[Maxparker]

Looking for some help with this problem getting gas in my crankcase.
Heres the story in order for the last few weeks...
Riding around 60mph for about 20 mins bike started to lose power on acceleration at around 50 mph just a little bit,( like when im low on gas and i think the weight in the tank helps gravity feed the carbs). Stopped at a gas station, filled it up, didnt change anything. Got home, checked plugs, good, checked oil, bad. Smelled pretty strong like raw gas.
Emptied it out right away. Left it draining and open to air out for a couple days.

Pulled carbs, ordered carb rebuild kit from common motor, got new oil, in the meantime adjusted cam tension, valves, points, cleaned carbs, did the carb rebuild, double triple checked float needle valve and petcock, checked floats, height, bench synced, bike synced, oil changed, centrifugal oil filter cleaned, did the carb rebuild new fuel lines, checked crancase breather hose is working.

Ok so i just did all that, and i start it up today, it sounds beautiful, Only had it running for about 7 minutes as i dialed in the idle and mixture screws, turn it off, and it smells like gas in there again. I imagine some lingering smell is going to be there but im pretty disapointed.

Here are my specs, they are probably wrong as ive had a hard time getting straight info about the carbs.
71' cb350 k3
3-d kei hin carbs
float height 24mm round floats
2.2 float valve
Main jet 105
Secondary 68
pilot 35
Air mixture 1-1/8 out
Valves inlet .002
Exhaust .004
Stock airbox
stock exhaust
Compression perfect 170 both sides

Any help would be very much appreciated, im kind of lost as to what i should do next.

 

[Boomer343]

Float level spec is 26mm, I set mine to 27 to 27.5. Fuel density has changed a lot since the 70's. Make sure you are setting them using the proper method in the FSM. The float specs are the same for the 3D and 722A carbs, your jet sizes are typical.
Aftermarket carb kits can be a crap shoot. I have had issues with the o-rings sealing. Pilot jets are usually oversized compared to OE.
Honda has an o-ring set available, they call it a gasket set.
You may be overly sensitive to the fuel smell if you are comparing it to a new FI engine.

Bikes that have no overflow tubes are known to have issues when the carbs overflow and the fuel has no place to go but into the cylinders and crankcase.

 

[Maxparker]

Float level spec is 26mm, I set mine to 27 to 27.5. Fuel density has changed a lot since the 70's. Make sure you are setting them using the proper method in the FSM. The float specs are the same for the 3D and 722A carbs, your jet sizes are typical.
Aftermarket carb kits can be a crap shoot. I have had issues with the o-rings sealing. Pilot jets are usually oversized compared to OE.
Honda has an o-ring set available, they call it a gasket set.
You may be overly sensitive to the fuel smell if you are comparing it to a new FI engine.

Bikes that have no overflow tubes are known to have issues when the carbs overflow and the fuel has no place to go but into the cylinders and crankcase.

Thanks boomer,
I am going to set the floats to 26 when i open Them up again. However, i do have overflow tubes and they are clean and im watching them like a hawk.
I cant imagine that the gas would not go down them and still escape into the crankcase. It seems like its happeNing while its running, and it is running a little rich, but i would think i would notice if its getting more fuel than the engine can use and contaminating the oil in like 5 minutes of idle.

right now i have tape marking my fuel lines with petcock off and fuel is moving up and down in both of them. I dont think its a great method of monitering but i feel like my nose to the dipstick isnt great either.

i blew into valve needles directly with gas line pressed againstvalve seal right before assembly and it was a good seal. The bike sounds great, it idles smooth, good throttle response, im just afraid to ride it and run it with the fuel problem

Also, if i did do any damage to my bearings, what would i be looking/ listning for? Other than knocking and obvious bearing failure?

does anyone have any method to accuratly checking for fuel in oil? I know thar gas will rise to the surface as its lighter than oil, could it be that im just getting a very thin surface residue that rises when it warms up?
Thanks

 

[Maxparker]

Also, to clarify, By fuel moving in lines, i mean very very slowly, like 1/4 - 1/2 inch over a few hours and i just looked this morning and they have barely moved past my tape marks all night,

 

[Boomer343]

Fuel expands and contracts quite a lot due to temperature so watching it in your fuel lines is probably not a good indicator.

The only way I know to establish what is in your oil is to send a sample to a testing lab.

The most vulnerable area is the camshaft for oil issues as it is steel running on aluminum. The bottom end has very few oiling issues in my experience. Do some research on fuel contamination of engine oil, it will probably surprise you what is considered normal.

Definately address the rich mixture and I would suggest upgrading coils as well to get a better spark thus better combustion.

