Only max rpm 4,000

jimmyebay

Petty Officer 3rd Class
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Jul 26, 2009
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83
Got a all weld 20 ft boat. Flat bottom. Has had a lot of aluminum added to front. She's def heavy. Have a 1987 johnson 175 hp. Model is j175tlcua. Have about 14 inch by 24 pitch prop on it. Motor runs great. I can't get much over 4200 rpms out of it with some gear in boat. Had about 50 gallons of water in a tank this weekend. Brought down to 4,000 rpm. Thinking it's prop to steep and loaded motor hard. I wanted to check high speed ignition timing but says has to be at 5,000 rpm under load. Was curios if I could check the timing at high idle in driveway and disconnect the linkage that adjust timing and pull it to max and check it that way. Is there thing else electronically that adjust the timing besides throttle linkage that swings pickup forward?! Also, think it's pitched to deep?! Thanks.
 

emdsapmgr

Supreme Mariner
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Dec 9, 2005
Messages
11,551
That engine is a high-port block, designed to run between 5250 and 5750 rpm's. So your current 4200 is way too low-actually you are lugging it at that rpm. Before you fiddle with the prop, make sure the engine is mounted the correct height on the transom of that flat-bottomed boat. You want the engine's anti-ventilation plate to run just above the water flowing from under the transom when you are on plane. If your engine mounting height is ok, then try another prop. I'd get the correct prop on that engine-so that it will run right at the 5750 rpm's with a light load and just you in the boat. Try a 21 pitch and see if it does not perform much better. If the engine does still not perform up to the target rpm's you may want to consider a 19 pitch. That engine is no slouch. It actually puts out about 10% more hp than the cowling says it does, or just over 190 hp. You can check the WOT timing at idle-but it will not be correct on that crossflow when running WOT. The ignition timing will creep up as the rpm's increase, maybe as much as 4 degrees from what it is at idle. That's why the factory says to set at 5000 rpm's. If you do set the WOT timing at idle back it off 4 degrees from the factory degree recommendation. See the Joe Reeves method at the top of this web page in the "top secret" files.
 

jimmyebay

Petty Officer 3rd Class
Joined
Jul 26, 2009
Messages
83
That engine is a high-port block, designed to run between 5250 and 5750 rpm's. So your current 4200 is way too low-actually you are lugging it at that rpm. Before you fiddle with the prop, make sure the engine is mounted the correct height on the transom of that flat-bottomed boat. You want the engine's anti-ventilation plate to run just above the water flowing from under the transom when you are on plane. If your engine mounting height is ok, then try another prop. I'd get the correct prop on that engine-so that it will run right at the 5750 rpm's with a light load and just you in the boat. Try a 21 pitch and see if it does not perform much better. If the engine does still not perform up to the target rpm's you may want to consider a 19 pitch. That engine is no slouch. It actually puts out about 10% more hp than the cowling says it does, or just over 190 hp. You can check the WOT timing at idle-but it will not be correct on that crossflow when running WOT. The ignition timing will creep up as the rpm's increase, maybe as much as 4 degrees from what it is at idle. That's why the factory says to set at 5000 rpm's. If you do set the WOT timing at idle back it off 4 degrees from the factory degree recommendation. See the Joe Reeves method at the top of this web page in the "top secret" files.

Wow. Lots of good info. Appreciate it!! I'm not sure where my anti cav plate is sitting but someone followed me in fishing tournament and thought my motor was too high out of water. Could that cause lack of rpm?! I would think cause excessive rpm if fighting for water at prop. I do have a jack plate on this. Going to lower motor on plate and take out this weekend. Have someone drive and adjust motor up to where anti cav plate at correct spot and see what does. If still rpm issue, change props out... Agree? Thanks
 

emdsapmgr

Supreme Mariner
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Dec 9, 2005
Messages
11,551
Is your jackplate a fixed or adjustable one? If it's adjustable, you should have infinite adjustability, so that would not usually be a problem. Could be- if it's fixed and you have not really checked it out from a height standpoint. Again, get your setup right, then get into the prop issue. Keep in mind that a high rake, cupped prop (even a 4 blade) will help lift the bow. Less boat in the water=more speed.
 

