Yamaha g9 “choking”

[Jwcc89]

Hey all! First post here. I have a Yamaha g9, bought about a year ago, has a lift, otherwise appears bone stock. A few weeks ago I was driving down the road, full throttle as I usually do and the engine started choking.
I’m not a mechanic, but have an ok knowledge of engines motors etc. to me it seemed to be a lack of fuel. The cart runs ok up to half throttle, after that it starts to bog down, and at full throttle it chokes.

I have replaced the carb, fuel pump, air and fuel filters, and intake tube (it felt soft so I thought maybe it was collapsing). If the intake tube and filter are taken off, it runs pretty good, seems a little sluggish than it used to, but can be full throttled. Put intake tube in and it starts to choke, put the air filter on and it is even worse.

When adjusting the air/fuel mixture on the carb, it makes no difference in the way the engine runs. All the way in to all the way out and everywhere in between, air filter and tube in or off, no changes when adjusting the carb.

So I’m stuck on what to look at or check next. Also, when running at half throttle down the road it will maintain about 13mph, but if it even comes to a slight hill, it starts to bog and choke like there is no power.

EDIT: I drained the fuel, and put new gas in, I also adjusted the valves, which were pretty close when I started. I bypassed the governor in the axle thinking that could have been part of the issue, however same issue.

[Jwcc89]

Another thing to note, I don’t have the spark plug cap on, the original owner had the cap on with the BPR4ES plug, but it didn’t fit properly so he ground down the plug. When I replaced the spark plug I just put the wire straight on to the top of the plug. I ordered a new cap, and it still didn’t fit, so trying to find the correct one. Not sure if this would even make a difference or not

[slonomo]

If you think it's a fuel delivery issue you can diagnose it properly and get a definite answer. Take the fuel line off the carb and put it into a jar/clear container. Crank the engine for 30 seconds and watch the fuel. The fuel stream should squirt out a few inches and in 30 seconds you should get a couple ounces of fuel.

Carb: if the carb you are using is a cheap china aftermarket, this could be your issue. They have been known to act the way you describe. Your best bet is to use the original "Mikuni" brand carb, which can be soaked and cleaned up easily, and parts are available if needed.

Plug: if you are running the engine without a rubber boot on the end of the spark plug wire you could be getting ignition interference. Definitely make sure you have that part fixed. A new wire from the coil to the plug will solve this.

With a gasoline engine, always check the basics:
1. Air - good clean un-obstructed air flow
2. Fuel - good clean fuel delivered to the carb
3. Spark - Blueish-White bright spark, use a spark tester
4. Compression - use a compression gauge and do a proper test

Most times if you have all of these in order the engine will run properly.

If the engine runs, but poorly, the carburetor and/or fuel quality are the most likely place to look.

If a worn out engine is suspected, a leak down test is in order.

[Jwcc89]

Thanks for your reply. I plan to do a compression test as soon as I can find someone to borrow the gauge from. I see in the stickies there is a g1-g9 specs…but the pages listed are for a g2, and the compression specs the same do you know?

I’ll clean up the original carb and see what happens in the meantime

[CP241]

G2 is essentially the same as a G9 with minor differences such as a different ignitor and the G2 had an oil level light on the dash and a float in the crankcase to trigger the light.

[Jammy]

Where are you located? I have a compression guage in daytona beach, fl area.

[Jwcc89]

I’m located in central illinois.

I’ve determined it’s not a fuel delivery issue.
Good unobstructed airflow to the carb.
I replaced the boot in the spark plug to eliminate any interference.

Next to check is the compression, which according to the sticky should be which 8:1, not sure what psi is supposed to be on the gauge there.

Does anyone have a link to a good write up on how to check the coil/igniter? I saw somewhere here it’s a common problem and several people have done the Chrysler swap.

How do I know if I have that original mikuni brand carb? The one I took of has no markings, so not sure if it was an aftermarket or the original.

[Jwcc89]

Originally Posted by CP241

G2 is essentially the same as a G9 with minor differences such as a different ignitor and the G2 had an oil level light on the dash and a float in the crankcase to trigger the light.

So I read through your post here https://www.buggiesgonewild.com/show...=141085&page=5 and it seems mine is acting very similar to yours. I plan to get the parts to do the HEI rather than looking for the OEM parts at $400.

I saw in there you mentioned checking to make sure the air box lid is completely sealed, well see mine doesn't have the complete airbox. My cart has the lid, with the filter attached to the bottom, and the other rubber line attached to the lid, but no actual air box. Could this be causing my problem?

[CP241]

A mikuni carb will say “mikuni” on the side of the carb body. Cheap China knock offs either say nothing or some say “mokini”.

If it’s not an actual oem mikuni it’s junk, and good luck getting it to run.

If the airbox lid is not completely sealed they run lean. They’ll fart, stumble, and fall on their face. Sometimes better when you pull the choke. My last yamaha was a G2 and I somehow hit a stick that cracked the bottom of the airbox where it mounts on the frame. Ran like dookie until I jb welded the crack shut. Ram perfect again after that.


There are some on here who argue that it will run just fine without the entire (complete) OEM airbox and it being perfectly sealed. They say it runs great on a cone filter. But I’ve never seen one run worth a crap without it.

If you don’t have the airbox you may be able to hog out the jet enough, a little at a time to get it to run right. But that’s gonna take some tinkering

[Jwcc89]

The thing that gets me is it ran just fine without the complete open air box running a cone filter on it prior to this issue, so for now I’m going to say that isn’t the problem. Once I get a compression gauge I’ll report back the findings.