carburetor idle problemo

[Gregory]

Hi dudes Im new around these parts. Well new as far as posting goes, Ive used this site for reference for a while now and it has been a life saver. Thanks. So hopefully someone more experience than I can advise me on my problem. Now Im gonna lay it out.

xs400
right cylinder not firing on idle (spark plug tells me its running rich)
new points, condenser, spark plugs, wires, timed to perfection, nice fatty spark!

pod filters, emgo shorty mufflers, 3 sizes up on pilot and main jets (maybe a prollem?)

ok so the carbs have been disassembled, cleaned, reassembled 586 times and the result is always the same... right cylinder does not fire on idle! carbs balanced by eye, all passages in carbs cleared with compressor and air, idle screws turned out 2.5 rotations.

the last time i had the carbs off, cleaned, and back on I got the bike idling perfectly. whilst celebrating with a cigar and some whisky when the bike idled high then stopped runnin. I had forgotten to connect nipple on the right carb boot to the petcock. the spark plug told me the cylinder had been running a wee bit lean at that point.

Soooo I conclude that somehow the right carb is giving excess fuel into the cylinder at idle or the idle air passageway in the carb is blocked (I do not think this is it as I made sure the passageway was cleared. Is there any way the carb would be squirtin more fuel into the cylinders at idle besides using the idle passageway? the choke is fine, not stuck open or anythin... im officially stumped...

 

[bcware]

The pilot is probably too large.

I ran pods and emgo shorty mufflers on my '78; +2 on the mains +1 on the pilots. Going to +3 on the mains would probably be fine for colder weather/higher elevation. I could maybe bump the pilot to +2 (especially when it's colder out), but +3 sounds too big. It's possible to tune it down with the screws, but I've never gone that big.

Also, do a proper synch; eyeballing it is often enough to get the bike running, but not well.

What is your float height? If you're flooding even a little bit your idle will be fubar.

How is your float needle action? Do they both open and close the same? Is the spring-loaded protrusion on the back of the needle moving smoothly and is it springy?

 

[16VGTIDave]

You need to buy or borrow a vacuum gauge to adjust each carb for best idle mixture. Counting turns is just a baseline to get the bike running.

Once you have each carb adjusted for strongest idle, you will need to sync the carbs. I use a length of clear vinyl tube with ATF in it to sync them. Instructions on making and using it can be found by using the search function.

Hopefully these 2 steps will resolve your idling issues.

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[Gregory]

thanks fellas! whats the appropriate float height? do i measure from the gasket or the bare metal? yea my float needles are new and the springy things are workin great.

Correct me if I am wrong but I need to get the right cylinder at least firing before I balance carbs. I have adjusted the balance screw both ways and compensated with the air/fuel mix screw to keep the bike running... in all scenarios, only the left cylinder fires at idle.

It just baffles me that the left side runs so stinkin well with the same setup as the right side...

 

[bcware]

For your '77, assuming you have the same brass floats as I do, about 26mm should do the trick. This is measured from below the gasket. If the gasket is in place and you're measuring over it you need to adjust accordingly (add the height of the gasket).

Example:

26mm measured without a gasket might be 24mm with a gasket in place. You add the height of the gasket (about 2mm I'd bet) to get a 26mm height.

 

[Scorpio1963]

Have you checked both bowls for fuel?Not sure what your jetting combination is from but as BC said 2 up mains 1 up pilot.If both bowls got fuel then sync the carbs that should help the other side.

 

[Kdog]

This is amazing, I also have a 1977 XS400, doing the EXACT same thing, all rebuilt carbs, taken on and off 34223 times, cleaned over and over…and the floats were wrong at first and at 26mm the bike runs like a scalded dog…EXCEPT at IDLE…same thing right cylinder will be cold at times. Won't idle well, or at all…..sometimes popping on the right cylinder. So my bike is stock, stock mufflers, all sealed. Electrical all new, all timed good spark…Emgo air filters in original boxes. I just finished putting it all together tonight, at 9:30 in my shop opened up the fuel line and ..outta gas, so the next test will be tomorrow….

