1991 ZX7 track bike - carb issues? | GTAMotorcycle.com

1991 ZX7 track bike - carb issues?

smudger

smudger

Well-known member
Hi gents,
Came to start my 1991 ZX7 up last week & it wouldnt start as it should do.
It would fire up after a lot of coaxing but the RPM would be at just under 1000, she sounded like a V twin & would then cut out, this happened every time I tried to start her up
When she went into storage I stupidly left the gas tank half full with treated gas & didnt drain the carbs.
Sooooo, I replaced the battery & drained & re-filled the tank with fresh gas & eventually the old girl started on the choke & puffed a load of black smokey crap out of the exhaust before finally settling down & running ok - no more smoke out of the exhaust or anything like that.

However, now mainly when shes warm & I blip the throttle the RPM doesn't return to idle, it sticks around 2500-3000 even though the throttle is fully closed - any ideas - does she just need a spray with WD40 or is it a carb strip & clean scenario?

Martin
 
If the idle hangs, you are lean or have a vacuum leak. Carbs may need cleaning (especially the pilot jets) but check the intake manifolds for cracks or leaks.
 
ninjanut said:
If the idle hangs, you are lean or have a vacuum leak. Carbs may need cleaning (especially the pilot jets) but check the intake manifolds for cracks or leaks.
Click to expand...

Could also use a carb sync.


"You lost 15 friends on motorcycles? and you have only been riding since 2008? was this a group ride that fell off a cliff or are you being serious?"-ZX600
 
Thanks guys, bike was running fine before being put in a tent (Can Tire Shelterlogic thing) for the (very cold) winter.
I got the bike in Oct last year so I havent really ridden it & have no history on it at all but now I'm leaning towards removing the carbs & stripping & cleaning them - I am reasonalbly mechanically minded, is this something I could do myself or should I just remove the carbs & take to my local bike shop to get the job done?

Ninjanut - when you say intake manifolds are you talking about the rubber boots the carbs mount into & is there anyway of testing if one of these is maybe cracked or leaking?
Also the air cleaner box was a total b-tch to remove, is there anyway I could have damaged or moved the carbs in their rubber intakes while removing the airbox?

Smudger
 
I would definitely recommend removing and thoroughly cleaning the carbs as they are very finicky on 7s. Pay particular attention to the pilot jets and make sure they are extremely clean and all the small passages are clear. The airbox on theses is a total b**** to remove and install again. The manifolds are the rubber boots that attach the carbs to the intake. You can physically inspect them or you can check them when the bike is running by spraying carb cleaner around them and see if the idle speed drops.
I would definitely recommend you do it yourself as a shop will charge big$$ to work on them.
 
Much appreciated ninjanut, I'll have a look at the intake manifolds initially, if I cant see anything wrong there then I'll remove the airbox again & the carbs.
Local bike dealer in Guelph quoted me around $200 + any required parts to strip & clean the carbs if I remove them from the bike but I really, really want to learn how to do these maintenece tasks myself.
 
They are not difficult to do yourself, just be organized and meticulous. Once you do it yourself, you will not spend money at a shop for this again.
 
A bit of an update, still need your help please.
I had the bike out at TMP for its first trackday on Saturday & it wouldn't rev past 7K & sounded/felt to be missing/running rough & then every now & again it would kick in & run normally for 10 secs or so before going back to 7k max revs.
It was also popping & farting a bit at idle while waiting to go out on track.
I still have the issue of the revs notdropping back to idle staright away but hanging at 2500rpm then slowy returning to idle.
I took the carbs off yesterday & will take them into the shop to get them stripped & cleaned as I wont have the time this week due to work but I need the bike running for the weekend as I'm back down TMP for track school day on Saturday afternoon.
The inlet rubber boots look like new (to me) as i can see them now the carbs are off.

Any other suggestions guys?
 
If its is hanging like that, it sounds like a vacuum leak.
 
Yea, I'll check the rubber boots again & also the caps on the vacuum sync tubes to make sure they arent damaged or missing as well when I get the carbs back today.
The shop told me the carbs were actually pretty clean inside but they gave them a good old once over anyways.
I have noticed that the fuel lines where they connect to the tank outlets on both the main & reserve were pretty seriously kinked immediatley below the brass oultet fitting from the tank.
You can still blow through the line & but its proibably only 30-40% of the opening it should be.
I'm now thinking (hoping) that this allowed enough fuel to reach the carbs & run at low to medium rpm but starved the carbs at high rpm & couldnt fill the float bowls quick enough due to not enough fuel coming through - do you think thats a reasonable asumption?
Anyways for $12 I've replaced both fuel lines from the tank to the fuel tap & we'll see how it goes once I have the carbs back on tonight.
 
If the fuel line from the tank is kinked at all, it will be an issue. OEM is actually moulded with the correct bends in it and would highly recommend going with those. Where they fit under the tank is also a potential pinch point if they are not routed correctly.
 
Thanks Ninjanut, the kink was directly under the tank on both lines.
I'll definately look into OEM if thats the case but for this weekend I'll route the replacements the best I can to avoid any kinks
Crappy picture but it gives you the idea, must have only been letting through 35% of the gas:

View attachment 36915
 
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That is a serious kink. I would say that it was definitely the issue. If you are running pieces of cut fuel line, make them longer and gradually bend them so you don't have the same issues. Strongly recommend the OEM moulded ones as a permanent fix though.
 
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