could it be... Spark adavance

[boaterntexas]

My 1976 115 hp merc does not seem to have the woer it shuld, even when lightly loaded, compression is fine, fuel delivery is fine, just had carbs cleaned. What else could it be, I was thinking that proir to having my carbs rebuilt I messed with the spark advance, throttle stop and idle stop screws on the distibutor. Could the sprak advace being off cuase it to lose power, At WOT I get plenty of rpms, and top end speed is about right, boat just doesn't have and power. Spark advace I hope<br /><br /> Thanks,<br /> Thomas

 

[Kenny Bush]

Re: could it be... Spark adavance

Yes, check it out with a timing light. Make sure it is to your manuals specs. Timing and syncronization is both done together. Even your idle is controlled by a different timing mark. You should have a throttle pkp mark, and a maximum advance mark on the flywheel. Follow the procedure in your manual.

 

[boaterntexas]

Re: could it be... Spark adavance

what exactly does the sprak advance do,? and coudl even just half a turn on the screw cuase this much lose of power?<br /><br /> Thomas

 

[jim dozier]

Re: could it be... Spark adavance

Fuel/Air mixture takes a finite amount of time to burn. It is a controlled burn that produces power. There is a flame front that moves from the spark plug though the cylinder. The mixture has to be ignited before the piston gets to the optimum spot for max push (something past top dead center) because the flame front takes a certain amount of time to develop max push. The faster the engine spins the more you have to advance (fire it eariler) the ignition so that max push from the flame front still occurs approximately at the best position for max push. The advance mechanism simply moves the position relative to the piston that the spark occurs in the firng cycle. It is ESSENTIAL that it occurs in the correct position both for power and the longevity of the engine.

 

[mellowyellow]

Re: could it be... Spark adavance

maybe you're dropping a cylinder? pull plug wires<br />one at a time. if no change in performance when<br />a wire is pulled, that's a dead (no spark) cyl.<br />BTW, been following your "slow speed" problem<br />under many different posts over the last several<br />months... assume you have taken the previous advice<br />given here? would be nice if you let us know that<br />one or more reasons have been ruled out.<br />you ever find out why your turning 6500rpms?<br />try a new prop yet?<br />curious,<br />M.Y.<br /><br />BTW. jimd, great explaination!!!

 

[madecool]

Re: could it be... Spark adavance

I agree with jimd. You must use a timing light to set the timing advance back to the proper place.<br />This is very important. It not that hard I just did mine 2 weeks ago it was the first time I used a timing light. Just take your time and don't get in a hurry.

 

[boaterntexas]

Re: could it be... Spark adavance

Awesome point Mello. I have had the carbs cleam which improved my bogging down and my top end speed, however my prop hub is spun and cuasing my high rpms and lack of top end speed. Now I'm just having trouble with power.. have a need for speed and I desire for power.! <br /> Okay so basically I need to test and se if I have a dead cylinder, the guy that cleaned my carbs did a sprak test and compression test and said everythign was okay. I will still pull plug wires, if I can find a way to do it with out shocking the **** out of myself. Also if I purchase a timming gun to adjust the timming and spark advance will I also need a service book, or is there a cheaper alternative.. Who much would it cost me to get it done at a shop?<br /><br /> Thanks,<br /> Thomas

 

[Hooty]

Re: could it be... Spark adavance

For Christ sake, break down and buy a manual! You'll save yourself and everybody else beaucoup time and trouble. Trying to explain to you how to time that thing is going to take hours. Get the manual and read how to do it in fifteen minutes.<br /><br />c/6<br /><br />Hooty

 

[boaterntexas]

Re: could it be... Spark adavance

Man I would get a manual but I cant find one for that year and model, espicially not in my area, and not for under 30 bucks. I don't want to have to wait the 2 weeks to get the thing, I don't want to spen 30 buck for the book, the 20 for the timming gun when it would only cost 50 buck to get the guy at the shop to do it. Hooty if you don't want to tell me how to itme the thing then don't If nobody here want to tell me how to time it, that is completly fine, I wasn't looking for a hour presentation on how to time an old merc. Maybe a website or an old post that I could fallback on. Just looking for advice not grief. Hooty I do not expect you to take time off of you job, fly down here to bfe and show me how to time this thing out, Just was hopping I could be lead in the right direction. I now see the only wasy to satisfy you, and obvoisly christ as well ("oh christ sake")is to buy a manual. thanks for the advice.<br /> Man typically every one on this forum is really kind and helpfull without being sarcastic, I love this site, it has saved me lots of money, and trouble. Thanks for all the back breaking typing and grueling think all of you guys have done for me.<br /><br /> Thanks<br /> Thomas ---> rushign out to buy a manual for the sake of Christ our Lord Jesus.<br /><br />Sorry, no intent to offend anyone just felt that hootys reply was a little harsh.<br /><br />PS this is what the alphabet would loko like if Q and R where omitted

