JAE Help- .12 engine tune

[Ted buckley]

I went and re-read your original post again, and noticed this part of when you were having trouble. I had the same issue, but I have a TOP .12 and a Mac pipe.

Here is your quote: "Today i richened it rite up and slowly started leaning.. Extreamly rich i would get 3 laps ultra slow... any leaner and it would loose revs in the corners, fall off the pipe and die. i have tried an ultralong pipe and slowly shortened it..i just cant seem ro find a happy medium/.

I don't know what your Ultralong pipe is, or what your initial measurement is; but try going out a little on this pipe instead of in. You may be suprised that you were'nt out far enough to begin with. My pipe likes to run @ 7-1/2". I know this is kinda far-out for a pipe length to be, but if I put it in to 7-3/8, I have nothing but problems. As a test, richen it up and pull-out the pipe.

 

[camaroboy383]

robin,,,re-read the last post on page 1,,,by chris.... "i ended up cutting the pullstart off" .....

oh and your prop went out today my good friend..

 

[anthony_marquart]

I think you may have a compression issue. Take the motor out and turn it over past TDC back and forth. If you get less than 30 times across TDC and the pressure goes away, the fit is gone. THis did the exact same thing to me in a .12 with bad compression. Loose head bolts will also do this..

Let us know.

 

[chris armstrong]

Ok/ All the fuel lines, pressure is all fine.

I did alter pipe length from ridiculously long to ridiculously short.

Yes i did remove the pull start and cut the shaft behind this. I cut the shaft square of the back plate. I did run this past a few boaters on here and they all said that the pull start does not seal at all. The shaft was cut flush with the back plate.

What is ment by Carb mod?? I know what it meens but what needs to be done to the carb?

As far as temp, i have played with this too.. Even to the point of letting it idle and heat up for a min before i launched this. at the same needle setting the boat would stall every launch. My way of thinking is it lost compression as it got hot and when it was launched loaded up the engine too much.

as far as prop sizes go, i have an off the shelf 35mm.. i understand these boats will pull a larger modded prop however i want to get it reliable before changing prop sizes. I have tried a 40mm (too big) , 38mm (too big) and a 35 should do it easily.. Perhaps the prop is still too big?

all of your efforts are much appreciated fellas.

I think i will buy a 21 next..

 

[anthony_marquart]

I think you have lost the compression. It will run ok till it gets hot, then die or have no torque when warm...

Swap motors.. don't need a .21,.. try any .12 that you know has good compression. get a new P/L for your motor maybe...

Since you have checked all the other things... this is probably the issue.

you are runing a small prop,.. you know your getting fuel, we think it's sealed, compression is next..

Ok/ All the fuel lines, pressure is all fine.

I did alter pipe length from ridiculously long to ridiculously short.

Yes i did remove the pull start and cut the shaft behind this. I cut the shaft square of the back plate. I did run this past a few boaters on here and they all said that the pull start does not seal at all. The shaft was cut flush with the back plate.

What is ment by Carb mod?? I know what it meens but what needs to be done to the carb?

As far as temp, i have played with this too.. Even to the point of letting it idle and heat up for a min before i launched this. at the same needle setting the boat would stall every launch. My way of thinking is it lost compression as it got hot and when it was launched loaded up the engine too much.

as far as prop sizes go, i have an off the shelf 35mm.. i understand these boats will pull a larger modded prop however i want to get it reliable before changing prop sizes. I have tried a 40mm (too big) , 38mm (too big) and a 35 should do it easily.. Perhaps the prop is still too big?

all of your efforts are much appreciated fellas.

I think i will buy a 21 next..

