compression test

just going through my bike to see why it isnt running right , carbs are surgically clean with no air leaks synched and colourtuned. valves are all set and just done a compression test where all cylinders are at 120psi, does this sound right to you guys. bikes done about 32k miles not KM. still runs like a bag of crap

 

What do the plugs look like?
Has it ever run well with its current carbs to your knowledge? I have seen the wrong jets or incorrect placement of jets etc.

 

i have only owned it a few months and its never ran great , carbs are completely standard

 

Depending on where you live and how you did the compression test 120 is a bit low. Not so low it shouldn't run well if all cylinders were even and everything else tuned well.

 

Check the plug caps....remove them and cut about 1/4 inch off the wire and put the cap back on. Install 4 new plugs.

Kenneth

 

What bike?

Stock airbox? Stock air filter?

Stock exhaust?

Float levels set individually using fuel and the "clear tube" method?

What method did you use for your running vacuum sync?

Was YICS blocked for the vac sync? (if applicable, we don't know what bike.)

Give us a better idea of exactly what the issues are, too please. "Runs like crap" covers a lot of territory.

 

righty ho , sorry I thought I had posted it on another thread .
750 seca

bike has 4-1 exhaust ( jama) i beleive
it has pods ( yeah i know but didntthink it would affect idle too much)
carsb completely reapired and cleaned with all new seals
Yics is blocked and float levels set with tube method .

that is why I tested the compression as I couldnt think what else it could be . I then borowed a colourtune . I knew it would be lean due to the zorst and pods but with the colourtune on and the engine warm i was suprised that i couldnt get the colourtune to go yellow (rich) . Main jets are 124's but no changes have been made to the pilot circuit .
do you think that would be the problem !!!! is it just way too lean and should I go for bigger pilot jets or if I put the standard airbow back on would it let the colourtune indicate a rich mixture so I have a mark to get the mixture right . It is showing other attributes to a lean mixture like revs not dropping and a spitback through the carbs

 

Bingo! Welcome to the seventh circle of hell, tuning for pods. Keep in mind that the following advice ONLY applies once everything else in the carbs is 100%, you can't have skipped over anything like pulling the pilot screws and replacing their o-rings, etc.

Chacal has a set of recommended jetting changes for various intake and exhaust mods; it's in "Church of Clean," way down toward the end: http://xjbikes.com/Forums/viewtopic/t=14692.html

What method did you use for your vac sync? (Although that's not going to affect mixture.)

Check Len's recommendations and get about re-jetting. Understand that it's never going to run quite like an unmodified bike.

 

but it should still idle !!!!!!!!!I think you maybe jumping on the " blame it on pods" wagon here .
even with no air filters at all it should still idle once warm and be a little lean . not to a point where you cant richen it up using the mixture screws ,or is it just that the Hitachi carbs are so finnicky, maybe too finnicky hence why there are hardly any over this side of the pond , and like I said all carb rubbers have been changed throttle shaft/ fuel line/ mixture screw , and no a vac synch wont make any difference untill i get the mixture right.
I need suggestions , not ohh you got pods your doomed

 

Are you sure your pilot jets are correct in size and location?

Pods, no filter or airbox will make a difference at the speed and shape of the airflow through the carb. True for idle or WOT. And a given size jet will only allow a given amount of fuel. The pilot screw is to fine tune once you're in the range.

If everything else is setup correctly and you're still seeing lean then you need a bigger fuel jet.

You'll likely need larger main jets as well.

 

i did take the pods off and slip the airbox rubbers on to see if it was to do with airflow but it makes no difference

 

are your airjets reversed under the hats? They fit in the same holes and one manual has them backwards.

 

yes Ive done all that , in fact Ive followed the guide on here to the letter. this has just stumped me

 

I didn't say "oh, you've got pods you're doomed" I've never been able to get either of my (stock) 550s to idle worth a squat (or even stay running) with the airbox unhooked. It's not a matter of "jumping on a bandwagon," science is science. You've got both intake and exhaust mods to deal with.

