81 SRX More help needed !

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Vmax540

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38 round slides off a 540 jetted as Left Mj. 290, Pilot 40, Power 135, PAj. 1.5 Right Mj. 280, Pilot 35, Power 130. PAj. 1.4, Both Main Air jets in throat of carb backs. are the carb body size (none installed like the 540). Air screws are at 3/4. We are running 50 to 1 premix plus a injection oil pump (red dot) off a 540 with a new rebuild (smoking like crazy). The primary spring is the square yellow in a 102 with engagement of 4200. It will not idle and is very, very boggy with a very lazy throttle until the rpm's get above 5000. Compression is 130+ both sides. We dropped the Mj's from 300 and 290 which helped a small amount and then moved the needles to the top which helped noticebly. 45 degree temps ! Thanks for any help !
 
DUDE, GET ENGAGEMENT UP. YOU WILL SCREW WITH JETTING WITH THIS FOR KNOT!!!! THIS MOTOR DID NOTHING BUT BOG AMD PUKE TO 6000 RPM. YOU HAVE CORRECT CLUTCHING UPDATED COMET RIGHT FROM YAMAHA. GET TO YOUR LOCAL COMET CLUTCH DEALER AND ORDER A PURPLE SPRING, PART # 207758.ALSO GET THREE RPM SHIMS AND START WITH 1. 3:16 (tony)
 
Thanks, Tony I have that Purple spring we'll give it a try ! Someone insisted I needed one for my 540 but, the 47-4800 engagement wasn't something I wanted to deal with on the trail ! I'm running a different Comet purple spring with 1 shim at 4100 engagement.
 
by the way, just wanted to say that with you mixing the gas in the tank and the oil injection, you are in fact leaning the sled out even more, so be carefull here. The oil displaces the fuel and results in a leaner mixture then richer, more oil=less fuel.

back in my 81 srx days, I never found that engine to be engaged and do anything good under 5500rpm. those are peaky little fella's, they do run very good once you get them dialed in.
 
DON, YEP. I ICE RACED A 81 SRX LONG TIME AGO. TWO THING ABOUT THIS SLED AND REALLY TOLD ME IT HAD A MIND OF ITS OWN, GET CLUTCH ENGAGEMENT AS CLOSE TO 6000 AS I COULD AND THE COLDER IT WAS OUTSIDE, THE BETTER IT RAN. RHEY LIKE TO RUN RIGHT AROUND 9250 !! 3:16 (tony)
 
Thank guys ! The purple and 1 shim seems to be comming in at ~4950 maybe still too low ? The throttle still hesitates above engagement even on a jack stand, this can't be good ?
 
DUDE ANOTHER THINK YOU MIGHT CONSIDER IS TAKING CLUTCH WEIGHTS OUT AND ADDING A ENGAGEMENT NOTCH WITH A SLIGHT FLAT SPOT SO IT DOSE NOT BANG THE HELL OUT OF YOU CHAINCASE. THIS FOR SHURE WILL INCREASE ENGAGEMENT. 3:16 (tony)
 
My 81', which still has the stock butterfly carbs, is pretty similar. Yellow square in the update 102C and she comes on at 4200 like yours. Lazy from idle, but okay once you hit engagement RPM. After that she pulls stupid hard. No problem with idle on mine though. No amount of carb tinkering seems to cure the weak bottom end and I agree with the others that this is its nature. Not very trail friendly! And yes, colder the better!
 
You guys may want to upgrade your clutching

With the 81 I just bought I got some neat original yamaha factory upgrade notices and posters, one for ign cdi box, trail friendly carb settings and suspension set ups and 1 for clutch tuning, the clutch tuning is right from yamaha with the comet clutch 102c installed, it says to change to the purple comet spring part number 207758, along with comet cam arms "N" part number 203911, and use 2 spring shims part number 203849.
It also tells you to remove 1 of the 2 spider shims from beneth the spider, this changes your neutral and belt side clearance.This makes a big differance.

Long ago when I ran 81 srx's I had to engage them at 5500-6000 rpm for them to do anything good, they are not a low end grunt motor, very peaky but make good hp up top. This above set up is much more to what I ran long ago, the yellow sq. comet spring is a low engagement around 4000rpm give or take a few rpm.
 
i started this post at 11:30 and finished it 12:15.... im tired... so please bear with all of my typos, cause im not proofing this im going to bed

