high rpm miss under load in high gear

[Anonymous]

i have an 80gs1000e with about 15k miles that i have been messing with too much. i'm at the point i need to ask someone smarter than myself.

it has a vance&hines 4-1 pipe and individual filters. i installed the dynojet stage 3 kit. currently running a 170 dynojet main. it hasn't really run right ever since.

it cruises like a champ now and i can give it WOT to redline in lower gears but at about 4-5k rpm in 4th and 5th if i give it more than about 3/4 throttle it falls on its face. if i back off the throttle the bike will start pulling again. i assume it's a lean condition. the plugs show no sign of fouling.

i have tried changing main jet size both richer and leaner and it only seems to make the problem worse both directions. it seems to pull about equally well with a 165 or 170 main. a 175 main seems to make the bog occur at lower rpm and a 160 main caused the plugs to foul which seems odd since it's a leaner main.

i installed a nifty feul cut-off solenoid and removed the petcock diaphragm because i had gone through too many. i did block off the petcock vacuum line. i was thinking i was running the float bowls dry so i ran a line straight to the carbs and chucked the solenoid. this didn't seem to help although the sucker was restrictive- was running 360cc/min with the solenoid, now at 1200cc/min with an in-line valve.

i have rebuilt the carbs, repleced the floats, adjusted float height (i know it shouldn't affect high rpm) synched the carbs. taping off part of the air filters seems to slightly decrease the severity of the bog (leaner) while pulling the choke seems to have little affect (richer)

i'm starting to think it may not be fuel related at all. i checked base timing and advaned time. both are where they should be. could this be an ignition module issue? weak spark? there are no points to float and it's got a mechanical advance (flyweights). do i need to engineer some sort of vacuum advance?

dynojet techline has been no help. i have searched past forum posts and am running out of ideas. i have tried to be as detailed as possible. any help would be appreciated. i really don't want to spend another season in the garage instead of on the road.

thanks for your time,
Scott

[cbxchris]

Have you ran a plug chop? By that I mean run it up hard to redline in third gear and hit the kill switch plus pull in the clutch then coast to a stop. Get off then check the plugs. That will give you a main jet reading. From the way you described it I can`t tell what`s going on. Same thing with the needle except you need to get on a road and cruise...no backing off or idling...just cruising at around 4 to5 K. Stop get off and check the plugs. from my experience with dyno jet kits they tend to be very rich. I`ll check back be glad to help you if I can. Btw you don`t have to much oil on your filters do you?

[KEITH KRAUSE]

If backing off the throttle a little minimizes the bogging during higher speed roll-ons, then you're too rich. The combination/overlap of the needle position and the main jet (during roll-ons) is supplying too much fuel to burn, so there is a lag period until the rpm's can pick up enough to burn the fuel. Either the main is too big, or the needle is raised too much. The easiest thing to do would be to go down on the main first.
Some others will argue that you determine the main jet size first, but it's my experience to test, take plug reads, and get the needle position right, and THEN find out what is the largest main the bike can burn without touching the needle position anymore. It saves me time.
I don't know what you mean by "taping" the pod filters, but you should not be semi-blocking their air intake, if that's what you mean.

[Anonymous]

ah-ha! thanks guys.

did you mean lower the needle first?
i experimented with needle height and found it pulls the best at mid throttle in the 4th clip position, a little richer than base. this is , however, with an apparently too rich main. i ran with a leaner main (160) at a leaner needle position and ended up fouling out the plugs. i didn't try the current needle position with a leaner main. i did try lowering the needle with the current main jet and high end was unchanged but mid throttle didn't pull as well.

i will run plug chops as soon as it stops raining. i'll give you guys some news when i have some.

keith and chris, thanks again,

Scott

[KEITH KRAUSE]

I'm a bit confused too. You should not be fouling plugs when you go to the leaner jetting. Don't worry about the DJ "base settings", they are commonly not close.
We'll wait for your plug readings at steady 75 mph or so and your main reads. Be sure to remove any tape(?) from the pod filters. I assume you drilled out the vacuum ports to piston/diaphragm assy' like the DJ instructions say? You also must do a VERY good carb synch to avoid mixture problems. Are you sure you're also getting 100% fuel flow to the carbs? I don't recommend filters or anything else between the fuel valve and the carb. And what height did you set the floats at? Have you made any adjustments to the mixture screws? Do you have a manual? Lots of questions, but they keep popping up.