 

[moparbarn]

robin,,,re-read the last post on page 1,,,by chris.... "i ended up cutting the pullstart off" .....

oh and your prop went out today my good friend..

alden, cutting off the pullstart really threw me off, never saw one that didn't unbolt :blink: . but chris cleared that up with his last post. i'll let you know when the prop arrives, thanx my friend .

what anthony says is a good test. when you roll the engine back & forth across tdc, don't go very far. you want to keep recompressing the same shot of air. oil the engine lightly, put the plug in tight, roll the engine to tdc. then don't go far enough past tdc to uncover any ports, or the "test" won't be valid. you want to work with the one original shot of air. i've never heard 30 times, more like 12 - 15...... if it holds 30, it's in EXCELLENT shape!!

 

[camaroboy383]

gotcha....do the compression test,,,see what it brings..... might be the culprit for sure....

when you cut off the end of the pto shaft,,,did you bevel the edge before sliding it back through the brass bushing in the backplate??? as far as pullstarts not sealing,,,it does seal through fit of the brass bushing and the pto shaft...there is only so much leakage that can pass that area before the engine becomes un-needleable..(just like a crank bore).. hence the question of the bevel on the shaft before sliding it back through...

sliding it through with a sharp square cut edge will surely drag some kind of brass from the bushing,,,causing more of an air passage....

thats all i was gettin at fellas....gotta touch all bases before home plate....

ac

 

[moparbarn]

gotcha....do the compression test,,,see what it brings..... might be the culprit for sure....

when you cut off the end of the pto shaft,,,did you bevel the edge before sliding it back through the brass bushing in the backplate??? as far as pullstarts not sealing,,,it does seal through fit of the brass bushing and the pto shaft...there is only so much leakage that can pass that area before the engine becomes un-needleable..(just like a crank bore).. hence the question of the bevel on the shaft before sliding it back through...

sliding it through with a sharp square cut edge will surely drag some kind of brass from the bushing,,,causing more of an air passage....

thats all i was gettin at fellas....gotta touch all bases before home plate....

ac

alden, i meant the actual pull start/recoil assembly not being a seal. for sure the pto/crankshaft end HAS to seal in the bushing. even more important in smaller engines, leaks of any size affect them worse. you're right, can't miss any bases .

 

[camaroboy383]

gotcha....do the compression test,,,see what it brings..... might be the culprit for sure....

when you cut off the end of the pto shaft,,,did you bevel the edge before sliding it back through the brass bushing in the backplate??? as far as pullstarts not sealing,,,it does seal through fit of the brass bushing and the pto shaft...there is only so much leakage that can pass that area before the engine becomes un-needleable..(just like a crank bore).. hence the question of the bevel on the shaft before sliding it back through...

sliding it through with a sharp square cut edge will surely drag some kind of brass from the bushing,,,causing more of an air passage....

thats all i was gettin at fellas....gotta touch all bases before home plate....

ac

alden, i meant the actual pull start/recoil assembly not being a seal. for sure the pto/crankshaft end HAS to seal in the bushing. even more important in smaller engines, leaks of any size affect them worse. you're right, can't miss any bases .

:lol: ,,, i ctually read it so quick on my cell phone i didnt catch the joke.... ,,but im on the pc now and re-read it robin... i get it now... ....

 

[chris armstrong]

ok.

What about this.. If the cg is transom heavy, this would mean that there is more load on the ass end? Could the engine be loading up too much?

Another strange thing.. When turning into the corners the engine would slowly drop revs. This to a point where if i didnt let go of the rudder, the engine will stall..

With the compression test, how is the carb set? full open, closed ect?

 

[camaroboy383]

doesnt matter,,,,you are trapping air...

 

[anthony_marquart]

With the comp test you only move the piston back and forth over TDC. Carb setting has no relevance.

I am almost certain you do not have compression at this point. Slows in the turn because it take more torque to turn than go straight, dies or slow after a lap or two becasue it's warming up and the liner has expanded and the compression is now gone..

ok.

What about this.. If the cg is transom heavy, this would mean that there is more load on the ass end? Could the engine be loading up too much?

Another strange thing.. When turning into the corners the engine would slowly drop revs. This to a point where if i didnt let go of the rudder, the engine will stall..

With the compression test, how is the carb set? full open, closed ect?

