Topic: Only #1 runs very rich, carbon fouls in 45 miles, WORST NIGHTMARE just happend

[USCG_C130]

Hey guys my 73 CB750 build is about done and my only big issue remaining is that #1 plug will carbon foul in about 45 miles. All my other plug run great and are a very nice golden brown. I have checked the spark, the jet passages, the float levels, choke and it's all good all my jets and clip positions match and my A/F screws are all match at 1 1/2 turns out. And today after posting on my build thread I went and checked my intake boot and found some fluid on it, the fluid smells mostly like wintergreen oil so it's hard to tell, but I'm sure it's fuel. Would this cause the plug to run as rich as it is?

Also this morning I put a brand new plug in it and started it up for 30 seconds to a minute and then pulled the plug, and it was wet with fuel and already black, I never went more than about 1/8 throttle, so I know it's an issue with the idle circuit for sure

Here's some pictures of the boot, would this indicate an issue? And cause the rich condition?

[harisuluv]

did you move the clamp to take the picture?  cause it's off and unclamped in the picture

[Black 750K8]

+1 Hari First thing I saw so why is the clamp like that?

[USCG_C130]

Lol yea, sorry I didn't mention that  I moved it to look for cracks and holes or anything out of the ordinary, but it normally is I'm the normal position, just needed to look under it and take pictures.

Will a air leak like that cause it to be so rich.

[Duke McDukiedook]

No, a leak would cause a lean condition due to too much air entering the combustion chamber.
Check your float level and your plug wire end and cap to make sure it is bringing the spark.
 

[Trad]

Are you sure it's gas fouled and not oiled fouled? compression test? Could have piston/ring/jug wear causing blow by on cylinder 1. Just a thought if the carbs are all tuned the same.

[USCG_C130]

Yea pretty sure it's not oil, when I pull the plug it smells like fuel and it isn't slick like oil buried can always double check, and I have double checker the float level. I know it gets a spark but I will investigate that further.

What are the possibilities of the needle being worn or is there a guide or something it slides though that could be worn? Sorry for the short resposes, I'm at work and stuck here for 24 hours

[harisuluv]

No, a leak would cause a lean condition due to too much air entering the combustion chamber.
Check your float level and your plug wire end and cap to make sure it is bringing the spark.
 

In Hondaman's book he says that an air leak like this (hypothetical) on "pulse type" carbs as opposed to CV carbs can actually cause a RICH condition. 

[harisuluv]

What are the possibilities of the needle being worn or is there a guide or something it slides though that could be worn? Sorry for the short resposes, I'm at work and stuck here for 24 hours

It could just be #1 is out of sync?  Check the easy stuff first I would think.  Oh by the way, what does the other end of the carbs look like?  you can get leaks on the other end too.

[USCG_C130]

No, a leak would cause a lean condition due to too much air entering the combustion chamber.
Check your float level and your plug wire end and cap to make sure it is bringing the spark.
 

In Hondaman's book he says that an air leak like this (hypothetical) on "pulse type" carbs as opposed to CV carbs can actually cause a RICH condition. 

Thanks harisuluv, I have hondamans book, but my buddy who is rebuilding a 76 cb750 has it, I will have to scoop it up this weekend,  and as for the other end it is clean, only leaking at one end I will try to work on seating and clamping that end mAybe trying the spacer thing between the clamp and boot.

[HondaMan]

Hey guys my 73 CB750 build is about done and my only big issue remaining is that #1 plug will carbon foul in about 45 miles. All my other plug run great and are a very nice golden brown. I have checked the spark, the jet passages, the float levels, choke and it's all good all my jets and clip positions match and my A/F screws are all match at 1 1/2 turns out. And today after posting on my build thread I went and checked my intake boot and found some fluid on it, the fluid smells mostly like wintergreen oil so it's hard to tell, but I'm sure it's fuel. Would this cause the plug to run as rich as it is?

Also this morning I put a brand new plug in it and started it up for 30 seconds to a minute and then pulled the plug, and it was wet with fuel and already black, I never went more than about 1/8 throttle, so I know it's an issue with the idle circuit for sure

Here's some pictures of the boot, would this indicate an issue? And cause the rich condition?