A vac sync WILL make a difference; although the accuracy of your bench sync comes into play until you can get it running well enough to do a vac sync.

This is the point you're now at, pod-tuning wise. Not "doomed" but simply time to start adjusting for your mods, intake AND exhaust.

If you want "concrete" suggestions, mine would be: try re-jetting per chacal's recommendations, pilot fuel at the very least.

 

well ive just had a look and its got 124 mains and 43 pilots so they are both on the large side

 

OK, but how do those square up with the recommendations? Just "being larger" isn't the only criteria.

Recommendations excerpted below, from the link I posted:

MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:

Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust
or
+4 main fuel jet sizes for 4-into-1 exhaust
or
+4 main jet sizes for no muffler (open headers)

Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)
or
+2 main fuel jet size for drilling holes in the airbox with stock filter
or
+4 main fuel jet sizes for individual pod filters (no airbox)

Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.

PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.

PRECAUTIONS:

- Make sure your carbs are in perfect working order before making ANY jet changes....meaning fully cleaned internally and rebuilt, operating properly in their stock configuration, proper sized air jets and needles, etc. Otherwise, you'll like find that all of your efforts are going to be a HUGE waste of time.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!

 

ok just to prove its nothing to do with the filters I have put the airbox back on and the standard exhaust and it still does the same , it will pop through the carbs and back fire a bit whilst not returning to idle as it should . I think this one may make a good bonfire

 

With the stock setup will it go rich on the color tune?

Are you sure no one has drilled any of your jets. Can't always go by the numbers.

 

ive tried two sets of jets and still the same so they havent been drilled ( that would make it rich anyway)
it still wont go rich on the colourtune , the only way I can get it to go yellow is to very lightly pull the choke , ive just taken the carbs off again and pilot jets and mixture screws and thoroughly blown through them all with a compressor . put it all back (with the benefit of the airbox arrrgghhh) and its just the same . I even tried raising the fuel level to 1mm below carb line but that has made no difference so I put it back to how it should be .

 

If the air jets were drilled then you would have more air and be lean. Extra Air is getting in from somewhere. What do the carb to head boots look like? are the vacuum caps good and tight?

 

carb to head bolts are all fine and new with new gaskets on the inlet rubbers , vacuum caps are al sealed and I know I had the air jets in the right way around but to be honest i didnt check thier sizes , I have another set so I will go and double check . I Guess it must be something silly that I have just overlooked but I just cant find it , Ive checked dozens of times now

 

righty ho i have just checked two sets of pilot air jets and they are all 195's as they should be and none have been drilled , please someone confirm for me that the pilot air jet is the bigger one of the two air jets and it the one nearest the engine side , seems odd that the pilot air jet is bigger than the main air jet .

 

From our good freind Chacal's catalog:

"NOTE: the Haynes workshop manual for the XJ650 and XJ750 models has the incorrect placement noted for these air jets----the main air jet and pilot air jets are reversed in their picture and caption. Just remember that the main air jet goes directly above the main fuel jet, and is thus located in the "center" of the three holes in this area."

Main Air Jet:
#80: all 1981-83 XJ750 North American models and 1981-84 XJ750 UK/European (11M) models.

Pilot Air Jet:
#205: all 1982-84 XJ650 Maxim North American models, 1982-84 XJ650 UK/European (11N) models, 1981-83 XJ750 Canadian models, and 1981-84 XJ750 UK/European (11M) models.

So if you have 195's and a 750 you have carbs from a 650 or a rejet previously done.

 

ok cool so it looks like after buying 3 sets of carbs in the uk for a uk bike that all ahve the wrong pilot air jet which is wierd , surely though if I put a bigger pilot air jet in it will make it even leaner !!!!!!!!!

any idea what diameter the 205's are so i can enlargen one of the many 195's I have here so I can rule it out

 

And where did you but those carbs? (Don't answer.) You have no way of knowing for sure what model XJ they came off of, and the only way to tell the difference would be to...

look at the jets in them.

