Carb problems

[yaggis57]

Hi folks I,m struggling with carbs.
Bike will only run with choke on just dies when pushed in.Also whilst running on choke if I try and accelerate engine just dies.Is there one jet or hole that is more likely to cause this as I have cleaned the carbs a couple of times and the jets etc seem clear.I am only running the bike with a tube to the carbs which I keep topping up no tank connected does that make a difference.I have set mix screw to 3 turns and the bike starts very well any ideas please.

 

[Scorpio1963]

Are you missing the vacume port on the left hand side carb?Should have a plug covering it up.Also check out the many carb threads here on the site,theres a lot of threads covering carb issues.Good luck

 

[xschris]

Make sure you have a good supply of fuel for the carbs. What air filters and exhaust do you have? Also when you cleaned the carbs did you take them completely apart and clean everything including the needle jet and all the tiny holes the carbs have? Next I would check your float height witch should be 26mm with brass floats.

 

[yaggis57]

Vacuum port cover is in place I have original new air filters exhausts are not original but are very similar in length and diameter so I wouldn't expect too much difference.I think I've cleaned all the holes in the carbs but I havn't checked float height think I will clean them again and check float height.
As I said before I am not using the tank for fuel supply therefore the vacuum pipe from the fuel tap to the right hand carb is not connected would that make any difference.

 

[xschris]

Make sure both the barbs are plugged if you don't have hooked to the tank. Also when cleaning the carbs make sure the float bowl holes are open and clear. If you put carb cleaner in the top hole it should come out the bottom. 150# of compressed air works well too, also for the rest of the carb.

 

[Scorpio1963]

Heres what I did when i was testing my bike to start before.I took an oil bottle
9plastic) drilled a hole on the lid of the bottle for a piece of clear fuel line to fit snug.Ran it to the fuel inlet on the carbs and bike ran fine that way.If you have an air leak through your container with fuel more than likely your sucking air also.The bike will hardly run.Like as mentioned check your floats I dont have the exact measurement in my head but that answer is probaly in this thread already or on the forum if you search it.YOU HAVE TO CHANGE THE WAY YOU ARE FEEDING THE FUEL INTO YOUR CARBS ITS PROBALY MOST OF YOUR PROBLEM.No I wasnt yelling with the caps it just my way of saying how important this is with alot of emphasis on important.Oh also keep the bottle at the or near the level of the tank.I have learned this trick many years ago being an auto mechanic bypassing electric fuel pumps that have failed.

 

[yaggis57]

Can anyone tell me what rpm my xs400 should tickover and at what rpm should it tickover when choke is on

 

[xschris]

1200 rpm's is a normal idle. With choke it will be higher but with no specific number.

 

[yaggis57]

My pilot screws do not have the washer and seal that most people seem to mention on the forum looking in the haynes manual at the two position choke type carb, which mine is, it only shows the screw and spring is this correct. I can now get the engine to rev if I start the bike with kick and work the throttle but still no tickover.I have not yet taken the pilot jets out think thats next have cleaned and checked everything else.

 

[xschris]

Yes the pre-80 bike don't use a washer. I would make sure all the passages are clean including the pilot jets and set the idle mix screws to 3 turns out from seated. Check and make curtain that those screws have not broken off in the carb bodies it is very common. Always have air filters and mufflers on the bike or it will not idle proper. After all of that you should use a manometer to sync the carbs.

 

[yaggis57]

Thanks Chris for your input. Call me stupid - is the hole at bottom of pilot jet supposed to be clear or sealed? The top hole & 6 side holes all now clear but I dont want to try clear the bottom one if its supposed to be sealed.

 

[XSLeo]

All those holes must be clear. The bottom one is where the fuel flows through. The side holes are where the air gets drawn through. The jet mixes air with the fuel then delivers it to the idle circuits.
Leo

 

[yaggis57]

Thanks Leo Bottom holes(thin end of jet) were blocked. Both now clear! Hopefully that could have been at root of my problem. watch this space ...

 

[yaggis57]

success at last we have tickover and revs give or take a bit of fine tuning

Thanks for help

 

[Anthonyvan]

I need some similar help with my carbs =( I have a 2-1 mac megaphone exhahst on a 79 xs400 sohc. I'm running pod filters on a fully rebuilt motor. New rings, timing chain, tensioner, slider guides, and a freshly sealed motor with new gaskets everywhere.

My "quarter throttle" range is normal and strong

My mid throttle spits and sputters, and, if not riding, it will kill the bike. If running, when I hammer the throttle it will sputter past the middle throttle range until it hits full throttle range and then it flies like a bat outta hell!

To get the bike running (as good as possible) it has required me taping off one pod filter fully, this restricting airflow to one pod filter. It also will only run on half choke. Today I jetted to a 140 main jet, (which made an awesome difference with power as I'm running with the pods and an open exhaust with no baffle), and I raised my needles a clip, well see where it goes tomorrow, but my main question is... Is there anything in specific, such as a different jet I have not attended to, that would heavily affect my middle throttle range? Someone please help! I'm so close to being done!!!

 

[xschris]

Your mid range is the needle jet. Make sure all the holes in it are clean. What type of " pods" are you running and what clip are you on the needle. How about some pics of the bike.

 

[Anthonyvan]

They're just some cheapo pods I grabbed off ebay, and I just readjusted the needle last night, (I moved it up, so it's one clip away from the very bottom clip). I'm yet to run it with that needle setting, about to here soon. I'll see if I can't get some pictures up! It's come a long way! So the needle jet, is that the jet that's beneath the flathead screw?

 

[Anthonyvan]

Not sure if that loaded correctly, here's a picture though

 

[Anthonyvan]

That needle setting was a no go, bogged it down, definitely too rich. I'll go back to the middle clip and resize my needle jet first thing mañana! Any idea what is the stock needle jet size?

 

[xschris]

From left to right. Needle, needle jet and main jet. Did you remove the needle jet and clean all the tiny holes?