petcock question

I opened the float bowls .surprisingly clean.no gasket on right side carb .floats in one carb seem to be higher than the other.main jet 140 should be 142.5.starter jet 55 should be 30 .I'll send pics soon.in my manual it says there is a starter jet .yous will see it in the pics.thanks
 
here some pics for u guys.
 

Attachments

  • 20230920_092410.jpg
    20230920_092410.jpg
    125.4 KB · Views: 39
That does not look like the right airbox.

There were two XS400 models in 1981. They were both SOHC. You have a SOHC motor. SOHC intake looks like this:

upload_2023-9-20_17-50-14.png


All that mounts into a metal box that looks like this:

AIL4fc-lN_3nycWLKAW6hzgGW2tXiMUqkMnkmvVcVI__brcxa4PUK3cx9tGMs0PMfFLtdm9-CaeyiOfcwhFw9P5kSKCKV4PiE2rhfeByR2Qpv0ow2ajP9s7Np7HUwWhtwAC9Nb1qbgtS0-2r4LhG8TqqMo4zYuGpAGY5agwyL0YtysqS-va7JixY_5V3RgfdONgLP3S-ucATT2XIe6tPHKiTGUPFqm4BHAWU7JTLfqbM0RJ-9L5H5hWiao8U3hc4H3s05bpGheStddM1wZDhvuktNXT-56DsH6qqpNLzVyzs_ve85fgIzUuLTk101aMhE8fNjzAbDWxmdt_aTFKJwaMM0xDFchs1Ssc61oSGtt895Nd6oGcKwfCoOW0xpwLXepKJrXRbJ7F4mOPQtCy-Z7mb1_-ehCxuzgrYPmorZwgjVKbRG4r5aHhYfN8t11Du0EbEsqJo1YSwcl-XuoQRGD0LbDmTvmV8xG4VO4XOLPBluGXXyBAnskux3kXziR5MsAI8P5IYwB0RXbXmI1wfdm7Vrsz-zUgVj_H1UWc26MSbPGcPznrmEfT9RrQghvUfSy9bk5jPbLhm34VRi1n62xiOT0DR8P6we0UW1W_1cjF-rmHAm-1R_SWZ-LeWWkCQkOb3XQnDRfVqbuNLYVGudpTqbdW_fwXs-y5XgfSMEAFbp36_QinRBy_JKJ62TIIYMt191oi5-v3UuWjcI1OfOTImzLpP4YUlDhjRkiVSAUycjGZ4q5ZlLkp98qN7VjKnH8d0nB8vF9z_5kP31ZvNopKtqAMqK3fSNHiyMO_5An-j5fT05qUtRDSj7qJF_iDs9EfZR-SWJfoiVyF_02J1HQpu_n7C9UMUMDuX7sG_8lxclKDMVhwSBrljZgE_bAZ2qhG4nt0mCVC-zYx-zwBvBhHb0Q=w698-h931-s-no
 
That does not look like the right airbox.

There were two XS400 models in 1981. They were both SOHC. You have a SOHC motor. SOHC intake looks like this:

View attachment 38222

All that mounts into a metal box that looks like this:

AIL4fc-lN_3nycWLKAW6hzgGW2tXiMUqkMnkmvVcVI__brcxa4PUK3cx9tGMs0PMfFLtdm9-CaeyiOfcwhFw9P5kSKCKV4PiE2rhfeByR2Qpv0ow2ajP9s7Np7HUwWhtwAC9Nb1qbgtS0-2r4LhG8TqqMo4zYuGpAGY5agwyL0YtysqS-va7JixY_5V3RgfdONgLP3S-ucATT2XIe6tPHKiTGUPFqm4BHAWU7JTLfqbM0RJ-9L5H5hWiao8U3hc4H3s05bpGheStddM1wZDhvuktNXT-56DsH6qqpNLzVyzs_ve85fgIzUuLTk101aMhE8fNjzAbDWxmdt_aTFKJwaMM0xDFchs1Ssc61oSGtt895Nd6oGcKwfCoOW0xpwLXepKJrXRbJ7F4mOPQtCy-Z7mb1_-ehCxuzgrYPmorZwgjVKbRG4r5aHhYfN8t11Du0EbEsqJo1YSwcl-XuoQRGD0LbDmTvmV8xG4VO4XOLPBluGXXyBAnskux3kXziR5MsAI8P5IYwB0RXbXmI1wfdm7Vrsz-zUgVj_H1UWc26MSbPGcPznrmEfT9RrQghvUfSy9bk5jPbLhm34VRi1n62xiOT0DR8P6we0UW1W_1cjF-rmHAm-1R_SWZ-LeWWkCQkOb3XQnDRfVqbuNLYVGudpTqbdW_fwXs-y5XgfSMEAFbp36_QinRBy_JKJ62TIIYMt191oi5-v3UuWjcI1OfOTImzLpP4YUlDhjRkiVSAUycjGZ4q5ZlLkp98qN7VjKnH8d0nB8vF9z_5kP31ZvNopKtqAMqK3fSNHiyMO_5An-j5fT05qUtRDSj7qJF_iDs9EfZR-SWJfoiVyF_02J1HQpu_n7C9UMUMDuX7sG_8lxclKDMVhwSBrljZgE_bAZ2qhG4nt0mCVC-zYx-zwBvBhHb0Q=w698-h931-s-no
thanks for that. when I bought the bike the owner gave me a box of spares. this air box must be for a different model.i doubt I'll need to run the bike with these stubby filters.ive had the carbs off readjusted the floats as per manual. havnt tried to start the bike yet.do I need to bleed the fuel system. when I open the float bowl drain screw no fuel is coming out ?
 
No bleeding of fuel needed. Once the flow starts (either by vacuum petcock or you selecting 'prime') then both carbs fill and their respective floats halt the flow.

Suggest getting gaskets for the bowls else they are likely to leak when the floats are properly set.

Your airbox is missing one of the boots, so not usable unless you can find a replacement. Meantime if you have separate pod filters then use them. OTOH if I understand above that airbox doesn't fit your bike anyhow...

Suggest do not mess with the jets in the air inlets pictured in post #45- just make sure those passages are clear. Same with the jets accessed via the bowl. The time to consider changing the bowl jets is once you get the rest of the carb system sorted out and working properly.

Suggest not messing with the butterfly assembly, except perhaps to get their balance adjusted so they both are equally closed. I'd do it by backing out the idle adjust till one of them is closed, then adjust the balance screw until both are closed. Then they'll at least be close, and the idle adjust is done while running the engine.
 
No bleeding of fuel needed. Once the flow starts (either by vacuum petcock or you selecting 'prime') then both carbs fill and their respective floats halt the flow.

Suggest getting gaskets for the bowls else they are likely to leak when the floats are properly set.

Your airbox is missing one of the boots, so not usable unless you can find a replacement. Meantime if you have separate pod filters then use them. OTOH if I understand above that airbox doesn't fit your bike anyhow...

Suggest do not mess with the jets in the air inlets pictured in post #45- just make sure those passages are clear. Same with the jets accessed via the bowl. The time to consider changing the bowl jets is once you get the rest of the carb system sorted out and working properly.

Suggest not messing with the butterfly assembly, except perhaps to get their balance adjusted so they both are equally closed. I'd do it by backing out the idle adjust till one of them is closed, then adjust the balance screw until both are closed. Then they'll at least be close, and the idle adjust is done while running the engine.
thanks for your reply.think I've messed up with the floats .set them as per manual and they must be out couldn't start the bike took carbs bk off.no fuel in them .have I set the floats to high making the needle stay in shut position. also should the butterfly's be closed tight with no gap .thanks
 
thanks for your reply.think I've messed up with the floats .set them as per manual and they must be out couldn't start the bike took carbs bk off.no fuel in them .have I set the floats to high making the needle stay in shut position. also should the butterfly's be closed tight with no gap .thanks
right enough. I had adjusted floats incorrectly. the settings I used were for the 250 and 360cc .oops.found a good video on utube ,adjust any floats with no tools required. got the bike going took lots of choke and throttle. very smoky.going to tune it tomorrow. also would only run with that pipe going from carb to carb .maybe needs tuning with this pipe disconnected and caps on each carb.
 
if its white gasoline smelling smoke then you are running choking rich, fuel dumping into the cylinders. That could be float position and/or needle/diaphragm.

I think I'm failing to communicate about the butterflies. They are held open by the idle adjust screw, that is adjusted to get a reasonable idle rpm with the throttle released. Butterflies should both be approximately the same position, which is controlled by the balance screw. Don't worry about closed or not- that will be worked out as you get the idle stabilized.

