Topic: one sooty spark plug

[Schnell]

New to me bike runs great. Carbs cleaned. First time I've checked the spark plugs. All air screws are 3/4 turn out but plug #1 is mad sooty. I turned out the #1 air screw a further 1/4 turn. That should do it, right? I'll check again after a bit of a ride.

[grcamna2]

Could the #1 float have a spot/dimple on the 'tang' where it catches/snags the float needle and causes the float needle to overflow that cyl. ?  I've had worn float needles/seats overflow carbs before.

[scottly]

plug #1 is mad sooty. I turned out the #1 air screw a further 1/4 turn. That should do it, right? I'll check again after a bit of a ride.

The mixture screws are for idle, and don't have much influence at larger throttle openings.
You should either replace that plug or burn the black off with a propane torch, then check it again after riding the bike. If it's sooty again, you have a problem with that carb.

[Schnell]

Thank you the pointers! I'm going to try to remove the float to adjust height, with carbs on the bike. Luckily it's cylinder #1. I was able to replace all 4 main jets this way. I've already had the carbs off the bike so many times.

[Schnell]

I could not get the float pin out so I used a screwdriver to adjust the float hieght tang. After a little ride I pulled that plug again and noticed a good improvement.

[Deltarider]

I could not get the float pin out so I used a screwdriver to adjust the float hieght tang. After a little ride I pulled that plug again and noticed a good improvement.

Oh dear, oh dear. You shouldn't have touched that tang. Have a look at its design and you will understand that to arrive at a 1 mm higher or lower fuel level, you'd have to bend the tang maybe no more than a tenth of a mm, due to what we call 'arm' (Dutch) or leverage. How good are you at that? My gut feeling is the swivel pin is the real cause. If you can't get it out, there's a good chance up and down movement of the float is hindered.
So far I have never met a float that needed adjustement. It's this crazy thing here in this forum only. Leave it alone!

[rotortiller]

I could not get the float pin out so I used a screwdriver to adjust the float hieght tang

Good move, if the float is not leaking the position should be similar to the others. I carefully adjust floats all the time that way. If the pin needs to come out later care is needed so the pin support ears do not break off. The manual has the ruler spec for the float height, you likely checked that too I bet.

[Schnell]

Bike is running great. Plug #1 is no longer sooty. I was riding along today and have about 100 miles on it since it was licensed last week. Suddenly the engine sounded different and there was a partial loss of power. I limped home on what felt like 3 cylinders. Once home I took header temp readings to find he affected cylinder. #1. I dropped the float bowl and there in the bottom was the slow speed jet. Vibrations unscrewed it. I srcewed it back in and tightened it. Bike runs great again.

I also installed the brake light deceleration switch. Don't know if it works. Can't see the brake light while riding.

[scottly]

Oh dear, oh dear. You shouldn't have touched that tang.
So far I have never met a float that needed adjustement. It's this crazy thing here in this forum only. Leave it alone!

In reality, the floats DO sometimes need adjustment, due to the strength, or lack of strength of the springs in the ends of the needle valves, especially when the floats are set with the tang of the float is just touching the pin in the end of the needle. Just because you have never seen this doesn't mean it doesn't happen. It does, and the proper way to test the float setting is with the clear tube method, which eliminates the variables. 

[scottly]

Bike is running great. Plug #1 is no longer sooty.

Good job!

[Deltarider]

[...]
In reality, the floats DO sometimes need adjustment, due to the strength, or lack of strength of the springs in the ends of the needle valves, especially when the floats are set with the tang of the float is just touching the pin in the end of the needle. Just because you have never seen this doesn't mean it doesn't happen. It does, and the proper way to test the float setting is with the clear tube method, which eliminates the variables. 

Sorry to disagree. As the video I've posted recently shows*, the spring function does not play a role under normal circumstances. Mind you, the video demonstrates what goes on, filling a floatbowl from completely empty. Even then the spring is not being compressed. In normal circumstances, like in riding, the rise force is far, far less than when filled from completely empty. It's only there to serve as a shock absorber when things go really, really wild, to then protect the tang. Feel and judge the tension of a float needle's spring function with your fingers and you will sense it's very, very unlikely all of its travel will ever be used. I cannot comment on aftermarket products as I have no experience with them. It seems Keihin designed it so well, one can do 140.000km and not having to readjust even once (see pic). Unless the situation with CB750s is very different, I see no reason why one would have to readjust and certainly not before an impeded movement by a bent or corroded swivel pin is ruled out. Even in a good condition - the video shows - the movement is in little shocks, so imagine the swivel pin is bent, corroded or even pinched. I've always been able to remove them with my nails. When pliers are needed, extreme care must be taken not to pinch the ends. I am not alone in this: the subject of readjusting floattangs is practically absent in other fora.
The irony is, that I have never had to adjust a float and yet have presented all video's on the matter and in addition posted a better and fool proof diagnosis test which any amateur can perform without damaging/distorting a thing. http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647
* From 17:00 - 18:20 the video shows what goes on in practice.

video courtesy Gruzzel

[jwurbel]

Delta rider, my German was never that good.  However, are you saying that new floats do not need to be adjusted as they are correct as received? 
 
