Very rough idle 1.3 carb sj50

[BZOOK]

I'll give the blocked jet fix a go then consider the coil. Thanks for the input.

[christover1]

Correct coil is important if needed.
I for get wether it is an R or not.
My 1.0 was a resistor type, not sure with 1.3

[gwagensteve]

I'd recommend getting hold of a factory service manual and looking at choke operation. If the choke was sticking you'll get the outcome your describing. In any case, a FSM will help you get everything back to baseline. It's easy to get lost in variables and get a (poor) result but with everything miles out of adjustment.

Yes otherwise, idle jet.

Coil is a bit tougher. I'd have thought if it was going to misbehave it would be at low revs high load, when spark needs to be strongest. Lots of cars with broken down ignition will idle and free rev but won't take any load. Same with fuel pump.

Steve.

[BZOOK]

Seems the auto choke was bypassed by a previous owner. There is a cable tie holding the butterfly open. It hasn't been an issue till last week. I assume the wax element is stuffed. Sure it takes some revs for it to warm up but hasn't really seemed to have any issues. It does sound like my mower does when the filter was clogged with oil. I think I'm going to have to take it to a mechanic. Thanks all for your input.

[BZOOK]

Hi all. Got my mechanic to take a look. He confirmed it was definitely the carb and likely a blocked jet. After completing my first carb strip and rebuild the only visible issue was a stuffed seal on the primary slow jet. All the gaskets were toast. All back together and is running much better. No rough idle or backfire. Haven't taken it for a drive yet. It is idling a little high so some fine tuning needs to be done. Great news is I'm back in business it seems. Thanks to all for helping me work through this.
Brenton.

[christover1]

Extra fuel filter between pump and carby is a good idea. As is a new pump, as they can break down and put bits into carb.

[Mike57]

Or the plug leads are breaking down and there is cross fire happening to cause the backfire. On low idle it can just stall due to lack of spark. After you are sure the carby is Ok change the plug leads and then the coil.

Edit - Well maybe I should have read the second page before posting that!