Welcome, Guest
Username: Password: Remember me
  • Page:
  • 1
  • 2

TOPIC:

Valves out of spec symptoms 12 Jun 2018 15:23 #785046

  • Troubled1
  • Troubled1's Avatar Topic Author
  • Offline
  • User
  • Inline 4 ever
  • Posts: 50
  • Thank you received: 2
I have an 81 kz750H (18000km) and am having some runability issues. When cold with the choke on the bike fires up with a quick touch of the starter button. After warming up a little I can ride without choke but the idle is quite low and wants to stall out at traffic lights. However, once fully warmed up, the idle is much higher (almost 2k rpm). I have removed and cleaned the carbs, set the idle mixture screws at 2 turns out, vacuum synced (within 1/2” mercury), replaces plugs (NGK B8ES), fresh oil, oil filter and air filter. I haven’t however checked the ignition timing or advancer as I haven’t found anything online pertaining to my model.

As far as I know there are no modifications to the bike as I got it from the original owner. I am getting a little popping in the exhaust once the bike is fully warmed up so I’m thinking I’ll have to check my valve clearances. What I have been searching for all over is a list of symptoms of intake valve adjustment out of spec and the same for the exhaust valves. My main issue is hot starting. After riding for a while,(full operating temperature) and I stop for gas or whatever, the bike if it doesn’t fire up right away (feathering the throttle) it takes some serious cranking to start it. Once running it seems fine again.

I’m thinking the exhaust valves my be a little tight and once fully warmed up are not fully closed when they should be. Could it possibly be ignition advancer or more likely valve adjustment? I love the bike but I don’t want to have to worry about it stalling and not possibly starting again. What do you fine folks think??
1981 kz750H

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 12 Jun 2018 15:32 #785047

  • Scirocco
  • Scirocco's Avatar
  • Offline
  • Premium Member
  • Never change a running system
  • Posts: 3921
  • Thank you received: 1892

Troubled1 wrote:
I’m thinking the exhaust valves my be a little tight and once fully warmed up are not fully closed when they should be.


Lift the valve cover and check the valve clearance for hard facts, do a write up for later adjustments. Get a service manual @

www.750turbo.com/manuals/GPz750_Base%20Manual.pdf


Attachments:

Please Log in or Create an account to join the conversation.

Last edit: by Scirocco. Reason: add pictures

Valves out of spec symptoms 12 Jun 2018 15:40 #785048

  • Nessism
  • Nessism's Avatar
  • Away
  • Sustaining Member
  • Posts: 7257
  • Thank you received: 2658
Yes. Check/adjust the valves. This shouldn't even be a question.

BTW, a hanging idle is unlikely to be the valves. More likely an air leak. Sync should be closer than 1/2 if possible and pilot screws at 2.5 or 3 turns open. Tend to the valves first though.

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 12 Jun 2018 15:42 #785049

  • Troubled1
  • Troubled1's Avatar Topic Author
  • Offline
  • User
  • Inline 4 ever
  • Posts: 50
  • Thank you received: 2
I have a gasket on order which should be here within a week so I will be pulling the cover off and checking the clearances. Thanks for the link to the manual. It is definitely appreciated.
I will update with what I find out.
1981 kz750H

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 12 Jun 2018 17:26 #785055

  • Troubled1
  • Troubled1's Avatar Topic Author
  • Offline
  • User
  • Inline 4 ever
  • Posts: 50
  • Thank you received: 2
I had the mixture screws at 3 turns out previously but I was getting a lot of popping in the exhaust so when I had the carbs off to adjust the choke link, I set the mixture screws to 2 turns out to reduce the popping. I’ll try it at 2 1/2 turns and see if things improve.
ETA; I’m still running the stock 4-2 exhaust as well as what was mentioned in my original post.
1981 kz750H

Please Log in or Create an account to join the conversation.

Last edit: by Troubled1.

Valves out of spec symptoms 12 Jun 2018 19:03 #785059

  • Nessism
  • Nessism's Avatar
  • Away
  • Sustaining Member
  • Posts: 7257
  • Thank you received: 2658
Leakage at the rubber carb boots and airbox boots is common and will lead to the symptoms you mention.