 

[Maxparker]

Thanks again, boomer. That makes sense as now the fuel is cold and staying in my lines... on the lines on my lines.
i did just find a new clue, on my left carb on the inside of the top of the float chamber there is a brass hole, on the opposite side above the gasket surface, there is a little brass stem, this stem seems to be weeping gas, what is this for? Air escape passege?
also the little ball valves on the bottom of where the air filter goes on are also wet with gas, hopefully these pictures come through

 

[Boomer343]

Brass tube on the side is an air vent, very small hole on the side of the tube and a small hole inside the float chamber. Should be drier than what shows in the photo, same for the ball that seals a drill passage .... but that is an internet observation and not a diagnosis.

BTW if you followed common motors videos on how to tune carbs you have introduced a lot of raw fuel into your cylinders that will wash down into the crankcase.

 

[Maxparker]

Yes, i did watch those videos... they say set the floats at 23mm, i went 24mm because my manual says between 23 and 26mm. Im going to go 26 now.
Pretty frustrating, i want this gas out of there.

what else would i have done wrong from their videos?
I bench sync them with high e guitar string, (9gauge i think) so the string just drags out with throttle closed as they say to do in that video

Another confusing part is my air mix screw,my manual actally says in lean out rich, and says the opposite, and it also says 3/4 turn out, and also 1-1/8 out
so assuming that in is rich out is lean is true, i opted for the leaner side 1-1/8 and i havnt even gotten to riding and looking at the plugs yet, hopefully soon

Thanks so much for reading and for your advice!

 

[Montanabill]

Make sure your float bowl overflow hoses are clear and unobstructed clear thu to the float bowl. I have seen them plugged which will drive you crazy. The fact you are getting gas out the small brass vent points toward something amiss with the drain hoses. I have seen people "fix" the leaky hose by plugging it or connecting it to the other carb.
My general rule on some older bikes is to adjust the floats till it doesn't leak and the bike still runs well.
As far as gas in the oil once you get the carbs sorted take the bike out and run it on the road. Get it good and warm and that should take care of a small amount of gas. The human nose can detect gas vapors in very small quantities.
And be kind to your air cooled engine and don't run it for many minutes idling and not moving.
An ultrasonic cleaner and a new O ring kit if at all possible rather than the cheap carb kits that sometimes work, just my experience working in shops for the past 45 years and owning multiple 350's myself. Here's a photo from a couple weeks ago on a trip on my 77 XL350....it snowed the next day here in montana.

 

[Maxparker]

Make sure your float bowl overflow hoses are clear and unobstructed clear thu to the float bowl. I have seen them plugged which will drive you crazy. The fact you are getting gas out the small brass vent points toward something amiss with the drain hoses. I have seen people "fix" the leaky hose by plugging it or connecting it to the other carb.
My general rule on some older bikes is to adjust the floats till it doesn't leak and the bike still runs well.
As far as gas in the oil once you get the carbs sorted take the bike out and run it on the road. Get it good and warm and that should take care of a small amount of gas. The human nose can detect gas vapors in very small quantities.
And be kind to your air cooled engine and don't run it for many minutes idling and not moving.
An ultrasonic cleaner and a new O ring kit if at all possible rather than the cheap carb kits that sometimes work, just my experience working in shops for the past 45 years and owning multiple 350's myself. Here's a photo from a couple weeks ago on a trip on my 77 XL350....it snowed the next day here in montana. View attachment 319100

Make sure your float bowl overflow hoses are clear and unobstructed clear thu to the float bowl. I have seen them plugged which will drive you crazy. The fact you are getting gas out the small brass vent points toward something amiss with the drain hoses. I have seen people "fix" the leaky hose by plugging it or connecting it to the other carb.
My general rule on some older bikes is to adjust the floats till it doesn't leak and the bike still runs well.
As far as gas in the oil once you get the carbs sorted take the bike out and run it on the road. Get it good and warm and that should take care of a small amount of gas. The human nose can detect gas vapors in very small quantities.
And be kind to your air cooled engine and don't run it for many minutes idling and not moving.
An ultrasonic cleaner and a new O ring kit if at all possible rather than the cheap carb kits that sometimes work, just my experience working in shops for the past 45 years and owning multiple 350's myself. Here's a photo from a couple weeks ago on a trip on my 77 XL350....it snowed the next day here in montana. View attachment 319100

Thanks Bill!

Appreciate the tips! I just rebuilt the carbs, new floats, jets, and petcock, as well as cam, valves, and points, and i believe ive solved the fuel oil problem. I do think im a little extra sensative to gas smell now, but im pretty sure my petcock was leaking a tiny tiny bit, floats were too high, possibly pushing gas out vent tube, and also the time spent idling trying to tune didnt help either, but yes, those drains are clear, and im pretty happy with how its running. I think i have to go back in and check my valves again because im getting a bit of tapping noise, however, from what im reading, if my specs are good and im accurate with my settings it could be normal to have some valve tapping. Hopefully im back on the road soon!
Looks beautiful out there in montana!
Thanks!

 

[Maxparker]

Thanks everyone for your help! Update, the bike runs perfect now. Very happy, had to do everything twice, but it made me do it all twice as careful and it paid off, thanks again,
Max