is my prop the problem?

[handymantim]

I have a 21' Arrowglass Carisma bowrider. The boat is new to me and came with a blown motor(mer 5.7). I replaced the motor with a Chevy 305 with a 218 cam,high performance Elderbrock intake with quadajet 4bl. that came with boat. The distributor is original to boat with a new coil.

All the info I could find on the prop is that it is a 3 blade 19p. I am running WOT @ 3400RPMS with speed about 30mph. I am a little slow out of the hole but with my 90lb son on a knee board the boat does not want to plane for a long time.

I am not a boater and am learning as I go. Please help me! Should I go with a different prop and if yes what size. If you need more info post and I will try to find it.

Thanks in advance.

 

[45Auto]

Re: is my prop the problem?

Something is wrong with your boat. Your RPM is nowhere near where it should be in a 21' boat with a V8 and a 19" pitch prop. Normal prop pitch on your boat should probably be somewhere between a 17" and a 21", turning 4400-4800 RPM.

To get the 1000 extra RPM you should be seeing would require dropping about 5 inches in pitch, which would put you WAY outside the normal range.

Are you trimming the motor in to accelerate, then back out as it comes on plane?

Is the throttle cable adjusted correctly, opening all the way

Is compression/timing/firing order/etc on your new 305 good?

Are the water shutters in it? Have you checked the exhaust system to make sure no old pieces of shutter are clogging it?

 

[steelespike]

Re: is my prop the problem?

I can't be too specific.
I believe a marine engine requires a marine specific cam grind.
If not marine performance parts your power curve could be wrong.
I believe the advance curve on the timing needs to match the cam grind.
If the 305 is a 5.0 and the 5.7 a 350 gear ratios appear to be the same though newer ratios appear to be 1.62:1 older ones 1.50:1

 

[handymantim]

Re: is my prop the problem?

Something is wrong with your boat. Your RPM is nowhere near where it should be in a 21' boat with a V8 and a 19" pitch prop. Normal prop pitch on your boat should probably be somewhere between a 17" and a 21", turning 4400-4800 RPM.

To get the 1000 extra RPM you should be seeing would require dropping about 5 inches in pitch, which would put you WAY outside the normal range.

Are you trimming the motor in to accelerate, then back out as it comes on plane?

Is the throttle cable adjusted correctly, opening all the way

Is compression/timing/firing order/etc on your new 305 good?

Are the water shutters in it? Have you checked the exhaust system to make sure no old pieces of shutter are clogging it?

Yes I am trimming the motor in to accelerate and backing out.

After spending the day on boat today I am wondering about the throttle. As soon as the secondaries open I am not getting any increase in RPMs. Maxing out at about 3400RPMs. It does not seem like I am getting any more power?!?

Compression I feel good about.

timing: I set it the other day with light to TDC. When I tightened down the bolt it slide just a tiny bit to retard the engine. I thought about advancing it some but enough to compensate for 1000 rpms???

Firing order: I feel pretty good about that. Idles good with no back firing?!?

Water shutters? Now that one stumps me. I do not think I have that I googled them I have not seen any thing like that on my boat.

The exhaust seems to be clear.

 

[handymantim]

Re: is my prop the problem?

After looking around I think timing is set to 6ATDC . I am going to adjust that first chance I get. I will post results.

 

[dutchdog]

Re: is my prop the problem?

Sounds to me like your timing is way off. Try 6 degrees before TDC. Also check that the spark advance is working by reving the engine up to about 2000 rpm and checking the timing. Not sure what it should be but I think it should be at least 25 degrees before TDC.

 

[EddiePetty]

Re: is my prop the problem?

......
I am wondering about the throttle. As soon as the secondaries open I am not getting any increase in RPMs. Maxing out at about 3400RPMs. It does not seem like I am getting any more power?!?:

Don't just wonder, investigate. From memory, your secondaries are vacuum operarted. Try blocking the secondaries closed and see if your rpms increase. (you may have insufficient fuel supply). [/QUOTE]

......Compression I feel good about.

Compression is NOT a "feel good" thing. Do a compression TEST.

......timing: I set it the other day with light to TDC. When I tightened down the bolt it slide just a tiny bit to retard the engine. I thought about advancing it some but enough to compensate for 1000 rpms???

Don't just think about advancing. Set your timing to specs. (8-10 BEFORE TDC) and check TOTAL ADVANCE.

......Firing order: I feel pretty good about that. Idles good with no back firing?!?

Again, NOT a "feel good" thing. Ensure the proper firing order. SBC's run quite nicely with #5 and #7 plug wires reversed!!

...... Water shutters? Now that one stumps me. I do not think I have that I googled them I have not seen any thing like that on my boat.

You can't "see" them unless the Y pipe is removed ( or they have come apart and lying in the exhaust passages)

And a foot note:

Our V-20 with a 170 HP 3.7 (2/3 the engine you have) tries it's best to jump to plane at 2200rpm's pulling our 100# grandson on a knee board !! (I'm constantly bumping the throttle back to keep the boat right at plane....if I don't keep an eye on the tach the engine will walk past 3K and the kids start yellin') And that's with a 14.25 x 19 x 3 blade. The kids perfer I use the 20 x 4 blade when we tube.

 

[45Auto]

Re: is my prop the problem?

If the timing is set to 6 degrees ATDC (After TDC) that would cause a major loss of power. As earlier posters have stated, depending on your ignition system, it should probably be somewhere between 8-10 degrees BTDC (Before TDC).

 

[sethjon]

Re: is my prop the problem?

Get a 4 blade. 17"

 

[handymantim]

Re: is my prop the problem?

timing!!!

I went out today with a friend. I checked the timing and it was a few degrees ATDC in neutral. When I put it in gear I was at least a inch and a half away from the timing marks all together. I adjusted until I was 8degrees BTDC by the marks while engine in gear and at idle.

Now I am coming out of the hole a lot better! I am getting 3800 to 4000 rpms now and getting real close to 40mph. This is a lot nicer than it was.

I did have to adjust the carb screw to let the engine idle down to around 800 rpms.

I am now a lot closer than I was. THANKS to all!

I am still using the same wires,cap and button from old motor. I plan on changing them this week. I do not know if they will help but can not hurt.

Now I will ask a easier question: How do I pick up an extra 400rpms??