1982 gpz550 - Power loss at high rpm. Help =[

[sheatona]

What's up everyone, I've finally got my bike running better then it has since I bought it today, however after a series of short test rides I still cant quite seem to get the "power curve" or whatever you call it, to yield a nice even climb. I'll break it down and try to explain it as best as I can.

I've cleaned and inspected my carb parts/jets/ins and outs and holey things.

I've upgraded to stage 3 jetting via dynojet kit.

I have an open exhaust, and free flowing intake [no filters at present, but will have pod filters on street]

I've replaced spark plugs with new NGK plugs and set the gap within recommended specs

I've tested both ignition coils, plug wires, and plug caps and found nothing out of spec or not functioning correctly.

I've replaced the cylinder base, head, and valve cover gaskets.

I've checked all valve clearances, and replaced necessary valve shims to meet the manufacture specs and confirmed after, shortly after realized how much it royally sucks to do.

Set cam chain/timing correctly with TDC 1 and 4 piston positions to manual steps.

Torqued everything down to spec in sequence.


Okay, here's where I went on my latest test ride, nothing spectacular but enough to get up to speed and go through all the gears. I did take a ride and got essentially the same result with the circlip on my needles in the recommended 2nd position, and also 3rd position. Both rides with fuel mixture screw at the rec. 2.5 turns out.

Bike cranks easily and idles with choke on and off, I can rev up smooth from idle to wide open throttle just fine with minimal bogging, no abnormal heavy smoking, there's a slight hesitation at the bottom of first gear but will get up to cruising speed just fine
when I really start to feel my power loss is near the top end of all the gears, after the little delay the bike will speed up and run like a scalded dog until the top end of the gear, I can feel the bike shudder a bit and it doesnt want to give anymore, but will continue to speed up in the next gear until the same aprx rpm and will do the same problem.

I'm not really sure where to go from here, a side note - I have not done a carb sync, or checked to see if they are currently sync'd though I plan too with some help from my friend, I dont know how dramatically that could effect the performance in this aspect. I also havent confirmed the state of the in line fuel filter although it seems to flow without a hiccup.

The video didnt pick it up as well as I wish it did, but it may help someone point me in a better direction.

http://www.youtube.com/watch?v=Y03kEi_1aVA&feature=share&list=UUxj2wpqcxFMuTodw3io9ZqA

Any help's appreciated guys.

 

[teazer]

Couple of questions for you:

What kind of carbs CV or Slide and what make
What intakes or filters - nothing at all?
What exhaust system - you said open but does that mean no mufflers or a straight through muffler design?

What revs is that misfire happening at - Hint we need to see the tacho
What throttle opening does it relate to?

What parts did the jet kit come with and which were fitted?

 

[sheatona]

Couple of questions for you:

What kind of carbs CV or Slide and what make
What intakes or filters - nothing at all?
What exhaust system - you said open but does that mean no mufflers or a straight through muffler design?

What revs is that misfire happening at - Hint we need to see the tacho
What throttle opening does it relate to?

What parts did the jet kit come with and which were fitted?

Carbs are slide carbs, diaphragms appear to be ok, not as plyable as new, but have no tears and operate freely.

Carbs have no filters on them while testing.

Exhaust is the factory 4 into 1 header, with stock exhaust pipe just shortened about 3 inches and removed the S pipe, no other restrictions.

I would say the problem occurs aroung 6-8k, above 80% of the throttle position, I will try to dig up my stock gauges and connect them for a more accurate visual today.

 

[sheatona]

Oh and also, the jet kit consisted of new needles with a different taper, with adjustable circlip rings at the top, it was recommended to use position #2 for free flowing intake/exhaust setup, and also included different sized jets, they were actually a little smaller if i remember correctly, which suprised me, but i guess the new needle accommodates for that.

Also just curious but, how exactly do you sync carbs when the ratio screw is located on the inside?

 

[teazer]

If they have diaphragms they are CV carbs and the butterflies have to be synched first. Are they TeK or Hitachi or Mikuni carbs?

CV carbs of any make are typically harder to jet than simple slide type carbs. They typically run like crap without stock filters and chopped exhausts usually make them worse. Do you mean that there's no muffler on the bike? If so, that needs to be fixed. Pictures please so we can see what you are dealing with.


Above 8000 and above 80% is all main jets. Go bigger and see if that fixes it.

