kmiller

Well I changed my powervalve from a 6.5 to 3.5 ( based on a 6.5-7 reading a idle) and now I can idle my boat. Runs fine but I could reach 5200rpms before and now I can't get 5000rpms. What would have changed to lose top end? Is this going to be a jetting isue?? I have a 26' scarab cv 3200lbs 340hp sbc and cant get over 5000rpms with a 19p mirage. Please Help!!!! I should be running a 21p at 5000rpms at least.......

kmiller

Here is my set-up.... open link..... What should I see out of this? I am seeing only 52mph on gps at 5000rpms with the 19p prop... I was told I should see 65mph out of this set-up and I am far from it....

Vinny P

You may have gone too low with the power valve. You have to check out the vacuum readings to see when and if the valve is opening. Get a reading at cruise speed and w.o.t. and adjust the valve accordingly. Providing that the jets were right before the change, if the valve is not opening now, you will be running lean.

kmiller

All new set up / not sure if the jets were right before. I feel I have a lot to get out of this set up and I know its all prop and carb work. Im new to tuning so I feel lost tring to find the best settings or to get the most out of this set-up..... I will try a 4.5 or a 5 powervalve. (is it poss that a 3.5 would not be open at WOT????)

vette131

if your carb is a little on the small side or your flame arrestor
is restrictive, you may have enough vacuum to stop the power valve from opening. a vacuum gauge will tell you if
that's the case. you need an air fuel ratio gauge(wideband)
or an egt to accurately tune your carb. after you set your timing & tune your carb at wot you can try raising the idle
speed slightly to keep the higher power valve from opening at idle.

kmiller

Its a 650cfm demon on a sbc / and I dont think its the flame arrester.... I will have to check vac at wot....

HARRISONMIRAGE

You probably are not dropping to 3.5" vacuum at full throttle.If this is the case be careful because you will be leaning it out.As mentioned above hook up a vacuum gauge and do some runs.

kmiller

I think I may have found my problem / my other problem was that the secoundary needle had been staying open ( drit what ever ) I cleaned it and then reinstalled it & that fixed the problem of it always starting like it was flooded after it sat ( gas was pouring from the rear blosters when I shut the key off....... That was maby fatting up the secoundarys ( it was a used carb and was always like that for me ) If that is the case will going up on my sec jet size help / I was thinking from 80 to an 82 / would that make up for over flowing from the needle..... I was at 5200rpms and olny 4900rpms now... Thanks for the help so far / I want this to run good for the sunsation rally tomorrow.......

FloridianSon

What do you have your base timming set at .Rum Runner asked the same question.That carb likes 18-20* base timing.Your vaccum will come up if you bring up the base.You said that you had 12-13* at high idle and that is why I told you to run the 6.5 power valve was right.That motor will make 12-13 at Idle with the base set right.

kmiller

My base is 12* and total is 32* how do I up one and not the other??