Holey Piston!!

[Jeff Lutz]

With the HUGE carb you are trying to run on the engine, the huge amount of mixture is being or trying to be compressed in a given amount of physical space that would normally work great with say, a 11MM bore carb.

Carl, You have uncovered the reason behind the huge carb which has many hours of flow testing and mods done to it. It draws and vapourises better than any other carb i tested. I would post a picture of my carb flow bench but you would probably laugh

Im going for better crankcase filling which leads to a bigger bang upstairs. All the mods i have done are reversable, just trying to see what i can achieve without big port timing numbers.

Also keep in mind that with that huge carb you are supplying a tremendous amout of air/fuel to try to ignite & you can only compress a given quatity so much before it will ignite. Just a thought.......

Don,

very true, by keeping the temp below ignition point long enough so that it can all be compresed for the plug to light it off at the right time there should be a bigger bang

Ken, I agree you may indeed have pipe/port combo problems, I have not seen your boat in the gallery, but if your running stock ports a large volume pipe with large cone angles will most likely work best.Also you mentioned a 64mm prop at 4.8" pitch, I don't know what the prop was based off of but it sounds like you may be running out of prop.I had a 1 inch in an SG and one day I was at the pond with a full blade 1667 5.7" cup.The boat ran into a rich condition , I found myself leaning it trying to get it to clean out, it would

not.I put on a 1667 with 6.6" cup richened it back up , launched it ,burned up the pond and made several passes in the 89-90 mph range, brought the boat back in and the plug was good,this is just one good example of being under proped. Just curious, you mentioned having a custom piston, was this a oversized cmb that you machined or a custom piston all together,If so, what piston material did you use? Jeff

Pipe stinger has a huge influence on engine temp, i have modified it so its all ready to test again.

Ken

With the HUGE carb you are trying to run on the engine, the huge amount of mixture is being or trying to be compressed in a given amount of physical space that would normally work great with say, a 11MM bore carb.

Carl, You have uncovered the reason behind the huge carb which has many hours of flow testing and mods done to it. It draws and vapourises better than any other carb i tested. I would post a picture of my carb flow bench but you would probably laugh

Im going for better crankcase filling which leads to a bigger bang upstairs. All the mods i have done are reversable, just trying to see what i can achieve without big port timing numbers.

Also keep in mind that with that huge carb you are supplying a tremendous amout of air/fuel to try to ignite & you can only compress a given quatity so much before it will ignite. Just a thought.......

Don,

very true, by keeping the temp below ignition point long enough so that it can all be compresed for the plug to light it off at the right time there should be a bigger bang

Ken, I agree you may indeed have pipe/port combo problems, I have not seen your boat in the gallery, but if your running stock ports a large volume pipe with large cone angles will most likely work best.Also you mentioned a 64mm prop at 4.8" pitch, I don't know what the prop was based off of but it sounds like you may be running out of prop.I had a 1 inch in an SG and one day I was at the pond with a full blade 1667 5.7" cup.The boat ran into a rich condition , I found myself leaning it trying to get it to clean out, it would

not.I put on a 1667 with 6.6" cup richened it back up , launched it ,burned up the pond and made several passes in the 89-90 mph range, brought the boat back in and the plug was good,this is just one good example of being under proped. Just curious, you mentioned having a custom piston, was this a oversized cmb that you machined or a custom piston all together,If so, what piston material did you use? Jeff

 

[Ken Retallick]

Ken, I agree you may indeed have pipe/port combo problems, I have not seen your boat in the gallery, but if your running stock ports a large volume pipe with large cone angles will most likely work best.Also you mentioned a 64mm prop at 4.8" pitch, I don't know what the prop was based off of but it sounds like you may be running out of prop.I had a 1 inch in an SG and one day I was at the pond with a full blade 1667 5.7" cup.The boat ran into a rich condition , I found myself leaning it trying to get it to clean out, it would

not.I put on a 1667 with 6.6" cup richened it back up , launched it ,burned up the pond and made several passes in the 89-90 mph range, brought the boat back in and the plug was good,this is just one good example of being under proped. Just curious, you mentioned having a custom piston, was this a oversized cmb that you machined or a custom piston all together,If so, what piston material did you use? Jeff

Jeff, 4.8 is the pitch over 30 degrees, Cup itself is over 5, cant remember exactly. Boat isnt near as light as an SG or other modern hydro. No rear sponsons either. Piston I machined myself, 30%silicon. Had another custom piston done by someone else but it had an issue with foreign material... just not enough room between piston and liner for outside guests! So Ive started making them for myself.

Ken