125 engines ... Pros and Cons ...

[AOFoffice]

Neal,
Since Oroville will also be awarding AOF points, a few of the AOF drivers will be there also. Brian Payn will be there with his 125 VRP and Krier Runabout from Iowa. You can check it out.
We won't be testing the wine barrels. I haven't had the luxury of Napa wine country, but after a couple of bottles of $1.97 (Wal mart price) Boone's farm, the wine all tastes the same anyway. .
Connie

[epugh66]

We won't be testing the wine barrels. I haven't had the luxury of Napa wine country, but after a couple of bottles of $1.97 (Wal mart price) Boone's farm, the wine all tastes the same anyway. .
Connie

Thats funny, the Iowa perspective...alot like the Tennessee perspective.

My opinion on PRO....Its easy. If you are good at stock you will be good at PRO. Just look at the previous crossover racers.
Also, dont buy some backmarkers used up crap. Racing aint cheap, travel aint cheap. If you like to drive and campout or stay in motels, there are easier ways to do it than going to a race and doing your homework there.

[Dr. Thunder]

125cc Performance/Technical Issues ...

.
<snip>
"... Jetting takes a little practice and is important to pay attention to the engine's performance when testing on race day. The majority of engine problems in 125 hydro (and 250 and 350) is running the jetting to lean.
DW

A recent thread related to the AOF/APBA Kilo event at Oroville discussed the problem of the inability of a 125 engine to "take the pipe". this was explained to me as ... " when he (the driver) tried to slide the pipe "up", the motor wanted to fall on it's face (decreased performance). Therefore, he was lacking the top end power band of the motor."

So, what I would like to understand is what might have caused this failure ... was it related to improper "jetting" for the conditions of the day or to other causes?

Additionally, can any of you Pro types tell me more about how the phenomenon of "pulling the pipes" affects the engine performance. Go ahead ... be as technical as you need to be. What happens to the engine and why when you shorten the length of the pipe?

Thanks

[sam]

The short version is that pipes only work right at one rpm. To work at a lower rpm they must be longer, for a higher rpm shorter. The long length will be the rpm coming off the turn, the short length will be right on the straight.


More detail as to what would cause a motor to bog or die when pulling the pipe probably ties directly with Mr. Weaver's comment. When the motor is "running on the pipe" it gulps a tremendous greater amount of air compared to when not "on the pipe". A correctly matching amount of fuel must be available with the air. A very good carb will be set up to supply reasonable mixture when off the pipe and dead on when on the pipe.

Sounds like the motor was adjusted too much for the off the pipe operating loop and not enough for when on the pipe ... most likely not enough fuel when the pipe was gulping.

Something sort of like the inverse could also be happening ... the motor may have been on the pipe for the speed it was running and with too much pitch or too heavy a driver ... the pipe was pulled too far too fast and the pipe went out of the range for the motor speed without the motor speeding up ... now the pipe is pulling less air (because it is too short to work, as in waaaay to short) and the carb is suppling enough fuel for operation with the pipe working, but the pipe isn't making the motor gulp ... the motor is just sipping air and being drowned by the carb.

Not only does the carb and pipe have to be in balance .... everything has to be in balance.

[Dr. Thunder]

125 Engine Performance/Technical Issues

<snip>
" ... the motor may have been on the pipe for the speed it was running and with too much pitch or too heavy a driver ... the pipe was pulled too far too fast and the pipe went out of the range for the motor speed without the motor speeding up ... now the pipe is pulling less air (because it is too short to work, as in waaaay to short) and the carb is suppling enough fuel for operation with the pipe working, but the pipe isn't making the motor gulp ... the motor is just sipping air and being drowned by the carb."

"Not only does the carb and pipe have to be in balance .... everything has to be in balance."

Thanks Sam ... now, if possible, take me around the course in a 125 hydro from the time you leave the pits to the end of a lap ... what is the driver doing relative to the length of the pipe, engine rpm (throttle open/close) etc. What is the driver listening to or reacting to relative to throttle position and pipe position? Hope the question makes sense ...

