Not your standard Jetting question.

[tyler540]

Ok guys, i dont have many posts on here but i have read one heck of a lot of over the past couple years. here is my deal:

i have a:
• 82atc200e bottom end, cylinder (bored to 66mm, wiseco 10.25:1), and stock head
• 97? xr200 carb, cam, and intake boot
• big exhaust custom exhaust, somewhere around an inch inside diameter (please dont immediatley point fingers at this
• NO air filter
• 93 octane gas
• ALL IN A CRAFTSMAN LAWNMOWER, wish i could tell you the gearing but im not sure

heres the problem:
with no air filter, the motor revs out great, but has a very bad "death spot" when punched from idle. by this i mean that it will idle "just ok". if i turn the idle up (not high enough to engage the centifugal clutch tho) it will sit there and run forever. but when you slam it WOT, it will stall. i found that giving it about 1/2 choke will take this away. but once the motor gets on the main jet it starts spitting and wont rev until you quickly get it to normal choke position. if you get the machine rolling a little and then stab it, it rev right up. (mainly being experienced in yamaha warriors i would say the accelerator pump is not working but this doesnt even have one.)

with some chinese piece of crap air filter it wont rev out. unfortunatly im not sure how it acts on a punch, i should have tested a little more with it on. this is the air filter: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&_trksid=p3984.m1439.l2649&item=180703589329&viewitem=&sspagename=STRK%3AMEWNX%3AIT when running this filter for a short time i realized the area behind the filter was getting misted some with gas. not sure at what rpm this was happening.

with or without the air filter it starts like a dream, no choke without the filter and a little choke with the filter

the carb has stock xr jetting, i believe, it is 38pilot, 110 main, the air screw is around 2 turns, maybe more, the needle is in the bottom position currently but it acted the same in the middle.

the timing is set in the middle i believe

the engine runs ignorantly hot, like 325*F when measured with my laser temp guage from harbor freight. thats hot enough for spit to BOUNCE off the head (this is even without the hood on, almost forgot this was in a lawnmower didnt ya?! haha)

my thoughts: im having a hard time putting my finger on the stammer/ stalling on a stab. im not sure of if it is the nature of the beast with the carb and cam. or if there is something i can do. without an air filter it will rev to the moon. the cam supposedly makes its power at at least 9000 so thats great i guess. but im thinking it is probably lean on the main jet, which is why it gets soo hot. in my opinion, the fact that it starts so easy and idles tells me that the pilot is good. it seems hard starting is generally due to a lean condition, and therefore the air needs to be choked off to richen it up for cold starts. if i could just get rid of the stammer from idle to WOT i would be happy.

EXCEPT!!

i dont plan on running this thing without an air filter. my thoughts on the air filter are as follows: i think the design of the air filter i bought kills the velocity of the air coming in and it simply cant get enough air fast enough at the higher RPMs. the filter is so short and close to the carb that i think it is just killing it in the upper rpms. i know with my warrior, when the main jet is too rich it will act EXACTLY like it has a rev limiter. this is different though. it is a more random series of pops, bangs, and burps. i think with the air filter it is rich on the main jet, but that is actually being caused by the lack of sufficent air. i really wish i would have paid more attention the reaction it had when i stabbed it.

"i got a buddy" that thinks i need to get bigger jets all the way across the board. he is actually the guy that built/ engineered most of the mechanical things on the mower. im simply the idiot who spent all the money, pushes the loud pedal and does the reading on the internet, but i think he is wrong.

i understand that this is not a cookie cutter answer and that jetting questions never really are, but think about my symptoms and tell me what you think.... i really apprieciate any advice...

PS if the answer is jets, does anyone in western pa have some i can buy, or test with... i may just have a swingarm bolt you need? :naughty: @atctim

pss how about a picture or 2 of this animal....

[tyler540]

ok here are the pictures.. maybe this will entice someone to give me thier input

[Vantage]

I see a few things that might, maybe contribute. No choke needed to start may indicate it's fairly rich on idle jet. If any air bleeds are clogged up in carb circuits it won't get the message to richen the mixture when you nail it, fuel will be slow catching up to air column. Might be enough to kill the engine.

Sounds like you need to start it, warm a bit, then crack throttle to cause it to kill. Pull the plug & see if it's wet or dry, to help diagnose carb circuits. I always use small wires [not copper!] to gently clean out the air bleeds along with spray solvent in a carb when rebuilding.

When the slide opens in carb it supplies the air, but it's the vacuum circuits or air bleeds that pull the fuel to match the air. Of course everything wants the proper float height too. Needle height having no effect can also indicate clogged circuits, dirty carb.

Engine running hot may indicate ignition advanced too far, which can give very quick starting, sometimes a little kick-back. It may also contribute to the stalling condition, but work okay without the quick cracking of throttle. I'd also want to be sure that it is a fat bright blue spark, not weak & yellow. If it's weak the fuel can douse the spark. With today's gas you should see a light golden brown color on porcelain surrounding center electrode.

