finally it runs, BUT...

the damn mechanic couldn't get his sync sticks to read any vacuum when connected to my carbs. Found a small vacuum leak on top of intake manifold boots, sealed with rtv sealant. still couldn't get vac. pressure.

Also, she pops really bad when decelerating/coming off throttle, initial acceleration is poor, and she only runs on "prime"

SO
my route for fixing this would be:
1. use propane to check for other vacuum leaks, then fix those.
2. If no leaks/fixed leaks, try to sync and colortune.
3a. sync and tune works, popping stops, i hop on and ride.
3b. sync and tune work, popping continues. what do i do here?
3c. sync and tune don't work after leaks fixed. what now?


only running on prime would indicate that either the petcock is bad OR I'm not getting enough vacuum to pull gas, correct? so check for leaks, fix em and see if it will run on normal petcock setting, replacing if this s not the case?

poor off the mark acceleration is probably just a carb out of sync deal right?


valve clearances are in spec. any suggestions OTHER than checking for more vacuum leaks? something with the carbs themselves perhaps? I'm pretty sure i set the float heights correctly....

 

You sound like you're on the right track to me.

 

shouldnt be the carbs the vac port is in the intake the only way it would be the carbs is if the butterflies were wide open if they were it wouldnt idle it would be full throttle unless the shaft seals were non existant but . you have to have vacuum or it wouldnt suck gas thru the carbs at all. first pull the hose off the vac line that goes to the petcock run a pin thru the vac port make sure its not plugged start it up on prime see if you have vac put your finger over the vac port. do all the vac ports that way. check your compression also should be somewhere around 125 could be more some of the guys on here can give you a better idea that have the same bike as you do. bottom line is you have to have some sort of vac or the bike wouldnt run check the boots real good for leaks
you could have a bad petcock pull the gas line off that goes to the carbs suck on the hose that goes to the petcock gas should start to flow if it doesnt move the petcock to reserve and try it just in case rust or something is blocking the screen prime works off the reserve line . hope this helps you will have to have a yics tool to sync them right if it has yics if it does it will say it on the crank covers good luck keep us informed

 

soooo

no vac leaks anywhere, but it still won't read any vacuum on the carb sync tool. professional mechanic who worked for yamaha and has nice sync gauges couldn't get it to sync (no vac reading ~1psi) either. YICS tool is in and working. what gives?

the petcock is just dirty, gonna seafoam the tank.

mechanic said to colortune, then sync, so I'm going to do that tomorrow

 

that is strange whats the compression? must be running really bad with no vacuum. the only possibility i could think of is burnt valves or rings maybe the valves are to tight compression will tell for sure if the rings are bad if so a tsp of oil will bring the compression up if it doesnt valves arent seating

 

If your engine runs, you definitely have vacuum somewhere (maybe not equally, but...). You are measuring the vacuum in each of the manifolds between the carbs and the engine. There are brass tubes on the tops of all 4 manifolds for the vacuum connections (3 are normally capped with rubber plugs; one has a vacuum hose that runs to the petcock to allow fuel to flow when the engine is running). Check to make sure some PO did not fill the brass tubes with RTV. When syncing the carbs you will either need the OEM tank removed and use an auxilliary fuel tank or the OEM tank removed from the frame and set on a bench/shelf/toolbox with the petcock on PRIme to allow fuel to flow to the carbs and room for linkage adjustment. [You will also need a box fan blowing on the engine to prevent overheating.]

Definitely do the Colortune first, then sync.

You did check for proper fuel level in each of the float bowls, right?

 

floats are set, compression is good (lowest is 115). new head, valves in spec, no leaks, carbs clean and bench synced (a few months ago when it wasn't running).

neither I nor my mechanic can figure out why it won't read any vacuum on the sync stick. this makes it impossible to sync the carbs.

been riding it carefully. pops on right side. top speed (5th, open throttle) is only 60mph. methinks all this is sync/mixture issue, but can't rectify this if the sticks won't work.

thanks for all the responses, keep em coming if you have good (any) ideas


quick question on the colortune. adjust screw till combustion flame color is blue, correcto?