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 12 Jun 2018 20:24 #785061

  • loudhvx
  • loudhvx's Avatar
  • Offline
  • KZr Legend
  • Posts: 10868
  • Thank you received: 1615
The initial symptom that shows up when the valve lash becomes too small over time is that the bike will stall after a hot highway run. This is what an owner will experience if he has had the bike long enough that the valves were originally in spec, and they became out of spec over time.

The bike will start and run absolutely fine until it runs down the highway for an extended ride. The internal engine parts get hot and the valve stems lengthen and so they can't close all the way. Symptoms won't be felt while riding on the highway, but as soon as the bike comes to a stop, it will stall. It will usually start right up again and will run if the throttle is held open enough. Driving on side roads, the engine will return to normal operation in a few minutes as the internal engine parts cool.

If the bike is neglected for a long time, I suppose it could eventually get bad enough to affect normal running, but most people would have done some troubleshooting and/or routine maintenance by then.

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 12 Jun 2018 21:28 #785063

  • SWest
  • SWest's Avatar
  • Offline
  • Sustaining Member
  • 10 22 2014
  • Posts: 22347
  • Thank you received: 2598
Some don't and sell the bike saying it needs carb cleaning or jetting. :whistle:
Steve

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 14 Jun 2018 10:47 #785156

  • Troubled1
  • Troubled1's Avatar Topic Author
  • Offline
  • User
  • Inline 4 ever
  • Posts: 50
  • Thank you received: 2
I turned the mixture screws out to 2 1/2 turns and now it’s worse when hot starting. I can also smell a strong odor of gas as well. I guess my next step is to try the screws at 1 3/4 turns and see what happens.
One thing I did notice when stopped at a red light is when taking off, it was hesitating and then cleared once I got going. Maybe a little rich at idle and loading up. I did set the float level using an auxiliary fuel tank using the clear tube method the last time I had the carbs off so I think it’s safe to assume it’s not the float level but I guess it couldn’t hurt to double check.
1981 kz750H

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 14 Jun 2018 15:34 #785176

  • Troubled1
  • Troubled1's Avatar Topic Author
  • Offline
  • User
  • Inline 4 ever
  • Posts: 50
  • Thank you received: 2
Looks like I’ll have to pull the carbs again. I was out earlier and when I got home and parked, I had fuel coming out of the air box. I ran out of gas the other day as when I reinstalled the gas tank I forgot to reconnect the fuel level warning light connector. I’m assuming I got some crud from the tank stuck in one or more inlet valves.

I picked up an in-line fuel filter and some new fuel hose. I did the sniff test and my engine oil seems fine. I guess that explains the loading up at idle. I’m glad pulling the carbs isn’t a big deal and it will give me a chance to double check the float height. I may as well empty the fuel tank and remove the petcock. I rebuilt it but the thing still dumps fuel with the engine off. I may have to go to a manual setup if I can’t get it working correctly.
1981 kz750H

Please Log in or Create an account to join the conversation.

Last edit: by Troubled1.

Valves out of spec symptoms 20 Jul 2018 21:20 #787315

  • Troubled1
  • Troubled1's Avatar Topic Author
  • Offline
  • User
  • Inline 4 ever
  • Posts: 50
  • Thank you received: 2
Ok, I checked the clearances and this is what I got. 
Cyl 1- in. .13mm
          ex. <.06mm
cyl 2- in. .07mm
          ex. .13mm
cyl 3- in. .07mm
          ex. .13mm
cyl 4- in. <.06mm
          ex. .12mm
My smallest feeler gauge is .06mm and it would not slide into #4 in or #1 ex. So 3 intake and one exhaust valves out of spec. 

I have never shimmed valves before before so I assume my next move is to pull the cams and see what size shims are in the out of spec  valves and use the chart in the manual to determine what shims I need to order. Do I need to remove the cam chain tensioner to do this? And does it get installed after everything is buttoned up? 
1981 kz750H

Please Log in or Create an account to join the conversation.

Valves out of spec symptoms 20 Jul 2018 23:00 #787316

  • Nessism
  • Nessism's Avatar
  • Away
  • Sustaining Member
  • Posts: 7257
  • Thank you received: 2658
Pull the cap off the tensioner, that removes the spring force.  And be sure the cap is off when the valve cover is installed because the rub block in the cover will overtension the cover otherwise.

Please Log in or Create an account to join the conversation.

  • Page:
  • 1
  • 2
Powered by Kunena Forum