 

[sheatona]

I will post a picture of the bike when i get home ,i don't have a way to post here at the shop, however i do have the tock exhaust pipe on the bike, its just shortened about 2 inches, and removed the factory s pipe inside (the piece that gives back pressure and reduces the pipe to 1.5inches roughly), so its flowing without any restrictions now.

Today i mounted the stock gauges back on, and between 2k and 5k is great, but I have very little power and a very noticeable delay when in the bottom of each gear, and then the shudder begins almost exactly at 5k, it will push to about 5200 but doesn't want to increase from there.

Yes the carbs do have diaphragms, i believe they are tk brand. And the small jets are still stock, only the mains were included in the kit, i replaced the fuel filter with a larger right angle style one today, with no noticeable increase found.

 

[teazer]

TK carbs are not the worst anchor in the world but they are hard to set up and harder to get parts for.

5K sounds closer to the noise on the video. That's mid range and it's a combo of main jet, fuel level and needle position.

You may be able to tune out the low end stumble on the slow speed mixture screws if you are lucky.

The exhaust mods will also hurt power and jetting. It's not that engines need back pressure, but the carbs have to match the pressure profile. I'd go back to stock intake and exhaust and get it running right in that configuration and then work out what, if any, changes you want to make.

 

[sheatona]

Here's a better visual demo, with factory tach connected of the power loss up to at low end up to about 3k, and consistently at 5k, all power seems to be in the midrange. You can clearly see at the end of the video, the engine has no problem revving to the point of redlining without a load, but when under load shudders at aprx 5k, if I hold it just below the shudder, and then give it more throttle, it will "build up" and allow to 6k-ish but continues to shudder.

http://youtu.be/GMtIx7E-HEs

Video will not be viewable for about 40 minutes from this posting while it's uploading.

This was directly after syncing the carbs today [thanks for the tidbit on the location of the thingamabobs on the butterfly connecting rod] I wasnt sure what those did until this point.
And also replacing the in line fuel filter with larger angled clear filter I can see and verify fuel is flowing freely.

I cant really go back to factory configuration of exhaust/intake, as I threw away the crappy airbox and stock filter long ago, but I did just realize since I bought the bike, it obviously needed a carb cleaning but originally didnt rev over 4-5k without load, and that was with the stock airbox and filter. The exhaust however was a factory 4 into 1, just with the back of the stock slip on muffler cut off leaving it open at the end.

Since the factory config isnt really an option to go, where would you recommend going from there to start? F/A ratio screws? Larger main jet size? Perhaps a smaller pilot, since it kind of feels like it wants to fall on its face in the low end, but isnt getting enough at WOT? I dont really have the experience in differentiating between what to rich or to lean feels like.

 

[teazer]

If it was crappy before when it was all stock either the carbs are still blocked or it is electrical or mechanical. Let's do electrical. is it a mechanical advance/retard on that bike or all electronic? If it's mechanical, make sure it's advancing and springs back to retarded OK.

Does it have good (new) spark plugs and good plug caps? Remove all 4 plug caps and check for resistance and then unplug the coils and check their resistances too. You need a manual for the spec to compare your results to. Trim the end 1/4" off the ends of teh plug leads and re-fit teh caps IF, and only if, they are within spec. Fit new plugs and try it again.

The easy answer is to go all stock, so if you want to stay with those carbs, all we can do is to try to make it a little better. The low end didn't seem bad to me, but you can probably clean it up a little. Try adjusting the mixture screws out 1/4 turn and see how it runs and then a second 1/4 turn and see how it runs.

With the 5000 up problems that's more serious. Try to drop the needles first by one notch and then to the bottom notch and see if that improves anything. Remember that as the clip goes lower, the needle is raised, so it gets richer. Test one step richer and then two steps and see if it gets better or worse. That might give us a hint as to which way to go next.

If it's jetting, we'll need to either go up or down with the jets to see what it needs. Depending on which kit you got, Dynojet lists a few different main jets. What size was stock and what's in there now?

 

[teazer]

I just checked through your older posts and saw that you said it had a misfire when you got it. Looking at the pics of the carb slides, those diaphragms look torn or cracked. Even the smallest hole or tear will stop them from opening up. Fire the bike up with no filters and look at the slides. as you blip the throttle watch the 4 slides to see if they rise and fall evenly. If one rises and falls much faster than the others it leaks and if any of them fail to lift, that's an issue.

With the engine stopped, try to lift each slide one at a time and see if they all feel/look the same.

