BS38 Carburetor Issues

[XSLeo]

There are no 70-75 carbs. There are 70-71, 72-73 and 74-75 carbs, they changed every two years. They changed the jetting mostly but in 72 they went from a raised floor carb to a flat floor carb. As well as how the enricheners worked.
Don't buy a kit. Most of the parts in kits won't work. About the only part that will is the float bowl gasket.
This will help ID your carbs www.xs650.fi/pohja_files/fi/XS650carbs.htm
this will help with the tear down, cleaning, inspection, reassembly and adjustments, www.amckayltd.com/carbguide.pdf
Once you tear down, inspect then you will know just what you need to replace.
Leo

 

[BCoop]

I believe I have 447 carbs. The reason for this is that I have two carbs that are not linked. They have two tubes shared between. There is only choke on the left carb and the jets are located in the float bowl. There is no "Solex" on top of the carbs so this has led me to believe they are 1974-75 447 bs38's. If I can give you any info that will help solidify this let me know.

 

[XSLeo]

As mentioned before read the carb guide. It tells you how to tear down, clean, inspect what you have. If something is worn or bad this inspection will tell you this. Replace just what's bad.
Now reassemble and follow the steps in the adjustment section.
Leo

 

[BCoop]

I took out the float needle and the seat. It was really gummy inside. It made me want to soak the carbs in a solution to clean them. Is this more effective than the spray can carb cleaner?

 

[hard_y_rd]

Cleaning the carbs should have been step 1. You have to totally disassemble them to get all o-rings and seals out. Soaking rubber parts is bad. Do one carb at a time.

 

[BCoop]

Yeah I understand I am supposed to clean the carbs. I was really just asking if soaking them is better than using the spray carb cleaner?

 

[XSLeo]

The gallon can carb cleaner work well. You just need to totally disassemble the carb. There are seals on the throttle shafts that need to come out before the dip.
Leave all the non metal parts out of the dip or they won't be usable after.
Using the spray cleaner method works well if done well. And you don't need to do a full tear down.
Leo

 

[nooch]

Hey guys, I have a 78 xs650 I just finished and now having trouble tuning my carbs. I am running with mikes xs performance air pod filters and I have strait through drag pipes. timing is good. idles ok and runs fine from idle to about 3000-3500rpm then starts breaking up pretty bad, like it is starving for fuel. im assuming ill need to re jet but not sure where to start or what size jets to use, as well as what notch I should have my slide needle set at. if anyone can give me a base setting to start with, with the mods I have would be greatly appreciated!

 

[BCoop]

Sorry for the long period between my last update. I recently made the move from Orlando, Fl to Asheville, NC and it has taken my attention for a while. I have finally gotten off the tarp in the elements and into a run down old shed that I can do real work in.

I have a compressor and carb cleaner and will be going through my carbs thoroughly. Just wanted to thank everyone for their helpfull responses so far.

My question right now is with pod filters and open pipes are my jets too small? Right now they're at 127 on the mains and 45 on the pilots. Considering I will be going up and down in altitude all day long I was wondering if bigger would be better for my area? I also live about 45 minutes from Hughs handbuilt so I was considering getting some of his baffles for back pressure.

Any thought would be appreciated.

 

[5twins]

From the jetting you found, it does sound like you have a '74-'75 carb set .....

Yes, some re-jetting will probably be needed. The usual scenario is one up on the pilots and one or two up on the mains but only testing will tell you for sure what's right and works best. The needles may also need to be leaned a step with the larger jets.

 

[XSLeo]

www.amckayltd.com/carbguide.pdf has a "Tuning For Mods" section. It will tell you how to test and what to do with the results of the testing.
But as 5twins said one up on the pilots and one or two up on the mains is a good starting point.
Leo

 

[BCoop]

I noticed today that when I turn my bike over while putting my hand over the end of the left tail pipe there is suction for the first half of the crank and then a pop of air at the end of the full rotation. This does not happen on the right hand tail pipe. I have both the spark lugs and the carbs off the bike at this point. Could this be due to a blown piston ring?

 

[TwoManyXS1Bs]

Might be an exhaust valve. When/where these events occur relative to the 4 strokes (intake, compression, power, exhaust) would be more helpful. A compression and/or leakdown test (on both cylinders) would also be revealing.

 

[BCoop]

I was checking something's out on my day off and realized i may have over filled my engine oil. It is at the top of the fill range almost above it. Would too much oil cause a fould spark plug? If so could I simply drain some oil and see if it solves the problem or is the damage already done to the rings or valves? Ps a compression test is not an option for me at the moment.

 

[peanut]

your ignition sounded retarded to me in your video but we won't go there as you've got your hands full with the carbs at the moment.

Suggest you leave the crankcase to drain completely overnight then refill the next day with the correct amount of oil . Too much oil might blow an oil seal or gasket.

