Welcome, Guest
Username: Password: Remember me

TOPIC:

Sputtering Under Hard Acceleration 05 Jun 2013 22:02 #590991

  • Topper
  • Topper's Avatar Topic Author
  • Offline
  • Platinum Member
  • Posts: 1611
  • Thank you received: 133
I'm getting a lot of sputtering and misfires under hard acceleration in the 6-7k rpm range.

If I creep up on those high rpms it's fine. But if I'm accelerating hard it sputters when the rpms get high.

Also, I can go wide open throttle and have no sputtering as long as I keep the RPMs below 6k.

What I've tried already:

Set float levels with clear tube method
Cleaned petcock screen
Replaced fuel lines and filters
Carbs have been cleaned and synced within the past year

I'm thinking I need to play with either the main jet size or tweak the needle position.

Any suggestions? Which should I try and would you suggest going leaner or richer?
Permanent and perpetual noob.

1979 KZ750 Twin
2009 Kawasaki Versys

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

Sputtering Under Hard Acceleration 05 Jun 2013 22:46 #590998

  • 650ed
  • 650ed's Avatar
  • Offline
  • User
  • Posts: 15344
  • Thank you received: 2828
Has this been an ongoing, long term problem or is it something new? Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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

Sputtering Under Hard Acceleration 05 Jun 2013 23:09 #591005

  • Topper
  • Topper's Avatar Topic Author
  • Offline
  • Platinum Member
  • Posts: 1611
  • Thank you received: 133
I'm not sure Ed. I'm riding a little harder than I used to.
Permanent and perpetual noob.

1979 KZ750 Twin
2009 Kawasaki Versys

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

Sputtering Under Hard Acceleration 05 Jun 2013 23:41 #591010

  • 650ed
  • 650ed's Avatar
  • Offline
  • User
  • Posts: 15344
  • Thank you received: 2828
Just a guess, but make sure your fuel tank vent is working properly. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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

Sputtering Under Hard Acceleration 06 Jun 2013 00:28 #591015

  • Topper
  • Topper's Avatar Topic Author
  • Offline
  • Platinum Member
  • Posts: 1611
  • Thank you received: 133
You think that might slow the fuel supply down? That'll be easy enough to look into. Any other ideas?
Permanent and perpetual noob.

1979 KZ750 Twin
2009 Kawasaki Versys

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

Sputtering Under Hard Acceleration 06 Jun 2013 08:40 #591048

  • 650ed
  • 650ed's Avatar
  • Offline
  • User
  • Posts: 15344
  • Thank you received: 2828

Topper wrote: You think that might slow the fuel supply down? That'll be easy enough to look into. Any other ideas?


It's possible. One other thing might be to make sure the timing advancer is lubed and working smoothly; if it is binding that could be a problem. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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

Sputtering Under Hard Acceleration 06 Jun 2013 09:28 #591054

  • Topper
  • Topper's Avatar Topic Author
  • Offline
  • Platinum Member
  • Posts: 1611
  • Thank you received: 133
Sounds like you're steering me away from carburetion as the cause. You don't think this could be related to main jet size or needle position?
Permanent and perpetual noob.

1979 KZ750 Twin
2009 Kawasaki Versys

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

Sputtering Under Hard Acceleration 06 Jun 2013 09:30 #591056

  • bluej58
  • bluej58's Avatar
  • Offline
  • Sustaining Member
  • The chrome don't get you home
  • Posts: 2484
  • Thank you received: 511
If you haven't changed the exhaust or gone to air pods I wouldn't mess with the jets or needles ,
I think Ed is on to something with cleaning and lubing the timing advance.

Do you have a timing light ?

JD
78 KZ1000 A2A

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

Last edit: by bluej58.

Sputtering Under Hard Acceleration 06 Jun 2013 09:48 #591057

  • 650ed
  • 650ed's Avatar
  • Offline
  • User
  • Posts: 15344
  • Thank you received: 2828
It is possible that it is a carb jetting issue, but if the carbs have the stock jetting and you are using the stock airbox it seems unlikely the carb jetting is the source of the problem, so before getting into rejetting the carbs I would check out all other things that might cause the stumble. Otherwise you might spend a bunch of time & $$ changing things in the carbs and still not solve the problem. Since the problem wasn't noticed until recently it is possible that something has changed to create the problem. This could be normal wear on parts that require periodic replacement or something that needs to be cleaned or lubed. It might be best to perform a full tune-up to ensure all the normal maintenance stuff is in spec as this might eliminate the problem. It could be something as simple as points/condenser needing to be replaced. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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

Sputtering Under Hard Acceleration 06 Jun 2013 09:51 #591058

  • Motor Head
  • Motor Head's Avatar
  • Offline
  • User
  • FIX UP YOUR BIKE RIGHT AND CHEAP
  • Posts: 5138
  • Thank you received: 391

Topper wrote: I'm getting a lot of sputtering and misfires under hard acceleration in the 6-7k rpm range.

