Freestyle Fuel Starvation

[Citizen]

How many bolts to f/a or to adapter on top of each carb? 3 or 4?

3 Bolts. They really could be anything i guess lol, I was told 46's from the guy I bought my RN off years ago.

Not great pics but here you go. Have not had time to tear into carbs yet to check for 2nd pump.

 

[Citizen]

If you have dual 38's( with the jetting your specified) and your engine is shutting off when you ride full throttle you better hope your piston isn't lean seizing over and over. The suction when you put your hand on the carb is from your pistons seal/ compression, not the pulse line. You should do a compression check asap. Also upload pictures of your carbs. Sounds like you have some Frankenstein issues going on here

I am leaning towards fuel starvation over lean seizing as I had to prime the motor again to get it started once it happened. But regardless it is not good and I need to resolve. Problem is I have not run into issue off the water so engine apparently needs to be under load for it to appear.

 

[pigpen]

Those are 38's. probably way too small for your setup. The 38's only run one fuel pump and the other carb is just a "slave".


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[Sasquachcrap]

I have a set of oem 44 carbs. Thay are taper bored with flame arrestors. I can jet them to your specs. Pm me if your interested. I'll make you a good deal. I hate to see you damage your new motor. I don't think the 38s will work very good even if you could get them jetted right.

 

[eastcoastjumper]

I am leaning towards fuel starvation over lean seizing as I had to prime the motor again to get it started once it happened. But regardless it is not good and I need to resolve. Problem is I have not run into issue off the water so engine apparently needs to be under load for it to appear.

so under load, your motor is shutting off because its lean. You're revving it high and there is not enough fuel going in those cyls that are getting hot. Hopefully you did'nt scuff up the piston a little against the cyl wall. You can seize a motor enough to shut it off. It will cool quick and restart many times until it gets a ring stuck or worse. 2 strokes will run when they're hurt and until they blow up.(for future reference)

You're using 125p, 135m. Those are probably starting specs you were given by motor mfg for 46mm carbs only.

I use around 75 p, 140+ mains in a 780 setup. (You're pilot is bumped up, but i don't know if that is enough to work on your setup)



Take a compression test/ buy 46's asap

 

[JetManiac]

Those are 38's. probably way too small for your setup. The 38's only run one fuel pump and the other carb is just a "slave".

Exactly, you have taperbored dual 38 carbs, no question.

so under load, your motor is shutting off because its lean. You're revving it high and there is not enough fuel going in those cyls that are getting hot. Hopefully you did'nt scuff up the piston a little against the cyl wall. You can seize a motor enough to shut it off. It will cool quick and restart many times until it gets a ring stuck or worse. 2 strokes will run when they're hurt and until they blow up.(for future reference)

You're using 125p, 135m. Those are probably starting specs you were given by motor mfg for 46mm carbs only.

I use around 75 p, 140+ mains in a 780 setup. (You're pilot is bumped up, but i don't know if that is enough to work on your setup)

Take a compression test/ buy 46's asap

I agree. You are starving for fuel because of the pulse line nonsense and also from too small carbs for that motor size.

 

[jo5hi3]

You may be able to get those 38's to work with that motor, but I wouldn't waste my time. I would find a set of 46's at a minimum.

If the engine shut off while you were wfo, it was probably a lean seizure. You have definitely shortened the life of that engine.

 

[Citizen]

Thanks for all the feedback guys, definitely not want i wanted to hear. I will check compression but I am unsure what my starting compression should have been to begin with. The builder has been impossible to get any feedback from, but that is another issue.

I will look at sourcing some carbs, wife is going to throw a fit lol. Will PM you Sasquatch, but if i am going to have to spend the money i am thinking I will try to get 48's or 49's. 44's might get me back on the water a heck of a lot faster tho!

Thanks again guys.

 

[FlyinRyan324]

If you end up going with bigger carbs, @DAG has some Full Specs for sale

 

[jo5hi3]

Thanks for all the feedback guys, definitely not want i wanted to hear. I will check compression but I am unsure what my starting compression should have been to begin with. The builder has been impossible to get any feedback from, but that is another issue.

I will look at sourcing some carbs, wife is going to throw a fit lol. Will PM you Sasquatch, but if i am going to have to spend the money i am thinking I will try to get 48's or 49's. 44's might get me back on the water a heck of a lot faster tho!

Thanks again guys.

@DAG has some nice 48 full specs. That is the direction I would go.