jimmyebay

Petty Officer 3rd Class
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Jul 26, 2009
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83
Is your jackplate a fixed or adjustable one? If it's adjustable, you should have infinite adjustability, so that would not usually be a problem. Could be- if it's fixed and you have not really checked it out from a height standpoint. Again, get your setup right, then get into the prop issue. Keep in mind that a high rake, cupped prop (even a 4 blade) will help lift the bow. Less boat in the water=more speed.

It's hydrolic jack plate. When i mounted motor on it, mounted as high as possible. Right where anti cav plate with bottom of boat with jack plate all way down. I know flat bottom boats do different things to water out of back if boat. So moved motor down on plate so can lower deeper in water if need too.

What you mean high raked/ cupped prop? That pitch or whole different world? I know front of my boat is heavy. Will also have 60 gallon live well in the front after this winter.
 

emdsapmgr

Supreme Mariner
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Dec 9, 2005
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With outboards and variable height possibilities, you can get into trying various props. Aluminum props perform very differently from high-tech stainless. If you are a performance nut, or looking for bow lift, they are the way to go. Only problem is making sure the one you buy is exactly the one that works best. So, maybe you've got a buddy running a V6 OMC that you could borrow a prop or two from..... I would not want to plunk down $500-700 and find I bought one that did not perform well for my application.
 

jimmyebay

Petty Officer 3rd Class
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Jul 26, 2009
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Only problem with stainless is im on the river a lot and would rather break a prop then a lower unit. 4 blade prop be worth looking into?
 

emdsapmgr

Supreme Mariner
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Dec 9, 2005
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11,551
If you run the river, aluminum props are probably the best way to go. Better to sacrifice one blade of an aluminum prop than bend a propshaft that has a stainless prop on it. A potential option for you to consider: There is one good aluminum 4-blade prop for these larger V6 gearcases. Made by Mercury Marine. Made in 18, 20 and 22 pitches. Blades are high rake and lots of cup on them. Buy the Quicksilver version (without a hub kit) then also purchase an Evinrude hub kit for use with that Quicksilver prop.
 

jimmyebay

Petty Officer 3rd Class
Joined
Jul 26, 2009
Messages
83
If you run the river, aluminum props are probably the best way to go. Better to sacrifice one blade of an aluminum prop than bend a propshaft that has a stainless prop on it. A potential option for you to consider: There is one good aluminum 4-blade prop for these larger V6 gearcases. Made by Mercury Marine. Made in 18, 20 and 22 pitches. Blades are high rake and lots of cup on them. Buy the Quicksilver version (without a hub kit) then also purchase an Evinrude hub kit for use with that Quicksilver prop.

Appreciate the prop info!!! I'll def look into it. Def wanna run aluminum prop. Rivers tend to have lots of surprises!!! Are the pitchs on the 4 blade similar effect as the 3? In other words, running a 24 and I try a 20 with 3 blade and like it. Then get a 20 with 4 blades for the lift. Will it Be whole different rpm range as 3 blade? Sure no way for you to know but figure ask

Boobie. Tach is new. That means accurate, right? Ha. Got big plans to play with this weekend. My dvom has tach option and have a lead for it. Use that to compare. Any other ideas what else I could use to verify rpm?
 

jakedaawg

Rear Admiral
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Jun 26, 2012
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4,275
My dvom has tach option and have a lead for it. Use that to compare. Any other ideas what else I could use to verify rpm?

The best diagnotic tach, IMHO, for Evinscrew/Johnson or any out board is a Stevens analog Tach/Dwell meter made by Stevens Instrument Company. I also have an old snap on but I like the stevens because it can do 2strk/4strk and double spark.
 
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