backfire but no start.

I bought and swapped in an engine in my cj5, f-head. it ran when i bought it, i put it in (sat for a year) and now when i try to start it it wont start and just pops or backfires out the carb. any ideas? i checked the plug wires, all on right, spark at all cylinders. gas in carb and i even tried ether. Any ideas? i'm lost. Thanks, Geoffrey.

 

Stuck valve(s)? Checked the compression?

Also, is the exhaust clear? - I had squirrels fill my muffler with acorns once, over the winter. It would start, but had no power at all. Smelled good, though.

 

cap is dry, but i can clean it, exhaust is not hooked up. havn't tried a compression test yet. i'll inspect the cap tomorrow.

 

Have you checked the condenser ? A bad one will make it backfire.

 

how do i check the condenser?

 

The only way I know is to go to parts store and buy one and put it in. Don't throw it up on the dash and forget about for a week while you spend a ton of money on all kinds of new parts and get no were . Then remember to put it in and truck fires off with a turn of the key.

 

While your in there might as well replace the points as well, both are cheap

 

Could be a timing issue. If you had the distributer out and put it back in 180 degrees out it will cause your problem. Also valve train problems, stuck valve, collasped lifter I.E.

 

Never had the distributer off, i cleaned the points with a nail file, i'll try the condenser.

 

No hydraulic lifters in an F-head.


"i cleaned the points with a nail file"
If so, you ought to polish them clean with a business card or similar, to eliminate any particles.

 

Do a static timing on it.

Line up all of your timing marks, make sure the rotor is pointing to the 5 o'clock position as if it were the hour hand on a clock. This should be where the points are just beginning to open, and it should run. Can be 180 degrees out if some one has fiddled with the oil-pump, though. Pour a capful of SeaFoam down the throat of the carb. Or a shot-glass full of gas. Just takes a small splash to see if it is firing right.

 

Well i sprayed the cap with crc to displace whatever water there might be and still nothing. i'm trying new points and condenser tomorrow. it could be the wires possibly, i had them all off and i put them on and checked them against my 3B and i put my finger over the first spark plug hole and turned the engine over untill i felt compression and then checked the rotor against plug placement and it was 1-3-4-2, the firing order. i'm pretty sure i got them on there right, they go in that order counter clock wise on the cap.

 

Easy way to check the points and coil.........Pull the coil wire off the cap and leave the other end hooked up to the coil.....turn the key on and place it about a 1/2" away from the block or other grounded metal and turn the motor over and see if you get a spark? No spark.........check your primary voltage to the coil and make sure you have 12 volts. Backfiring out the carb is usually a timing issue.....IE: early Ignition while an Intake valve is still open.

 

His original post said he had spark at all four cylinders

 

Sorry about that...........after rereading I would go as others have mentioned with a condenser...............as he also mentioned the points were dirty and needed to be filed which normally means the condenser is leaking or sometimes the coil is down on energy....

 

So if it ran before and won't now after sitting for a year without any exhaust system on it I would certainly run a compression check as previously suggested. Popping/firing up through the carb sez stuck open intake valve to me.

 

x2