 

all three sets of carbs were off british registered bikes but who knows!!!
so do we think 195 =1.95mm and 205 is 2.05 mm

 

mmmm wonder if theres a chance Chacal is wrong on this one as I have just rang a Yammy dealer that has looked it up and he states my bike should have the 195's, mm the plot thickens

 

You'd be better-off with Compression numbers higher than 120psi.

The popular remedy for alleviating the Lean Conditions presented when the Carbs have Air Pods installed is exchanging FUEL Jets and SHIMMING the Diaphragm Piston Needle.

Experimenting with various sized FUEL Jets may not resolve the Lean Condition if the underlying Lean Condition is the result of an INSUFFICIENT VOLUME of ::: ➤ AIR ... available at BOTH the Main and Pilot AIR Jets to
regulate the Siphoning functions needed to assure the correct volume and atomization of FUEL actually reaches the Combustion Chambers.

 

I disagree totally with this statement.

If you are not drawing enough air through one carb, you can play with the mixtures for a long time and it will not idle nicely. It is an important step.

Mixtures then a running synch and then recheck mixtures. Otherwise you will chase your tail.

My XJ has a tired engine and uses oil, but still idles fine. Mac 4 into one pipes and standard jets.

 

like i said, the bike is now stock , I know I would also be better off with compression numbers higher than 120 , but they are all uniformly 120 which is more than acceptable . most aircooled bikes will idle and run fine on 90 psi as long as all pots are the same.

 

Ok I agree with what you say Dark but at the minute using colourtune the mixture screw from all the way in to all the way out will not show a yellow (rich) mixture , hence being way too lean .And in my situation no amount of Synching will help to get the mixture right . When i have sorted this dillemma I will do the mixture/synch and then another mixture check

 

The point I was trying to make is the chance the synch is far enough out that the carb is almost offline. Considering the amount of work you are doing rechecking everything, why not check the one item you do not know is correct.

It is an old bike with a very basic setup, being methodical will get it working.
Rejecting a suggestion is not being methodical.

But hey, I'm just an experienced mechanic and an XJ owner.

 

oh I agree and it has been synched evertime , but as an experienced mechanic you must also agree that with the Yics blocked and a colourtune in working one cylinder at a time it doesent matter wether its a twin or has 20 odd cylinders
That only comes into it afterwards when you know each carb is doing what it should be and then Synching them all together. Providing compression is ok, vacuum will be similar on each cylinder you are just bringing the carb in line so it can deal with that vacuum . remember the vacuum pipes are before the carb and not after it .But as an experienced mechanic you would know that.
But then what do i know , I am also an experienced mechanic with nearly 18 bikes and have owned 50 over the years , some I have made myself and others are more modern. Mostly Kawasaki's and Hondas and i must admit none of them have been as troublesome as this one .

 

hee hee..................he said 'what if Chacal's wrong'........hee hee, that's a good joke. I'll have to remember that one and tell it to some of the guys I work with.

Oh, man.......Chacal's wrong.................that's a knee slapper! Geez, I'm laughing so hard I'm cryin' and the screen's all blurry now.

dave F

 

well either he has made a mistake or the Yamaha dealers have on the pilot air jet . I dunno I am just stuck trying to get it to run right , who should I beleive , the internet or the dealer , i am off to find a coin to flip .

Anyhooo In the hope Hitachi jets are measured in mm rather than flow rate i have bought a 2.05mm drill bit to open out some of the 195's I have and see how it goes

 

I was going to make a harsh comment and went back and re-read the entire thread first. My comments were based on a mistaken assumption, that the problem was on one cylinder only.

My apology.

Slightly low compression and lean, have you double checked the valve timing?

