Not starting after running previously day. -carb issue?

Bummed out here, I picked up a non-working XJ750 and was told bike was running 3 years back and now needs carbs rebuilt and gas tank rust taken care of from sitting outside. So after doing a meticulous cleaning job I was certain bike will run... and it did! Sunday I started the bike and drove it around the neighborhood but it certainly had a rough idle and i noticed condensation on the carbs after running for 30minutes (I live in S.FL). So the next day I searched the forums to find out how to increase the idle rpms to take care of the hesitation and discovered that the main air jet and pilot air jet in the Haynes manual is incorrect - i thought that was solution, all I need to do is reverse the jets. So I took it apart and reversed the two jets, put it back together - and thought okay for sure everything will work. Nope, cranked over and put putted a bit but no idle =/ I tried many times that I ended flooding the carbs and having a gas puddle on the ground.

Pretty bummed out, thinking I have to take out the carbs - and more than likely having to buy intake boots as it will crack this time taking it out. Any suggestions if it could be something else than the floats? Maybe I need to clean the spark plugs?
Thank you in advance

 

Thoroughly clean the carbs (see thread on "Church of Clean", replace throttleshaft seals and o-rings so you have no leaks, bench synced, measure and adjust valve clearances, check all your safety relays, flush and clean tank and make sure you have fresh gas, make sure your petcock is in working order, the vacuum caps are on, the vacuum line is hooked up, drain and replace engine oil and filter, a GOOD battery, etc.... once it's running, do a running sync and colortune.

That will get you to a good running condition, but you still have the brakes, tires, etc.... to go before youre SAFE.

Others will chime in here too----

YES, there's a LOT of work to do.......do NOT get discouraged. You WILL end up with a stone-reliable bike if you take the time to do it RIGHT.

Dave

 

+1 ^ on all that. Key words,"if you take your time and do it right". Short cuts won't work.

Gary H.

 

Did you check Valve Clearance?
How is the fuel filter? is it letting enough fuel through?
how about the air box and or filter? is the engine getting proper air?

 

Update: After a busy two weeks, I had some time and clear weather to work on it for an hour. The issue I believe was that the incorrect air jets caused engine to run rich and covered my spark plugs in carbon deposits. I cleaned them up and got 3 out of 4 cylinders running now - starts up first push. But idles at 3K before it would idle at 1K with the incorrect air jets. The 2nd cylinder (2nd from left sitting on bike) gets spark but no combustion. Gas smelling when plug removed, so its getting gas and spark... meh

I cleaned the tank, fresh gas, rebuilt petcock, new fuel lines, new fuel filter, carbs are clean clean, i followed church of clean & Haynes. I will do the valve clearance after I gather the tools and gaskets. and then a compression test. Before touching brakes, lines and forth to make road safe.

What you guys think of cylinder #2? Its totally cold exhaust pipe, its getting gas and has a good arc spark. It ran before when the air jets were incorrect... thats what confuses me.

 

You should do the compression test asap.

Gary H.

 

another thing to consider is the fuel you are using
I got cheap towards the end of the season and used regular fuel 10% Eth
and wow.. after 4 days of sitting my carbs were completely gummed up
4 days!
I did the seafoam trick to get it started.. looks like I am in for a deep carb clean
as well this winter
Always use Premium!

 

Already compression test results: cold engine
#1: 94
#2: 100
#3: 95
#4: 92

btw I'm using premium fuel only.

So I am working with a good engine, I'm thinking it must be incorrect air.fuel mixture?

 

Those numbers are low but also close enough to not suggest anything major. Briefly explain how you did the compression test?

Gary H.

 

It was a dry test on a cold engine. I unscrewed the spark plug, replaced it with compression tool adapter and jump started it from a battery bought a month ago - that perhaps isn't fully charged.

 

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Compression Test per the FSM for XJ650 and XJ750 Seca:

1. Make sure valve clearance is correct
2. Remove headlight fuse from fuse box
3. Warm the engine 2 to 3 minutes
4. Remove all spark plugs
5. Install compression check gauge
6. Turn the engine with the electric starter (make sure battery is fully charged) with the throttle wide open until the pressure on the gauge does not increase further.

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Standard….. 156PSI
Minimum….128PSI
Maximum…171PSI
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Warning: When cranking the engine, ground the removed spark plug wires to prevent sparking

1. If the pressure is too low, squirt a few drops of oil into the cylinder being measured. Measure compression again. If there is a higher reading than before (without oil), the piston rings may be worn or damaged. If the pressure remains the same after measuring with the oil, either or both the rings and valves may be the cause.
2. Check each cylinder. Compression pressure should not vary more than specified value from one cylinder to any other.

Differences in gauge reading:
Less than ….. 14 PSI
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Disconnecting the TCI is probably easier than grounding the plugs. Need to do one or the other to avoid risking damage to the coils.
Disconnect head light fuse to reduce load on the battery
My experience I typically get very close to same numbers whether cold or hot.
Opening the throttle is critical to allow a sufficient volume of air to be drawn in.
With questionable numbers, always compare to a second gauge, preferably a known good one.

The gas puddle on the ground has already been addressed as the need to service the carbs. You should not get a puddle of gas from just trying to start it - it is an indication of a float that was stuck or not properly wet set during your previous work on the carbs.

Sounds like #2 is running overly rich, the swapped air valves may have allowed enough air to allow combustion, and now that they are correct, the plug is fouling from excessive fuel. I would suggest using the clear tube method while the carbs are on the bike just to rule out a sticking / misadjusted float valve.

Bench sync may also be an issue, if a good bench sync was not performed it makes life difficult not having a good baseline to start.

Fouled plugs either from fuel or oil are sometimes difficult to clean, suggest starting with a fresh plug or swapping between cylinders to verify after checking carb float levels.

 

Christmas update: Bike is now running!

Issue was in the coil-packs, ordered two 'used' ones and started on first attempt!

I got drive it around and through all the gears, no hesitations and nice pull through gears. I will be now working on fine tuning using color tune and getting other parts road worthy.
Closing this thread since initial question was solved.