[sam]

Most alky drivers tell me they squeeze the throttle leaving the pits and hold it wide open the rest of the time, using the pipe length to control the boat speed on the course.

So you would leave the pits with the throttle wide open and the pipe long ... get up on plane and when pointed straight .... pull the pipe short .... when setting for the turn, drop the pipe back long and when pointed straight or done accellerating in long pipe mode .... pull it back short again (duh).


The maximum and minimum lengths of the pipe have to be just right for the speed of the boat when turning and when running on the straight. The resonant power of the pipe changes the amount of air entering the carb just as much as opening and closing the throttle.

On my open stack 6 cylinder I have water injection that changes the speed of the sonic pulses in the exhaust. While I was in my proof of concept testing I discovered that switching the water on and off with the carb half open was almost the same as opening the carb fully and returning it to half.

[David Weaver]

With the 125, you might also use the pipe to go on plane. Once put into the water, you pull the pipe and increase the rev's. As the boat goes onto plane (get's over the hump), you gradually let the pipe fall back. This takes a little practice, but is not hard to learn.

Generally, these days we pull the pipes forward steadily. With many of the Konigs, you could slam the pipes forward coming out of the turns. Again, a little practice goes along ways. Your ear becomes trained to revs.

As I was not at Oroville, I cannot say for sure what kind of problem that Brian ran into. His 125 typically runs as good as any around. Most likely, he experienced a fuel problem of some sort, but probably not jetting. Maybe a bad check valve or a blockage in the fuel line. Also, the float may have been sticking. There is an outside chance that of an ignition problem, but the VRP and Rossi igntitions rarely fail.

[Richard K.C. Mo.]

So Right!

Sam i am, Ted May told me very same thing in the 70s i worked with him one day at practice in SanDiego flood channel, worked all day on that jonrude V4.
Richard F.

[Dan M]

Dr. Thunder,
I'll give it a try. I only have limited actual experience due to a neck problem, but here goes.

Boat is cranked on a stand and lowered gently into the water. Pipes are in the full up position to give maximum rpm and power. 125's have very little torque and need all the rpm's they can muster. As the boat comes over the top, the prop starts to take a big bite into the water and wants to load the motor, back the pipe all the way off so that as the rpm drops due to load, the pipe offers more power at the lower rpm. As the boat accelerates, the pipe can gradually be fed in slowly to adjust the power as the rpm increases. This is more a "feel/ sense" that you acquire as you get more familiar with the setup. Accelerate down the straight pulling the pipe all the way up usually about 1/3 the way down the straight. Come into the corner with the pipe still up and set the boat for the turn. As the boat slows slightly, back the pipe down 1/2 to 3/4 of the way extended. Finish the corner and again slowly feed the pipe back in slowly as rpm increases. Full up 1/3 of the way down the straight and set up for the next corner. The throttle stays wide open the whole way around the course. The pipe can almost be used as a secondary throttle to control speed.

In Brian's case, he may have had too stiff a prop and never got the motor up to the rpm where the pipe would function properly. 125's have so little torque which make them very unforgiving on setups.

There are numerous article on how an expansion chamber works. The exhaust pulse travels down the pipe and reflects back toward the exhaust port. This pulse wave has to be timed so that it hits back at the exhaust port just as it closes. This pushes some of the fresh charge that has been drawn through the cylinder back into the cylinder and " supergharges " the combustion. Cone angles, lengths, diameters all play a role in how weel the pipe will work.

Hope this helps a little,

Dan

[mercguy]

Dr. Thunder,
I'll give it a try. I only have limited actual experience due to a neck problem, but here goes.