 

no worries , this thread is going on a bit :roll: :roll: :roll: beleive me I wouldnt have asked but it has realy got me stumped , after spending weeks going through the forum I started off with the valve clearances as i do with most bikes . I then found the intake cam was running a tooth behind. i thought this would cure it but it hasnt made any difference and I made a manual cam chain tensioner like I have done on my kawasaki's to ensure the chain has correct tension.
going methodically through the carbs more than once made me get the colourtune which showed they were all lean . spraying " easy start" around them didnt make much difference and I couldnt find any intake leaks. I then got fed up and fitted the standard airbox and exhaust back on and it still didnt fix it . the only thing there is a discrepency on is this pilot air jet so i am going to give that a go failing that the head will have to come off and get it "crack tested " to see if there are any cracks in the inlet tracks or somewhere along the Yics sytem.

 

Did you check the valve clearance in addition to the timing?

 

As I believe I mentioned previously, this concerns me. How can you be sure you're not OVER-tensioning the chain, which could throw off valve timing?

I'd replace it with the correct style cam chain tensioner for starters.

 

no thier fine , How would over tightening throw off the timing ?????? as the slacks on the back of the chain which will have constant pressure on it .

I have used them on most of my Kawasaki's and they have been fine , they are simple to adjust and cannot fail on the over-run, I made one for a mat's turbo'd ZX10 and thats done 3000 miles no problem and that includes a couple of drag days

 

Just a quick update . I swapped the air jet over so the pilot had the small air jet and vice versa. with the much smaller air jet the bike runs very rich. so rather than getting a bigger pilot air jet 195 to 205 i think it needs to go smaller like a 150 .

or as I have a large pilot fuel jet #43 i may need to go bigger to maybe a #45 ..
the plot thickens as its exactly the same with or without airbox and filter

 

Just an idea - you have to take the carbs off -

Run a thin wire not just thru the Pilot Screw hole, but there's a couple small holes ajacent, a half inch away, little transfer ports that also must be clear, and flowing some emulsified Pilot fuel.

This will give the symptoms you're seeing.

and - how does a cam jump a tooth??

Despite your idle mixture problems, does your bike now run great @ WOT ??
meaning, do you now have no other running issues??

 

i will give those little holes a try . i know the pilot hole is nice and clear . when i say it jumped a tooth i mean it was a tooth out so it either jumpes or the previouse owner set it wrong . Bike revs nicely from idle upwards

 

whoohooooooo it runs . I used a .50mm drill bit and opened the pilot jets out a bit , It indicates lean on the colourtune out to 4 turns on the mixture then goes yellow so I reckon a .52 or .53 pilot jet will sort it so the rich/lean change is around 3 turns on the mixture screw.
just going to give them another synch and take the yics tool out and see how it runs .
doesent realy explain why it would need such a big pilot orifice even with the standard filter but at least I am getting somewhere

 

Possibilities:

Incorrectly placed AIR Jets.
Incorrect Sized AIR Jets.


Flattened-out, Mini O-rings at the bottom of the Pilot Mixture Screw orifice.

Passages connecting Pilot FUEL Jet, Pilot AIR Jet and Pilot MIXTURE Screw are partially clogged and need flushing with a strong solvent and compressed air.

 

Ive been through all of those things and carbs were soaked and blown through with 120psi .
One thing I cant get my head round though !!! if the misture screw sealing o rings were flattened , wouldnt it make the bike rich ????

 

Not it you left it in there and put-in a new one.

 

The fuel comes in across the Pilot Screw, then down the opening, all under the "O" ring. The "O" ring seals out air from above the Pilot Screw, which is supposed to be capped-off, but we're just too lazy to put caps back on there, so in the event of a flattened, mangled, broken, or missing "O" ring, you end up sucking a bit of air, making the setting go lean.

It goes rich when the screw is turned counter-clockwise.

-------------------------------

Next point - Rastacia,
If you jetted 25% or more rich to compensate for some unknown, and it happens to be hidden varnish, be prepared to re-correct your jetting months from now, when the varnish finally dissolves in the Hexane/Naptha/MTBE/or Techron in the gas this summer. (just sayin) :wink:

 

cheers I get it now . I am prepared for more adjustment after a few good runs but I am just glad I am at the point where it can be started and idle

 

cheers I get it now . I am prepared for more adjustment after a few good runs but I am just glad I am at the point where it can be started and idle