 

[chris armstrong]

Thanks all. I am convinced its compression also.

I will try with the os cv-15 and see what happens..

I did the compression test last night.. Im not sure if the pressure dropped off a hell of a lot however it didnt feel to have too much to begin with.

 

[chris armstrong]

oh by the way, Where is the cg ment to be on the JAE .12 rigger??

measurement would be awesome.. there is no measurements in the instructions.

 

[Jeff Schindler]

Have you thought about changing your Head clearance? I started learning about car motors and was amazed to hear that they are set up with about .060 head clearance in a .21. I would bet that setting your clearance to around 0.010 will:

a) get the boat on plane easier

B) get more heat into the engine

c) you will be able to run a richer needle setting at launch = not starving of fuel on the top end

You may also be using too much prop.

My Top .12 would take a lap or 2 to come on plane and then it was sluggish in the turns. I changed the clearance to arounf 0.010" and it pops right up, and gets on pipe reliably with more fuel usage.

There are some good methods on this forum about setting the head clearance if you haven't done so before.

Good Luck!

 

[Geraghty]

oh by the way, Where is the cg ment to be on the JAE .12 rigger??

measurement would be awesome.. there is no measurements in the instructions.

A CG measurement on a JAE boat is not needed..............if you built the boat per the instructions the proper weight distribution

of the boat has already been taken into consideration.....the rear of the boat is supported mechanically with the ski......

Unless you are putting 2# of lead on the rudder bracket, a "balance point" means virtually nothing.....

Your problem has nothing to do with a CG measurement...........

What pipe are you using and where is it set?

 

[chris armstrong]

Thanks

Ok, the only difference i made to the plan is i used a full size servo for the rudder.

The pipe i am using is just a buggy one.. I do plan to build another.. I am not sure if this is where the problem lies tho.. The engine runs fine under no load but as soon as loaded up, the issues start.

I have tried the pipe really long and slowly shortened it from there.

 

[Geraghty]

Thanks

Ok, the only difference i made to the plan is i used a full size servo for the rudder.

The pipe i am using is just a buggy one.. I do plan to build another.. I am not sure if this is where the problem lies tho.. The engine runs fine under no load but as soon as loaded up, the issues start.

I have tried the pipe really long and slowly shortened it from there.

The full size servo isn't your problem either....

I sure would try a different motor & pipe..........like a MACS pipe #1110 set at about 7".......

I am about 95% sure the problem the motor/pipe combo.....

Take the pipe off the motor and run it open stack once and see what you get.......

 

[chris armstrong]

Thanks

Ok, the only difference i made to the plan is i used a full size servo for the rudder.

The pipe i am using is just a buggy one.. I do plan to build another.. I am not sure if this is where the problem lies tho.. The engine runs fine under no load but as soon as loaded up, the issues start.

I have tried the pipe really long and slowly shortened it from there.

The full size servo isn't your problem either....

I sure would try a different motor & pipe..........like a MACS pipe #1110 set at about 7".......

I am about 95% sure the problem the motor/pipe combo.....

Take the pipe off the motor and run it open stack once and see what you get.......

Yeah but if i take the pipe off, how will i get pressure to the tank?

 

[Geraghty]

Thanks

Ok, the only difference i made to the plan is i used a full size servo for the rudder.

The pipe i am using is just a buggy one.. I do plan to build another.. I am not sure if this is where the problem lies tho.. The engine runs fine under no load but as soon as loaded up, the issues start.

I have tried the pipe really long and slowly shortened it from there.

The full size servo isn't your problem either....

I sure would try a different motor & pipe..........like a MACS pipe #1110 set at about 7".......

I am about 95% sure the problem the motor/pipe combo.....

Take the pipe off the motor and run it open stack once and see what you get.......

Yeah but if i take the pipe off, how will i get pressure to the tank?

As long as you leave the tank vent open,and the motor is in good shape,the motor will draw fuel .......

It will require a needle change but it will tell you where the problem is......