35 Mercury RPM's

[Adaboat]

Does anybody know how many RPM's a mercury 35 should turn at WOT? The butterfly is all the way open, but mt Tach shows 3400 at top speed.

 

[Barnacle_Bill]

Re: 35 Mercury RPM's

It should be somewhere around 5,000 RPM. Check for a strong spark at all plugs.

 

[verado7]

Re: 35 Mercury RPM's

from 1981 to 91 5400 - 6000 rpm you need to change props maybe if all else is running well - you want to get those numbers up to 5800 rpm area 3400 is gonna kill it quick - mercs like high revs .

post your year ,boat length , weight and approx. weight of total passengers and gear and the current pitch# of the prop - i can figure a good estimate of how the motor is running from there .

 

[Adaboat]

Re: 35 Mercury RPM's

1986 Glasstream 13' Bass boat, 1986 Mercury 35, Boat with gear and two people probably 1000 lbs? Not sure about the pitch of the prop, I'm sure it's original if that helps. Also, the motor has a "wing" on it to help get on plane faster, but I'm not sure it does help, takes a good minute to get on plane unless the waters very calm then it still takes 30-45 seconds.

 

[verado7]

Re: 35 Mercury RPM's

the wing is debatable - sometimes they help - sometimes hinder .
look on the prop and there should be a set of numbers - post those numbers . thats a nice light boat - it should fly pretty good with the 35 .

 

[Adaboat]

Re: 35 Mercury RPM's

Do you know where the numbers are typically? Inside where the exhaust comes out? I looked all over it very good with out taking it off and saw none. What size prop would you recommend? This prop has been hit and straitened many times, I think I need a new one anyway. I just dont know what to get.

 

[Adaboat]

Re: 35 Mercury RPM's

I measured the prop. It is 10 1/2" round. Have no idea how to tell the pitch. When I use the prop selector above only 11, 12, 13" pitch is available with a 10 1/2" dia. prop. With my RPM's running around 3400 at wot would I be safe to start with a 10 7/8 X 11 pitch prop? According to my calulations that should at least get me up to 3800 rpms or so.....if I have a 13" pitch now. (I'm guessing on that based on my wot rpm's of 3400)

 

[starcraft1982]

Re: 35 Mercury RPM's

youd better not start w/prop.You need to check compression and spark.That prop would have to be waaaaay off to only be turning 3400.

 

[Adaboat]

Re: 35 Mercury RPM's

Okay, I'll check compression. I'm pretty sure spark is okay....would the engine skip like a car engine if a cylinder wasn't sparking or had low compression? Engine fire right up and seems to run smooth. I replaced the plugs and it did idle alot better? How can I check the spark running on the lake? If I connect a timing light to the wire will that verify spark?

 

[starcraft1982]

Re: 35 Mercury RPM's

You just need to get a sense of what youre starting with by checking compression.If that checks good,then move to fuel and spark.That engine is telling you something isnt right.When you check spark,it should jump at least 7/16" gap w/bright blue spark.After you check compression and spark,it will be time to tear into carbs,clean thoroughly and make sure jets arent clogged.After this is all completed,run again and report back with either good outcome,change in symtoms or if still the same.

 

[starcraft1982]

Re: 35 Mercury RPM's

Just to add,it does no good to"think"spark is okay.It can be decieving if its not tested properly.The only way to troubleshoot these things is to test things and eliminate them,systematically.Not trying to sound rude or anything,Just want to help get to the bottom of this.It could have low compression,spark issues,fuel restriction issues,or other.Testing and eliminating requires the least money and least frustration in getting to the bottom of things.Good luck

 

[Adaboat]

Re: 35 Mercury RPM's

First let me say THANKS! (I'm not yelling, just thankful) for all the help. I may be frustrated with the problems but I'm excited to be learning so much. OK, so I checked compression and had 150 on each cylinder. As far as spark, I hooked up a water hose with the suction cup adapter and started the engine. Each plug wire had a good blue spark that sounded and looked good and strong. So now to the Fuel....I have a manual ordered that should be in this week, hopefully it will explain in good detail about the fuel system. Any tips you can provide in checking the fuel system? I've already checked the primer bulb it stays pretty firm. I did notice a small amount of gas in the engine compartment under the carb, I may have cause this by running the motor with it tilted....not sure.....Thanks again!!

 

[starcraft1982]

Re: 35 Mercury RPM's

so,compression is good.spark SEEMS ok.So now is the time to tear down the carbs and thoroughly clean them.Might as well not even open them unless you have a gasket set for them.Make sure jets arent clogged.BTW,if you dont have a fuel filter installed,get one.And also still wouldnt be a bad idea to rebuild fuel pump.The reason i say get a filter is that you dont really need to spend the time cleaning carbs only to suck some more junk up in them and have to tear down again.This will also allow you to see if youre getting debris in there from tank or failing gas lines or bulb.Once this is done,run it breifly and report back.good luck