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Need more rpms. Or do I?
http://mudmotortalk.com/mmt_v2/viewtopic.php?f=3&t=10604		 Page 1 of 1
Author:  bbb [ Thu Jul 01, 2010 7:20 pm ]
Post subject:  Need more rpms. Or do I?
19x60 boat
2010 35hp gdsd CDI with 4 hrs

With me(215) and 150#s of gear. I was running 23.5-24 at 3600 rpms.

Last night:
3 guys (650#'s)
150 pounds of gear
I was hitting 3200-3300 rpms before the prop would blowout and the speed would drop. Max speed hit was 20 when in real shallow water, but deep water speed was 18.5-19.

Today:
3 adults 1 kid (600#'s)
150 pounds of gear
I was running 3350 rpms at 21.5-22mph deep water

I've already loosened the throttle cable and pulled it til it hit the stop, and tightened it back down. Its running the max rpms out of the water, 4200-4300.

Do I just have a big boat and load for a stock 35?

I'm not unhappy with the speeds so much, but just thought the rpms were low.
Author:  Caleb W. [ Fri Jul 02, 2010 6:07 am ]
Post subject:  Re: Need more rpms. Or do I?
With max out of water rpms at 4300, thats about as high as you wanna go. I think the CDIs have a belt in rev limiter though? Dont let me lie to you though. Sounds like you got a hauss of a boat, alot of load. On a size boat that fit, in water by yourself would be around 3900-4000. Id play around with weight distribution, you can usually find a couple mph hiding somewhere.
Author:  MaXXis85 [ Fri Jul 02, 2010 6:52 am ]
Post subject:  Re: Need more rpms. Or do I?
Just because you can spin 4300 OOW, dont mean you gonna get to that with a load. It takes HP and torque to me able to spin RPMS with load on the prop. You are pushing a barge with a 35HP engine, dont expect much more out of it unless you mod it. 3600 RPM with what you are describing is about right. My 1748 with a load of 3 people and gear to go to the camp i will push 3700-3750 stock. Any more than that the motor is trimmed to high and you lose bite from the prop.
Author:  caddobrook [ Fri Jul 02, 2010 8:11 am ]
Post subject:  Re: Need more rpms. Or do I?
Your other option would be to prop down a little.

It will lower your top end speed a little without a load, but will increase your ability to carry a load.

I went from a 32 pd prop to a 27pd prop and gave up about 2-3 mph on the top end but had way more hole shot and could carry 3 people and stuff almost as well as just me....

Just a thought..

and x2 on playing with your load distribution... I have picked up rpm and speed by moving people and gear around in boat-forward and back, and left and right. you want your load centered...
Author:  bbb [ Fri Jul 02, 2010 8:35 am ]
Post subject:  Re: Need more rpms. Or do I?
I know some folks running a boat my size are running twins to get their speeds in the high 20's, so I'm not expecting anything like that from a stock 35.

I am also going to try a few different props as this 3 blade may just have too much bite for a load. Maybe I need to find a sand flat to run across a few times and knock some cup off of it. :mrgreen:

Maybe double up the governor spring or get one with less stretch?

My 31 GDLT with the same load was pushing 16-17, so I've still gained 3-5mph.

I figure that once the warranty is up, I'll let a motorhead friend do some headwork on the motor. He says the headwork will give me the most gain and that a Mikuni carb isn't a bad idea either, but when you compare $$ to HP gain, headwork is the way to go.
Author:  MaXXis85 [ Fri Jul 02, 2010 9:54 am ]
Post subject:  Re: Need more rpms. Or do I?
Being you cannot acheive the amount of RPMs due to the load on the engine, a stiffer spring will not help. Your simply at the limits of what that engine can do.
Author:  Josh [ Fri Jul 02, 2010 10:43 am ]
Post subject:  Re: Need more rpms. Or do I?
Author:  bbb [ Fri Jul 02, 2010 10:47 am ]
Post subject:  Re: Need more rpms. Or do I?
Author:  Brinkleydog [ Fri Jul 02, 2010 10:01 pm ]
Post subject:  Re: Need more rpms. Or do I?
why do u say the governer has nothing to do with it? or are you saying the sping has nothing to do with it?

if the spring was tighter would it not chenge anything?

The readon i ask is after i pit a ziptie on mine to keep it from stretching as much i picked up almost 2mph....all with the same load.....i did this when we had a group make a trip up Caddo to Jefferson. I even cut the ziptie off after i noticed the gain to double check what i was origanaly getting.

looking forward to what the FE say about this situation.

later
Author:  bbb [ Sat Jul 03, 2010 10:15 am ]
Post subject:  Re: Need more rpms. Or do I?
With my GDLT I put a wrap of wire around the spring and also saw a gain. also jumped out of the hole alot better. Thought I might be able to do it with the GDSD too.

I'm about to leave for a few days at the coast. I'll take a couple zip ties with me and try it out. Also got a MB big blade12.25X10 and a 11x10 prop that I'm gonna try out also.
Author:  50fps [ Sat Jul 03, 2010 10:57 am ]
Post subject:  Re: Need more rpms. Or do I?
Author:  Brinkleydog [ Sat Jul 03, 2010 12:06 pm ]
Post subject:  Re: Need more rpms. Or do I?
It is the CDI.

Why you aks?
Author:  50fps [ Sat Jul 03, 2010 2:31 pm ]
Post subject:  Re: Need more rpms. Or do I?
Author:  Brinkleydog [ Sat Jul 03, 2010 10:15 pm ]
Post subject:  Re: Need more rpms. Or do I?
never thought of that....might be right on that.
Author:  bbb [ Sun Jul 04, 2010 9:42 pm ]
Post subject:  Re: Need more rpms. Or do I?
Problem solved. I bought Metermans MB Big Blade prop and put it on my GDSD.

Woke the motor up big time. The 3 blade that came with the motor must just have too much pitch for a heavy load with a load. I couldn't believe how much better it sounded. Finally sounded like I was getting something out of it.

I ran the boat today and with me, wife and kids, 550 pounds in all, plus about 40 pounds of gear.

Ran best around 3750 rpms and was running 22.5-23 with this load. I dropped them off on a sandbar and was hitting 24-25 alone(215). And these were all deep water speeds.
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