first off i put the stock 81 oil pump back on, with a vmax cable that runs to the thumb throttle(duh) got that back to gether after dropping the one allen bolt for the pump about 5 times then i put the oil tank back on, and replace the vent tubes on top of the carbs., next held the thumb throttle open with my trusty rubber band(the only way it will start, that i have found) no choke, just pull it about 5 times and it with each pull it trys to run more and more... finially it starts and is real boggy but eventually revs up. by this time you best have the rubber band off or else the motor sounds like it is going to scatter even tho it is only turning around 6000 (guess thats the norm?).. i revved it off and on untill it got warm and then i started to do MY best assement of it... clutch engages right around 5200 with the purple spring and two shims (thats a plus), it seems to WANT to idle around 3500 or so, althought it wont idle for long with out shutting off.... when i hammer on it from idle it snaps for about 250 rpm and then bogs until right about them time the clutch engages from there it seems fine up until 7000 (thats as fast as i have got it to date)(the motor only has like 7 miles on it) all the while im watching all of the fuel lines suck air ocassionally, must be running out of gas i think.... i continue to play with the throttle with no real improvement from the last 5 setups i had.... so i got to grab a screw driver to turn the air screw..... it stalls.... i pull it three times and it starts just like it did when it was cold... reall boogy for ahile(im talking 15 secs) and then lookout it starts reving fast! (not really faster than any other sled ive ever rode but fast) ne ways i get the damn thing started and turn the air screws in about 1/4 turn (this should make them, form what i recall, 1/2 out) didnt seem to change ne thing.... so then i continue to think as keep it running.... this is about the time i watch the fuel lines go from some air to nothing but air..... and about 10 secs after than it shut off... outta gas.... si i fill the thing with about 4 gallons of raw gas.... now mind you there appeared to me 1/2 gallon of mixed that it couldnt pick up... so technically my gas still has a small amount of oil in it... (im not about to try to guess the ration as it is midnight, and im tired).... ~5 pulls and it starts up as usual..... now im expecting to see less smoke....... i wait and wait and wait and wait... i must have held that thing at 4000 for 2 mins and still the smoke just poured out. hmmmm, i think, thats dumb.... i think this is about the time i see some fuild that looks a little thin near the exaust.... upon further inspection i realize that the belly pan has a wonderful fuel/oil mixure puddling in it.... yikes!! i dont wanna catch this thing on fire before it even sees snow!.... so i starting shinning around with my light.... turns out i find fuel "spritzing" out of the area near the airbox flange......"alright that can be good"... i couldnt really see where it was coming from but there was a fuel line there i a figured it must have got cracked or something even tho it is brandnew... so i turn off the gas and run it untill it runs out of gas.... (my theory used to keep it from flooding the crankcase).... i begint to take the airbox out.... this time i decided to leave the carbs in and just take the carb-airbox flanges off and then the air box.... as i take the left flange off(near the belt) i find my problem..... the airbox has mixed gas in it... and theres enought of it that i can see it is blue.... of course the airbox has a little drainage hole and thats where the gas was coming from!..... i tore the airbox out and thats where im at with that... there was enough gas in the belly pan that i started draining onto the floor, through a "centerless rivit"... so i am praying that im not leaking fuel ne where else... it really cofunses me because up to that point i never found any other sources for my mysterious oil in the belly pan.... i dont know enough about carberation to know what causes mixed gas to go into the airbox to even know where to go from here... so pretty much im going to sit back think about this for awhile.....on a side note... when i got it up to 7000 i left off and it backfired.... i just shit myself, cause it scared me.... im so lost on this thing now that i dont know if it is getting too much oil and not enough gas, too much of both, or what the deal is..... grrr, i just dont know....


NE IDEAS GUYS!?!?!?
 
well my take is you have a classic case of a lean idle circuit going on once the sled is started. The engine will rev erratic(boggy) and idle high, and it will also backfire thru the carbs when they are lean. A piston port motor requires MORE fuel in the low end then does a case reeds engine to rev up smoothly. The problem with these old srx's is that they have a very narrow fuel curve, so your either lean, or very rich with out very much room in the middle to be right. First off on the pilot jets, I would have something in the range of 45-50 pilot jet, you can adjust the idle quaility some with the air screw on the carb bell. the carb circuits overlap each other and if your idle circuit is lean, you may have a overly rich needle circuit trying to make up the differance allowing the engine to rev once its past the pilot jet circuit, then onto the main jet, the power jets just add fuel to the topend to help keep it rich enough on wide open throttle.

Now I believe you also may have a float hanging up or high float level there as well, thats where the fuel is coming from, this may also be the reason why it needs to be held wide open to start. A high float level wull come out the overflow vent tube and out the vent hoses and into the engine bay, will sometimes just drip when the engine is running if its not off too far. Will it not start with throttle closed and just the choke lever used? usually though when you have a high float level, it makes the sled run very,very rich. Now the only reason I posted up above information was you told me it had a high idle, backfiring, and slow revving till a certain rpm. Have you looked into the sparkplug holes after it has run a few minutes with a mini mag light or bore light and see if the pistons are colored at all or are they bright silver yet? spark plugs wet after its run for a while?

If you can do this check list and let me know:

1.) after you start up the sled, with airbox removed, engine warmed up,does the backfiirng come from out of the back of the carbs when you nail the gas?

2.) are the spark plugs wet after it runs for a few 4-5 mins on the stand, you need to warm it up good, check with your hand on the cylinder, should be good and warm. Is the piston tops bright silver after same run time?

3.) will the sled stall if applied wide open throttle from 5000rpm from a stop?
Does it help the engine to rev faster, smoother if the choke is barely applied and then engine revved up?


4.) With the engine running, can you see where the fuel is dripping from, vent hoses on carbs, back of carb bell?
 
1.) after you start up the sled, with airbox removed, engine warmed up,does the backfiirng come from out of the back of the carbs when you nail the gas?

