moparmadman40

this was my first personal bore and hone job, so i guess i did an all right job if it is in the normal range

i got things going and broke in my new engine yesterday, did a compression test on the freshly assembled engine and it was 145 psi. Today i did another compression test after seating the rings yesterday and was surprised to see 168 psi. So i'm wondering if anyone else has measured both fresh and seated ring compressions and what the differences were?

i really thought about it all night and yes i should try a larger pilot. it just didnt jive with what i was seeing in the exhaust and plug. i'll jump it up and see how it works. i started thinking about the hollow sound when revving off of idle and i now think that it was a lean bog because it didnt sputter. I only had room for a single carb, this isnt actually a banshee. you can check out my other post in jetting about a tm-38 single starting point for a picture.

ok, so i've finally got my bike running with the single tm-38 carb. i started off with a #25 pilot and i couldnt get the thing to run right without turning the idle up, seemed very rich but my highest idle was with the air screw turned all the way in. decided that the smoke don't lie and i put in a #20 and the bike seems to run better, but i turned the throttle all the way closed and the bike was still idling way high, highest idle seemed to be with the air screw all the way closed, and it is still smoking like its rich at idle. bike also had a pretty hollow sound and hesitation when revving off idle. This doesnt make sense though, if it was rich, turning the air screw out should have made it better not worse. can anyone comment on this? bike is a 4 mil, ported 198/130, single tm-38, approx 3500 ft elevation and 32 degrees Farenheit

UPDATE! i need help folks. so i got this carb on the bike and have been trying to get it running for the last two days with no luck. This has me really stumped, set it up with a 35 pilot, 340 main, air screw turned out 1.5 and kicked it over alot with not even a cough. tried everything, choke on/off, air screw adjusted in and out, idle stop adjusted from all the way closed to a bunch open. bike has spark and the plugs were a little wet. i swapped out the 35 pilot for a 55 and it didnt help, i get a little smoke out of the tailpipe but it won't fire. checked the pickup gap and adjusted to 0.020", checked the resistances on everything and it was all good except for the coil secondary winding which i could only get infinite resistance on, didn't know what to make of that because its got decent spark on both plugs. one odd thing though was that i could only get spark on both plugs. if one was left un-grounded neither would spark. does any of this make sense?

and here is my intake

well, this is why i need to jet at -10

Hey, i can't wait any longer for my smartcarb to come so i am going to pick up a 38mm mikuni tm flatslide this weekend to tide me over. can some of you experts tell me where to start with the jetting. brand new engine never run and its my first banshee, 4 mil, ported stock cylinders approx. 127/200, 2 into 1 custom tube intake, vitos dual stage reeds, charriot head, 40 thou squish, 145 psi compression, +4 timing, 3000 ft elevation and -10 degree's celcius temp.

well i got them with a chariot head that i bought off e-bay. cut them for 0.045 squish, it brought the chamber down to about 19.5 cc's which is just about perfect other than the band being 60%. ported stock cylinders for the 4-mil to 130/198. with all that it kicked out to 145 psi on a fresh build no break-in at 3500 ft i think. So i'll have to buy new domes if i want a narrower band (if i do that it'll be 18cc and race gas), which is why i am going to run them and see. But like i said, i'm just wondering if someone has run both wide and narrow bands and what the actual differences, pro's, con's and possible problems are.

cut an old set of stock stroke 23cc domes to clear a 4 mil stroker setup and it ran the squish band width up to about 60% i'm gonna give them a shot and see how it goes. but does anyone have any actual experience with the effects of a higher or lower squish band on the banshee that could share their knowledge. i've heard that some people shoot for 45% ish or 10-11 mm width. and i've heard that a small squish is more efficient at higher rpm's while a wider squish band will give more low end torque.

is anyone custom cutting piston crowns here? i'm building a 4 mil stroker with wiseco 795 pistons, but the previous owner had the cylinder bases milled 0.030" so i am ending up with the crowns 0.060" above deck with 0.050" base gasket. Seeing as it is easier to cut a piston crown vs. properly cut combustion chambers and the fact that flatter top pistons just plain burn better why not cut the piston crowns? There is alot of material up there, so i guess the question is if anyone has done any playing with this. And if so, what are the practical limits to retain strength and reliability?