 

[zzylstra]

O boy nothing like 38's on a performance engine. I'd immediately do a compression check and post the numbers, if you requested pump gas compression from the builder your going to have pump gas numbers no questions asked


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[Sasquachcrap]

I know I'm going against what josh has posted but it's my opinion that you probably weren't experiencing a lean seize. (Trying to be optimistic for you). It is possible that you were just sucking all the fuel out of the carbs. Now depending on how fast this happens could determine whether or not you were seizing. But I certainly don't think the carbs were under fueling. 38's have such a strong vacuum signal with those large pilot jets I feel like you were just using all the fuel in the carbs faster then the pump could supply it. I have killed pistons before when my (in pump) filters have gotten stopped up. But they were only partly clogged when I burnt pistons. The one time they got clogged quickly. The ski acted like it had stuck needle and seats. It would run until I asked for wide open throttle then within 1 second it would die of fuel starvation. Took a little cranking and priming to refill the carbs then it would run again and run well at low part throttle positions. I think the same thing may be happing to you but because of huge jets not a clog.

 

[Citizen]

I know I'm going against what josh has posted but it's my opinion that you probably weren't experiencing a lean seize. (Trying to be optimistic for you). It is possible that you were just sucking all the fuel out of the carbs. Now depending on how fast this happens could determine whether or not you were seizing. But I certainly don't think the carbs were under fueling. 38's have such a strong vacuum signal with those large pilot jets I feel like you were just using all the fuel in the carbs faster then the pump could supply it. I have killed pistons before when my (in pump) filters have gotten stopped up. But they were only partly clogged when I burnt pistons. The one time they got clogged quickly. The ski acted like it had stuck needle and seats. It would run until I asked for wide open throttle then within 1 second it would die of fuel starvation. Took a little cranking and priming to refill the carbs then it would run again and run well at low part throttle positions. I think the same thing may be happing to you but because of huge jets not a clog.

I am leaning(hoping) this is the case as well. Right off the bat I noticed my carbs were creating barely any vacuum while trying to hand prime my motor, took a lot of cranking to get fuel to even trickle into the fuel filter. My buddy said this was most likely due to just the way the new motor was setup (we are both new to high performance PV motors) but i said a few times i wondered if the pulse lines or something might be causing the low vacuum.

I could VERY easily see mid/high throttle sucking the fuel filter dry and the motor just dying. The fact that I had to prime the motor to get it going again seems to back this theory up. The engine shutoff was like a light switch so while i'm sure it wasn't good for the motor in that split second where it started to run out of fuel and burned lean to the motor just dying, i am hoping it wasn't enough to actually damage anything. I reproduced the issue 4 times, but only let the motor die once, as i was ready for it the other times. Low and Mid continued to work just great.

I am very well known in my riding group for running out of fuel almost every time I ride, so very familier with the feeling of a motor running out of gas, and this was that feeling to a Tee.

Will get a compression test done this week and my buddy msg'd me with a set of 44's I can have, so that will get me back on the water for now. I should be able to keep the jetting the same as what i currently am running? If not ideal it should still be ok i think?

 

[Citizen]

OK so I may have found a set of 44/46's that a buddy will trade me, but it has zero screws on the f/a adapter...so hoping you guys can help me identify. I couldn't get the last nut off to measure the bottom of the barrel but they appear to be 44's. Did they make anything between 38's and 44's?

 

[JetManiac]

Those are 44s or 46s that have been modified.

 

[Citizen]

Those are 44s or 46s that have been modified.

Thanks Chris, any idea how they would have been modded? Should I be concerned or just run them.

 

[Shonuff]

They look like Full Spectrum carbs.

 

[JetManiac]

Thanks Chris, any idea how they would have been modded? Should I be concerned or just run them.

Tops of carbs were cut off and machined for pressed on top for a/m f/a, etc. Need to see if bomb site has been modded or return restrictors drilled out, etc. to get a better idea.

Be careful this time before you leap, what is the age of the carbs? How long since a rebuild? Are shafts, butterflys, linkage, etc. worn out? You do not want to chase your tail again. It is better to buy new or clean used carbs, than to spend more time and money on unknown carbs and still end up unhappy and possibly with a blown motor from carb issues.

 

[Citizen]

Tops of carbs were cut off and machined for pressed on top for a/m f/a, etc. Need to see if bomb site has been modded or return restrictors drilled out, etc. to get a better idea.

Be careful this time before you leap, what is the age of the carbs? How long since a rebuild? Are shafts, butterflys, linkage, etc. worn out? You do not want to chase your tail again. It is better to buy new or clean used carbs, than to spend more time and money on unknown carbs and still end up unhappy and possibly with a blown motor from carb issues.

These carbs came on a built square my buddy has been riding for the last couple years, so they are functional and he has not had any issues with them. I do plan to swap internals though as i have a fresh rebuild kit in my 38's (pretty sure internals are the same?)

I inspected what I could with the carbs in the ski and butterflys and linkage all looked good, will tear them down tonight to verify everything though, will take more pictures so hopefully you more experienced eye can point out any potential issues.

 

[x2mafia]

i cant believe it ran at all. And I cant believe you put those carbies on there and didn't know or check anything!