2 stroke Carb question

[Fiveohhh]

I'm working on a yamaha Jet boat 110hp motor now, and need some help. I don't know much about a carb besides the fact that it mixes gas/air. If I dump gas straight down the carb, it will fire(if it matters the motor has a reed cage) and normally run for about 5-10 seconds till it runs outta gas there is one carb for each of the 3 cylinders. I know this problem is pretty much impossible to diagnose over the net, but I'm looking for some ideas on where to start. I checked the fuel pump and its good, the fuel filter is good, so Its getting up to the carbs, but just not going anywhere from there, or it is going and its just not firing for some reason. Thanks in advance for any help

 

[wetobasura]

make sure that the jets on the carb arent gummed up and that the floats (if there are any) are working properly. had a problem with my 25 hp boat motor not running cause the jets in the carb were gummed up.

 

[Kalvin00]

Yeah. Did it sit for a while? The gas may have broken down inside the carbs..

 

[GalvanizedYankee]

This is only a shot in the dark. I've only worked on m/c's.

The float bowls should have drain plugs. remove or open them. After they drain, leave them open and turn on the fuel pump. If fresh gas does not come out of all of them the float needles maybe
stuck shut with scum. Some ppl will rap on the carbs w/a plastic mallet to unstick em' but remove and clean is better........:sun:

 

[Bulk Beef]

Like yankee said, start by draining the float bowls. If that doesn't help, Yamaha also makes a great carb cleaner that you fill the float bowls with and let sit overnight (don't run it through the motor or put it in the tank). I've used that stuff on some seriously nasty carbs w/green mossy crap growing in them, and had them come out looking clean as a whistle.

That will be a start.

 

[Eli]

Sounds like you need to overhaul the carbs.

I do hope you're dumping fuel/oil mix in it...

 

[Fiveohhh]

The carbs are vertical so air in on the top and out to the reeds on the bottom. so I'm not sure where th float bowls. The motor was running just fine one day and than it just stopped while he was going down the river. I'll look into some of your suggestion. thanks for the help so far

 

[Eli]

Originally posted by: Fiveohhh
The carbs are vertical so air in on the top and out to the reeds on the bottom. so I'm not sure where th float bowls. The motor was running just fine one day and than it just stopped while he was going down the river. I'll look into some of your suggestion. thanks for the help so far

They probably don't have floats, lol... 2-strokes typically use pumper carbs, but then again I'm not familiar with the larger 2-cycles.

You might want to check compression. 2-cycles are very picky, and it's possible that if the cylinders have become scuffed, it doesen't have enough crankcase compression to draw fuel/air mix in, but it will run when you dump it in manually.

I'm not sure how familiar you are with engines... Just go through the typical troubleshooting process. It sounds like you're on track with the fuel system guesses, but that can also be mechanical in nature as stated above.

 

[Bulk Beef]

They probably don't have floats, lol... 2-strokes typically use pumper carbs, but then again I'm not familiar with the larger 2-cycles.

I've never seen a 2-stroke that didn't have plain old slide-type carbs (with floats), but that was all bike stuff. What do you mean by pumper carbs?

 

[Eli]

Originally posted by: sward666

They probably don't have floats, lol... 2-strokes typically use pumper carbs, but then again I'm not familiar with the larger 2-cycles.

I've never seen a 2-stroke that didn't have plain old slide-type carbs (with floats), but that was all bike stuff. What do you mean by pumper carbs?

You're probably right, I'm more familiar with the single cylinder 2-cycle engines, such as used on handheld power equipment, which use a carburetor that uses crankcase pulses to drive an internal diaphram fuel pump.

Since he said there is an external fuel pump, they probably are floaters.

Look for a bowl shaped appendage near the lowest part of the carb.

To check the cylinder for scuffing visually, you'll have to look into the exhaust ports or perhaps through the spark plug hole if you can get a good view. Otherwise, check compression. I have no idea what it should be for your engine, but if it's below 120 I'd say you have problems. Also, the compression in each cylinder should be +-5% to eachother.

 

[cavemanmoron]

compression test first;if all 3 cylinders are over 100 psi,

then;look at fuel pump/carbs again

sounds like fuel pump diapraghm may have a pin hole,or dirt clog

if all 3 under 100 psi,time to rering

 

[GalvanizedYankee]

I think Eli was referring to diaphram type carbs. They can run in any position.

If this was running sweet and suddenly developed this problem,it maybe electrical in nature. Like a safety to cut fuel flow in the event of a roll over that doesn't right itself.
Just a consideration..................:sun:

 

[slag]

There are no float bowels.. they are vacuum actuated with diaphrams via a pulse fitting to the crank case.

couple of things to check. Each carb should have an individual filter in it. Are any of these clogged?

Have any of your fuel lines collapsed like with age?

there is probably a large amount of trash in the carbs if they havent been cleaned out in a long time.

Post your problem over HERE. I guarantee they will be able to troubleshoot and fix your problem really quickly. You can also buy carb rebuild kits from them there at a good price.

 

[Eli]

Originally posted by: slag
There are no float bowels.. they are vacuum actuated with diaphrams via a pulse fitting to the crank case.

couple of things to check. Each carb should have an individual filter in it. Are any of these clogged?

Have any of your fuel lines collapsed like with age?

there is probably a large amount of trash in the carbs if they havent been cleaned out in a long time.

Post your problem over HERE. I guarantee they will be able to troubleshoot and fix your problem really quickly. You can also buy carb rebuild kits from them there at a good price.

Are you familiar with his engine?

Are you sure they use diaphrams? He said it had an external fuel pump..

 

[Cyberian]

Originally posted by: slag
There are no float bowels.. they are vacuum actuated with diaphrams via a pulse fitting to the crank case.

couple of things to check. Each carb should have an individual filter in it. Are any of these clogged?

Have any of your fuel lines collapsed like with age?

there is probably a large amount of trash in the carbs if they havent been cleaned out in a long time.

Post your problem over HERE. I guarantee they will be able to troubleshoot and fix your problem really quickly. You can also buy carb rebuild kits from them there at a good price.

Wouldn't it be quite unusual for these symptoms to have happened suddenly, and at the exact time?

 

[Fiveohhh]

well I just got back in and it seems to run after I put it back together. but not very well, I'm gonna find a compression tester, and see whats up sounds quite boggy compared to the other motor. I have the service manual for the carbs they have a float arm, not sure exactly how it works not like the typical carb that I've found on every sled I've worked on with a bowl under it, but kinda off to the side...ohh well, I'll get a compression tester and see what I can find. Thanks a lot for the help it really helps!

 

[slag]

Originally posted by: Eli

Originally posted by: slag
There are no float bowels.. they are vacuum actuated with diaphrams via a pulse fitting to the crank case.

couple of things to check. Each carb should have an individual filter in it. Are any of these clogged?

Have any of your fuel lines collapsed like with age?

there is probably a large amount of trash in the carbs if they havent been cleaned out in a long time.

Post your problem over HERE. I guarantee they will be able to troubleshoot and fix your problem really quickly. You can also buy carb rebuild kits from them there at a good price.

Are you familiar with his engine?

Are you sure they use diaphrams? He said it had an external fuel pump..

While I've never worked on this specific engine, I am a jetski enthusiast and have worked on kaw 900, 550, 440, and 650 motors and they all utilize basically the same principles.

The diaphram takes the place of the fuel bowl and float. The external pump is another mechanism altogether. Basically, the diaphram compresses a small lever and spring which releases the needle from the seat and allows fuel to flow. If you get any junk in there, it can clog the seat or cause the needle to get stuck and not pop off.