 

See if you can get a small-diameter drill bit down the brass vacuum tube into the center of the rubber manifold.

Screw-in each of the idle mix screws until lightly/fully seated. Unscrew each about 2.5 turns to start. Get engine warmed up. For each cylinder, adjust mix screw so that it just starts getting a mix of yellow/blue (yellow=lean, blue=rich) then back off until steady blue.

 

just did color tune on cylinder one. couldn't get it rich even with the screw all the way out; with the screw all the way in it wasn't firing. me thinks I'll have to run thru the carbs again since they sat with stabil in them for over 6 months. grr... might go the sea foam route first because im lazy.

 

if you are having a problem getting vacuum i wonder if the YICS bolts/plugs on the sides of the head (under the carb boots) are loose or even missing, that might cause you to lose vacuum... however i don't think the bike would run very well if at all if that were the case...

 

vacuum connector thingies are clogged? Let it run and pull the caps, any vacuum on the hose that goes to the petcock?
Like other said, can't imagine it running at all without pulling a vacuum somewhere.

 

ok.... I'm going to recap all this for my benefit; hopefully it will help y'all out too.

the good news:

valves in spec.
good compression.
no vacuum leaks.
vacuum connector thingies are not clogged.
YICS bolts tight.
starts right up on enrichment and will maintain idle. needs to warm up a lot before it will hold idle off enrichment
carbs squeaky clean including bowl pilot holes etc.
float heights set to 17.5mm dry (44/64")
bench synced
new premium gas.

the bad news:

began colortune process on cyl 1. until 3+ turns out no flame at all. started to get a blue flame around 4 turns out. want to fix the super lean condition before i go any further.

SyncSticks don't read any vacuum on any carb.

popping on both sides, trouble maintaining idle off enrichment.

my thoughts:

seems to be extremely lean condition, so lean that some cylinders wont fire.

I still don't understand why the carb sticks won't read any vacuum, despite the lean condition. leanness doesn't affect vacuum, does it?

mixture screws all the way in is lean, all the way out is rich, correct?
I turned all four mixture screws all the way out and it still ran like sh*t.

popping is a sign of lean mix and bad sync, right?

sounds like fuel delivery issue, but fuel rail is clean and all carb bowls are full. new premium gas, plus seafoam...

going to try colortune again on all cyls. will post back results

sorry for so many q's; im just very confused and a tad frustrated

 

i would do a leak down test to check for leaky valves. also did you check the timing when you had the valve cover off? if there is a leak you will need to pull the head to lap the valves and/or replace the damaged parts if the timing is out.

cheers,

Trev

 

Check the FUEL LEVELS in the bowls, don't rely on float height measurements. The FUEL LEVEL is the target/goal, not any particular float height setting.......

 

timing set, valves are not leaky.... at least that's what i paid the mechanic to be sure of. how do i do a leak down test? how do i know if the timing is off?

i've personally replaced my head before and the timing was pretty easy to get down... its just lining up the mark on the cam with the mark on the cam retainer when piston is at tdc, correct?

 

leak down tester is a tool that allows you to pressurize the cylinder at tdc and shows the pressure in realtime (as opposed to a compression gauge that only shows peak pressure achieved).

that sounds about right for setting the timing...

so you're not reading vacuum at all on any of the cylinders? there has to be a reason. are you sure the carb sticks are good (no vacuum leak at the sticks)? if the thing is running at all i would think there has to be some vacuum... do you have a basic vacuum gauge or access to another set of sticks you could plug in to it?

chacal has a good point as well, it's always better to set the floats wet.

cheers,

Trev

 

A vacuum leak could be causing the lean condition if its leaking enough air to dilute the fuel/air mixture.

 

Just a small correction as well on colortune colours.

Yellow combustion is RICH and blue is correct, whitish blue is LEAN.

 

valve seal was checked by inverting the head and pouring diesel oil on the valve seat face. head was left like this overnight to see if oil leaked thru. none did, so i assume (hope) valves are leak free.

i will set the float height wet soon.

thanks for all the help!