the carb synch work. Get the timing close enough for gubmint work, then recheck after the carbs are tuned. Pay close attention to balancing the throttle cables with the engine at approx 3500 rpm. This will balance mid-range mixture and provide you with a smooth cruising Beemer.

And that little thumbscrew below the twist grip is there to hold a specific rpm during the timing and carb work. I also use it as a cruise control.

BTW, my mixture screws are opened less than three-quarters out.

Monte

Carb Synchronization by Hugh Kenny, ABC #6051, Cheyeene, Wyoming

http://www.airheads.org/content/view/183/98/

[Crossrodes]

Thanks Monte.  I printed that article and I'll read it.

My big problem right now is setting up the timing correctly.  I have tried moving the bean can back and forth but cannot find the timing mark.  I'm using a good timing light but I just don't see the mark (It's a drilled hole on my '79...If I remember correctly that's what we came up with during a conversation here with some others).  I can rotate the engine by hand and find the mark but it's just not there when I use the light.  Have you learned any technique to use to get good visibility through the timing hole (that may be my problem)?  It's difficult to get a clear view of the timing marks because the carb and fuel line restricts my angle of vision.

I don't have the screw on the throttle on my '79 that you are talking about.  I know what you mean.  I have seen them.  However I do have a throttle lock that I may be able to set up and use.

Thanks for all the info.