- Posts: 18
- Thank you received: 0
New VM28SC on KZ1000A2 - how to dial it in?
- kwaker
- Topic Author
- Offline
- User
The bike fired right up and idles fairly well after adjusting the idle screw, however it keeps back firing when idling.
No fuel issues (clean tank) and there are no vacuum leaks.
There are no hesitations revving up the bike, but coming down from high rpm's it back fires on the way down.
Any pointers where to start would be greatly appreciated.
1980 KZ 1000 LTD (daily driver)
1978 KZ1000 (project)
Scottsdale, AZ
Please Log in or Create an account to join the conversation.
- wireman
- Offline
- User
- The most interesting prick in the world
- Posts: 4761
- Thank you received: 299
posting from deep under a non-descript barn in an undisclosed location southwest of Omaha.
Please Log in or Create an account to join the conversation.
- Patton
- Offline
- KZr Legend
- Posts: 18640
- Thank you received: 2098
coming down from high rpm's it back fires on the way down --- would suspect too lean pilot circuits.
Try turning in the pilot air screw on each carb clockwise, say 1/2 turn, to enrichen the pilot circuits. This reduces the air allowed into each pilot circuit.
Would also assure all valve clearances are within specs. A too tight intake valve clearance may allow combustion within the cylinder to escape through the intake port into the carb.
Good Fortune!
1973 Z1
KZ900 LTD
Please Log in or Create an account to join the conversation.
- wireman
- Offline
- User
- The most interesting prick in the world
- Posts: 4761
- Thank you received: 299
posting from deep under a non-descript barn in an undisclosed location southwest of Omaha.
Please Log in or Create an account to join the conversation.
- kwaker
- Topic Author
- Offline
- User
- Posts: 18
- Thank you received: 0
I took the timing cover off and to my surprise I found that the advance had been changed to a Z1 Advancer (3 digits). The 78 KZ1000A should have a different advancer (one with 4 digits).
Since I dug into the timing I went ahead and installed a new Dyna ignition.
I checked the timing with a timing light prior to changing the points out for the Dyna, and low and behold the timing was way off!
Since I did not have an Advancer for a 78 to 80 KZ1000 I used the one presently installed, but changing to the correct advancer will improve things further.
After the timing was adjusted I tinkered with the pilot air-screws and attempted to sync the carbs. Boy, these VM28's are not liking to stay in sync...
So far I managed to tune the bike to a state where it is not backfiring. It idles pretty well, no back-firing. The only thing I could not accomplish is to get rid of the "popping" when coming down from full throttle..
My next step I think will be to change out the old Z1 advancer for the correct one.
The "popping" from coming off full throttle probably means that it runs a bit too rich under full throttle... but I guess that is better than too lean at full throttle.
Do you think there is a way to dial in the VM28's to get rid of the "popping" when coming off full throttle?
Thanks again for all our feedback. Your advice has been great!
1980 KZ 1000 LTD (daily driver)
1978 KZ1000 (project)
Scottsdale, AZ
Please Log in or Create an account to join the conversation.
- baldy110
- Offline
- User
- Posts: 2272
- Thank you received: 512
It is virtually impossible to set up carbs that were never on a particular bike for pods and a header by "bench" tuning them. You have to do that on the bike and that is what you doing now.
Please Log in or Create an account to join the conversation.
- mtbspeedfreak
- Offline
- User
- Posts: 1413
- Thank you received: 36
www.z1enterprises.com/ItemDetails.aspx?i...l+Set&item=MP08-0022
2000 ZRX 1100
1976 KZ 900- Daily Driver
1980 LTD 550- Dalton Highway survivor!
If it has tits or tires, it'll give you problems!
Please Log in or Create an account to join the conversation.
- DesertKZ
- Offline
- User
- Posts: 227
- Thank you received: 20
baldy110 wrote: If you mean by backfiring popping through your carbs at idle then it is running to lean, go up one size on the pilot jets, your VM28 probably have #15 pilots go to a 17.5. Popping through the exhaust at closed throttle could be either to rich or to lean. However if they are popping through the carbs also then I would say your idle circuit is to lean.
It is virtually impossible to set up carbs that were never on a particular bike for pods and a header by "bench" tuning them. You have to do that on the bike and that is what you doing now.
I thought pilots didn't come into play until the bike was off idle? I'm a noob at this BTW.
1979 KZ1000 Shaft
1979 CX500C
1975 GT750 Smoker
Please Log in or Create an account to join the conversation.
- baldy110
- Offline
- User
- Posts: 2272
- Thank you received: 512
Please Log in or Create an account to join the conversation.
- kawasaki mike
- Offline
- User
- kawasaki mike
- Posts: 128
- Thank you received: 4
Am addicted to Z1's and kz 900's have an el camino, fly rc helicoptors and am strung out on horsepower.
Please Log in or Create an account to join the conversation.
- roy-b-boy-b
- Offline
- User
- Posts: 3255
- Thank you received: 103
1979 LTD Street Fighter.1977 KZ1000
Please Log in or Create an account to join the conversation.