Kawasaki Motorcycle Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
Ok, I'm stumped. I have a '79 KZ1000ST 60,000KM, very good condition and have been riding it since '81. Reliable as a hammer as you all know but a couple of years ago I installed a Vance and Hines 4 into 1 and started having rough running, feels like fuel starvation, won't respond to throttle problems in strong headwinds and gusts at mid throttle settings. In calm air it runs fine. I know, it's wierd. I thought it was underjetted with the new pipe so rebuilt the carbs with kits from Z1 Enterprises with 17.5 pilot and 115 main jets. I installed a K & N air filter at the same time. My first ride this year was on a windy day and guess what? It didn't make a bit of difference.
My theory is that somehow gusts are lowering air pressure around the airbox intake. That's all I can come up with. I'm about to remove the first, lower section of the airbox to see if that helps.

Any idea's? I've run out.

Roger
 

·
Registered
Joined
·
11,328 Posts
For some bike's, installing K&N's can lead to a lot of problems. If they get wet while out driving, the engine will usually start running rich and foul sparkplugs. Side wind gusts can really have you scratching your head as to why the engine is surging, so you adjust float levels and tear into the carbs for a waste of time/money.

If you can, re-install the stock air box and paper filter along with the stock jetting, and then see if the engine performs better. When many parts are changed/replaced at once, it's hard to figure out just what is making the engine run sour.
 

·
Registered
Joined
·
522 Posts
Sounds like he's still got the standard air-box fitted Mike, with a K&N inside.

Strange that, never seen or heard the like with an airbox fitted Roger

I suppose the airbox lid is on, silencer-box still attached and sealed and the inlet pipe facing the standard direction?

If it's got the reed-valves and switch in the head is the pipe connected to the airbox?

Is the crankcase-breather pipe fitted?

Sorry if all this is too obvious Roger.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #4
Stock airbox, no changes with a K & N filter. This is a Canadian model - no reed valves going to the head. The crankcase breather is untouched. I had it open during the work I did and it's not blocked. Forgot to say I also raised the slide needles one notch when I overjetted. Jet sizes were recommended by an administrator on this forum. I've been running completely stock except for the pipe till this year. These changes haven't helped but I'm sure the bike is breathing better now. I don't know - it's baffling. How about gas cap vent blocked? I don't really want to mess with the airbox - I know it's designed to flow a certain amount of air.
 

·
Registered
Joined
·
522 Posts
Stock airbox, no changes with a K & N filter............How about gas cap vent blocked?
Hmmm, fat lot of use i were ;)

Can't see it being cap 'cos it'd be happening even on calm days.

How are the carb float-bowl vent-pipes routed??
 

·
Registered
Joined
·
96 Posts
I had a SIMILAR problem on my ZR550 .. I kept stripping carbs and it kept having issues riding into the wind. I'm not sure if this was the real "fix" but I ended up re-routing the carb breathers out of the direct airflow - some were stuck outnear the frame of the bike where I could see them. That was about a year ago and haven't had any issues since ..
 

·
Registered
Joined
·
11,328 Posts
Sorry, thought the bike had the cone shaped K&N's (which for some bikes, can be a real bugger to sort out). My understanding of the K&N's is they can cause more problems than they fix.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #8
Oneshadeofgreen mentioned the carb bowl vent pipes and that struck a chord. Poor fuel delivery might be because of low pressure inside the float bowl and guess what? One of the vent pipes was blocked - probably with a spider nest. I blew it out and voila! The bike pulls like a KZ should again!!! I've put up with that problem for ages and didn't look at the obvious.
Thanks everyone for your help.

Roger
 
1 - 8 of 8 Posts
Top