Prop, motor, altitude?
 

After a couple weekends on the water I'm really happy with my Mariah and how quickly I get up on plane with the 4.3L and SS 19 pitch prop combo. I'm pretty sure the prop is 14" diameter but I'll verify this weekend. I'm a little disappointed with the top end though. I'm barely touching 40 (GPS) on mostly smooth water with two adults and two kids. I thought I'd see closer to 45. The RPMs at WOT is around 4100, a bit on the low side. I would think that prop would be sized about right for the motor.

The boat had just come back from being serviced and had the heads machined and a blown head gasket replaced. The receipt said there was some water in the no. 6 cylinder. The guy I bought it from also said they made some adjustments to the throttle. It seems to have a good inch and a half of travel after the outdrive engages and the throttle engages. Is that normal? Is it possible that they left too much freeplay in the throttle cable adjustment? Wishful thinking that it's that simple?

I think I mentioned this before but my Dad built Searays for a few decades and he suggested looking at the gear ratio on the outdrive. Could altitude at 4500 ft be a factor?

Re: Prop, motor, altitude?
 

There is usually a tag on the drive indicating the drive ratio. It will be stamped something like 1.50R, meaning a 1.5:1. Have a look. I don't know what qualifies as high altitude, but if the previous owner was closer to sea level it's quite possible it doesn't have the correct gear set for operating at 4500'.

Re: Prop, motor, altitude?
 

I have the exact same boat but a 2000. I am running a 21p prop. I hit 54mph by myself at WOT (not GPS) .. Running a 19 should increase your RPM not reduce it. I believe my ratio is a 1:1.62 ratio. I have seen in the past about the effects of altitude I think it was 10 4% per 1000ft of altitude. Here is an article I found on the effects of environment on HP. http://www.bwbmag.com/output.cfm?ID=942751.. I am also running the 4.3LEFI so I don't know which engine you are running. I would get the motor checked. I would suspect that your are not getting full RPM.. Or not making full power..

Re: Prop, motor, altitude?
 

I'm wondering if I'm not getting full RPM because it's cable adjustment. I'll check this weekend to see if when at WOT there is still more play in the throttle.

I plan on doing the exhaust manifold conversion to ditch the batwings and add the Edelbrock 1409 carb and 2114 intake manifold. I'll also swap to a K&N flame arrestor and replace the fuel filter at the same time. If that doesn't get me closer to where I think I should be, then I'll have someone take a look at it.

BTW, has anyone swapped in the Edelbrock manifold? Any clearance problems?

Re: Prop, motor, altitude?
 

22empire, I'm running the same gear ratio and it is a 14x19. This weekend I tinkered with the throttle adjustment and now that I dialed in the idle right at 650, the top end really sucks at 3900. The cable felt mushy between the bracket and the throttle arm on the carb. It had some play in it. Enough that while I was on the water making adjustments, I'd start it and it'd run up to 2200 and if I tapped the cable between the bracket and throttle arm, it'd drop back to 800-1000 RPM. I've never set up a throttle cable that felt like it had dampening in it. Is that normal?

Re: Prop, motor, altitude?
 

Sounds like a stretched or poorly lubricated throttle cable to me.. The spring back or dampening that you are getting is probably resistence from the outer jacket of the cable assembly. I would look at replacing the cable.

Re: Prop, motor, altitude?
 

The easy fix didn't work for me. I replaced the cable and everything is still the same. Something else occured to me while I started with the cable. There's no throttle return spring on this carb. There's not a hole in the throttle arm for a spring. I asked the parts guys at the marina to see if there is supposed to be and he gave me a part number for the spring. They didn't have one. When I search for that part number, it looks like it's for a 4bbl. None of diagrams I've looked at show a spring on the 2bbl carb. Anyone with a 2bbl carb have a return spring on your linkage?

I'm going to check for water in the cylinders and the compression next time I'm out, but that was all checked out right before I bought the boat. The heads were machined and of course the gaskets were replaced and it was tested. I have the receipt from the shop in my hand detailing all the work that was done. I don't think that's the problem. The holeshot is great. It planes in a couple seconds but it's topping out at 3900-4000 RPMS.