lt1bird

as long as it keep pulling harder keep going up on the mains.... at some point it should start to feel flat... I find it to be weird on jeting the 421...... I have same carbs....535 engine and my mains want to be so much smaller(140). All I can think of is that i have a much stronger suction on the carb do to the larger stroke and displament so smaller mains work ok(185), where your engine is a shorter stroke, maybe alot less suction with the porting so the mains need to be large to supply the proper amount of fuel. anyone want to chime in?

I found that if its rich at idle it needs the slides open a bunch to make it idel.....lean the pilot jets bakes the idle go up....then the air mixture screws give you fine adjustment for throttle response.... turing them in richens it up....out leans it... for idle and part thorottle.

You said your air screws were out 4 turns.......your still too rich on the pilot if it will not idle...... keep going down on the pilots until it idles....then fine tune with the air screw and move the slide screws out....

If your too rich at idle you will end up turning the idle/slide screws in a ton....Thats a good sign your rich....cut that pilot jet down and you will notice the idle will start going up.... The larger the mains the more fuel at idle as well...there is some interaction and big swings in mains does effect the idle...thats what ive seen.... Im having a hard time beliving that the main jets are that big.... you are doing WOT testing correct? Like I said....mine would run with 175 no problem.....pulled hard but real flat feeling like a four stroke..... It would not really scream like a 2 stroke until I started lowing the main jets down to 148.....this is a 535 power valve engine...no porting..... maybe some other folks could chime in..... If you had full drag pipes and a drag port then maybe larger jets would be needed.... What air cleaner are you running?

mine wants the choke unless its warm....when warm i do 1/4 throttle and kick.... the 58 pilots might be a bit large so it will start with no choke....

Ya, thats the hard part....if you keep going richer mine did not seem to care......it did get a litle bit of a rich studder before the power band but once it reved....it seem to run good but definatly seemed down on power....The leaner and lean I went to better and better it runs... This is my theory...... at 1/2 throttle if I hold the throttle in the same position and let it rev up it will rev then at 6k it revs quick and gets on the pipe and pulls hard.....This is my goal at WOT.......currently at wide open throttle it pulls good in the midrange then in the upper rpms it still pulls good but I do not get a big increase in rpm or a good power hit... Im thinking im still rich on the mains.... plugs are still black/very dark brown.... I am going to go down on the mains until I get a power hit....Ive lowered the main jets a bunch and it keeps running stronger and stronger.....seems like im very very close..... are you getting a good power hit or is it feel a little more smooth like a 4 stroke?

mine always leaks a bit.....even when I lowered the float level.... just vibration etc....get use to it..... Jetting.....be carful..... I started at 175 mains..... ran pretty good with those....a bit lazy/flat...no real power band hit... now im at 148 mains....runs much stronger and gets on the pipe now.....Still feels like I could go smaller on the mains... getting nervous to go smaller as I have a 535 and smaller than 148 seems a bit extream but the engine does seem to keep responding as I lower the main jets.... Im running race gas so I cannot do a plug chop or read the plugs correct. Plugs still look black with current jetting.....

mine always drips...like a f-in harley.....get use to it..... long as its not a constant flow... Sounds very rich for some reason. Pull the air cleaner off and see how it runs...make sure the choke is not on or broken! The felling is a studder..... studders when getting on the gas.....ddda dda ddda daaaaaaaaa

Well, the one needle clip did effect the drivability....made it a tad richer at 1/4 to 1/2 throttle....A bit more studdering... as far as the bog goes... it did seem to get a bit better... did not bog as bad... but you could still feel that it was not recovering clean..... it was fighting to rev the whole time....Reving slow.....until it gets much higher in the RPM range.....It is much cooler here today so im not sure the one clip is enough to make a decision. Im thinking its a bit to rich still at lower engine speeds... I am going move the clip to one clip leaner see how that works.... overall I tend to think the midrange was a tad rich to start with anyway..... Im not going to spend much time on this as I see no secario when I woudl be in 6th gear at 2500 rpms and wacking the throttle open to full! If i quickly roll the thottle on it works just fine Any carbs have acclerator pumps? With a banshee on the dirt im sure the tires would spin engough to hide the problem....

I just moved the clip down one clip position to see how it effects it...Ill try that and report back... ya, I would have thought rich as well but I would have expected maybe a studder instead of a bog... im not conviced the needle cip will fix it seeing that at WOT the needle is out of the way... although it could be a timing thing......like when the throttle is wacked open...during the wack open it might hit a lean spot in the needle and cause the hesitation then bog to happen.....with a richer needle setting the slight histation might not happen thus the power may increase just enough to pull past the bog and run clean... Ill post what i find... It was running super rich on the mains....It now gets on the pipe and pulls hard....I would not doubt if the mains are still too large.... I have big bore pipes tweeked for street use...(this engine is in a street bike)... Thanks!