Boat is cranked on a stand and lowered gently into the water. Pipes are in the full up position to give maximum rpm and power. 125's have very little torque and need all the rpm's they can muster. As the boat comes over the top, the prop starts to take a big bite into the water and wants to load the motor, back the pipe all the way off so that as the rpm drops due to load, the pipe offers more power at the lower rpm. As the boat accelerates, the pipe can gradually be fed in slowly to adjust the power as the rpm increases. This is more a "feel/ sense" that you acquire as you get more familiar with the setup. Accelerate down the straight pulling the pipe all the way up usually about 1/3 the way down the straight. Come into the corner with the pipe still up and set the boat for the turn. As the boat slows slightly, back the pipe down 1/2 to 3/4 of the way extended. Finish the corner and again slowly feed the pipe back in slowly as rpm increases. Full up 1/3 of the way down the straight and set up for the next corner. The throttle stays wide open the whole way around the course. The pipe can almost be used as a secondary throttle to control speed.

In Brian's case, he may have had too stiff a prop and never got the motor up to the rpm where the pipe would function properly. 125's have so little torque which make them very unforgiving on setups.

There are numerous article on how an expansion chamber works. The exhaust pulse travels down the pipe and reflects back toward the exhaust port. This pulse wave has to be timed so that it hits back at the exhaust port just as it closes. This pushes some of the fresh charge that has been drawn through the cylinder back into the cylinder and " supergharges " the combustion. Cone angles, lengths, diameters all play a role in how weel the pipe will work.

Hope this helps a little,

Dan

whew................boy, no wonder I stick to stock/mod racing.............it sounds to complicated for me to race a PRO engine............I can only do one thing at a time!!

[Bill Huson]

right, Daren . . . to much stuff to do

Did the one-shot driver thing in a 125 back when they were converted motorcycle engines. This had the usual throttle, a pipe to pull, AND a switch to operate the water injection pump! Had to fiddle with all three to get it up on plane. Of course I couldn't all that stuff and the engine flamed out about 100 yards out. Bugger bears.

CONCLUSION: The 125 class needs more multitasking female drivers.

[Kristi Ellison]

If this multitasking female can drive one any of you can!!!

[David Weaver]

Did we mention the Yamato Shuffle?

whew................boy, no wonder I stick to stock/mod racing.............it sounds to complicated for me to race a PRO engine............I can only do one thing at a time!!

Come on Darren, that is not even to race one, we are just talking the basics.

Plus for that little effort, you get a great ride, no tear down at inspection and you know that the class will be around the following year.

Dr. Thunder, on occaision, as you leave the pits you may also want to make an arching turn to the left. Sometimes this helps bring the rev's up enough to get the boat on plane.

Should all of the above not work (which will be rare), you may have to resort to the classic Yamato Shuffle. Eric Pugh can best describe this elegant two-step made so popular by Yamato 250's and 350's in the early 80's. If you get dizzy easily do not try this!!

Of course, if you have a good prop (not too big) and a proprer set-up then your 125 should plane-off without too much effort.

[Bill Huson]

Methinks I'm familier with the &quot;Yamato Shuffle&quot; . . .

Back in the early 80s I had an old Craig Craft A hydro with a Mk 15 I was running in A stock. The only way I could get that sucker on plane was get way foward in a sweeping left turn until it was on the "hump", and then a huge body weight shift to right and turn right. Repeat - repeat - repeat until the combo turn and weight shift put `er over the hump.

[Dave_E71]

Most alky drivers tell me they squeeze the throttle leaving the pits and hold it wide open the rest of the time, using the pipe length to control the boat speed on the course.

So you would leave the pits with the throttle wide open and the pipe long ... get up on plane and when pointed straight .... pull the pipe short .... when setting for the turn, drop the pipe back long and when pointed straight or done accellerating in long pipe mode .... pull it back short again (duh).

Sam,

One small observation, depending on set-up and driving style, you could change "when setting for the turn drop the pipe back long and when pointed straight or done accellerating in long pipe mode .... pull it back short again " to " dump the pipes about the middle of the turn and be standing on them by the time you hit the exit pin". Not sure how well this works in the 125 but in the larger displacement classes it seems to do the trick.

Dave