it is on my 84 d/r brat with a weber , i put on acell coil regaped plugs , set timing at .8 check all vacuum hoses , any suggestions ,it ran fine with a regular coil ,but wanted a better coil

Sounds kinda like you need to advance the timing a couple degrees? But dont trust me on it.

set timing up to .15 still same problem , when setting timing is there a vacuum line that has to be removed and then put back on when timing is set ?

yeah it runs from your disty to some weird looking spaceship doohicky... you pop one end of that hose off.. plug both holes? or at least make sure the spaceship thingy isn't getting air... but I plug both when I do it.

ok, will do , also could i have mixed up the wires on the coil ? but it will idle just fine ?

that's possible. if you put the wrong length of wire going to the wrong plug. In my brat I put:

 

3) Shorter.. 4) Longest

1) Shortest. 2) Longer <--- Motor

 

...........1

.........3 - 4 <--- Disty

...........2

 

I hope my "Ascii" skillz come out good And I hope it's understandable!

Timing alone (if just a few degrees off) shouldn't really give you backfire. Having a couple of spark plug wires switched can/will. When does it backfire? Did the idle speed/quality change after your work? Did you change anything in the ignition secondary other than just regapping the plugs?

 

As far as vacuum lines and timing, I haven't had to deal with this for awhile, and I don't have an 84 EA81 to check. Typically, the distributor has one or 2 vaccum hoses going to it. If one, that is the vac-advance; if two, then one is advance and one is retard. Disconnect both, plug both just to be sure, and set your timing. Or you could always RT*M... assuming you have a manual.

 

Seriously, though, the backfire is probably not related to a slightly misset ignition timing. More situational info would help.

 

Don't make me come there just to test drive your Brat! (hhhmmm....)

it will back fire after it warms up and winding up the gears ,like between 2-3 gear , but just a week before it ran fine , i took 1 plug wire off at a time to regap the plugs , tomorrow i will recheck and close off vac lines when setting timing , :-\

Having some random thoughts of my own about timing and found this thread from a few weeks back. Ever get it fixed 86?

no doing outside house work , will look at it monday - tuesday 27th -28th, i did notice that one of the steel ends are not hooked up ,close to the dist