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No high Rpm work in progress

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dale_c

Member
"Advance thank you's to Gr

"Advance thank you's to Graham and Benjamin for help so far. My 87 135hp merc OB220895 runs much better but I dont have a hole shot and can not get over 4000 rpm. What I have done so far; cleaned/adjusted carbs, fuel pump kit, new fuel lines & bulb,checked linck & synch,changed stator/trigger,checked/replaced coils(2),new plugs, replaced switch boxes(2). This was all done by a good friend and myself, he had most parts from previous rebuilds, all new, and didnt accept any money.It runs so much better, but not much speed. Any suggestions? I want to think max spark advance, but I dont know."
 
"spark advance will definately

"spark advance will definately make a difference, the best way to check it is when going along with engine cowling off get to WOT and then whislt someone steers the craft just manually gently advance the spark if it picks up rpm and speed good, keep an eye on tacho (if fitted) you are looking for about 5200max rpm at WOT for your engine, also check trim of engine and what sort of prop you are running they 2 can make a lot of difference."
 
"I'll take a guess here, b

"I'll take a guess here, bet your down a cyl either due to no spark, compression or dirty carb again. Check spark with timing light on each plug wire, have buddy steer boat and look through each carb for fuel flow. At idle check each carb for sucking in by placing your hand over carb. Do a compression test before spending time and money."
 
"We did a compression check fi

"We did a compression check first last saterday, all between 123 and 126 ( thank god) We checked for spark cause he kept hearing a miss, all wires, plugs, and now coils are ok, good spark now. He held rag over carbs while I ran it, and noticed something wrong on bottom carbs, we removed all again and sure enough, trash was in bottom carb again, we cleaned and checked floats also, but maybe I need to repeat process again if no one has other suggestions. I am running a 19" prop with a jack plate, but I keep it trimmed in at take off and dont trim out much at all. I've driven bass boats for 25 yrs but obviously not with this motor. Thank you to JB and Brent, more suggestions welcome....please."
 
"Dale, what do you have it han

"Dale, what do you have it hangin' on. I'll throw all your numbers into a prop calculator just to see if your pitch seems ok - might be overpropped...

Just off the top of my head, a 135 turning a 19 pitch should be pushing about 1500 pounds of dry weight in a 17/18 foot hull - sound like your rig???"
 
"I have it on a 16 1/2 ft glas

"I have it on a 16 1/2 ft glasstream bass boat. My guess is boat with me and accessories maybe around 1400 lbs. Prop is about 4 1/2" below pad. I just cant help believe the motor should rev to 5500 or so and move well. I had single console boat just like this with a 140 suzuki few years back and it had a heck of a hole shot and would go around 65mph (spedo). I must be doing something wrong. Thanks Graham, all advice welcome."
 
"Dale, on that particular set-

"Dale, on that particular set-up, a 135 with a 19 pitch should be just smokin' - almost to the point of over-rev at the top end.

That motor pushing a "total" weight of say, even 16-1700 pounds should be able to easily turn a 21 or even a 23 pitch."
 
"Dale, also noticed you mentio

"Dale, also noticed you mentioned timing some posts above.

You can set your max timing on this model at "cranking speed".

If set to 21 degrees BTDC using the starter it should be correct (19 degrees) at max advance under normal running conditions..."
 
"Graham, I was under the impre

"Graham, I was under the impression that they gain degrees of timing when set that way, so you set it to 19 and it hits 21 when running.
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"Thanks Graham & JB. I hav

"Thanks Graham & JB. I have a 21" ss prop for the motor if I can get the rpms. I have set the timing at 11 degreesATDC and 18 BTDC, at cranking, supposed to be at 16 degrees at running, is that right? God I hope I have the pointer right, at TDC I am exactly on 0 degrees. That "backoff till .462" confuses me. Thats why a friend set the timing, but I fear that may not be right even though it runs good at low rpm. Thanks gentlemen, this is getting personal now, I gotta know!?"
 
"JB, looks like depending on t

"JB, looks like depending on the model - the 2 liter 150's lose timing, the 2.5's gain..."
 
"Graham, 2 things... 1st, I ha

"Graham, 2 things... 1st, I have been using two books to work on my motor, the CLYMER mariner for 2-220 hp and the SELOC mercury. After you posted I checked again and they both say 11ATDC and 18BTDC @ cranking.Are both these books good for kindleing for my fireplace? What book do you suggest? 2nd, since I DO have this motor apparently set wrong on timing, would this be a good reason for lack of rpms and power? Once again your wisdom has shown my ignorance, I am going to owe you a steak sometime
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"Dale, in general I have found

"Dale, in general I have found the Seloc's to be quite good overall for explaining how to work on something, like the little do's/don't notes etc (find the Clymers extremely lacking in all cases - but that's just personal).

In any event, nothing beats the factory service manual for "specs". It's specific to a given motor or given series far more so than an aftermarket manual which is trying to cover often 20 years worth of motors in say the 4/6 cylinder range - doesn't mean the aftermarket manual doesn't have it's place, it's just I like to use it in conjuction with the factory manual.

Anyhow, if your max timing is set too low, then yes, you will lose some top end speed and that super hole shot when you really lay on the throttle. With the timing set (lower) it will fire too late in the powerstroke which results in a less than complete burn on a motor that is grossly ineffient in the first place. (and I'm just talking about 2 strokes, not necessarily your particular model)...."
 
"Thanks again Graham. Cant wai

"Thanks again Graham. Cant wait to re-do timing and sync and see what it will do.Reading ALL these posts have helped me understand my motor ( a little) so I am better prepared on the water. Thanks mostly to you, but also JB, Brent, and Benjamin. You guys give a lot of time and knowledge out for free so people like me save money and are safe. MY admiration and thanks to you all. I will let you know how this next phase works out. Respectfully, Dale"
 
"Dale, you forgot to add that

"Dale, you forgot to add that you hope that all of us combined know what we are talking about - but just in case, make sure you have a paddle on board
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