[Anonymous]

let's see. yeah, i just taped the filters on one run to see if it would change anything a while ago.
i did drill the slides-hairy business. i've syched and rechecked the carbs several times-trying to get all the mileage i can out of that tool.

the floats are currently at 22mm and i have adjusted the screws each time i change the mains. i believe they are currently at about 1 1/2 turns. i have been leaning them out until that carb begins to miss lean then backing out 1/2 turn. is there a better way? the only thing between the tank and carbs is a gas valve. i have a manual that covers the 4-valve shafties. i have not been able to find one for the 2-valves.

was able to run a main jet chop before the tornado hit this afternoon. there was some carbon but not the amount i was expecting. hopefully the weather clears tomorrow.

thanks,
Scott

[KEITH KRAUSE]

The mixture screws should be set to achieve the highest rpm and then you re-set the rpm to about 1,100 rpm with the idle screwknob. Warm up the bike first and put it on the centerstand. Turn "two at a time" in 1/4 to 1/2 turn increments to more easily hear the rpm's. Fine adjust those two and then do the other two. Then lower the rpm with the idle screwknob.
Is 22mm float height what the manual says for those carbs? Did you make the adjustment with the bowl gasket removed? What part of the float did you measure at? (I believe you have those "odd" shaped floats?)
Be sure to give us those plug reads when you can.

[Anonymous]

call me captain retardo. i kept tryingh to figure out why change the main jets has no effect and why i'm not getting any carbon deposits after a main jet chop. lo, i am an idiot. in my frenzy to junk the vacuum petcock i managed to use 1/4" fuel line. i put the proper 5/16" fuel line on and like magic i can achieve full throttle at high gear under.

now all i need to do is get to proper tuning. if i run in to any more complete lapses i'll let you guys know.

thanks,

Scott

[Anonymous]

I was gonna say, sounds like classic fuel starvation, not anything about mixtures or jetting.

I have a similar setup on my 450, the inline shutoff valve instead of the vacuum operated dealie. And I hit fuel starvation quickly at 90mph and 7500 rpm in 6th.

Michael

[KEITH KRAUSE]

If you read his first post, he just installed a jet kit and then had bogging problems. He described it as a jetting issue. Both me and cbxchris could'nt make full sense of the way he described it. I did question at one point if he was getting 100% fuel flow, and I did think about a too small fuel line but he sounded like he would'nt make a mistake like that.

[Anonymous]

thanks again fellas but i have a new problem. i think i'll start a new post. i got the bike tuned perfectly. of course i promptly wrecked it on the first ride.

i'm not too mobile yet so i haven't gotten a very good look at the damage but i already know i can easily replace the handlebars and guages. the forks don't appear to be bent nor the frame. the bad part is the engine.

i'm trying to figure out whether i can rebuild it or if i should replace the engine. i shattered the timong cover along with part of the case it bolts to. the timing plate and pick-up coils are trash along with the flyweights. the bolt holding the sensor ring to the crankshaft snapped so i suspect i bent the crankshaft. i haven't tried turning the motor over because i laid the bike down on the clutch cover hard enough to knock a nice hole in it and drain the oil. forunately the timing went first so i don't think it was starved for oil. is it worth replacing the clutch cover, and timing components, to see if it will turn over? will i know for sure if i just replace the clutch cover?

thanks,
Scott

[RacingJake]

Dude, talk about bad luck. I feel your pain.

Now tell us all the details. We all got one or two war stories of our own.

[Anonymous]

well, i'm an idiot and my buddy'd an idiot. i was riding with my brother and a few guys. my friend ahead of me pointed out a turtle in the road. not like "hey look at the cute turtle" but more like "don't hit that thing in the road." i pointed it out to my brother behind me and made the stupid mistake of looking back to make sure he didn't wipe out. let me back up by saying my brother behind me and my friend in front of me are new riders. i've only been on the road a few years so i'm still a moron too. anyway, when i was sure my bro didn't kill himself i looked up to see my buddy stopped i in the middle of the road directly in my path of travel. i had a few feet to swerve and picked the wrong way. he was turning around th get the frigging turtle out of the road. i smashed my timing cover on his rear wheel and smacked him in the back with my handlebar. this sent me chest first in to the guage cluster and head first into the pavement. i slid for 20-30 feet. i'm lucky. only lots of road rash. he got a serious gash in the ankle from my shattered timing cover.

[cbxchris]

Wow!!!!! 8O I grew up with a couple twins that had exactly the same accident. Except it killed the one in front. Glad to hear you made it through and so did the other rider.