Topic: When does elevation kick in for carb issues?

[Nortstudio]

Hey folks.  Been wrestling with the newly rebuild carbs on my 1976 CB550K.  Had them on and off a ton preparing for a trip up to Vermont.  They seemed to finally be running well before I left, and then I carted it up there in a van (bouncing probably not so good). 

When I first went to ride, the bike was experiencing heavy hesitation just-off idle, almost like someone was running along side of me, turning the bike on and off.  I'm talking probably 0-1/8 throttle.  It also started and warmed up rougher than it ever has, needing the throttle for longer periods before it would idle/warm on it's own.  It would want the air choked off for a second to get it going, and then immediately wanted it on, or else it would stall.

I finally decided to "zen out" and just enjoy the riding, knowing that the only time I would be just-off idle would be getting 300 yards to the main road.  The trip was amazing and i enjoyed every minute of the open and twistie roads, sans traffic (like here in Brooklyn!).

Then I returned home (more bouncing in the van) and finally started it up, before tearing the carbs out again, and to my surprise, the bike was running with very little hesitation.  I still believe that I need to get the carbs off, to make sure the slow jets are spotless, but I am now wondering if the elevation of the location in Vermont may have had something to do with the issue.  I looked it up, and found that I was only at about 1600 feet above sea level, but compared to Brooklyn, that is about 1600 feet higher

The rough warm/idle is still happening, which may be the needed carb clean (again!), but I have been wondering about this elevation effect.  I guess I assumed that elevation issue kicked in for places like Denver - dramatic changes like that.

Is 1600 feet enough elevation to have played a part in my carb/hesitation issue?

Thanks,

Scott

[tlbranth]

Your carbs are more advanced than mine (Amal copies). Mine in a 1970 CB750. But I've been over 10,000 ft passes with no noticeable degradation.

[BobbyR]

Scott, when I go up to the Mountains on the Hudson I get up to 1200 ft with no noticeable issues. I did have a Firebird that did not want to start in the mornings, got it back to NY and she started one shot even in the coldest winter day. I think our NY motors can't handle the clean air up there.   

Here is an article on the topic:  http://www.4strokes.com/tech/howtojet.asp

[Nortstudio]

Thanks Terry. I figured 1600 feet would not really effect it. But that leaves me with I bounced my carbs out of whack on the way north, and bounced them back INTO whack on the way south

Bobby, I actually thought of that!  My carbs need to wheeze and choke (pun intended) on this beautiful, polluted air!

[crazypj]

Shouldn't be an issue below 2,000 ft, may need leaning off a bit at 3,000ft and higher

[KingCustomCycles.com]

I had an Aeronca Chief that didn't begin to show signs of richening mixture and misfiring until 5000 feet.  There are a couple of thoughts that came to mind when I read your post.  What was the temperature doing?  Was it significantly cooler?  Another is the shaking, or severe angle changes from loading and unloading, may have dislodged some water, or debris, in the fuel system that had to work its way out.  Gas quality varies from region to region.  We have a ton of ethanol here in the corn state of Indiana.  It doesn't sound like it was a big issue, and altitude may have aggravated the problem but not much. 

[Danno]

the only thing you would have to do for that slight bit of higher altitude would be to turn the air screws in a half turn at the most but more likely a quarter turn unless it was winter

[Nortstudio]

Thanks guys.  I have been chasing carb issues all summer, after rebuilding and installing a new rack of 087A's.  Total PITA, considering I was hoping this would FIX my previous hesitation issues, not exacerbate them.  But of course, they ARE carbs, so what are you gonna do?

The bike is running just about the same that it did before I left, and I figured the angle/bouncing that occurred from getting the bike in/out of the van could have had something to do with it.  The ethanol seems to be causing havoc with these bikes, and once a friend talked about his fuel line breaking down (possibly due to the ethanol?) it made me think that I should try installing some more modern type fuel line, to see if that helps.

