cracked carburetor -- thoughts?

[DogBunny]

The intake bell of my carburetor has a 1-5/8" long crack in it. Crack was discovered while chasing a weird intermittent running issue, which had to be either the ignition or the carbs. A routine check of the ignition came up empty, so I removed the carbs and found this.

The crack does not seem to extend to the outside of the carb body.
I went to a great deal of trouble trying to determine if the crack extended to the air jet passage (red arrow) and/or the float bowl vent (blue arrow). I used suction, carb cleaner spray, and flooding the passages with paint thinner. All tests came back negative, i.e. no smoking gun was found. However, that doesn't clear the crack as the source of my problems.

It's still possible that my intermittent problem is in the ignition, but I'm leaning toward this crack as the cause.
This is a carb that I've probably been using for a couple of years. Bike ran like a top, but recently it started to become hard to start. More importantly, sometimes it would start and run fine, some times it would start but idle poorly and run at slow speeds poorly. I could shut it down, re-start it and it would be good. Shut it down again, re-start it, and it would be bad. About a 50-50 crap shoot.

 

[jetmechmarty]

If I awoke and found I was you, and I had a spare, I would replace it and not look back.

 

[Jan_P]

I don't believe that crack is the reason for running problems
Even if it was a through all crack I don't see any major air flow passing through.
The other side would make it start OK if it was a carburetor problem I do believe.

Would be possible apply some chemical Silicone ? and test or replace as Jet M says.
But my guess is electrical problem somewhere

I would stare at the regulator if stock. Testing another one to start with Plug in as a quick test

 

[gggGary]

When's the last time you've cleaned the Iggy n kill switches andd other likely weak 'lectric connections

 

[DogBunny]

If I awoke and found I was you, and I had a spare, I would replace it and not look back.

I am definitely replacing that carb. Even if the crack is benign, it's going to grow until it is a problem.

I don't believe that crack is the reason for running problems
Even if it was a through all crack I don't see any major air flow passing through.
The other side would make it start OK if it was a carburetor problem I do believe.

Would be possible apply some chemical Silicone ? and test or replace as Jet M says.
But my guess is electrical problem somewhere

I would stare at the regulator if stock. Testing another one to start with Plug in as a quick test

I don't like the carb as the cause of my problems either.
The stock reg/rec (TCI ignition) is a possibility, easy to replace, but it doesn't really explain the intermittent issues. I have the same issue hot or cold, immediate re-start, or sitting overnight. It's a total crap shoot at this point.

When's the last time you've cleaned the Iggy n kill switches andd other likely weak 'lectric connections

I've been running a wire (with a fuse and toggle switch) directly from the battery to the coil. I've checked the fuse and the toggle switch for squirrlieness.
Checked the pick-up coil, it's connector (which I re-did), and the TCI connector. Looked at the spark plug wires.
Still a couple other electrical things to look at, including the coil, but nothing that would explain the intermittent nature of the problem.

I now need to make a carb set, so that's my next step.

 

[gggGary]

Gonzo box A-B testing?
Open the stator pigtail in the sprocket area looking for issues with the pickup wires.
There's been several similar cases (me, 5twins) of erratic running traced to a "barely hanging together" wire there.

 

[DogBunny]

Gonzo box A-B testing?
Open the stator pigtail in the sprocket area looking for issues with the pickup wires.
There's been several similar cases (me, 5twins) of erratic running traced to a "barely hanging together" wire there.

I've actually been testing several Gonzos, and they all do it. Also tried several verified good TCIs.

 

[gggGary]

If you haven't, coil swap.

 

[MacMcMacmac]

Chain sawing through the ignition leads around the sprocket? Been there twice.

 

[DogBunny]

If you haven't, coil swap.

Will do.

Chain sawing through the ignition leads around the sprocket? Been there twice.

Will look.

Although that crack doesn't really look like the cause, I still kind of like it as the culprit. I have to put a carb set together before I do anything else, so if new carb set doesn't fix it I'll-revisit electrical possibilities.

 

[Jan_P]

This is something I have been doing close to 40 years
Electrical fault finding in this context .. makes it difficult
Is that it is not as Mechanical fault that are there and stays there.

The really nasty ones can be heat / vibration / voltage / connector /And water dependent
and maybe more

That is why I am rapping about the regulator I had one working fine cold but not hot and fault finding hot is virtually impossible burning your hands and then cold the fault don't manifest itself.
No one can find faults that is not there

If fuses not going open the extra Voltmeter helps .

