Rough Idle/Backfire

Sat Apr 27, 2013 3:57 am

Hey fellow Cubbers, I have a 54 Cub that Ive been having some recent hiccups with. When I first purchased the Cub, it was an old barn find and hadnt run in many years. You can imagine what it takes to get an old machine up and running so I wont go into too much detail. Long story short is that the Cub has been hibernating for about 6 months now. Went to start it up a few days ago to put her to work and it would crank but not fire. Took carb apart thinking no fuel and still nothing. Noticed there wasnt a spark. Cleaned distributer cap and sanded contacts, still nothing. Went a little deeper and saw my points were fried. Ordered new points, installed and now it cranks, coughs and dies. Took apart and made sure everything looked correct, pulled carb off again, cleaned, back together and left it overnight. Came out again today and it fired right up on half throttle but was rough in idle and eventually died. Cranked on full throttle and let it run for about 5 minutes successfully until it started bogging down and began to backfire through the exhaust (small carbon clouds flew from the muffler) where it then continued to bog until it died. Now it cranks like before and no start.

Not sure where this puts me at all. Ive corrected the timing before manually (played a guessing game until I got it right) and it worked great! Ive taken the Cub to parades, tractor shows and worked it nonstop. It couldnt possibly be out of time from just working with the points right?? Nothing was taken off except the distributer cap and the cover to get to the points.

Re: Rough Idle/Backfire

Sat Apr 27, 2013 5:29 am

I'm sure some of the other members will respond shortly but I'll throw out a few things until the "Pro,s" wake up :bellylaugh: ....Recently I was with a friend who's tractor ran fine while it sat but died when moved..It turned out to be the ignition switch, discovered by sometimes fire to the points and sometimes not..How about the coil...The backfire thing suggests that somewhat....Cracked dist cap....firing order correct...Theres's 2 1/2 cents worth... :headbang ....Keep us posted....Dave

Re: Rough Idle/Backfire

Sat Apr 27, 2013 7:22 am

AgTires4295 wrote:It couldn't possibly be out of time from just working with the points right??
Incorrect.

Could be several causes for hard starting, rough idle, and backfiring through the exhaust.

Start with a complete tune up including compression tests, valve tappet adjustment, plugs, points, condenser, service the distributor. Check and test for ignition faults, check for fuel flow problem, check for air leakage at manifold.

Re: Rough Idle/Backfire

Sat Apr 27, 2013 11:11 am

Thanks for the quick responses Dave and Eugene :big afro: Those mentioned by Eugene are a little over my head mechanically (valve tappet and compression testing) but I may be able to use that to start somewhere. Havent been out to look at it yet today but will keep this thread handy when I do. Will report back to yall with any updates.

Re: Rough Idle/Backfire

Sat Apr 27, 2013 5:26 pm

Is the fuel six months old?

Re: Rough Idle/Backfire

Sat Apr 27, 2013 7:05 pm

AgTires4295 wrote:........ Took carb apart thinking no fuel and still nothing. ............. Took apart and made sure everything looked correct, pulled carb off again, cleaned, back together and left it overnight........
AgTires4295 wrote:.......Those mentioned by Eugene are a little over my head mechanically (valve tappet and compression testing) but I may be able to use that to start somewhere. .......
Don't sell yourself short mechanically. If you can get the carb off; apart; back together; and back on, you can do everything Eugene mentions.

Tune up; you've already done most of it taking the distributor cap off and looking at the points. Just have to loosen a few screws and replace some parts.

Compression test; you can change a spark plug right? That's all there is to it. You just need the gauge, a cheap one or a borrowed one from a friend or auto parts store that loans tools.

Tappet adjustment; Well you can take the carb off, just two more bolts behind it to get to the tappets. Just need a feeler gauge and a couple normal wrenches. Most difficult part is getting #1 cylinder to top dead center which isn't really that difficult if you have a hand crank.

Plenty of help here if you need it. Just take some time and read through the service manuals on what the steps are, and ask questions if you're not sure.

