- Posts: 1611
- Thank you received: 133
Engine racing at idle
- Topper
- Topic Author
- Offline
- Platinum Member
Suited up and started my '79 KZ750 to go for a ride today and the engine just started racing. I pushed the choke lever all the way off and the racing topped out at about 5k.
I checked the throttle cables and everything is moving as it should. The throttle stop seems to be working. It's not like the throttle is stuck open or anything.
I tried spaying some WD-40 around the intake boots but it had no effect.
Carbs were removed and cleaned thoroughly less than a year ago. It's been running great.
The only recent work I've done is on the starter motor and starter clutch. After re-assembly the bike started just fine and I didn't experience this racing. That was about a week ago and I haven't ridden since.
So, do I need to just pull the carbs again and see if something's stuck in there?
Permanent and perpetual noob.
1979 KZ750 Twin
2009 Kawasaki Versys
Please Log in or Create an account to join the conversation.
- martin_csr
- Offline
- User
- Posts: 8068
- Thank you received: 1656
Please Log in or Create an account to join the conversation.
- Topper
- Topic Author
- Offline
- Platinum Member
- Posts: 1611
- Thank you received: 133
I pulled the carbs and checked everything making sure the butterfly valves and slides were moving freely. Nothing looked wrong with the diaphrams. Everything checked out.
Put it all back together and everything is fine. No engine racing.
I guess it had to be a bad seal at the intake boots or carb holders. I just couldn't find it with the WD-40 trick.
Gonna go for a short ride and make sure everything is good.
Permanent and perpetual noob.
1979 KZ750 Twin
2009 Kawasaki Versys
Please Log in or Create an account to join the conversation.
- dshelly
- Offline
- User
- Posts: 259
- Thank you received: 5
Occupation:Machinist 25+ exp.
'77 Kz1000B1
'78 Kz1000A2
'76 Kz900LTD
Please Log in or Create an account to join the conversation.
- Topper
- Topic Author
- Offline
- Platinum Member
- Posts: 1611
- Thank you received: 133
It wasn't the idle adjust screw. I checked that and backed it way out, made sure the throttle linkage was back as far as it would go and the engine just hung at 5k.
I'm really leaning towards a leaking intake boot. When I was putting the carbs back in, the right intake boot popped free of the airbox with very little pressure on it. I think that's where the leak was.
Permanent and perpetual noob.
1979 KZ750 Twin
2009 Kawasaki Versys
Please Log in or Create an account to join the conversation.
- MFolks
- Offline
- User
- Posts: 6650
- Thank you received: 540
1982 GPZ1100 B2
General Dynamics/Convair 1983-1993
GLCM BGM-109 Tomahawk, AGM-129A Advanced Cruise Missile (ACM)
Please Log in or Create an account to join the conversation.
- Patton
- Offline
- KZr Legend
- Posts: 18640
- Thank you received: 2098
Topper wrote: ...I'm really leaning towards a leaking intake boot. When I was putting the carbs back in, the right intake boot popped free of the airbox with very little pressure on it. I think that's where the leak was.
Leak at the carb holder area on the engine side of the carb may result from whatever reason such as a crack in the carb holder or just a worn out carb holder, or perhaps an insufficiently tightened clamp that holds the carb inside the carb holder -- typically results in a racing idle due to overly lean air-fuel mixture attributable to extra air being sucked in through the leak.
Am thinking that a slight air leak on the air box side of the carb doesn't generally result in a racing idle.
Good Fortune!
1973 Z1
KZ900 LTD
Please Log in or Create an account to join the conversation.
- Topper
- Topic Author
- Offline
- Platinum Member
- Posts: 1611
- Thank you received: 133
Patton wrote: Am thinking that a slight air leak on the air box side of the carb doesn't generally result in a racing idle.
Hmmm... well that throws a wrench into my theory about what was wrong.
The boots and carb holders are in pretty good shape. There's no visible cracks or wear and they're all still pretty flexible.
The other thing I noticed when removing the carbs was that one of the ends of the balance tube (that connects the carb holders) had slipped a little. It hadn't come off, but it was a little loose. Maybe that would do it?
Permanent and perpetual noob.
1979 KZ750 Twin
2009 Kawasaki Versys
Please Log in or Create an account to join the conversation.
- Tomolu5
- Offline
- User
- Posts: 421
- Thank you received: 45
Mine:
04 Honda rebel 250(wifes)
04 GSXR 750(bolt on galore)
98 CBR 600F3(filter, pipe, adjustable cam sprokets, dyno tune)
76 KZ900A (LTD gauge pods, crash bars, LTD(style)pipes, dyna coils and ignition,headwork and mild port cleanup by cavanaugh racing, K&N filter pods, heck I dunno.
Please Log in or Create an account to join the conversation.
- mbosanko
- Offline
- User
- Posts: 3
- Thank you received: 1
I've been working on my KZ750 basket case for a while and had a similar symptom. On starting it would race up to 5/6000 rpm. It had pods and a 4 into 1. Long story short, swapped pods for stock air box, and after checking for (many) air leaks,finding and fixing 'em, it now idles WAY better. So I'd say keep checking for air leaks. Even the smallest leak made a BIG difference to the idling. Good luck, regards Bos
Please Log in or Create an account to join the conversation.
- Topper
- Topic Author
- Offline
- Platinum Member
- Posts: 1611
- Thank you received: 133
I've cleaned the pilot passages, set fuel float levels with the clear tube method and balanced the carbs with a vacuum gauge. I was about to re-test the carb balance, but this has me thinking maybe I've got an air leak on that side.
Permanent and perpetual noob.
1979 KZ750 Twin
2009 Kawasaki Versys
Please Log in or Create an account to join the conversation.
- KZJOE900
- Offline
- Admin
Topper wrote: The right carb on my twin has always run a lot leaner than the left. I have to have the mix screw out nearly three turns on the right, but the left is right around 1.5 turns out. (Out enrichens and in leans on these carbs)
I've cleaned the pilot passages, set fuel float levels with the clear tube method and balanced the carbs with a vacuum gauge. I was about to re-test the carb balance, but this has me thinking maybe I've got an air leak on that side.
Good deduction Topper. Maybe between your carb holders surface and the head. Maybe too small of a leak to be detectable using the WD-40 method but enough to have an effect you described on your right carb. Hope you nailed it. Good luck.
Current project 76 KZ900 (This was a Vetter model)
76 KZ900
81 XJ550H SECA (Current Project)
82 XJ550R SECA
Past:
86 FJ1200
74 Z1900
72 CB450
Please Log in or Create an account to join the conversation.