is there any detriment to having too large of intake ports? other than keeping the rings where they are supposed to be and not cutting them too high to interfere with timing. Or is the size of the intake port related to the size and/or timing of the transfers and exhaust?

no i'm talkin about the port directly above the main intake ports. on the stock cylinders it is a small highly angled port that is open to the intake tract but it is its own port. On the serval cylinders ther is no port by itself, it is cut into the main intake ports.

is there any reason why noone is cutting the intake ports on stock cylinders into the boost port like on the servals?

found this on google, super wampus cylinder map. thought some people might be interested in it. Can anyone comment on whether or not this is a stock serval port map. And i'm new to this 2-stroke thing, can anyone tell me what the ports above the two front transfer ports are? the ones right next to the exhaust. Are they more transfer ports or are they some sort of extra exhaust ports?

Yah, sorry misinterperetation. So what is the proper specs for connecting rod RADIAL clearance? didn't see that anywhere other than what i mentioned.

ok, here's an update. i took a better look at things today and to my advantage i found that the stock banshee cylinders have sleeves! when they were dirty i couldnt tell that they were not aluminum and thought that i was screwed that the piston scuffed one a touch. but now i'm all good and can just clean up with a hone. SO, i will be using the stock cylinders now.... and i did want a 4 mil for the extra power and torque. so if i put in a 4 mil long rod crank and stroker pistons, what sort of port timings would i want to run. From what i gather of reading on here i would call what i want an agressive dune port. what would i want for port timings/port heights on something like this? The cylinders i have are allready slightly modified. The guy that had it before me had 0.030" (0.75 mm) taken off the bottom of the cylinders for more bottom end. The port heights are stock so 30 mm exhaust and 43.5 mm on the transfers. Even better would be if someone could send me the port timing/height equations or an engine program. none of the ones i've been finding work.

pretty sure you dicked that up, no way is the radial clearance 2 mm. you might have your side clearance and radial clearance switched around. 2mm between the side of the rod and the crank web maybe, even that sounds high. but then your .25-.75 mm value for the radial clearance seems high. thats 0.007"-0.029". typically the service limit for radial clearance on crank bearings is 0.003"

another consideration i just thought of is the size of the cylinders and head, since this engine will not be going into a banshee (dirtbike frame) i do have some tighter clearances to think of. Can anyone comment on if there is a different height of the cylinders or height of the cylinder head required for them?

as of now there are no mods, i was planning on using the stock cylinders because they were just bored and new pistons. But because the job was done poorly i now have another decision to make. I haven't measured the cylinders yet but i think it might only be the first oversize. I guess another question is what a cleaned up serval 4 mil with a 2 into 1 pipe would make for power? if it makes enough i might just not need a turbo for a while. gotta remember its going into a 300 pound bike.

so i just tore the engine down that i will be using for a snowbike/banshee build, turns out that the "fresh" bore and pistons were done crap and one pison and jug is scored. So.... i will likely be using a custom 2-1 pipe, lets not debate that too much, i will be replacing the crank so probably go a 4 mil, and the reason i used a banshee engine is because i may turbo it in the future and did not want to turbo a single cylinder bike engine. What are the opinions on three different setups, cleaned up and re-bored the allready bored stockers OR send them away for a port job OR buck up and put a set of serval cylinders on it? the obvious differences in price will have to be made up somewhere else likely me not having it done and riding this winter what would the differences in power output be between these different options? and if i do turbo it later would the extra money now be wasted?

38 inches from the exhaust port to the rear cone. sound right to anyone?

the pipe is allready built basically. all i need is a length. the ktm pipe was used because it allready has the correct profile to fit a dirtbike where a banshee pipe would not. i had to add about an inch in the center of the pipe and i will need to add a piece behind the rear cone to match up with the silencer pipe. but i would like to adjust the length of the pipe at the rear cone before i finalize that. the only hint i have found on this entire site is a formula.... (EXH. Duration x 1700)/ pipe tuned length = RPM so this gives me about a 38 inch pipe for 8000 rpm peak