what should i do before spending $$$$$$$$$$$, help

tkq23111 · Feb 24, 2011

I have a 1985 35 hp johnson on a 16ft aluminun boat .It only goes about 10mph,I did a compreshion test and its good 110 on all.I read a little about it and came up with its got to be carbon build up.i looked in the cylender walls and its caked.I havent been on the water yet but I have done some procedureds i have read online.I have put seafoam into cylender walls for 10 min and turned by hand a couple roatations.then with plugs out i turned it over to blow it out.then i put fresh high grade gas in gas can and added good 2 cycle oil and seafoam into fule.I then put my muffs on and ran on idle for 30 minutes.Im hoping it helps.I would like to know the top speed I should get from the 35 hp,and a 50 hp thunderboalt 1968.I have a thunderboalt i can get cheap and looking for more speed but want to know what to expect before I buy .ty.If I buy the thunderbolt i got a spar that has a bad piston and i foud out the hard and expesive way that son of a _____.he said it was the wrong prop and when i get the right one it would go faster.lol so i will never buy a motor again without checking copresion.

1nebel0 · Feb 25, 2011

Re: what should i do before spending $$$$$$$$$$$, help

Depending on the prop I would imagine you should be going 30 plus mph....Sea Foam is the best to decarbonize your motor... Every motor that I buy I Sea Foam it.. It has brought the compression down in motors loaded up, and it has also evened out compression on my last 40h.p. purchase that wall all over the place..You need to do this once a year no matter what...Do it when the wind is blowing or the neighbors may call the fire dept. I use it in all my cars to insure they pass smog...Talk about smoking up the neighborhood!!!!

JB · Feb 25, 2011

Re: what should i do before spending $$$$$$$$$$$, help

No, it doesn't have to be carbon buildup and a different prop won't help until you have all cylinders making full power.

Check that all throttle plates are fully open at WOT, and that ignition is fully advanced.

Check that all plugs are getting spark.

Get an OEM Service Manual and do a full link 'n' synch.

Let us know what you find, and good luck.

jerry123 · Feb 25, 2011

Re: what should i do before spending $$$$$$$$$$$, help

If your close to a merc. dealer look at a can of power tune. Simular to sea foam. One way to decarbon is to bring boat to lake on trailer straped down , back into water start motor warm up if possible spray 1/3 can seafoam, powertune, directly into carbs.while running then shut down motor, wait at least 15 minutes, start back up spray remaining can into carbs. while running at periods of full throttle. BEST IF YOU CAN CHECK POWERTUNE CAN LABEL! Seafoam doesnt tell you the same but I think thier simuliar.

Wishiniwuzfishin · Feb 25, 2011

Re: what should i do before spending $$$$$$$$$$$, help

2nd JBs' post. Make sure both cylinders are getting spark. I know the smaller 2 cylinders can seem to be running fine but only 1cyl. firing. Only way you can tell 1 isn't is top speed.

jasper60103 · Feb 25, 2011

Re: what should i do before spending $$$$$$$$$$$, help

Wishiniwuzfishin said:
2nd JBs' post. Make sure both cylinders are getting spark. I know the smaller 2 cylinders can seem to be running fine but only 1cyl. firing. Only way you can tell 1 isn't is top speed.

^^^ +3
My 30hp was chugging along at 7 mph, it turned out to be a bad coil. Do the spark test and report back.

tkq23111 · Feb 25, 2011

Re: what should i do before spending $$$$$$$$$$$, help

I will do and post back .ty all

tkq23111 · Feb 26, 2011

Re: what should i do before spending $$$$$$$$$$$, help

I did it andits like a light blue spark.I have a fluke multimeter if its possible to use to check.ty

tx1961whaler · Feb 26, 2011

Re: what should i do before spending $$$$$$$$$$$, help

So it jumps a 7/16" gap on a spark tester on both plugs?
In the water, is the engine revving high with no speed or is it lugging?

tkq23111 · Feb 27, 2011

Re: what should i do before spending $$$$$$$$$$$, help

I seen blue spark not shure how strong it is but it was blue.when i take off if the water it sounds fin and while im going the top speed the motor will go it still sounds good but dosent go past 10mph .I could troll with the motor if i wanted to but i got a trolling motor.it stays running on low speed and sounds good.At full throtle it sound good but sounds like it should be going faster.If you were in it and i had it in full throtle you would say sounds great but not going fast.I could be wrong but from looking inside the piston walls with a flashlight and the plugs out i see crud.and when i start it and take the plugs out every time the end of the plugs are blake.Im open for any suggestions.ty all. ps .its almost fishing time and ill deal with 10 mph if i have to.lol .im going fishing lol lol

tkq23111 · Mar 6, 2011

Re: what should i do before spending $$$$$$$$$$$, help

I have an update .I bought a spark plug tester,mainly because i couldnt see the spark that good and turn the key at the same time,whithout the tester I did see blue and no orange.I dont know what the spark should look like on the tester can someone tell me there opinion it has orange.also I have done the procedure in this thread to clean carbon .http://forums.iboats.com/showthread.php?t=158076 it blew a lot of smoke.included is a video.

Mas · Mar 6, 2011

Re: what should i do before spending $$$$$$$$$$$, help

Is the cav/ventilation plate even with the bottom of the hull? Maybe your motor is too long or short?

Mas

JB · Mar 7, 2011

Re: what should i do before spending $$$$$$$$$$$, help

The more I read here the more I think you may have simply spun the hub on your prop.

Is the engine revving high but not pushing the boat to high speed? Can you turn the prop by hand with the engine off but in gear?

tkq23111 · Apr 21, 2011

Re: what should i do before spending $$$$$$$$$$$, help

not a spun hub .when in gear and i turn propeller it turns the flywheel whith resistants.I was told now its the throttle cable .i can include a pic if anyone can helpp.ty

tx1961whaler · Apr 22, 2011

Re: what should i do before spending $$$$$$$$$$$, help

tkq23111 said:
not a spun hub .when in gear and i turn propeller it turns the flywheel whith resistants.

That test really means nothing. That will work even with a spun hub. A spun hub does not mean that it is extremely loose, only that the hub will slip under heavy load.

Cofe · Apr 22, 2011

Re: what should i do before spending $$$$$$$$$$$, help

With the motor off.
Put in gear, move throttle to full throttle. Look at the carb and verify that the butterfly is wide open. If it is not, you need to do a link and sync.

The high speed jet is behind the fitting located at the base of the carb bowl. Remove that fitting, and use a bread tie with the plastic removed, to poke into and clean the high speed jet. The jet is #19 in this pic.

what should i do before spending $$$$$$$$$$$, help

Seaman Apprentice

Chief Petty Officer

Honorary Moderator Emeritus

Cadet

Chief Petty Officer

Commander

Seaman Apprentice

Seaman Apprentice

Vice Admiral

Seaman Apprentice

Seaman Apprentice

Lieutenant Commander

Honorary Moderator Emeritus

Seaman Apprentice

Vice Admiral

Lieutenant Commander

Attachments