BTW: Points gap has a dramatic effect on timing....good or bad!

[tyler540]

hmmm ya know i never even considered that the carb may have some dirt in it. i did use an ultrasonic cleaner machine and a ton of compressed air and carb cleaner before, when i put it together but i suppose it is very possible it picked up some dirt from the fuel line or tank.

as far as the heat goes i think i solved that problem when my air filter finially arrived from china. it was running at 325 now with the air filter, its reading 230 or so. my warrior shows 270 after a mile of WOT so i think im good with the honda running 230 after basically the same.

the biggest "duh" i discovered since the original post is that the air screw had vibrated completly out and is gone. i put the one from the original carb in and it didnt actually seem to make a difference but it has to be better haha

i might try to retard the timing a little and see what happens also. this is going to be hard to to tho because the my engineer/ builder is the kind of guy that believes if a little advance is good more is better. currently it is set just a hair more advanced then what it was when i got it.

all good comments but im afriad points gap isnt going to have any affect on this engine since it is cdi.

i think im going to tear that carb back apart and spend some serious time making sure everything is spotless. what height is the float supposed to be set at? where and how are you measuring it? i usually figure a level float when the carb is flipped upside down is right, and thats what this is

thanks

[Vantage]

I've never used ultrasonic so I don't know what it's capable of. I've always used small wires like smallest guitar string etc to gently massage the ports & air bleeds, along with carb spray cleaner. When the wire passes through you at least know it's open for sure, especially on the tiny idle jet hole & emulsion tubes. By the way, don't forget the little spring for that air bleed screw as that's what helps prevent it from vibrating out.

If adjusting air screw does nothing at all it seems almost a sure thing something's still clogged.

I have little hair left after dealing with a modified ATC110 engine, on & off for the past 4 years. Never knew it had a race cam in it, or vintage race type 1/4 twist throttle, and rejetted carb along with the DG Extractor exhaust etc. So, none of the stock numbers worked for tuning. Also the clutch was put together wrong, and the online diagram for it is incorrect, discovered by another poster on a forum! Just couldn't get there from here. Finally running now.

So, on that thing I need to set timing 25*-30* retarded from stock because of cam, or else it tries to explode itself! Crapped out bad on top end, or anything above idle, also a little backfiring until I retarded spark. For a fact, not all engines want more advance, and it can cook aluminum parts, melt sparkplug electrodes, splatter tiny aluminum deposits all over inside of cylinder or destroy engines if too far advanced!

Not a clue here on the float level 'cause I'm no pro on the XR200 carb. Should be info posted online, or maybe ask over at Thumper Talk, lots of good guys there.

[tyler540]

the ultrasonic cleaner is pretty awesome.. it was actually used in a hospital operating room to clean and sanitize tools and instruments... plop it in the solution, plug 'er in and wait like 30 minutes and out come a dmn near shining carb. it used vibration and some sort of solution to break everything loose. after that spray some clean and air and ive never had a problem. but like i said thats not to say it didnt get some junk in it from the fuel line

[tyler540]

also about the spring... i realized thats what it is for but wasnt thinking when someone else set it somewhere, where "its not even touching the spring" ... duh! i know that was either too far out or it needed a bigger pilot but wasnt thinking and figured i would just run it that was to make him happy... but now since i have an air filter that fits it, i think ill take over the tuning and do it right hahaha

[tyler540]

im begining to think that it is the xr cam thats making it stumble. tho i shouldnt be so quick to jump to conclusions. we had an extra stock sized jet, so even tho i know the defference in jet size is very very little, i allowed my buddy reem it out with a torch tip cleaner... he made it plenty big and it still stumbles. so i put the stock size back in, jabbed the throttle and let it die. the plug was dry. possibly it is lean with the 38 and rich with the custom jet. theres only one way to find out and thats try different jets, but i think i might just settle with having to roll into the throttle ever so slightly

[Vantage]

Well ya know there's a couple of more simple adjutments to try. You can pull the ignition cover & experiment some with timing. If you leave the adjustment screws pretty tight, but just loose enough, you can ever so carefully move the plate using a screwdriver for leverage, with engine running. When it gets to highest idle, back it off a bit towards where you started, lock down the screws, and try it out.

Another simple thing is to experiment with the needle jet's jet needle height. Raising clip on needle drops it down, so it's leaner. Lowering clip on needle raises it up for a richer mixture. Also may want to cross reference to be sure it has correct jet needle for the jet that's actually in it?

[shortline10]

Not sure if you checked this or not but the tips of the air screw like to break off and get jammed in this style carb leaving a little piece stuck in the carb . very common issue with the 185/200cc carbs .