But at times one has to take a chance replacing parts I go for the CSF rule
Cheapest Simplest First

I admit making mistakes on the learning curve buying a replacement Boyer Ignition
Plug it in just to find out it was the wrong part to replace.

That is why I use the CSF rule nowadays In your case you have them parts at home

 

[DogBunny]

This is something I have been doing close to 40 years
Electrical fault finding in this context .. makes it difficult
Is that it is not as Mechanical fault that are there and stays there.

The really nasty ones can be heat / vibration / voltage / connector /And water dependent
and maybe more

That is why I am rapping about the regulator I had one working fine cold but not hot and fault finding hot is virtually impossible burning your hands and then cold the fault don't manifest itself.
No one can find faults that is not there

If fuses not going open the extra Voltmeter helps .

But at times one has to take a chance replacing parts I go for the CSF rule
Cheapest Simplest First

I admit making mistakes on the learning curve buying a replacement Boyer Ignition
Plug it in just to find out it was the wrong part to replace.

That is why I use the CSF rule nowadays In your case you have them parts at home

For me, replacing regulator or coil doesn't cost anything. But, I have the problem hot or cold.

I'll add that when the bike is running in crappy mode, it will still move me down the interstate at 70 MPH just fine. I have a weekly appointment on the interstate, 10 miles each direction. When running in crappy mode, that 10-mile run sometimes clears the problem, sometimes not. I can finish that 10 mile run in non-crap mode, immediately re-start the bike (starting is always hard, not easy like it should be), and I'm back in crap mode. Turn bike off, re-start (starting is always hard), and I'm back in non-crap mode.
I know it sounds like I'm making this up or I'm delusional.
I know his sounds crazy, but I feel like sometimes the crack opens up, affecting the air-jet passage, and throwing the carb off just enough so that the bike runs, but poorly. And sometimes not.
If you think about it, that crack has to lead somewhere, like the air jet passage, or even the outside of the body, even though I not seeing anything.

 

[MacMcMacmac]

My symptoms were random misfiring/backfiring, sometimes kickback through the kickstart lever, and random dying at stop lights. There was one polished hole about the size of a mustard seed on one wire that randomly shorted against the chain.

I'd "seal" that crack with Krazy Glue or nail polish and see if anything changed

 

[Max Midnight]

If you are going to replace the carb then why not investigate the 'crack' to see how deep it goes?
If it is only a surface aberration you will have ruled it out as a cause and can always fill in the excavated area to make good again.

 

[bosco659]

That crack is in an odd place, I wonder how it got there. As suggested, replacement would be the best solution. I agree if you want to test the theory that this is the cause of your issues, gouging it out a bit with a ball headed bit on a Dremel tool and filling the crack with epoxy or as suggested nail polish or some other fuel resistant material, will allow you to test and eliminate one root cause.

 

[DogBunny]

No, I am not going to spend time trying to repair, or even investigate, a compromised carb body with a crack that is only going to grow worse over time.

This crack reminded me of what I learned about basic damage control while I was in the US Navy. Drilling holes at the ends of cracks can temporarily prevent them from extending by spreading the stress in all directions instead of just along the crack line.
Picture taken from the USN Handbook of Damage Control, NAVPERS 16191, 1945.

 

[AUTOMAN]

That is one shitty looking carb.
Clean it up first.
cliff

 

[DogBunny]

That is one shitty looking carb.
Clean it up first.
cliff

Why? It's just going to get dirty again.

 

[DogBunny]

It turns out the problem, all along, was that I am an idiot. I sorted out a different carb set, which I was sure was the problem, put it on, and nothing changed.

Gonzo box A-B testing?

And the winner is... Gary! ...again...

The negative and positive needed to be swapped on the Gonzo boxes I was using.
Yes, lots of the observations that I made in my earlier posts were erroneous. I could make excuses, but for the real answer see the video above.

I'd like to point out that the polarity reversed Gonzo boxes worked incredibly well, considering. They were hard to start, rode poorly at lower RPMs, but were otherwise quite rideable. I really did make more than one 10 mile out and 10 mile back freeway trip with them. And, I checked the timing on all of them while they were polarity-reversed. It was good on all of them.

As for the cracked carb -- it worked just fine before, so I put it back together and and put it on a different bike which I am preparing to sell, where it is still working just fine. I'm not crazy about doing that, but...