Only running with the pipe going between the 2 intake boots suggests carb setup is a mess.

What do the spark plugs look like- wet with fuel and caked carbon?
 
Suggest getting gaskets for the bowls else they are likely to leak when the floats are properly set.
Good call.

Your airbox is missing one of the boots, so not usable unless you can find a replacement.
His airbox isn't for his bike. He is missing a lot more than a boot.

do I need to bleed the fuel system. when I open the float bowl drain screw no fuel is coming out ?
The fuel system is the petcock, three inches of rubber hose, four inches of vacuum hose, and the carburetors. There isn't anything to bleed.

Carburetors work not unlike toilet tanks - they fill till the floats shut off the flow. The whole thing is gravity fed.

Petcock is really just a three-way valve. PRI is open and should flow freely. RES is the same, but it feeds from a different inlet lower down in the tank. ON is controlled by the vacuum valve and flows when the engine is turning and sucking air, and when the vacuum hose is connected to one of the nipples on the intakes. Doesn't matter which one has the tube and which one has the cap.

So. Disconnect the carbs.

If you set your petcock on PRI, and nothing comes out of the fuel hose, you need to fix the petcock. Or you are out of fuel.

Once you have that fixed, you can get on fixing the carbs. Or, you need a test fuel bottle.

very smoky
That's running rich. Floats may be too high.

would only run with that pipe going from carb to carb .
You need something on the carb nipples. Tube, caps, vacuum hose to a functioning petcock.

So, if "with the pipe" is the opposite of "with nothing on them", that's normal. If the other way you tried it was with two caps, then it isn't normal and something is out of whack.
 
hi.wish I hadn't set eyes on this Project bike.im 100% sure the floats are set correct.the needle diaphragms were checked.no splits or grazing, holes etc.the tank half full of fuel.at reserve and on no fuel flows just occasional drips ,full flow at prime .ive ordered a new gasket set for the petcock.ive attached a clear piece of fuel line so i can see if working when set at the on position. managed to set carbs using adjustment screw.when I started the bike I didn't let it run long enough to get to operation temperature had to keep it going with the throttle was late on at night didn't want to wake the neighbours as its pretty noisy. I'm going to remove the tank ,I have a small plastic tank that I can hang from the handle bars and will connect to the carb.get the bike going and hopefully with some carburettor adjustment will get some result.i think someone has been messing with the air screw.manual says 1 and a quarter turn out from seated .I reckon at present they are 3 and a half turns out from seated?hopefully get the bike started up in the nxt couple of days.just going to keep those cone filters .I'll keep yous posted. thanks
 
Yeah old bikes are never easy to straighten out- takes a while. I think of it as a method of practicing patience, and its a lot more useful than watching tv or facebook.

Small plastic tank really helps, I do the same :) If you can get to the A/F screws then put them in the factory positions. Keep the sparkplugs only snug, it will be helpful to pull them occasionally and see how the engine is running.

Once you get it started, if you can keep it running by cracking the throttle open a bit, thats the time to bring in the idle adjust screw to keep it running when you let go of the throttle.
 
Yeah old bikes are never easy to straighten out- takes a while. I think of it as a method of practicing patience, and its a lot more useful than watching tv or facebook.

Small plastic tank really helps, I do the same :) If you can get to the A/F screws then put them in the factory positions. Keep the sparkplugs only snug, it will be helpful to pull them occasionally and see how the engine is running.

Once you get it started, if you can keep it running by cracking the throttle open a bit, thats the time to bring in the idle adjust screw to keep it running when you let go of the throttle.
thanks yes I'm doing a lot of head scratching. your right a lot of patience needed. what's your method of setting the float height and needle. with the carbs sitting and floats dangling the needle was only about a third out its housing is that not enough or to much?
 
thanks yes I'm doing a lot of head scratching. your right a lot of patience needed. what's your method of setting the float height and needle. with the carbs sitting and floats dangling the needle was only about a third out its housing is that not enough or to much?
I ment to say .I haven't pulled the plugs yet as I don't have a socket to fit.an old mechanic told me .to thrash the bike in first gear .then hit the kill switch.dont stop the bike with the ignition key.take your plug out .this will give u a good idea how your mix is
 
lol, maybe... but its also helpful to keep an eye on them while debugging the setup eg is one cylinder running rich or lean, are the plugs worn out/broken/misfiring or not and so on.
 
Back
Top