If so, that would kill the plethora of questions on this forum relative to measuring fuel level as a critical component in carburetor set up.

[Deltarider]

Delta rider, my German was never that good.  However, are you saying that new floats do not need to be adjusted as they are correct as received?

Yes, OEM are. I always said: there is no harm in testing and maybe exercising your skill in measuring, but think twice before you conclude the tangs need readjusting. Even with the clear tube method you can make an error judging the results. It's for that reason I have posted my method. If you measure the same amounts of fuel after draining the bowls you can rest reasured.
The parts involved hardly wear as I have demonstrated. The culprit is the Clymer manual that always describes things you can do, without ever balancing it by a comment. If they had included what professional mecs have experienced in their workshops, they could have added: unlikely you ever have to do this, but here is the method anyway. Folks buy a Clymer and can't wait to 'tune' their bikes to 'perfection'. They interpret everything in the Clymer, as something you should do. Not so.
BTW, I remember the big Honda information cartons hanging down from the ceiling in a Honda dealer's workshop. It specified the float measurements for the few CB Four models we then had. It said +/- 1 mm.
Some carbs have been left unattended for years. Those will require cleaning and possibly polishing (extremely lightly!) of some parts.
Then there are owners or POs that have fitted aftermarket parts. Maybe others can help them. I can not.

[rotortiller]

Obviously the correct decision was made in adjusting the float. When you acquire a new antique bike god only knows what was tampered with by someone else. Over time valve seats wear in, over time the float is hammered and shocked into the valve needle through the tang which can require re-calibration, as the float lives in the full position. Some needles have springs which can weaken and affect the float position. Sometimes the float can lose buoyancy from leaks or fuel saturation which needs replacement and calibration. The reason the tab is there is for adjustment and it is a simple one to make just like the float in a toilet. It's a maintenance item meant to be used as needed.

[Deltarider]

[...] It's a maintenance item meant to be used as needed.

Can you point at where 'that maintenance item' is in the maintenance schedule?
Here's a rule of thumb. If the tang runs parallel to the rest of the float's brass, it is unlikely it has been tampered with.

[rotortiller]

Maintenance is mechanical work. 'Scheduled maintenance' is just that, scheduled are your words not mine. You sir are an ass lol

[BenelliSEI]

Nice work Frank. Sounds like you got this well sorted!

[Schnell]

Yes it is John! I'd like to come by some time and show you.

[BenelliSEI]

Away right now, next week. J.

[Deltarider]

Maintenance is mechanical work. 'Scheduled maintenance' is just that, scheduled are your words not mine. You sir are an ass lol

Your remark Sir, just illustrates how deeply rooted this idea of adjusting floattangs has become in this forum. Correct me if I'm wrong - I'm not a native speaker after all -, but doesn't the English language differentiates between 'maintenance' and 'repair'?
Adjusting a drive chain is maintenance, rebending a floattang is not. It's repair. Now who's the ***?

[BenelliSEI]

“I also installed the brake light deceleration switch. Don't know if it works. Can't see the brake light while riding”.

Frank….. will be interested to hear how yours works! I gave up on mine, they are sending a replacement. I was thinking I might add a lead to an old turn signal I can stuff in my tank bag map pocket so I can see what is happening back there?

[Kelly E]

Maintenance is mechanical work. 'Scheduled maintenance' is just that, scheduled are your words not mine. You sir are an ass lol

Your remark Sir, just illustrates how deeply rooted this idea of adjusting floattangs has become in this forum. Correct me if I'm wrong - I'm not a native speaker after all -, but doesn't the English language differentiates between 'maintenance' and 'repair'?
Adjusting a drive chain is maintenance, rebending a floattang is not. It's repair. Now who's the ***?

Sorry but adjusting the float height is maintenance. Lighten up dude, you seem a bit uptight. When machines are 40 to 50 years old things change and dead stock factory practices aren't always relevant especially with the quality of aftermarket parts. Don't even get started on the "stock is best" bit because it doesn't always apply any more because you can't always get factory parts these days.
There are times when someone figures a better way or improvement in 40 years. If we go with your theory the last smart person died in 1978.

Who's the ass now?

[Deltarider]

And the epidemic goes on and on, be it only the United States of Absurdistan, if we read the other fora in the world. Here's a question for all those who can't wait to do 'maintenance': when was the last time you did 'maintenance' on one of your car's float assemblies?

[dave500]

the thing with float heights as ive posted countless times before is they dont need to be dead critically set,1mm here or there is ok,humour me and picture a dirt bike pounding around,whats going on in the float bowl?its all over the place,sport bikes hard cornering,hard braking and accelleration,its a #$%*ing washing machine in those bowls!

[Kelly E]

And the epidemic goes on and on, be it only the United States of Absurdistan, if we read the other fora in the world. Here's a question for all those who can't wait to do 'maintenance': when was the last time you did 'maintenance' on one of your car's float assemblies?

The last time I had the Holley carb off my hotrod truck. Here we can have hotrods, build performance engines and put big engines in little cars. Same with motorcycles. Fun stuff and there's not a bunch of government regulations telling us we can't do it.