 

[sheatona]

Yes, all 4 spark plugs are brand new NGK plugs, replaced when I did the top end gaskets. I had the shop mechanic go through with me and check both coils, plug wires and plug caps, we did cut off about a half inch on the end of the wires on the cap side even though they didnt look to bad to begin with. According to him, that aspect was working correctly.

I went through the slides pretty thoroughly, I couldnt find any holes/tears/cracks on them, my only concern is they arent as plyable as nice new rubber would be, but still seem to function fine, I remember before when we were figuring why I had no suction on carb 4 [before the valve adjustment] we checked out the slides and such, each blipped evenly and had a smooth sucky whooshy noise and motion across all 4, and also today doing the carb syncing, they were only off a smidge and were able to even out pretty easily so I dont suspect the problem to be with the slides.

I want to say the main jets dynojet provided were an 80, which suprised me since my stock mains were actually a little larger, i cant remember exactly but I want to say an 85 or 90. The mechanic said it was typical since the taper of the new needles were different.

It's hard to capture the sluggish pickup when starting out on camera, but I wouldnt want to attempt to zip out in traffic the way it is currently, might end up on my back if I got a little twist panic going on once it decided to kick in lol.

I'll try to adjust the needle circlips tomorrow morning and see how that effects it, i'll pull the carbs off and check to ensure the jets are clear while I'm doing so to rule that out definitively, if no luck, i'll try the larger jets included in the kit and try to rule out more possibilities.

One question I'm not sure of, I know for a fact that the rubber orings around the tops of the plastic plug that covers the mixture screws are trashed, could those not sealing attribute to my symptoms?

I cant thank you enough for taking the time to help me diagnose this mess, it's been beyond frustrating and all the replies are appreciated in a big way, trust me, if I could afford to bend over and take it in the wallet, id gladly pay someone to fix this and call me when it's done haha.

 

[sheatona]

Well it would appear i spent almost 7 hours fiddling with different jet/needle configurations all equaling horrible bike that won't do anything over idle, only to find out m cylinder isn't doing anything, it has some suction i can feel, but the pipe isn't heating up , stays around 100 when the others quickly jump up to 450ish.

I did notice i forgot to drill out the lift holes initially, which i did, i guess once i get the suction sorted out, I'll have something to test from there.

i did look at my stock jets though, turns out stock was a 115, dynojet called for a 110 main which i have back in there again. Im done for the day, if i don't walk away from this thing its gonna ultimately end up in the retention pond.

Update; turns out I had suction, but all of the [air bleeder screws?] on top of the carbs were all different, after some adjusting we were able to at least get it idling, and could rev it to a decent level, just need to once again, go back and set the mixture screws to the rec level and go from there in the morning.

 

[teazer]

Sometimes we get so close to the problem we can't see the wood for the trees. Time to take a break and chill. And come back to it fresh and ready to approach it systematically.


Pull that plug and swap it with a cylinder that you know is good and try again. It may just be a dead plug. It happens. And see if the dead plug is wet or dry. If it's dry, it may be the float valve that's stuck. Try to crack open the float bowl drain on that one and see if it's dry.

 

[sheatona]

Slightly different direction, but until I can order my new ring sets, I know when we were trying to sync the carbs last time, the screw in the center to adjust the left and right carb pairs, the little bracket actually broke that holds the adjustment screw, I cant seem to even find that part on the kawasaki parts diagram, so I'm kind of shooting in the dark as to what direction to take to fix that as well, for the time bring I just took a valve shim and some aluminum tape to it to get it as close as the screw had it.

Any ideas?

 

[teazer]

BTW Dynojet jets do not flow the same as stock OEM jets.

 

[hvent90]

I might get a bike with this same issue. Was this ever sorted out?

 

[DohcBikes]

Its a gpz550 with wide open pipes, no air filters, and an aftermarket jet kit. It is not the bike that had issues, it was the tuner. This thread and the responses in it are a three ring circus. Only once was the actual jet size mentioned, no airbox whatsoever on cv carbs and they seemed to think that was ok. It isnt.

 

[barnett468]

Its a gpz550 with wide open pipes, no air filters, and an aftermarket jet kit. It is not the bike that had issues, it was the tuner. This thread and the responses in it are a three ring circus. Only once was the actual jet size mentioned, no airbox whatsoever on cv carbs and they seemed to think that was ok. It isnt.

im afraid...very afraid