Carb rebuild and other stuff - "Newbie with a pig"

[Justin B.]

[movedhere] General Announcements [move by] Justin B..

[DerekM]

Noticed the worlds tiniest grub screw on the table while starting the carb rebuild. Does this go with a 32mm cv carb, it's not in the diagram. Atomizer for scale.

[AlfromNH]

I don't recognize that from the numerous times I've taken my carbs apart.  :-?

[Barry]

Sure is small. I don't believe Bing CV's have such a thing.

[Luca]

I see you've found the $3000 grub screw  

But seriously, I don't think I've seen one of those anywhere on the entire bike.  Are the threads metric?

[DerekM]

Got the carbs rebuilt but not getting any fuel into the cylinder, I can get a rough start with throttle open and starter fluid but I'm going to run through the carbs again and double check everything.  

[Luca]

Sounds like idle circuit problems.  The small passageways for the idle jet and idle mixture are easy to clog, and compressed air/carb cleaner spray don't always clear them.

I took an old high E string from one of my guitars and cut it about 5" from the bottom end, which has a nice brass barrel on it for easy handling and locating.  Have used that for poking out passageways.  Yes, steel strings could potentially score the carb bodies... just be gentle.

Might be worthwhile to make sure the enrichener discs are also installed correctly and clear of blockages.

Congrats on getting the bike to cough and sputter.  First breaths are always a promising sign.

[montmil]

Didn't we just solve this very same problem within a similar thread? Derek, have you checked the Tech section for similar topic? The answer is there.

There are a couple tiny holes just under and very near to the butterfly. If these are clogged, no atomized fuel will pass thru the starting fuel circuit and the bike will not start. Have you confirmed these passages as being clear? Single piece of way thin copper wire will work as a probe.

[DerekM]

Gone through the carby and turns out the spring was missing off one of the idle screws, along with the plugged holes.

Got it running tonight, albeit rough and smokey from the exhaust like crazy. Starts up by covering the carb intake with my hand and it runs with the choke at 1500 rpms or so and climbs up to 3k without. So there is definitely an air leak and tuning to do. I don't have an exhaust wrench to use so hopefully the exhaust clears itself out after a couple rounds.  

I like progress. Progress is good.

[steve hawkins]

Its definitely progress.

Keep on  with it.

Cheers

Rev Light

[montmil]

If the enrichener circuits are clear and both enricheners assembled correctly, and all air & fuel passages open, you should not need to block the carb's air intake to get an engine start.

The idle speed increase is mostly likely a misadjusted idle screw/s. A complete carb balance is a future job but for right now, try closing down the idle mix screws and see if that does not help reduce the idle rev increase. The engine must be at full operating temperature before beginning carb tweaks. Anything less than completely warmed up is but an exercise in frustration.

Confirm both idle air screws have their o-rings in good condition. Helpful to use just a light touch of plumbers grease or dielectric grease as an aid in preventing those critical o-rings from rolling out of place or being torn.

Keep after it. Once dead, now alive. That's progress. [smiley=thumbup.gif]

[DerekM]

It's starts regularly with the idle screws all the way in and the choke on. It idles badly with the choke on, and races with the choke off as expected.
Loosen the idle screws 1/4 turn or more and it won't start with or without the choke. I think that indicates the idle circuit is blocked right?
I cleared out all passages with a strand of wire, including the idle jet.

[Luca]

I wouldn't expect it to race with the choke off during the first few minutes of operation.  A cold engine should be reluctant to run without the choke, and race a bit while the choke is on, especially as it warms up.

That, combined with the fact that it doesn't want to run with the mixture screws backed out at all (they fatten the mixture going out on CV carbs--opposite of slide carbs) makes me thing the bike is running way too rich.  If the smoke in the exhaust is black (black=excess fuel<-->white=burning oil) that would further suggest you have too much fuel.

Here are a few things you can check:
1) make sure the float/fuel bowl levels are ok.  Too much fuel in the bowl will richen the mixture.
2) make sure the enrichener discs are not backwards.  Pics here: http://bmwmotorcycletech.info/bingcv.htm  I'm not sure if having the discs in backwards will make the choke work backwards, but if you have the carbs back off it's easy to check
3) make sure your carb jets are stock.

[montmil]

Confirm the small brass 'jet' in the bottom of each float bowl is clear. The smaller reservoir feeds the enrichment circuit.

Idle circuit screws must be opened. Begin with the spec's percentage of turn.

Ditto Luca's comments on the enrichener discs, float levels and float needle function.

Confirm correct valve lash and timing. These two items really do effect start and engine ops.

[Luca]

One other thing, since you've replaced one of the slides, is to make sure the jet needles are the same and in the same position.  One needle position change makes a big difference in mixture.  I've never worked out how to adjust the jet needle, but you can measure from the base of the slides to the tips of the needles to determine their positions.

Pretty sure somebody around here knows the proper needle protrusion for stock settings.