Potential Petcock/Carb Issue 83 Midnight Maxim

Hello peeps to be fair I'm gonna be honest this is actually my first motorbike restoration its a 1983 Midnight Maxim. Its not far from it being able to ride properly on the road but I'm having engine issues.

Since i have owned the bike I had it running on two cylinders with bad spark plugs which was fixed and started back up onto 4 cylinders with good spark plugs and since then I have yet to start it until a couple days ago and its now not wanting to run. The cylinders are wanting to fire but there doesn't seem to be any fuel getting to them. I was thinking its the carb not taking any fuel in but I've just tried the petcock without any fuel lines and it gives a dribble of fuel out on "RES" and then stops and barely any flows out when its turned to "ON". I dont know if its vacuum and its just stopping the fuel until the engine turns or its the carb not taking the fuel.

I'm very much unsure and I dont really understand where the issue is coming from as I can point to multiple things that could be causing it. (I have injected fuel via the spark plugs into each cylinder and it happily fired on that and idled at 2200 rpm before dying strait out due to the small amount of fuel I gave it).

Can anyone help? I dont want to go and spend money on my carb if its my petcock that is causing the issue. Cheers

 

If your bike has been sitting for awhile there may be low fuel in the carb bowls. Since the petcock is vacuum operated, you should not see fuel flow while on Res or On setting unless the bike is running. Set it to prime to make sure gas comes out. If the bowls are empty, it can take a long time to fill them by cranking the engine. This may be your problem. To initially fill, set the petcock to prime for a short time. Then see if the bike starts.

 

Before i had it im going to guess maybe 5 years it has been sitting in america before it came over to the UK, i have tried starting it many times yesterday and the day before and it feels like it wants to go it tries to fire but theres just no fuel getting to it unless i manually feed it fuel via the spark plugs.

 

Set it to prime. Wait a minute or two. Set to on. Try starting. If no response, pull gas line off , set to prime, see if gas flows out.

 

Il give it a try, would that be i take the main fuel line off and leave the smaller hose attached?

 

The smaller line is the vacuum line that attaches to one of your carbs. The large line delivers fuel to the carbs. To check if your prime setting works you can remove the fuel line and set to prime an observe if fuel freely flows out, make sure to capture the gas in a rag or something. If it works, reattach to hose, set to prime for a minute or so and try to start. Watch you carbs when filling from the prime setting, if your floats are stuck in a carb or your float needle does not seat properly, you will probably overflow out of the affected carb. Check the floor for a puddle forming.
You can also check your petcock on Res or On by removing the fuel line and cranking the engine to see of fuel flows.

 

Another, and opposite possibility is that the carbs are full of fuel. With nowhere for the air to go, the whole system will essentially lock up until the carbs need fuel. Check to see if fuel flows when the line is unplugged like huntchuls says. You can also drain the fuel bowls via the plug, which would be good anyways if the thing sat for a while. Finally if you are really worried about the petcock, you can unplug the smaller vacume line and manually suck on the pipe on the petcock. If fuel flows out when you suck, it's working, if it doesn't, bad petcock. If all of this checks out, you can take the smaller vacuum line connected to the engine, plug it with your finger, and roll the engine over. You should feel a rhythmic sucking.... If it doesn't then check the other end.

 

This is a great job for a MityVac.

 

Just to say the petcock works well it decided to attack me with the fuel when i tried it even with a tub there so thats fine.

I think when i tried to start it the first time it probably had old dried up fuel in the tank and putting new fuel in pushed the old stuff into the carb and because its sat for a while since the orginal start its had time to stick inside so yeh i think its blocked. Time to get that fixed. Cheers for the help with diagnosing the issue with fuel not getting to the carb.

Also does anyone have a suggest on what i should repaint the bike to i like its black red and gold look but i was thinking white black and gold i dont know though any suggestions are welcome. Il leave a couple photos of my maxim below

 

I shouldnt of attached those images in the technical chat because its not really technical sorry about that im still new to the forums