scout 71 800 with 304 started to backfire after 5 days of no use.

[rivastian]

Hi guys, I did a couple of searches on this but i am trying to get as much current information as i can.

I have a scout 71 800b with a 304, 2bbl holey carb and manual tranny. The scout started to backfire through the carburetor after been on the driveway for 4or 5 days of no use.

The scout starts fine and run fine in idle but as soon i start increasing rpms, the scout starts backfiring and I am unable to use it as it has very little power due to the backfiring yet i am able to hit the gaspedal all the way and the it will rev up but backfiring.

I checked carb (make sure that there is enough gas going to the motor), check for any cracked hoses and check that spark was going to the sparkplugs.
also i removed each of the sparkplugs and cleaned them and make sure that they were snug there.

The scout developed a knocking awhile back and i am worry that the knocking and now the backfiring are related.

I sent an email to John fleck from bcc for pricing on motor heads and complete motors just in case but i would like to keep my current motor.

any help will be greatly appreciated.

thanks

Chris.


ps: some other things that i will do are to check the needle to try to adjust the gas but i dont think this will do anything.

I read that it could be a stuck valve but....

[damnesia]

I could be a stuck float. You could try to spray cleaner in the carb and tap the front of the carb a little and see if it unsticks.

[Dana Strong]

It sounds like a lean fuel mixture which could be caused by an obstruction of the main jets, perhaps some air leaks in the high speed circuit, or a very low fuel level due to various problems. I'd look inside the fuel bowl for anything obvious, maybe after first spraying (carefully) the outside of the carb (at the main body to metering body or throttle body) with starter fluid or gasoline to check for possible external leaks at the gaskets, while the engine is cold but idling. This requires a clean engine and appropriate caution, because fire is a distinct possibility if done carelessly.

[rivastian]

i failed to mention that i tried the following on all 8 cyl:

Now to explore each question, I will use a hypothetical situation. I have a small car with a 4 cylinder motor. I drove it home last night, and when I started it this morning, it had a definite miss.

To identify which of the cylinder(s) are misfiring, no actual tools are required. To find which cylinder(s) are having the problem, simply open the hood with the key "off," and check to see if anything is loose (i.e. a spark plug wire). If everything is snug, try removing one of the plug wires (NOTE: Only remove 1 plug wire at a time!). Then reach inside the car and try to start it. If you have a 4 cylinder motor any difference will become immediately apparent. In fact, most times the car will fail to start and stay running. If the plug wire you removed made no difference in the way the car runs, that means that cylinder is not firing. Replace the wire to its original location, and make sure that it is snug. Try another wire. Continue this process until you find the cylinder(s) that are causing the problem. (NOTE: Keep notes on which cylinder(s) are having the problem, and how the car behaves.)

Next will be to clean the carburater, check th efloaters, check the needle and if that does not work i will be planning on getting new heads and if that does not work, i will go checy on my poor scout.

[Dana Strong]

I somehow missed that you said it was backfiring through the carb; I'd run a compression check to see if a stuck-open or leaky valve might be causing the problem. I would expect that to occur at idle too, not just higher speeds, but I suppose it's possible.
If a spring in the distributor broke, the timing might be mechanically advanced too far so added vacuum advance at higher RPM might cause the problem too; that can be easily checked with a timing light.
IMHO, it's best to do the simple things first before resorting to hard and expensive things like pulling heads.

[rivastian]

DanaS,

do you think that a bent pushrod will do this? perhaps that the valve that correspond to the pushrod is not lifting or not closing?

I will check the distributor, and also i will open the valve covers to see if all there looks correctly i have extra gaskets that i've been wanting to replace and i think this will be a good reason to do so.

John fleck emailed me and told me that a 304 mortor head will be 50 bucks so...

I am just keeping my options open and a good simple way out.