If I creep up on those high rpms it's fine. But if I'm accelerating hard it sputters when the rpms get high.

Also, I can go wide open throttle and have no sputtering as long as I keep the RPMs below 6k.

What I've tried already:

Set float levels with clear tube method
Cleaned petcock screen
Replaced fuel lines and filters
Carbs have been cleaned and synced within the past year

I'm thinking I need to play with either the main jet size or tweak the needle position.

Any suggestions? Which should I try and would you suggest going leaner or richer?


What Filters do you have in your fuel line to carb rack? This may be restricting the flow enough that when demand is at its greatest that it runs the fuel level low.
Try it without the filter/s. Post picture of filter or link to it.
Be sure that the line doesn't have a Kink anywhere also.
1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
1979 MAZDA RX7 in the works, 13B...

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

Last edit: by Motor Head.

Sputtering Under Hard Acceleration 06 Jun 2013 10:05 #591059

  • Topper
  • Topper's Avatar Topic Author
  • Offline
  • Platinum Member
  • Posts: 1611
  • Thank you received: 133
I'm using these filters:

www.bikebandit.com/visu-filter-large-cap...0-degree-fuel-filter
www.bikebandit.com/visu-filter-large-cap...-in-line-fuel-filter

I've set the timing and point gap recently. The condenser has not been replaced in the time I've owned the bike (2 years).

I removed and lubed the shaft in the timing advancer. It looked really clean, no rust, buildup, crud, etc. But it was dry as a bone.

When I checked the timing and revved the engine the timing did advance at around 4k RPM, but it wasn't really smooth and I'm not 100% sure it fully advanced. I should check again.

The advancer was so clean and a replacement is so pricey, I was really hoping that wasn't the issue. I decided to just go with it, but maybe that is the problem after all.
Permanent and perpetual noob.

1979 KZ750 Twin
2009 Kawasaki Versys

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

Sputtering Under Hard Acceleration 06 Jun 2013 10:12 #591062

  • bluej58
  • bluej58's Avatar
  • Offline
  • Sustaining Member
  • The chrome don't get you home
  • Posts: 2484
  • Thank you received: 511
Because of all I have read about problems with inline fuel filters screwing with gravity fed systems,
I abandoned the idea and am putting all my trust into the petcock filter because the screen is very fine and I figure anything that passes it through will make it past the jets and get burned up.

9000+ miles and far so good .

Here is a little advise Wire George gave me on the order of how to tune a Honda that I am getting started after 30 years of sitting.

Quote ;

At this point, most owners, seeing the plugs don't look exactly as the textbooks would show them will start ripping the carburetors apart and turning every adjustment screw and swapping jets.... hehe or sending them to some shop.

Before you do, ride the bike a bit and let the rings settle in if the bike has been sitting. Compression will come up and the valves will seat back in. Change out all the tune up stuff in the ignitiion... plugs, wires, points, condensors and clean/lube the mechanical timing advance. Check resistance at the coil or coils; both primary and secondary and if out of spec, swap to modern coil(s) and check voltage going INTO the coil(s). Lots of folks have benefited from the coil mod described on my website.... even a couple of extra volts going to the coils will give you a much brighter spark.

Once these issues have been dealt with, look at any rubber bits connecting the carbs to the engine and anything that seals the combustion chamber is probably due for replacement such as exhaust gaskets... Most Hondas used orings to seal the carbs and these can't be too spiffy nor can any rubber carb boots. At this point, do a compression check or even a leakdown compression check and decide if a top end freshening is worthwhile (I just do the top end as a matter of course but that is a personal habit) and then decide where to go mechanically.... of course, don't neglect the cables, brake pads, chain and sprockets and such things... drives me nuts to see these items ignored and folks busy with paint and polish.
78 KZ1000 A2A

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

Powered by Kunena Forum