Now the only thing I am wondering about is this…I do not have the original petcock (vacuum) I run a regular gravity feed petcock…and I have the vacuum on each intake plugged (capped). My carbs are all rebuilt and can not believe what would make the bike act this way….I am down to timing again? or Syncing again (which wouldn't hurt anyway).

Open to ideas or solutions on this one.

 

[16VGTIDave]

Check the valve adjustment. Then adjust the pilot screws for the strongest idle on each cylinder. Then sync the carbs. If the pilot screw makes no difference in the running of the engine, clean the carbs properly...

 

[Gregory]

pilot jets switched back to 42.5, mains still at 150... right cylinder still firing rich all the time, really rich at idle, and not very hot at idle... not gettin much white smoke out of the right side when i rev it up now though... left cylinder is supposed to fire hotter all the time right? heard this somewhere in the past... is it possible that fuel is not vaporizing correctly going into the right cylinder? could my jet needle have something to do with this? whats the cheapest/easiest way to balance carbs?

side note: just checked my petcock diaphragm today, there was evidence of it leaking so i checked the diaphragm material had no tears so I resurfaced both surfaces, the cap surface appeared to be warped... I tested with the tank on prime and the vacuum nipples plugged and same thing... so im ruling out the petcock leaking...

 

[Gregory]

how do i check valve adjustment?

 

[Gregory]

my bike

 

[bcware]

150 mains are huge. I honestly think you're way too big. I tuned my bike with basically the same setup for months being methodical. I ended up with 142.5 mains.

What is your needle clip position set to? Count down from the top. Try the 4th notch from the top.

Valve adjustment is covered in the manual; it's pretty easy. An expert could probably do the job in 15 minutes. If it's your first time expect to spend an hour or two playing with it.

 

[Kdog]

Gregory, your bike is nearly identical to mine!

bcware what is needle clip? I have the exact same issues and have cleaned, set valves, synced, timed everything I can think of…but not sure what setting needle clip position

 

[Kdog]

However I am running the stock pipes and intake filters…..Gregory, what exhaust do you have on your bike?

 

[Scorpio1963]

Have you checked the plug itself?I mean have you tryed a different one?

 

[Kdog]

spark plug? There is good spark, and I believe my issue is the same as Gregory, but not sure what the issue is? Carbs are clean, jets are clean, diaphragms are good. Everything is sealed from filter boxes to motor good (including new boots between carb and motor)

I am wondering if it is a vacuum issue…I have them plugged, and removed the original vacuum petcock….only thing not stock I believe….bike runs great, but won't idle well, pops a little on the right side (the one not getting gas at times, exactly like Gregory's description) stumped?

 

[bcware]

Did you adjust the valves yet and synch the carbs?

The needle clip position won't fix the idle; it's just something to check while you have the carbs open. The older models have an e-clip that fits on the emulsion needle to raise or lower it. This is the needle that ultimately blocks the flow from the main jet.

 

[Kdog]

I checked my valves and did a sync, but probably need to do a resync… I will check into this..thanks

 

[Gregory]

I have emgo shorty mufflers... however on my bike the problem is im running too rich on the right cylinder all the time, and not even firing on idle... the spark plug is good, swapped it to the left to burn off the carbon deposits... I have the carb sync screw way out of wack so it idles ok but it aint right... every time after running the right cylinder spark plug is wet after idle and has a fair bit of carbon residue on it... I will try going to smaller jets, i believe i have a set of 142.5's. and i will go adjust the valve clearances... peace and thanks everyone... will keep yall updated

 

[Gregory]

KDog what do your plugs look like? my right one is soaked after idling, with carbon deposits but dry after running at <2000 rpms. ive run mine on prime with both carb boot niplets capped it ran the exact same. what about the passageway between your carbs? clear? just checked valve clearances they were off. now they are on. this bike is so loud so i wont run it tonight. will replace main jets tomorrow... concerning the jet needle and raising its position, what does this do and is it really worth it? how to i get those darn circlips out? is there a special tool?