7 replies to this topic

[77LeylandMini]

Happy Holidays! We replaced 73MiniSport's factory air filter with a cone K & N air filter this weekend, and the car is NOT happy. It wasn't running perfect to begin with - it sat for a month while it was being repaired in the body shop, when we brought it home it was much colder so it needed a little tuning. The timing was adjusted and the valves were adjusted as well, and we leaned it out - still seemed slow after that. Well since the new air filter was put on in the morning it backfires (it's pretty cold out) and seems quick on initial acceleration but then it hits a wall above 1000rpm - and this happens in all the gears. Too slow for a 1275...any suggestions? The manifold and exhaust are appropriate for the filter. The gas mileage seems poor as well. Thanks for any help!

[vasi]

You've not disturbed the vacuum pipe while working in the area?

[dan__wright]

sounds like timing / mixture is wrong.

[cooper_shaz]

Sounds l;ike the timing is too far advanced and the mixture is too lean.
Did you use a timing strobe to set it ??

and how did you lean the mixture, was it guesstimate or did you use colour tune or something similar ?

[77LeylandMini]

We used a timing light to do the timing (before the new air filter was put on), while we were working on that we found that the vacuum advance hose had fallen off and melted - so we fixed that. As for leaning it out, well, we did it by trial and error - which didn't work this time!

[dklawson]

Start with a static timing around 5 BTDC. Readjust your carb(s) using the lifting pin method... starting from the initial position (following a rebuild) as defined by Haynes and the SU manuals. Once you've got a working mixture, set your dynamic timing where you want it.

Backfiring through the carbs is typical when the mixture is too lean. Backfire through the exhaust when the timing is off and the mix is rich. If the timing is too far advanced you'll hear pinging from the engine when it's under load/accelerating.

[Leonard]

after changing the filter and exhaust, youll probably need a different needle. i agree it sounds too weak. if it runs better with the choke out, that confirms its too weak

[77LeylandMini]

Did a little tuning today - running better, but do think that the needle may be wrong. It runs better at higher rpms than lower - not backfiring anymore. Still seems to be more like a 998 than a 1275! Thanks for all your help!
We checked the numbers - it's a metro 1275.