King, the weather up in Vermont was certainly cooler than it was down here in Brooklyn, especially in the mornings, when I was warming it up.  But the cold start-up issue has followed me back down here, so I am not sure if temp is part of it.  I always had luck with very quick starts, even when the old carbs had their hesitation issues.  In fact, it really seems that the hesitation problem is worse when the bike warms up.  Although I am going to re-clean the carbs (especially pilot jets), I am starting to wonder whether the issues are ignition related.

Round and round I go...

Thanks for all the help and advice.

Scott

[Danno]

pull the plugs and look at the color of them look for a dark one or if they are white
if they are white turn the air screws in half a turn
if there is a dark one see if there is rust in the bowl as it could be causing the needle not to close and making it run rich in which case you need to clean the sock in the tank , derust the tank, or add a paper filter inline

[Nortstudio]

Thanks danno,

I've been through the plug deal for some time now.  I have been carbon fouling plugs for what seems like forever, despite now having changed the carbs, cleaned carbs MANY times, derusted tank, rebuilt petcock and cleaned sleeve, new fuel line several times, various online filters, new coil wires spliced in, new caps, probably 24 plugs, Air screws endlessly turned, and the list seems to go on....

After starting this thread, I had the most hesitation-free ride in quite some time.  Part of me feels like I need to roll with it until winter, when I will feel less bad about starting this whole dance over again.

[lucky]

First question.
Do you have vacuum operated carbs?

[scottly]

Scott, in your first post, you mentioned the symptoms were like someone turning the bike on and off. That might be a clue that you have an intermittent ignition problem. 

[Nortstudio]

Scottly, I may have overstated that a bit, but it was more dramatic than it had been. 

Of course, now that is gone, so I am back to a hesitation that occurs mostly when bike is warmed up, and not nearly as dramatic.  Yesterday it ran pretty damn well. 

It's time to get in and test the coils etc.

[crazypj]

You are running stock airbox with  filter?
I didn't notice any mention of modifications so everyone is assuming it's stock?

[Nortstudio]

Sorry, forgot to add all the details....

Stock air box with uni replacement filter (freshly oiled).

I need to get back in the carbs with fresh (hopefully) ethanol resistant fuel line, and then see where I'm at. The change from brooklyn to Vermont and back to Brooklyn has me more stumped than ever.

But...sun is shining today, and I'm enjoying the riding, despite the slight hesitation

[crazypj]

too much oil on filter?
 I wrap foam filters with paper towel and squeeze out excess.
 If it's a K&N, could be the wrong filter oil?

[Nortstudio]

It's funny you say that, because I thought that I may have had too much oil on it last time.  I made sure I had the right UNI type oil, but it was tough to ring out, since the filter is backed by razor blades!  Seriously, the metal mesh is so sharp that I cut myself severely...

But this latest time I ended up brushing it on after cleaning it.  I have a newish paper filter I could try too, just to see if that would help a bit.  But I did have it on there at one point, and I think it was the same.

[scottly]

The change from brooklyn to Vermont and back to Brooklyn has me more stumped than ever.

But...sun is shining today, and I'm enjoying the riding, despite the slight hesitation

Hmm. Was it cooler in Vermont?

[Nortstudio]

Definitely cooler.  But not by much.

[crazypj]

NEVER wring foam filters, it destroys them.
 Wrap a bunch  of paper towels inside and out then squeeze as much oil as possible out.
 Try the paper filter, as long as it hasn't got wet it should give you some indication if is part of the problem

[Nortstudio]

Just using a phrase. There is no way to ring the uni even if you wanted to. The wire would cut your hands off! I'm not exaggerating!!!

  I used paper towel, and blotted it until it was clean, and then this last time I used the brush instead of dipping. There doesn't seem to be a difference from the last time I dipped, but it was a while ago.

I'm going to throw the paper one in once the rain let's up (never apparently!) and see how she reacts. This week the carbs will come off again for sure - and I'll throw in some new plugs for good measure.

[scottly]

Post pics of the plugs, please...

[Nortstudio]

I'll get the pics as soon as I am at the garage again.  But they look stereotypically carbon fouled, like they are running rich.  Like the pics that float around here from that one website.