Technical Cold Start Issue

[John Nolan]

I am new to the forum and new to the Classic 500 community. I have been recently experiencing issues with starting up in colder weather although I now suspect that is not the root issue (40 def F / 4 deg C). My ‘72 had been starting and running great until recently.

Now it struggles to start. The choke is not assisting any more and have to throttle the gas pedal to get it going and takes 20+ minutes to get a good rhythm. I hear some popping and backfire that is unlike its usual behavior. Tonight was the worst of its behavior as it took a substantial amount of cranking with no audible sputter until a lucky turn got it going.

I have replaced the spark plugs and checked all connections. I am assuming the carburetor is the likely suspect now. Particularly because I am noticing fluid accumulation around it.

I do not suspect the carburetor had been over tightened as I have not adjusted this and was not an issue before (a common issue I’ve read in some research). Another suspicion is the float but I wanted to get some feedback before disassembly.

Picture is attached, thank you in advance for any assistance!

 

[348azeus]

It could be wet just because of the amount of time you take trying to start it and so it’s throwing fuel in. Is the choke actually operating ? I notice from the photo that the choke is not engaged make sure it moves when you pull the lever. I would always start from the basics make sure the plugs are good, that you’ve got a strong spark and if that’s ok then it could be that you have a problem with the starter valve or need a carb rebuild kit.

 

[StMarks]

Now it struggles to start. The choke is not assisting any more

This is going to be a bit obvious, and doubtless you will have already checked, but....: It couldn't be that when you operate the choke lever in the cabin, it no longer changes the choke lever on the carburettor.? (broken, snagged or slipped cable etc,,,)

 

[John Nolan]

It could be wet just because of the amount of time you take trying to start it and so it’s throwing fuel in. Is the choke actually operating ? I notice from the photo that the choke is not engaged make sure it moves when you pull the lever. I would always start from the basics make sure the plugs are good, that you’ve got a strong spark and if that’s ok then it could be that you have a problem with the starter valve or need a carb rebuild kit.

Thank you for the reply. The choke is functional and works once the engine is running. I am suspecting a carburetor issue because I had just replaced the plugs and the engine will not turn over unless I press the gas pedal and once running I need to periodically push the gas pedal to keep it from sputtering out.

Once the engine reaches a certain point it gets a good rhythm and the choke and throttle are not necessary to keep it idling.

Could there be something wrong with the float in the carburetor? In the pictures you’ll notice liquid accumulation around the carb, maybe it’s not accepting the gas and spitting it out?

 

[John Nolan]

This is going to be a bit obvious, and doubtless you will have already checked, but....: It couldn't be that when you operate the choke lever in the cabin, it no longer changes the choke lever on the carburettor.? (broken, snagged or slipped cable etc,,,)

Thanks for the reply. I appreciate the sanity check but yes the choke is functional. Once the engine is running if the choke is adjusted it appears to have the right effect.

 

[Toshi 975]

If you have a conventional ignition system have you checked the contact breaker points gap recently?

 

[John Nolan]

If you have a conventional ignition system have you checked the contact breaker points gap recently?

Thanks for the reply. I will absolutely check that once I get out of work. Reading up on some articles regarding the ignition system that would definitely explain a lot of the symptoms I have been trying to triage

 

[John Nolan]

Thanks for the reply. I will absolutely check that once I get out of work. Reading up on some articles regarding the ignition system that would definitely explain a lot of the symptoms I have been trying to triage

Amazing. Checked the gaps, adjusting the timing, and it runs like never before. Worked on it after putting the kids to bed so it was cold out and I didn’t even have to use the choke. Fired right up and all symptoms disappeared. Thank you all of the help!

 

[the hobbler]

Amazing. Checked the gaps, adjusting the timing, and it runs like never before. Worked on it after putting the kids to bed so it was cold out and I didn’t even have to use the choke. Fired right up and all symptoms disappeared. Thank you all of the help!

One thing to remember about the IMB carburettor that the 500 and 126 engines use is that they do NOT have an accerator pump, so pumping the accelerator pedal whilst trying to start one of these engines will absolutely NO effect---you are effectively just flapping your foot! I am not accusing you of doing that John, just pointing it out

 

[John Nolan]

One thing to remember about the IMB carburettor that the 500 and 126 engines use is that they do NOT have an accerator pump, so pumping the accelerator pedal whilst trying to start one of these engines will absolutely NO effect---you are effectively just flapping your foot! I am not accusing you of doing that John, just pointing it out

Thanks for the knowledge! Good to know