Popping back out of one cylinder is possibly an incorrectly set valve or burnt valve seat.
As twomany says you need to do a compression test if we are to know anything about the condition of your valves and engine.
They only cost $5 surely you can afford to invest that much in troubleshooting your problem ?
http://www.ebay.com/itm/RAC-PSI-KG-CM-Motor-Compression-Tester-Automobile-Tool-Pressure-Gauge-/271551829559?hash=item3f39c01637&item=271551829559&pt=Motors_Automotive_Tools&vxp=mtr

I'm assuming that the engine hasn't run correctly since the pod filters were fitted.? Changing to Pod filters weakens the fuel mixture by giving the engine too much air. As other have said you'll need to rejet the carb to suit the pod filters. As a rough test to prove this try wrapping some gaffa tape around half the pod filters to restrict the air flow and see what sort of difference it makes to starting idleing and blipping the throttle.
You'll probably find a distinct improvement.

 

[BCoop]

Thanks for the reply. I have new pilot and main jets coming in the mail on Monday. I ordered both #42.5 and #47.5 pilots as well as #130 and #135 mains. I am draining the oil tonight and picking up more. I also have new o-rings for the needle jets. My hope is that this will be the end of my carb problems for now. As far as a compression test I wasn't aware of how cheap it is I will definitely do that ASAP and post my results. Also I have a video that I will post so you can see first hand what I'm talking about. If there is something specific that anyone would like to see, let me know and I will get a vid of it up.

 

[BCoop]

Went out to the bike shed to get a video of my problem when I got distracted by my box of new carb hardware. Before I knew it I was swapping parts lol.

Changed the pilots from 45 to 47.5 and the mains from 127.5 to 130. I put new o-rings on the needle jets and installed the carbs. I changed the oil filter element in th right side cover and did an oil change with the correct amount of valvoline 20-50 motorcycle oil for wet clutch's. I then filled up the tank with ethonal free gas and installed new Ngk bp7es plugs.

Started up like a champ and sounded great. Took it around a bit and made some noise. On the way home bike cut out. Luckily I was going down hill so I dropped a gear and dumped the clutch. Got it going and pinned the throttle to get back home.

When I got back I checked the plugs and sure enough dry black carbon all over them. Naturally I thought too rich. So I cleaned the plugs and adjusted the air mixture screw to lean it out. Again it went out.

Then I noticed something strange. When I turned my fuel petcock on the left side of the tank to the on position the fuel would begin funneling into the inline filter but not filling it up. When I looked at the right side inline filter it was filling up all the way to the top. I was perplexed at first but thought ok it cold very well be the float needle or seat on one of the carbs.

Sure enough when I pulled the carbs the right one had a extremely brittle tab on the floats. It was so brittle that when the carb filled with fuel and pressed up against the needle it would actually bend and leave the float needle open. Thus when the fuel was turned on it would essentially over fill and poor into the other carb making it run extremely rich.

I'm getting new floats soon and will go from there.

 

[BCoop]

I also checked and the suction i feel coming through the exuahst pipe while cranking the bike is happening during the intake stroke in the left cylinder. I think perhaps my valve isn't closing all the way or the seal around the valve could be deteriorated. Could adjusting the tappet help seal the valve and solve this problem?

 

[TwoManyXS1Bs]

...When I got back I checked the plugs and sure enough dry black carbon all over them. Naturally I thought too rich. So I cleaned the plugs and adjusted the air mixture screw to lean it out. Again it went out...

There's no air mixture screw. There is a mix screw, it controls the amount of fuel delivered to the idle port. So, it doesn't lean it out. If too rich, normally must rejet.

But, with your rich symptoms, and you suspect a squeak sound, could look into the enrichner system (choke). Maybe the plunger isn't sealing, or its crossover is leaking.

...Thus when the fuel was turned on it would essentially over fill and poor into the other carb making it run extremely rich...

The fuel delivery from the petcock(s) goes to both carbs, they're interconnected. But, the fuel in the float bowls isn't shared, it won't travel to the other bowl. So, that's not why it's running rich.

As far as a compression test I wasn't aware of how cheap it is I will definitely do that ASAP and post my results...

That would help.

I also checked and the suction i feel coming through the exuahst pipe while cranking the bike is happening during the intake stroke in the left cylinder. I think perhaps my valve isn't closing all the way or the seal around the valve could be deteriorated. Could adjusting the tappet help seal the valve and solve this problem?

Adjusting the camchain tensioner, followed by setting valve lash, would be a wise move.

I could imagine that sucking in the exhaust occurring during the power stroke, piston going down, both valves closed with a leaky exhaust valve, pulling a vacuum on the exhaust pipe. But, on the intake stroke the intake valve is open. So, it can't pull a vacuum with the intake valve open, unless the carb is completely sealed shut...

 

[BCoop]

I believe that the carbs do have some function to share over flow of fuel. Otherwise the left side petcock could not fill the right carb all the way to the top and up the fuel line. In fact even when the right side fuel line is disconnected from the petcock and the left petcock is turned to the on position it still flows to the right carb and fills up into the fuel line.

Never the less I will set my valves and cam chain tension ASAP. My choke plunger is in the right position so I think its ok.

I think you are right about the power stroke. I didn't think about the intake valve being open thus relieving any pressure on the exhaust valve. Hopefully a new set of floats will solve my rich problem then it will be on to figuring out the timing. I have read the instructions on ignition timing and have to say it seems complicated to someone like me that has never done it hoping to find a video that will show I first hand.

Thanks for helping me out with this