 

[jim dozier]

Re: could it be... Spark adavance

I don't think anybody is trying to be rude, but seriously as much work as you have already done you should have sprung for the 30 dollars and have a manual already. You will save yourself (and us) a lot of work and worry and it will be a resource for you even after you get rid of that motor. Ante up.

 

[Billy_Pumba69]

Re: could it be... Spark adavance

Hootys remark was kind of crap. But that is how a few of the moderators treat people around here.

 

[boaterntexas]

Re: could it be... Spark adavance

YoUr right jimmd, hooty might not of been trying to be rude, he and you all are right on the money I do need a manual. They only reason I though Thootys post was a little off beat was be cuase of the use of excalmation marks, and "for chirst sakes" . I didN'T know that this was work for You guys, both of You have made comments about saVin you time, trouble, work, or hooplua, whats that about, is posting to this site, troublesome, or somethign your being forced to do, so you wish to rid it of use broke, lazy guys with old boat motors who desperatly want to get on the water a go fishing with a reliable boat.. <br /><br /> JB whats your take,?<br /> Thomas

 

[boaterntexas]

Re: could it be... Spark adavance

for what its worth thank you guys for your help, and I'm sure no one here is being rude, or frustrating. I just tend to take some things very personal.. I do appologize

 

[Hooty]

Re: could it be... Spark adavance

I didn't mean to sound rude or put out but the manual covers all the things that have troubled you in the past and present and it's all in one place and easy to understand. Regardless if it's a tuneup on a 5hp fishing motor or a major teardown of a 200hp V6, I want the service manual first. I have a hard time understanding why anyone, not knowing what they're doing, would attempt working on something as complex as an outboard engine without a manual. I want to fix it right the first time, not change parts until the problem is finally stumbled on to. <br /><br />c/6<br /><br />Hooty

 

[Hooty]

Re: could it be... Spark adavance

Here's the procedure for timing your engine. I used the search function. <br /><br /> Mercury Timing Procedure <br /><br />Hooty

 

[TELMANMN]

Re: could it be... Spark adavance

Hooty!!! Too nice!

 

[mellowyellow]

Re: could it be... Spark adavance

just make sure any adjustments are made under load.<br />much diff. when on muffs in driveway...this requires<br />either a test prop or having your boat in the water.<br />without the proper backpressure, is impossible to fine<br />tune her.<br />good luck,<br />M.Y.<br />PS. check the local library for a free manual!

 

[boaterntexas]

Re: could it be... Spark adavance

Thanks again guys, will get to workig of her this weekend as soon as my manual get in yeah I broke down and ordered one.. I think Selco was the name brand

 

[madecool]

Re: could it be... Spark adavance

I been lost to this posting because i forget to refresh my browser. So I finally found it and I like post my message about all of this.<br /><br />Thank god no told me to get a manual. I been worring about someone telling me to get one.<br /><br />I work on gas engines all the time.<br />So I pretty much know how figure out stuff with engines for some reason.<br /><br />The timing on my engine might be different than yours. On mine this is the way I figure out it was suppose to be done.<br />Anyway usually the timing gun will come with instructions on how to use it .<br /><br />I connected the wire to the 1 first plug then the others to the battery like instructions said.<br />It was noted what the timing advance was suppose to me on the engine. So I ran the engine almost full throttle I don't think you need to run that fast but I did and adjusted a bolt and nut that was under my flywheel till I got it set right after checking with the timing light. This is the best i do trying to explain it if your not sure just have the shope do it. Because you don't won't to do it wrong.

 

[Hooty]

Re: could it be... Spark adavance

I'm curious madecool.<br />Where did you run the engine at "almost full throttle"? <br /><br />c/6<br /><br />Hooty