Great lookin run..WOW..83 is movin!!
What boat do you have it on?
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Great lookin run..WOW..83 is movin!!
What boat do you have it on?
Hydro
The boat that I run the Yamaha on, is a hydro that I built myself. The hull was built for the 44ci Mercury @ 12ft, but it handles the lightweight Yamaha well.
Karl,
So far I've only got it going to 83mph testing. The reps at that run was 7800rpm. The cylinder compression is 175psi and I only run VP Race fuel with 16/1 oil.
Originally Posted by Karl Kretzmann
Carbs and internal mods
Karl,
Can you explain to me the specific advantage to the "square bowl" carbs over the "round bowl" ones. I was told that, of the 70hp carbs, the round bowl ones were the only ones that would fit within the tight cluster of 3 on the intake.
According to class rules, I have to run the 4 petal reed cages. It's quite obvious that this is currently a BIG choke to the intake flow. Did you do any modifications to your reeds/cages in your earlier modified motors?
The internal mods on my 40hp were basic. Crank was welded, head was tightened and all the block work was performed by, none other.............Tim Kurcz!
Did you find the photos of your modded Yamaha's yet. If you don't want to post them, can you P.M. them to me.
Thanks,
Joe
Hi Joe,
you running the old "D" Model block by the looks of things.the newer H model IMO is the better motor, however this is a hotly debated topic!
the 70 and 90 square carbs bolt right onto the H model motor. I'm sure with minor mods you could get them to work on yours.
Th e square carbs definitely "measure" fuel better and are much more responsive. airflow and venturi velocity is much better.
If you cannot change reeds, then you can definitely modify them(if allowed). we ran Bouysen reeds and left only a seat area of 1mm. This means that there is quite a bit of material you can remove. angles and flow are critical! but this is hard to explain without drawings or pictures. just picture airflow through reed block and make it as straight and smooth as possible!
try to find out what was done on the porting?
how much was taken off the head?
any squish angle mods?
haven't had chance to look for pics of my motor yet. will try asap.
Karl
Karl,
Can you explain to me the specific advantage to the "square bowl" carbs over the "round bowl" ones. I was told that, of the 70hp carbs, the round bowl ones were the only ones that would fit within the tight cluster of 3 on the intake.
According to class rules, I have to run the 4 petal reed cages. It's quite obvious that this is currently a BIG choke to the intake flow. Did you do any modifications to your reeds/cages in your earlier modified motors?
The internal mods on my 40hp were basic. Crank was welded, head was tightened and all the block work was performed by, none other.............Tim Kurcz!
Did you find the photos of your modded Yamaha's yet. If you don't want to post them, can you P.M. them to me.
Thanks,
Joe
Joe I don`t know if you have done any mods on the exh side but there is a lot to be gained there than any other part of the engine in my opinion ovaling the port and making it wider & raising the port approx. 3/16 to a 1/4 in.and installing a expansion chambers did more for our engine than any other thing we did. I would suggest also that you go to a aftermarket ignition either from MSD or ELECTROMOTIVE, We have MSD on our engine that was sold as a kit for 3 cyl SeaDoo. Fly wheel that we have on their now weighs approx 1 Lb. If I were do it over I would have used An Electromotive system simply because their Tech assistance is much more friendly and helpful. I wish we had more time to run thiengine. But our priorties now are D- E hyd & run in NBRA 4 classes in a day are more than this old man and my son can handle. Art KKarl,
Can you explain to me the specific advantage to the "square bowl" carbs over the "round bowl" ones. I was told that, of the 70hp carbs, the round bowl ones were the only ones that would fit within the tight cluster of 3 on the intake.
According to class rules, I have to run the 4 petal reed cages. It's quite obvious that this is currently a BIG choke to the intake flow. Did you do any modifications to your reeds/cages in your earlier modified motors?
The internal mods on my 40hp were basic. Crank was welded, head was tightened and all the block work was performed by, none other.............Tim Kurcz!
Did you find the photos of your modded Yamaha's yet. If you don't want to post them, can you P.M. them to me.
Thanks,
Joe
The outside of the square bowl carbs are much larger, hard to fit. I found that on my 90 the square bowl carbs measure 100 thousands less between the bolting flange and the dump tube. I did see better acceleration, but nothing else. Not one more rpm. Do you want me to find a set of squares for you? Just keep in mind that the 70s allow more airflow weather round or square.
Helping folks out around the globe.
Thats funny, I experienced a way more "alive" motor with the round carbs.Th e square carbs definitely "measure" fuel better and are much more responsive. airflow and venturi velocity is much better.
Depends on other mods i guess which is best.
I'll just stick with the round carbs, for now. Until I can open up the "choke" between the carbs and the crankcase, I don't think the inlet flow is going to help that much.
That's pretty spot on!!
The whole carb issue only really come into play on highly modded motors!!
The reeds limit any larger carbs effectiveness!
Exhaust port mods alone could give you extra rpm but if you want complete power mid and top end then it become a complete mod motor package! Ie: carbs,reeds,ports, heads, exhaust, plus plus plus...
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