.... ive run this sled quite a bit with the airbox on and only had it backfire twice... i think it was out of the exhaust, but that was only twice... so therefore i dont think that is a big issue... also it did it when i left of the gas which leads ME to believe it was caused by excess gas in the pipes....

2.) are the spark plugs wet after it runs for a few 4-5 mins on the stand, you need to warm it up good, check with your hand on the cylinder, should be good and warm. Is the piston tops bright silver after same run time?

the spark plugs are wet after its run, the cylinders get warm, and the pipes get ignorantly hot(of course)... the piston tops are still bright silver but i have noticed microscopic pits in them... the pits look like some one did it will a needle... they are real small (lean condidtion somewhere along the curve?)

3.) will the sled stall if applied wide open throttle from 5000rpm from a stop?
Does it help the engine to rev faster, smoother if the choke is barely applied and then engine revved up?

no the sled doesnt stall when wot is applied at any time... if its around 5000 it will rev up... if below it takes a bit to rev up.... it dies if i put the choke on


4.) With the engine running, can you see where the fuel is dripping from, vent hoses on carbs, back of carb bell?

... i havent taken the airbox off AND started but here is what i have noticed... i dont see fuel coming out of the vents, but i do see it dripping out of the air box drain hole... when i take the left carb off, i can see a puddle of gas in the airbox......

now heres the kicker!!

all of these answers are from when i could get it running!... now nothing has changed and the SOB wont start.... it has awesome spark and the fuel pump is working it has gas but... when i get the motor running it misses horribly and only fires enough to keep itself running and then eventually it cant do that... i strongly belive this miss has nothing to do with electrial so lets not go there.... choke has no effect AT ALL when it is trying to run like this....

this sled is very hard starting and im so confused that any help would be great... also check out some other related post at my website.... www.vintagevmax.com/vvforum

thanks for any help... any input is greatly appriecated
 
heres whats going to happen next for anyonbe who maybe following my post... probably saturday depending on work.... i am going to replace the 35 pilot jets with 50's... now my theorey is that it isnt getting ENOUGH GAS down low.... seems strange that 540 whould take less gas down low but im starting to believe it.... hopefully this will fix the problem... ive got my air screw 3 turns out and it seemed to help... so from what i figure i need a bigger pilot jet..... my only concern now is that when im running it, acts like it is running out of gas occasionally.... ill have the motor running about 4000(or whatever speed) and it will just die!.... not all the time tho, just randomly.... a pull or two and it starts back up..... this almost sounds like a scary electrial demon but we'll see how it turns out....expect some pics on http://www.vintagevmax.com soon, as i got my digital camera back from canon yesterday
 
bigger pilots= good!

hes how my bigger pilot jets worked out.... i replaced the orignial 35's with 50's... and wow what an improvement! still kind boggy when you land on it from a idle... BUT notice i said IDLE... cause it will actually do that now for the most part... i wish the idle was a little higher though caus eit wount idle for every it eventually shuts off, but ill bet it will idle for like 2 minutes before it dies... like i said though, if i land on it from idle it bogs but eventually starts reving..... very well to i might add.... it seems to work better if i ease into the throttle... als i have this nasty problem with extra fuel vapor coming out of the carbs and into the airbox... i took the airbox off to see which carb was causing it and found it to be both!... the vapor only really comes out when its in the 2000-5000 range..... if you put your hand near the carbs it gets soaked with gas in about 1.325 seconds flat hehehe (actually its probably faster than that)... im confused where to look now... the bigger pilot jets mad all kinds of a difference i wonder if i should go another size or two bigger in the pilot?.... gimmie some feedback all you experts hehehe... its starting to snow daily here and im getting antzy
 
oh the idle is a little low and the idle screw is the whole way in... also i belive the airscrew is somewhere like 3 turns out still which is way to far... im confused by that
 
tyler440 said:
oh the idle is a little low and the idle screw is the whole way in... also i belive the airscrew is somewhere like 3 turns out still which is way to far... im confused by that
Click to expand...
3 turns out on the air screw? is the air screw on the intake side of carb? the air screw turned out (leans the mixture) allows more air... if you turn the air screw in (richens the mixture) less air... unless you are talking about the air/feul screw, then out(richens it) and in(leans it).. that might explain why you need a 50 pilot at 3 turns out is close to a 35 or 40pilot, 1/2 turn out... I cant see a 440 needing a 50 pilot when the 540 uses a 35 or 40...



BM...
 
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you cant compare what the 540 used with what the 440srx requires, differnt pipes, porting, cdi box etc. its not the same.

it now sounds like you need to confirm the float level setting.

the little pin marks in the piston is detonation, so your using the wrong grade gas, or its lean somewhere in the fuel curve for the octane gas you have in it.

wheres the needle clip at ?

so now you have 50 pilots, what mains are in it?

lastly, the air screw is located in the rear bell of carb, airbox side of the carb slide, they run leaner the farther they are turned out from lightly seated.

fuel screws are located in front of the carb slide, closet to the engine side, these control fuel flow only, they get richer the further out they are turned from lightly seated.
 
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