550 fuel vaccum issue

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Thats not a 38BN that's a 44BN , I would ditch that like yesterday , you already have a manifold the SBN will bolt to you just need the spacers and gaskets. The vacuum hose goes to the pulse fitting on the carb just like on the one you have now , The SBN's have arrows and an infinity symbol on the carb that tells you which hose goes where. Aroow pointing away from the carb is the return , arrow pointing to toward the carb is the fuel inlet, the infinity symbol is the pulse line.

You are going to hear a lot of opinions on which manifold to get , here is mine , an intake manifold on a Piston port motor holds the carb on , that's it , you can Spend as much as you want on one but it won't make any difference in performance , only the weight of your wallet .

 
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Thats not a 38BN that's a 44BN , I would ditch that like yesterday , you already have a manifold the SBN will bolt to you just need the spacers and gaskets. The vacuum hose goes to the pulse fitting on the carb just like on the one you have now , The SBN's have arrows and an infinity symbol on the carb that tells you which hose goes where. Aroow pointing away from the carb is the return , arrow pointing to toward the carb is the fuel inlet, the infinity symbol is the pulse line.

You are going to hear a lot of opinions on which manifold to get , here is mine , an intake manifold on a Piston port motor holds the carb on , that's it , you can Spend as much as you want on one but it won't make any difference in performance , only the weight of your wallet .

Huge. Thank you. Again is their a specific mikuni sbn 44 i should buy or any oem yamaha will do? Also i noticed thick head washers i think. Is it pimped or is it stock size?
 

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Any Yamaha 44 will work fine , you will of course have to rejet it to match the engine but a Yamaha 650 SBN jetting should be fairly close as a starting point .

Thick head washers indicate that the head has been milled considerably , your compression numbers also verify that.

This of course won't be exact but 120-125 main 100-110 low popoff about 20-22 psi, should get you started, it will need some fine tuning.
 
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Any Yamaha 44 will work fine , you will of course have to rejet it to match the engine but a Yamaha 650 SBN jetting should be fairly close as a starting point .

Thick head washers indicate that the head has been milled considerably , your compression numbers also verify that.

This of course won't be exact but 120-125 main 100-110 low popoff about 20-22 psi, should get you started, it will need some fine tuning.
I imagine there are kits with higher and lower tension springs along with different jets? Do you have a link to a decent jetting kit with spings maybe?


Its my understanding that with the higher compession head im running a higher risk of detonation? Race gas 110? 40 to 1to keep things nice and lubed? Is dual cooling suppose to be a thing now?
 
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WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
There are no jetting kits as such , you have to buy the individual jets and springs and start swapping them out , you will also need a popoff pressure gauge to set the popoff. For sure I would start at the rich end of those jetting specs , maybe even a few sizes up and lean it out as needed , jetting one from lean to get it running is not a good idea , a cast iron 550 running lean equals instantaneous meltdown , think Chernobyl !

180 PSI is pushing it on pump gas, you could run 100LL avgas with no worries, 40:1 will be fine with a decent oil..

Dual cooling is probably needed on a cast iron cylinder with that much compression , cast iron does not dissipate heat the way Aluminum does , actually it retains heat , for sure it's not a bad idea.


I have been using that particular popoff tester for a while now, no complaints so far.
 
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There are no jetting kits as such , you have to buy the individual jets and springs and start swapping them out , you will also need a popoff pressure gauge to set the popoff. For sure I would start at the rich end of those jetting specs , maybe even a few sizes up and lean it out as needed , jetting one from lean to get it running is not a good idea , a cast iron 550 running lean equals instantaneous meltdown , think Chernobyl !

180 PSI is pushing it on pump gas, you could run 100LL avgas with no worries, 40:1 will be fine with a decent oil..

Dual cooling is probably needed on a cast iron cylinder with that much compression , cast iron does not dissipate heat the way Aluminum does , actually it retains heat , for sure it's not a bad idea.


I have been using that particular popoff tester for a while now, no complaints so far.
Thats funny i actually just broke that gauge on that kit as the guage hold enough pressure to test pop off pressure on a stock 94 raider. Need to replace the gauge and i should be good.

I used to run half and half 110vp race fueland 91 pump in my dirtbikes but 50:1. i imagine that same formula would work for this application?

Okay. Back to the drawing board with the pump. Iv already got it installed, gonna have to rip it out and fine a thread on how to dual cool my pump and head.
 
https://www.pwctoday.com/forum/technical-discussion/vintage-skis/1109-dual-cooling-how-to

Found it. Was so close to wrapping up this project. Probably gonna utilize the bilge line instead of drilling a whole in the hull. And gonna break the engine down and reseal it as i was just gonna run it but id rather protect someone else investment and my own time at this point. Im already in the whole over 2k at this point with the paint job. Might as well get every last bit done and hopefully have a sweet ski.
 

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
One more thing I can see in the photos that the solenoid -rev limiter is still in the ski , I would suggest removing that garbage SBN's already have a built in restrictor in the body of the carb so no need for one in the return line.
 
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