Carb troubles

Hello all,

Background: Bike is a 1983 Yamaha Seca 750 that had a oil change probably 80 miles ago as well as a dirty gas problem.

So I went to start up my bike this morning and it was having issues starting, I figured it was just being a little cold blooded so I continued to push it. I finally got it to start a little bit but it was chugging pretty bad, right as I was about to kill it I noticed gas pouring out of the airbox vent onto my foot. I immediately killed the bike and began to cleanup the mess. Thinking that was it I left for work in the car, and came back tonight to find a huge puddle of Gas and oil. It looks like the gas and oil mixed, my guess is the carb stuck open and flooded gas down into the engine. I also noticed when cleaning, the vacuum line to the petcock was cracked. So I believe the carb just flooded the engine and everything should be okish. I emptied the oil, which was mostly gas at this point and although it was mixed it was clean, no metal shavings or bits to be had. Well, besides the tools and bits I dropped into my oil pan out of frustration as I was draining the bike.

So I believe the correct course of action from here is get some more oil, take the gas tank off, flush the system and then do a compression test. If compression test comes back good I should dig into the carbs and get some new spark plugs. If all checks out in the carbs get them cleaned up, installed, synced, and such. I should also probably do the valve clearances before all of this.

What I believe I will need for my endeavor into the carbs if I get that far.
Carb sync tool
Carb Rebuild Kits
Yics Elim. Tool
Colortune 14mm for motorcycles

I imagine I should anticipate getting new intake boots, as well as a new air filter and plugs.

Feedback on my issue, as well as what I'm planning to do would be appreciated. I have done quite a bit of reading on this subject but I want to make sure I am not missing anything.

Thanks!
Mike

 

The way I understand it, the vacuum on the petcock is to open the small diaphragm in it to let the gas go down. If the line is cracked, it shouldn't open properly, but it shouldn't be the reason to a gas leak.

I'd bet your petcock AND your float bowl valves are to blame. Your petcock deosn't close properly AND your floats valves are stuck opened.

You mentioned a dirty gas problem, did you put an inline fuel filter? If not, it is possible that some debris from your the tank or the petcock itself and got stuck in your float valves.

Drain your float bowls in a small clean container and look for debris or crud in your gas.

 

I wouldn't be surprised if both were bad. I do have a inline filter but it was installed after I purchased the bike until I had a chance to clean the tank out.

Do you guys think it would be more cost efficient to pay a local shop to sync the carbs after I clean them up and such, or buy all the tools myself?

 

You ar better off ding the job yourself. A shop will charge you $250 to $350 to do a worse job thatn you can (unless you have a shop nearby that specializes in '80's motorcycles).

 

I would also take the petcock apart and look at the diaphragm.
I had a problem with the diaphragm being torn between ports.
This must have happened after sitting for a long period and then being turned to reserve or prime from the on position.
I ended up just cheaping out and buying a gravity feed one.
It works just fine but if you don't remember to turn it off, then you risk having the same problem you had if the float needle is stuck open.
Make sure you take the float bowls off and clean up or replace the needles.

 

Stripped the tank today after finally finding some time in prep today to clean it. Did this first because it was leaked gas everywhere. Drained the oil/gas out again and will be picking some more up on my way home from work tomorrow. Gonna pour it in, check compression, if that checks out check valves, then move to the carb.

On another note, is there any downside to tuning the carbs without a color tune? I've heard people say yay and nay on this subject, money is tight would love to just get by for now, but if it is required to do the job right I can wait for a bit so I can afford it.

 

Downside to not using a colourtune, in my experience, is that its bloody hard!

With the colourtune it's damn easy! besides the fact that it is really, really fast in comparison.

Then again if you are an old school bike mechanic with the 'ear' then its a whole other kettle of fish.