Set the air screws to 7/8 to 1 turn out, not 1.5 turns. That value is for bikes with PD carbs, like the F2/3 or K7/8 bikes. At 1.5 turns out, you're running about 8:1 A/F mixture, which will certainly wet things down, quick!

[USCG_C130]

Hey guys my 73 CB750 build is about done and my only big issue remaining is that #1 plug will carbon foul in about 45 miles. All my other plug run great and are a very nice golden brown. I have checked the spark, the jet passages, the float levels, choke and it's all good all my jets and clip positions match and my A/F screws are all match at 1 1/2 turns out. And today after posting on my build thread I went and checked my intake boot and found some fluid on it, the fluid smells mostly like wintergreen oil so it's hard to tell, but I'm sure it's fuel. Would this cause the plug to run as rich as it is?

Also this morning I put a brand new plug in it and started it up for 30 seconds to a minute and then pulled the plug, and it was wet with fuel and already black, I never went more than about 1/8 throttle, so I know it's an issue with the idle circuit for sure

Here's some pictures of the boot, would this indicate an issue? And cause the rich condition?

Set the air screws to 7/8 to 1 turn out, not 1.5 turns. That value is for bikes with PD carbs, like the F2/3 or K7/8 bikes. At 1.5 turns out, you're running about 8:1 A/F
mixture, which will certainly wet things down, quick!

Thanks hondaman will do!

[dave500]

how old are the plug caps?resistance check them.

[USCG_C130]

All coils, condensers, points, leads, caps and plugs are brand new and spark seems good, I will cut the #1lead and make sure its getting a good conection, and I haven't check thw cap resistance but it is brand new. It is sparking against the engine case. But thanks for all the good advice and things to check.

[dave500]

check it anyway as you have a problem,even new might be dud out of the box?

[Vinhead1957]

Sounds more like the float is either sticking so it won't cut off fuel when is supposed to or the float valve is bad.

[dave500]

i think it would flood and spew fuel from that carb if that was the case?

[USCG_C130]

Sounds more like the float is either sticking so it won't cut off fuel when is supposed to or the float valve is bad.

Vinhead I thoughththat was a possibility too too but thought, like Dave said that it would then puke, but non the less u took the bowl off and made sure the valve was closing and sure enough its closing just fine, so I know the level is correct and the valve is shutting off  fuel. I also float test the floats and then don't seem to be absorbing fuel or water when I checked them

[Vinhead1957]

Mmmm.  Could one of the valves be maladjusted where it isn't seated when closed?

[mitchie]

Check the most simple thing... The float stuck? 

[USCG_C130]

well now that i am home i have a few things to add.

first of all can i just swap #1 and #4 plug leads or will that mess it all up?

also i checked my caps and  #4 (the good cylinder) reads 5.34 Ohms and #1 (the trouble maker) reads 4.84 Ohms


i am searching to see if i just swap the #1 and #4 leads if ill hurt anything before i start it up.

[mitchie]

well now that i am home i have a few things to add.

first of all can i just swap #1 and #4 plug leads or will that mess it all up?

also i checked my caps and  #4 (the good cylinder) reads 5.34 Ohms and #1 (the trouble maker) reads 4.84 Ohms


i am searching to see if i just swap the #1 and #4 leads if ill hurt anything before i start it up.

You could try pulling the ends off and swapping them... But that little resistance difference is not enough to make a difference....  I'll bet it's fuel.

[USCG_C130]

okay well i found that it wont hurt anything to swap leads, so i did and just ran it quickly, and letting ti cool a few before i pull the plugs, i also trimmed #1 a bit and put it back into the cap, but mitchie, i think you're right and its a fuel/carb issue so ill update soon.

[mitchie]

Keep it simple first... Check to see if the float / valve is sticking on that cylinder...  Just pull the bowl off..... Cycle it up and down a few times or even pull the float off and check the valve... reinstall and try running it.  That's the easiest thing to try....  Every time I have had an ignition problem it has resulted in misfires.. Not dying cylinders.  Unless the wire is not making contact with the ends.

[USCG_C130]

well #$%*, my worst nightmare just happened, can we name this part and see whats wrong with the picture, theres a clue in the background. ohh man gunna be a while till shes back to running condition.