Merc 1150 Problems

[cmikee]

OK I have a 1970 Merc 1150. I rechecked compression on the motor. I let the motor turn over until the needle stopped moving on the gauge. Here are my results

#1) 135
#2) 140
#3) 135
#4) 130
#5) 137
#6) 135

I did this when the engine was cold.

Are these numbers good?

Here is what the engine is doing. At idle it is rough (idling around 800 RPM) seems to skip or lope while idling. When I try to put it in gear sometimes it will cut off. Usually the only way to get it in gear and keep it running is as soon as you put it in gear give it gas then it won't die on you. When I get above 2K RPM then it runs pretty good. The motor has good power. But the only thing is when I try to run WOT I can't. It will not get more than 4K RPM. Now I have not checked my Tach on my boat to make sure it's working correctly. I have not maintained this motor at all in two years (haven't run much either).

Here are some things I thought I would do:

-Get a Manual
-Clean Gas Tank and Carbs
-Readjust Carbs by book
-Change Plugs and rotor button and dist. cap
-Readjust idle and spark advance by book

Let me know if these are good things to do or if there is somthing worse wrong. Thanks for your help!!!

[Raceman]

The compression numbers are fine.

I'd do all the things on your list, but the rotor is the whole shaft through the distributor and doesn't pop off like an automotive one does.

I'd also look at the top of the pistons and plugs for signs of water. The low speed problems you describe almost sound like a reed possibility, but in all these years I've never had reed problems on an inline and doubt that you do either.

I'd go through the carbs and tank first, then go from there.

[sho305]

Most of the time 90% of inline problems can be solved with a tune up and fuel system check. It must have a good fuel supply, so the vent, tank, line, bulb, pumps, filters, and carbs need to be checked/cleaned. Put new plugs in if not, and clean the cap/rotor and test with a 5$ spark tester. Should jump spark about 7/16". As far as the idle, it can be the reeds and/or crank seals on the reeds if not the carbs...can't do much about that, so get it running good then adjust the idle mix and see where you are at before you worry. I leaned the idle mix as far as I could running it around in gear to still get a good idle, then I opened them all up about a 1/4 turn richer(on mine, two carbs are close and one the screw is about a third turn off for all three to be balanced). This seemed to be the best idle spot for me. This '73 1500 idles good at 850-900 in gear, but if it is hot like high 90s it still wants to die when I shift. That is with the SS prop...not bad at all with an alum or composite props. You can do a search for inline, and there are many inline posts here to read also.

My old gauge only shows 120-122 compression, some say the 1500 has more port timing and shows less comp, or my gauge could be off or maybe it is tired as well. I once had a goofy prop with a larger flare in the barrel that would not let it rev past 4500rpm. Also do you know if it is prop'd right? Not too big?

[cmikee]

The prop that is on it is a really Heavy Brass two blade prop. It's a 19 pitch prop. I tried a 21 pitch prop but it was about the same except I didn't have as good of a take off (it was a heavy brass one too)

[Raceman]

Pitch didn't dawn on me, but you may very well have way too much pitch, given the 1.78:1 gear ratio of the 70 model engine. Why don't you try a 17 3 blade and see where that gets you?

[sho305]

Mine is on a 17 vee checkmate with no pad. It runs 6K rpm or close with a 20p Laser SS, runs same rpm/speed (acts like same pitch) with 21 alum Merc prop but less as it can't get the bow up enough...so about 5400 and 6mph less with that or so. I'll guess yours should run less rpm but still over 5K for max power, if it is running right. That hull lists 930lb. Yours might have different gearing though...Raceman? Yep, there he is.:)

Yes, usually the motor would be pretty ragged out to have reed block seal/reed problems from what I hear, and would likely not have that good of compression if it was that worn. Mine has over 10lb less than yours and idles good. If it drops below 750 it just seems to lose power sputter and die. The hotter the weather or motor gets the worse it is, though I can make it a little better by leaning the idle mix...but then it is too lean when the weather is cooler and starts harder then too. I'm not going to set the idle mix every time I run it, but it does seem that sensitive to temperature.

[Raceman]

One other thing to keep in mind when you're comparing RPMs with other engines. In 70, 71, & 72, the 1150 was nothing more than a 1350 with the reed stops shut down and a fatter diffuser in the carb venturi, both of which restricted air flow. (there was no 1350 in 72, but the 72 1150 remained unchanged from the 2 previous years) These engines didn't exactly hunt for high RPM's. Even in 73 when Merc made a significant change in the 1150's, they lowered the port timing in comparison to the 1500's of the same time frame and those engines wouldn't turn either.

[sho305]

Er, I don't know about specific rpms for that, just figured they all would pull 5K.:confused: My manual is not handy today, but it might only go back to 73 anyway. Mine ran slower with a 19p at 6300 about, so then you know you gone too far. I didn't know when I got mine, so I got it all running good and started trying props. The Laser was about the sixth one. You should try to find some props to try, or a dealer like here that let me keep turning them back in...and take Raceman's advice. Just verify you have plenty of fuel to the motor with these inlines.