jumpybacon

Not getting the performance out of my '98 Scarab 29 like I think I should. Boat is new to me. Twin mag 350's. I trimmed up and down to no avail.

On the lake was only getting 57 and the tachs wouldn't go past 3000-3100. The motors were running strong and seems like the RPMs were higher. I previously had a single 454 and was comparing the sound between the two.

I had new hardin marine gauges installed and I think the tach setting was wrong. On the back there's a dial 1-2-3-4. I translated this, from the hardin marine website to, 2=6 cylinder, 3=8 cylinder, and 4=8 cylinder high altitude. The guy who installed put it on 4. I changed it to 3 but have not lake tested it yet. Idles right at 600 rpm either way. I'm thinking the tachs, if setup correctly, should probably be reading 4000 RPM. Just a thought.

Now, what has my attention is the throttle controls don't seem to go forward enough and there's no adjustability in the cables. The full forward position is short 1/2 inch. I unhitched the throttle cable at the carb and was able to move the carb throttle plate back more than the cable would. With the carb unhitched, I was able to move the throttle control more forward. Seems like the cables are wrong and I'm leaving some on the table? As far as I know from the previous one owner, nothing was changed on the boat.

I suppose there could be something else that's limiting the engines to 3k but nothing comes to mind.

See pictures for fully forward and fully back. Sorry can't figure out why my photos are always sideways.





Thoughts?

Rookie

That looks about right. The resolution of the throttle is determined by where it is hooked to the carb. What pitch props?

scarabman

As said, what props are you running? Also, throttle appears correct, but to check, simply make sure the butterfly is fully open at the point which is the end of your throttle travel. If it is not, then there is an adjustment issue. All things being correct, your rpm should be in the high 4000 range and the boat should run mid 60s

jumpybacon

The props are 23's. They are the factory ones...mercury props. I had the drives serviced with gimbal bearings before I put it in the water.

I didn't actually take the flame arrestor off but that's a good point about the butterflys. I suppose they could be fully open but the linkage still has some travel. I'll check that tonight. I did slightly adjust the port side carb cable because the throttle control on that side was not side-by-side with the other. So, when you grab both throttle controls they were obviously not side-by-side. Off by the width of a pencil. Annoying if nothing else. It was a very slight adjustment. Makes me think somebody was messing with the cables for that to be off a bit.....

I also checked the base timing (on the hose in the driveway) and it was reading close to 8 1/2 BTDC (not exactly 8). On the water I plan on focusing on this too, bumping it up a bit perhaps depending on how the motors respond.

I am looking for 4,000 rpm and at least 60 mph. I was using my phone gps speedometer app, which may not be super accurate, but it did jive with the speedometer on the boat mostly, although the needle bounces around quite a bit. Boat had 3/4 tank of gas, a cooler, me at 160 lbs, but the cushions and cabinets in the cuddy were not in the boat (in my garage as I have since replaced the carpet and hull liner).

scarabman

Mirage Plus 3 blades, correct? You should be able to spin those in the upper 4s if everything is as it should be. If you get it there you will be running 65-66 no problem. Shooting for 4000 rpm is not enough. You WANT to be in the upper 4s. Check the Merc specs for your motor for desired RPM operating range. You will see that is where it should be.

jumpybacon

Yes, the mirage. I shouldn't have said "looking for 4,000". I agree I need to be closer to 4,500. I'm hoping to find the RPMs are up but the tachs were just setup wrong.

Could there be anything limiting the RPMs in case they are setup correctly? The distributor? They are original.