Engine Struggles To Rev Above 4500 Rpm

[kawasakisnail]

Hi, Having problems with a 1979 z650b3 which doesnt seem to want to rev above 4500 rpms in any gear.
Idles great and revs up to 4500rpm great but then sputters and doesnt seem to want to go any higher.The revs seem to drop quite slow.
I have put new plugs in and re set the timing(electronic)and it has also started to foul the plugs(sooty).
The air/fuel screw is set to 1 1/2 turns out and it has a standard air box with new filter.
HELP GOT ME BEAT.

[jbsmd]

What made you decide to reset the timing, and how far off did you find it to be? Cause it still sounds like a timing prob to me

[kawasakisnail]

Reset timing as engine was out frame as bike has been restored ie frame powdercoated etc.Wasnt out much but it is bang on now.

[kawasakisnail]

Hi jbsmd,
When u say it sounds like a timing prob do u think it needs advanced ?

[jbsmd]

I don't know what your timing is supposed to be set at, so when you say it's bang on now, are you saying it's set at what it's supposed to be set at or TDC? There's valve timing and ignition timing. Either one will disrupt how the engine runs. Ignition timing, will sometimes limit rpm, valve timing sometimes makes it run rough. I'd make sure the Ingition timing is set to the proper setting then go from there. Also check your carbs syncronizing.

[zedx11]

sounds like a carb problem.

check the float valves. if one is bad replace them all.

[kawasakisnail]

It was the ignition timing i checked.It has boyer bransden micro power ignition fitted and it is timed to the full advance marks at 5000rpm as stated in the instruction leaflet provided with the kit.I will check it again today to make sure i have done it right as i suppose a small difference could cause it to lose power.

[jbsmd]

When you check your timing, how are you able to get it to the 5000 rpm. Did you set it at tdc of 1.4 or 2.3 and after warming it up, set the timing to full advance marks. Check your initial set up in fig. 3.....you do have the right kit for your bike? Special coils and suppressed plug caps?

[kawasakisnail]

Rechecked timing today,and its timed to the full advance thats specified by boyer.Was thinking it was a fuel delivery problem but that would surely make it run lean and wouldnt foul the plugs with soot?Was also thinking of removing carbs for cleaning,checking jets etc or am I on the wrong track ?

[jbsmd]

What else have you done to this engine besides this kit? Any other do overs? If you get this working right let us know if anything helped. Was your kit the 00287, just wondering? Does it run the same after you put the cover back on?

[jbsmd]

I was assuming your carbs were in good working order, but it could be that this kit, requires them to be in great working order. It is an older bike, and a rebuild my be in order.

[kawasakisnail]

Not sure what type it is as it was fitted to bike when i bought it.Leaflet i got with the bike just states micro-power ignition for kawasaki z400j-z1000.The only other mod that i know of is it is fitted with a MARSHALL DEEPTONE 4-1 exhaust.It runs the same with cover on or off.

[jbsmd]

Sounds like the right kit, don't think the pipes have much to do with your prob, maybe the other owner did a rejet. Sounds like you're on the right path. This is one reason I hate to buy used, I'm not good at figureing out the "what now" part. Let us know your progress it could help others.

[jbsmd]

Some other questions: Was this bike running good when you got it? Is this prob a sudden thing or has it been comming on gradually? Did this get noticed right after you put the engine back in? A vacuum guage should help to check valve timing. Check valve clearence and tensioner. Then go for the fuel delivery system. Check to see if you have the special digital coils type BB00008, and your system has the 5000 ohm suppressed plug caps. It may be a mute point, cause it may not even run if you didn't.

[kawasakisnail]

When i first got bike it was hard to start and idled rough.New plugs and plug caps,fully charged battery,new fuel filter and she starts great and idles great.Cant remember what she was like in the high rev range as i only had a few ride outs on her before i started the resto.Think i will start with fitting a fuel pipe with no filter so theres no chance of any kinking in the pipe as theres not a lot of room between fuel tap and carbs to rule out any fuel delivery probs.Check coils and battery etc to rule out a weak spark.Remove carbs for cleaning,check jet sizes etc.I think its the main jet that kicks in around this rev range so im thinking it could be a blockage as i read that a partially clogged main jet may allow enough fuel flow for part throttle operation but starve the engine at full throttle.These are all cheap fixes and if shes still not running right after that then its find a mechanic who doesnt mind working on old bikes(not many left)

[NCDave]

I was thinking carbs as well. One thought. I had a suzuki that I opened up the air intake and it would not rev but ran good at idle. It was getting too much air for the carb settings. I just reduced the air flow and it came back. I was going to do carb adjustments on it, but decided instead to have my son's friend total it instead!

[JimmyD]

Are you sure its not your coils crapping out on you under load?

[jbsmd]

If you're getting "soot" on all your plugs, then a carb adjust or if on just a couple plugs then check carbs for being in sync...could be running more rich in a couple cylinders.

[kawasakisnail]

Soot is on all plugs.I emailed the previous owner who told me bike was fitted with k&n filters at one point so i am thinking it has maybe had bigger main jets fitted but is fitted with standard airbox now.
Managed to set timing as it does rev past 4500rpm but at this rev range it starts to bog down and very slowly revs increase to 6000rpm max but it is a struggle

[jbsmd]

Now it sounds like since you have the intake cut back it is running too rich, so maybe it does have bigger jets installed....good detective work dude. Keep it up, good luck and keep posting.