Ok, my bike is running super....great power, drivabilty etc.... I does do one small thing..... If im in say 5th gear just putting along at say 2500rpm and I wack the throttle open fast as I can I get a very bad bog that really does not want to recover from... unless I back off the throttle ...... Im thinking the problem is that at such a low rpm that the engine cannot pull enough fuel from the carb as there is just not enough velocity to suck it out causing a lean condition.... My 250 2 stoke does not do this so im trying to figure out if there is an adjustment that would fix that....Im my mind im not sure what would fix it... the slide is full open, the neddle is out of the way... only the main and the pilot are adding fuel.... Am I being to critical?? Should I just leave it? As usual, thanks for the help folks.... 535 power valve engine 160psi 110 race gas +4 timing 39pwk's near sea level 148 mains 50 pilots cen needles center clips

Probably still rich on the mid as well...Can you move the clip on the needle up one clip position and try it....

Like he said...you are way to rich...my bike sputters bad at the top end when very very rich.... you will be suprised how much better the mid and low end will run once you put much much smaller mains in to get rid of the sputter! Its not a fuel dilevery problem...it takes a while to drain the bowls....not one gear Forget about the plugs and reading them for now...you need to get it to run before you do that crap... Keep going down on the mains until it starts to rev better... You will get to a point where it no longer studders and pulls clean. It will pul clean but seem kinda flat on power....Your still rich at that point! Its not gonna get on the pipe and pull real hard until you lean it out more! Then start checking plugs... tweek the needle for midrange and then finish on he idle jet/screw..... Get rid of the +4 timing until its running better...put back to stock....

Well, the +4 timing made it a bit more eager.....feels good...... the new needle did help with the studdering....Im going to g smaller on the pilot to help clean that up.....On the mains.......It pulls hard but still does not get a big power hit as it should, im thinking im still very rich... If i hold the throttle at 1/2 and let it keep reving i feel the power hit! I know the needle is very close to where it needs to be so I bet its still very rich causing the bike to not quite get on the pipe..... Im going to lean out the mains to 155 and see if it wakes up the top end more! Is this what others have seen? Running rich mains will make it still pull hard but never awsome.....and never get the power hit?

The 160 mains feel much more crisp... Bike seems to run very good...studder all but gone....just a hint before the power valves open up... it likes the smaller mains for sure....Trinty said start at 160 as that would be very rich stilll they said I would probably end up at 150.... I am going to put some mid 150's in and see how it feels... I am also going to bump the the timing up +5 as the 110 race gas, may as well get the most out of it... I am going to make one last needle change as well to try and clean up the little rich sputter at 1/8 to 1/4 throttle...going to end up with a CEN needle... CEL working good....CEN should work better

Thats what I assumed....trinty said it is really just a vent for the oil and air...... not adjustable.... Do you know someone who has been playing with them? Right now, I have very little power band Hit..... It pulls pretty good from down low all the way to redline.... I never do get a good power band hit.... kinda wierd..... my 250 2 stroke with power valves has a awsome power hit..... I kept wonderin about the power valves....like...were they opening? I dont think there is an easy way to check...

Im gonna go back to the 160s just to do a santity check.... Stroker...ill keep you posted as well....Trinity said the jets on the powervalves do nothing....Just a simpe way for them to hook the plastic tubes to them..... does not effect any power stuff.....

Funny you say about the washing....Thats kinda what i had seen...thats why I was upping the mains unitl it started to studder.... Thanks for the info!

With a smaller main it would run cleaner and rev good with no studder....It just seems to make a bit more power with the larger mains... It might like more fuel but in the midrange it suffers with the needle im using... Im gonna to go back to tune the needle for best 1/2 thottle power first...then fine tune the mains... Trinity said start at 160 and work my way down! Im at 175 now....I tried 160...seemed a bit buzzy but ill try again...

Yes, up to temp..... Its a 535, 165psi, big bore pipes ,modified, 38mm kehin carbs....... Ive got a bunch of work to do to it over the next few days..New throttle so i can go WOT easier... clutch lever etc.... Ill try moving the needle a clip leaner and see if it helps a bit....at least ill know im going the right direction... I guess my main question would be......WOT is the main jet.... I have power valves....Im kind thinking that the power valves when they open they will run fine with the larger main jet....When they are closed there is not enough rpm/velocity to run the larger jet. The power valves have jets on the front to control when the valves open....I might play with them as well.... just to see how it effects the power coming on....

Im running 110 now but would love to mix 1/2 and 1/2.... Funny, ive never seen that anyplace written about race fuel not being able to read the plug chop.... Sorry if I somehow offended you Everyone keeps saying DO A PLUG CHOP...... Im ready to do it and your saying the 110 race fule will not color the plug properly? So I should just tune by the seat of my pants.....No problem if thats the case..... Thanks!

When I try to do a plug chop it sputters if I wack the throttle open it will not recover unless I close the throttle to 1/2....then it pulls hard all the way to red-line and through the gears... If I roll the throttle to WOT then it seems to take it just fine and runs hard through the gears... I keep upping the main jets waiting for a top end rich sputter.. Looking to start at the rich point and work my way lean with the plug chops... All the tuning info says Main jet at WOT....Maybe 5K rpms is not enough rpms to use the fuel its dumping in if the main jet is too large?

Thats a great picture....That way you can see the whole ring

ill have to get that shift pro arm

detonation sounds like to pieces of metal rattling against each other.... If it sounds like that dont be fooled into thinking its something vibrating at that RPm Its 99% sure its detonation.....