Yamaha g9 backfire through carb

[slonomo]

Yep, CCW looking at the crankshaft.

Man I don't know what else to look for. Did you try the CDI from the other cart. That's what controls the ignition.

Did you actually check for spark? I don't remember.

4 stroke needs the following to run:
1. Compression
2. Spark
3. Air
4. Fuel

Those are the basics. Now, if your battery is low/weak it might not be spinning the starter fast enough to get it running. For that matter, if the starter/gen is not working properly it may not spin the engine fast enough. I know that sounds crazy, but it's true. The faster the engine spins the more cycles it will run through to try and fire. I've found that a slow spinning engine doesn't like to start.

Did you try and squirt some fuel into the carb? I use a small squirt bottle with fresh fuel and ethanol treatment. Just a little squirt will do. If you are getting spark, that should get it to fire. If it runs on the squirt bottle, but not otherwise, you have a carb problem.

If you have all that covered, not sure what else I can help you with.

[J-ROB]

Hey Bryan,

Yep the engine rotates CCW when looking at the clutch. Silly question, but are you 100% sure both of the pushrods are set in the top of the lifters? When I first got my G2 (same engine as you) I did a valve adjustment, when I went to start it would try to fire and then pop back out of the carburetor. I then took the valve cover back off and realized that I had loosened one of the valve adjusters too much and that the bottom of the pushrod was laying beside the lifter rather than on it. I did set the tension according to the manual, but all of the pressure was against part of the block which did not allow that one valve to open.

It sounds like you know what you are doing and are familiar with the golf cart engines, so I am sure that's not the issue you are facing, just wanted to note I had that issue before and its one other thing to double check.

I later rebuilt my engine and when I put it back together it fired right up first try, I know what you are dealing with must be frustrating, keep at it, sounds like you're at least getting closer to finding the issue.

Good luck!

[Bryans200583]

Ok so when I squirt the gas into the carburetor, should I squirt it in and then hook the airbox back up before trying to start or not. I have shot once up into the carburetor with starter fluid without the airbox hooked and it just blew it back out the carburetor. I know it’s not good to run them off starter fluid but I wanted to see if it would run for a quick second. Thanks. I’ll give another battery a try to to rule that out and try a squirt of gas and hook the box back up. Man I really appreciate your help and trying to help me get this thing going. It just bothers me that it would run before I took it apart and now it won’t. Thanks again

[J-ROB]

These carts run like crap with even a small leak in the airbox, so if you're struggling to get it started I'd say leave the airbox on it. Just a thought, but you could pull the spark plug and give it a shot of the good stuff in the cylinder and go that route. I've had good luck with WD40 sprayed into cylinder with engines that won't start.

[slonomo]

Everybody wants to use starting fluid.....

Starting Fluid/Ether doesn't really tell you anything. A low compression engine with no spark can actually start with Ether, so it doesn't even need to be a good engine lol. The other thing with Ether is if you spray a bunch of it in there....KABOOM! I've seen heads fly off of lawn mower engines, no kidding. That stuff is HIGHLY volatile! Plus it has no oil in it at all, and is a strong solvent so it will quickly take the oil off your cylinder walls if you use too much, that will eat your rings up.

Use the gasoline squirt. It will tell you real quick if it will fire. You can leave the air box off for now, since you just want to see if it will run with gas. Just a little squirt. Then try and fire it up. I keep a little squirt bottle with gas on my workbench. I can keep an engine running on the bench with just the squirt bottle. It works great for me.

Now, if you have compression, spark, and fuel via squirt bottle.....and it STILL doesn't start.....then you definitely have a problem.

[slonomo]

Now if you want to "SAFELY" use starting fluid.....spray it directly onto your air filter. Just a little bit. As air enters the air filter, it dries the ether into a vapor, then gets sucked into the combustion chamber.

Remember, with gasoline (and Ether) it's the evaporated fuel that gets ignited, not the wet stuff. Wet fuel won't burn. You can drop a match into a puddle of gas and it will look like it's on fire....but it's the vapors on top of the puddle that are burning.

So, using this info, let the fuel vaporize for a minute or two. That will allow the engine to suck in the evaporated fuel.

What happens if you get "wet fuel" into a cylinder? A flooded engine. Wet spark plugs don't like to ignite. If you get too much wet fuel into a cylinder you'll have "hydro lock" and you won't be able to spin the engine.

[J-ROB]

Yeah, scratch my redneck WD-40 idea, that's child's play compared to Slo's idea. Keep us posted, really interested in what is your root issue. I am still less than a year into golf carts and my G2 is my only cart, but I have learned so much from just reading relevant G2 & G9 posts that when I do have an issue I have most likely already read a post about that issue and have some sort of an idea as to how to fix it.

[Bryans200583]

Ok. I have sprayed gas into the carburetor but maybe I was waiting long enough for it to vaporize cause all it would do is backfire back through the carburetor and the engine didn’t seem like it wanted to turn over to well. I can turn it freely really easily by hand without the spark plug and with resistance with the plug installed I assume cause it’s building compression. I haven’t messed with it the last couple days but I plan on getting back on it this weekend. I did take the carburetor back off and just double check that I got all the ports and all cleaned. I’ll give the spray of gas and see what happens. Again I appreciate the help fellas.

[CP241]

Originally Posted by J-ROB

Yeah, scratch my redneck WD-40 idea, that's child's play compared to Slo's idea. Keep us posted, really interested in what is your root issue. I am still less than a year into golf carts and my G2 is my only cart, but I have learned so much from just reading relevant G2 & G9 posts that when I do have an issue I have most likely already read a post about that issue and have some sort of an idea as to how to fix it.

They make rednecks in Houston?

Yep ive used ether and yep, ive seen it do some pretty gnarly stuff. Especially if it isn't running right to begin with. It can blow fireballs out the carb too. Ask me how I know

A squirt of gas in thr spark plug hole is best.

[J-ROB]

Well there's rednecks that move to Houston LOL