Re: Rough Idle/Backfire

Fri May 17, 2013 3:53 pm

Hey all sorry for the tardy response. Ive been on midnights at work. Between that and a newborn, my life is upside down as some can imagine. I appreciate the additional helpful guidance. I had a few moments today and went out to see what happened. It fired right up at half throttle and half choke. It then started to again slowly turn to a rough idle and died about a minute later. I took the carb apart again and blew out the jet, made sure float was functioning properly, checked the gasket (less than a year old), put it all back together and attempted to start again. Cranked for about 10 seconds, fired, chugged and died 30 seconds later. Checked manifold for any leaks and found none. The little plug between the carb and manifold is also securely set in place.

There is 100% new gas in the tank as I ran the tank down dry before storing in my temperature controlled garage (to minimize condensation in the fuel). I guess I need to break down and find a compression test device (which it would be nice to know what numbers theyre producing but havent ever had a problem before). Im leaning towards timing but cant figure out how the heck the timing would have been thrown off my installing new points and condenser. Everything came out and went back exactly how I found it.

How do you go about testing the coil?

Re: Rough Idle/Backfire

Fri May 17, 2013 10:19 pm

check your fuel flow

Re: Rough Idle/Backfire

Fri May 17, 2013 10:28 pm

AgTires4295 wrote:cant figure out how the heck the timing would have been thrown off my installing new points and condenser. Everything came out and went back exactly how I found it.

Is the point gap set just right? If the points haven't been gapped correctly you can have problems.

Re: Rough Idle/Backfire

Fri May 17, 2013 11:43 pm

I've got great fuel flow. It fills the fuel bowl (I can see it churning around in there) and fills up the carb. Every time I attempt to start, I get a few drips (1 drip every 5 seconds) out of the bottom of the carb on the intake side (although it's done this off and on since I've had it, I'm not sure if that has anything to do with it). The float at one point was stuck in the down position, allowing fuel to gravity feed non-stop into the carb. I took the float off and checked it for leaks (checked fine) and dissembled the needle mechanism that moderates fuel. After cleaning the fuel gunk off and re-installing, it hasn't posed a problem that I've seen. This was about a year ago or so.

I guess when I get off in the AM, if I'm not too tired, I'll tear back into the points and check the gap unless anybody else has any more ideas to check up on without going to the store to buy anything :)

:)): Tired already :lol:

Re: Rough Idle/Backfire

Sat May 18, 2013 9:21 am

AgTires4295 wrote: Im leaning towards timing but cant figure out how the heck the timing would have been thrown off my installing new points and condenser. Everything came out and went back exactly how I found it.

How do you go about testing the coil?


Think of it like this. The points open in order to break down the electrical field, and cause the discharge (spark). That spark will occur when the points open exactly the right amount, depending on potential of the system. Now, in setting the gap, it might be a little different than it was before, so the points are getting to that open position either a little before, or a little after they were previously. That is a change in ignition timing. Since you said you adjusted it by ear before, I suspect your timing is now off a bit.

However, that probably does not account for it running 30 seconds, then dying. You likely have more than one issue.It could also be a condenser breaking down, especially since you said the points were fried. The condenser is there to keep the points from frying. I don't think you mentioned replacing the condenser.

Re: Rough Idle/Backfire

Sat May 18, 2013 1:06 pm

I didn't see where you replaced the condenser. They usually don't go bad but when they do the engine will run really rough and the points will burn rather quickly. It's a shot in the dark and may be all that's wrong.

Re: Rough Idle/Backfire

Sat May 18, 2013 1:40 pm

Here is where he said he replaced the condenser a couple posts up.
AgTires4295 wrote:Im leaning towards timing but cant figure out how the heck the timing would have been thrown off my installing new points and condenser.

Re: Rough Idle/Backfire

Sat May 18, 2013 5:21 pm

This is great that yall aren't giving up on this thread. I really appreciate logging in and seeing new responses to my problem. I'll see if I can make it out there tonight before work (the wife has our baby on a field trip to the grandparents today :{_}: ). I will be looking to double check everything yet again.

Re: Rough Idle/Backfire

Sat May 18, 2013 6:07 pm

Points affect ignition timing? Absolutely. Changing the point gap changes the timing- a little bit. Correctly mounting the points in the distributor is crucial for the first step. Checking the timing is the final step (absolutely last) in a good ignition tuneup.