Topic: Strange carb bogging issue

[thanantos]

So, I just got this bike running after taking possession and immediately removing the carb bank and cleaning them.

I just sync'd up the carbs and honestly it runs pretty beautifully except that when using very little (less than 1/4) throttle for sustained periods (like riding through small towns) there is a distinct bog when the throttle is rolled on from there. It will hesitate for about a second and then take off again. It seems to help to hammer the throttle.

This does not occur when in neutral or when at higher engine speeds.

Any ideas?

[Zodo]

I'd check the deposits on your plugs after letting the bike idle for a bit. It's possible that your mixture screws are set a little rich, causing things to drown when you apply more gas.

[thanantos]

Thanks, I'll give that a try.

[Nortstudio]

Let us know how you make out.  I've been having a somewhat similar issue.  Definitely getting carbon fouled plugs (rich) but it also does it sometimes at higher RPM too.

[thanantos]

Well, early indication is inconclusive. I figured the mixture might be rich, but I checked at the screws were set at 1.75 turns instead of recommended 1.5...I will get a chance to ride it tomorrow and report back.

[dave500]

have you got #40 slow jets?i find these run better with the #38 pottering along,it seems to make the transition better,did you get your cables at the throttle end sorted?

[thanantos]

have you got #40 slow jets?i find these run better with the #38 pottering along,it seems to make the transition better,did you get your cables at the throttle end sorted?

Although I did remove and clean the carbs, I did not note which slow jets were in it. I will check that if I can't get it working well with a mixture screw adjustment.

The throttle cable issue is sorted out now (thanks). The carbs fully close and open now.

[78whiteorbs]

Any cracks in jet towers ? I found two of mine are like that and are in need of repair. When I am trying o putt putt under 2-3k rpms its a little inconsistent. If I hammer on the throttle it is as clean and smooth as you could ask for.

just re-thought this , the towers are for the highspeed "main" jets so that wouldnt cause that hmmm, in which case I am also interested in a solution to this prob!

Does your bike have stock exhaust and airbox?

[Spanner 1]

Be sure your vent/overflow tubes are clear ( try blowing thru' each one back into each carb ) and be sure they are not pinched behind the swingarm tube too .... just a hunch 

[TwoTired]

I just sync'd up the carbs and honestly it runs pretty beautifully except that when using very little (less than 1/4) throttle for sustained periods (like riding through small towns) there is a distinct bog when the throttle is rolled on from there. It will hesitate for about a second and then take off again. It seems to help to hammer the throttle.

If the recovery is clean, then it was too lean.
If the recovery burbles before smoothing out, it was too rich.

I would note the pilot screw setting, the induction condition/variance from stock, as well as the exhaust.

[dave500]

further to two tireds response,that burble might only last an instant,and might be hard to pick depending on how fast you crack the throttle,if your too rich and crack it fast you might not get that blubber/burble or just miss it,if you crack real slow,,and you can get it to stay in the burble zone if you want,mostly at cruise conditions like just at the point in top gear when you should shift down to avoid a lugging situation,your everso slightly too rich,if you try and cruise just above that lug spot thats when the blubber can occur as you crack it a little more without really loading the engine,slightly rich,,,if you fang (lots of hard accelleration)all the time or live in the hills most people wouldnt notice it.

[orange550]

have you got #40 slow jets?i find these run better with the #38 pottering along,it seems to make the transition better,did you get your cables at the throttle end sorted?

Are you saying that the #38s are sometimes better then the #40s, or the other way 'round? I always thought that because of the lack of accelerator pump that you want it a tiny bit rich to handle the  transition from the slow jets to the main jets...

Thanks,
CHris

[johnrdupree]

I just sync'd up the carbs and honestly it runs pretty beautifully except that when using very little (less than 1/4) throttle for sustained periods (like riding through small towns) there is a distinct bog when the throttle is rolled on from there. It will hesitate for about a second and then take off again. It seems to help to hammer the throttle.

I was having the same issue on a 550K1.  It would burble slightly on about 1/8 throttle but pick up pick up pretty cleanly when I opened it up further.  After unsuccessfully trying to tune it out with the pilot screw, I checked the plugs and they were all sooty and black.  Obviously it was way rich.  Since the carbs had been cleaned and everything inside was stock, I got to thinking about what would make it rich.  All I could come up with was the float bowl height (I had never done that before and wasn't sure if I got it right on) or the air filter.

That's when I kicked myself.  I was still using the air filter that came on the bike, the original 36 year old paper filter.  I had never gotten around to replacing it.  As a test I removed the filter and took a spin around the 'hood (yeah, I know, not recommended) to see if I could induce the burble.  I couldn't.  So, one week and a new Uni filter later the burble is 97% fixed.  Every now and then it will still hesitate a tiny bit, especially when closing the throttle to 1/8 or so and holding it there.  I'm back to thinking the floats may not be 100% correct.  I've got new plugs to install and read this weekend, hopefully they alone will take care of that last bit of burble and I won't have to mess with the floats.

BTW, has anybody bodged together a tool to read the float levels on these carbs (022A in my case) from the outside?  It would have to be a replacement drain screw with a tube in  the middle for attaching a clear hose.  I'm not sure how useful it would be, but I would like a way to visually confirm that all the carbs are set to the same fuel level.

~john

[Nortstudio]

I got one of these on the suggestion of one of the members here:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=170670404799

Little pricy for what it is, but it works perfectly, and it was one less thing I had to cobble together.

[johnrdupree]

It turns out that the threads on the float drain screw are really odd, 6 x .75mm.  I can't find a screw or bolt in that size (to modify) in my dinky little town so the eBay item may be the way to go.  Thank for the heads up.

~john

[Nortstudio]

It definitely works as advertised.  There are plenty of things to get you frustrated on the carbs, ay least this doesn't have to be one of them