1350 Performance Issues

[CrayzKirk]

Hi all,

I finished my first rebuild and got through break-in of my 1350. Just about everything on it has been replaced. The inner water jacket had broken bosses in the block that had to be welded and tapped. Installed the update package and new bolts with red loctite. All of the bolts held torque so I believe the repair is good. Had all cylinders honed and fitted with new pistons and rings, new bearings throughout, new rod bolts, rebuilt carbs, fuel pump, water pump, seals, etc. The engine starts easily and performed good during break-in; I ran three six gallon tanks of premium fuel with 25:1 oil. Never getting the engine speed over 3500 rpm. Timing set at 20* BTDC and carbs are jetted at 0.080.

I have the motor on a 17' Glastron trihull that weights about 1100lbs w/o motor or fuel. I was running a '66 1100 on it and don't really notice much difference in performance. With an 16' prop, the 1100 would push the boat 33 mph at 4900 rpm, the 1350 will push the boat 35 mph at 5000 rpm. I pulled a slalom skier (160lbs) with the 1350 and it acted like it was loading up at about 3300 rpm. It finally cleanup up and pulled him out.

I am really disappointed with the performance. What should I be looking for?

Thanks!

Kirk S.

[Dave S]

I don't think you need .080 jets - put in what the carbs came with. I would raise the timing up some too,just don't lugg the motor. The 110 mercs do have good power for what they are, I used one on a 15 foot ckmate and it ran pretty good. If you are looking for speed, get a speed boat.

[CrayzKirk]

Dave,

I think I'm expecting too much outta only six cubic inches. I'd heard the old crossflows were about 65% efficient and the direct charge variant was about 80%. I was hoping for a lot more grunt for skiing and a little more top end. I've got a 1500 done and am now wondering if it will help at all. Or will the slightly higher timing hurt my hole shot even more? Should I try a vented prop to let the motor spin up a bit higher into the power band?

I just feel there is something wrong; the 1100 actually had about equal power before I 'adjusted' the carbs. It is too rich and loads up at idle.

I'll put the original 0.0785 jets back in and see what that gives me. The designers didn't make it easy to change jets. I may simply build another set of carbs and swap them since I'll have to take them off anyway.

The extra gas/oil probably hasn't hurt anything during the break-in period anyway.

Kirk S.

[Bruster]

I think you need less propeller. maybe 2" less pitch if you go from aluminium to stainless, 3 to 4" aluminium to aluminium. A stainless prop will make a noticable change. 5,000 RPM is not enough 56 to 5800 is more like it. Put the original carbs with what they call for jets in the book. Make sure the pick up and timing are right. 21 degrees total. Try that and report back.

[Dave S]

I don't know about that 65-80 effencey, xecuse my spelling. The 110 hp is timmed at 36 btdc, because the squench is less volumme and the domme is not prone to dettionation. Unlike the power dome that had most of the gas charge traped on the exhaust side to then be pushed to the intake side by the piston. After the spark, the gas is hot and the flame front wants to go back to the other side,and it is verry hot. Can anyone say melted piston with chesse to go. I had run 125,135 and150 motrors and I didn't see that much difference. 99.9 cubic inches is 99.9 cubic inches. Merc had to do some wild things to these motors to keep up with OMC, that should get me some points. HeeHee.

[CrayzKirk]

Currently running a 16 pitch Vengeance stainless prop. No vent holes or power trim. Cavitation plate even with bottom of transom. No pad, etc.

The 1100 would turn the prop at about 200 less rpm. That just doesn't seem right.

Kirk S.

[Bruster]

the 1350 has 1.78:1 (or something like that) gears.

[CrayzKirk]

Set timing and pickup statically as described here.

- set flywheel at 20* timing mark by turning clockwise
- remove spark plugs and ground #1
- turn on ignition
- advance throttle until I hear a *snap*
- set max advance to that point

set the primary pickup the same way and set the secondary to contact the throttle lever at full advance and no economizer engagement. By the book, I believe...

I ran with an 18 pitch for a while and only saw about a 200 rom change. I was under 5000 rpm and knew that was too low for that motor.

What does an engine that is too rich sound like? I always would adjust my old go-carts to start missing on the top end to protect the motor. Those were single cylinder motors; what does a six cylinder sound like?

Kirk S.

[CrayzKirk]

lower unit is a 2:1. I checked that thinking it may be the problem. The lack of speed change had me mostly convinced it did not have the 1.78:1 lower unit.

I've just about exhausted my options. People are telling me that I should be able to tell a BIG difference in performance.

Oh yeah, it does not have the exhaust divider plate in it nor has it melted and clogged up the exhaust.

I guess a compression test is in order.

Frustrated, dazed and confused...

Kirk S.

[Raceman]

I think you should be able to see a more significant differnce between an 1100 and a 1350. The 1350 DEFINATELY came from the factory with 1.78:1 gear ratio, so if it's 2:1 it's not original, but that's not where your speed is. Remember, starting with the 1400 in 72 and all of the inline 1500's the gear ratio is 2:1. I don't remember what the stock 1350 jets were, but I'd find out and go there. I also wouln't run the timing over 21º unless you want to go back in the powerhead.

A very small amount of water injestion will cost speed. You should be able to see signs of it on the plugs and sometimes the piston top. Since the engines are somewhat prone to it and you've had the problem in the side plates I'd be looking real closely at that first. Like you already said, compression is always an obvious first check too. At the risk of asking the obvious, have you checked to make sure the cable is pulling the throttle to the stop and you've got full timing AND fully open carbs at this point?

The motor DEFINATELY needs to turn harder than 5K or you're gonna burn pistons, but I don't think dropping pitch is gonna put speed on it at this point.

[CrayzKirk]

Raceman,

Yeah, the throttle vanes are opening all the way. I checked the plugs and they were all oily. Top of pistons and deflector are chocolate brown and oily. It doesn't have the original lower unit on it. I bought this on a skid for $300 a couple of years ago and have spent a lot of money getting it going. Someone had really abused it. I was hoping to slalom behind it however I don't think it would pull me out unless I had a 13 pitch prop which wouldn't let it go fast enough anyway.

I haven't checked the timing while running. I've got a new timing belt, floats, needles, seats and plugs. Original wires, cap and rotor all seem ok. I replaced all the bleed and balance lines, check the check valves. I replaced just about every bolt on this thing; from the intake covers, end caps and exhaust covers.

How can I tell if it is loading up? It studdered last time I hit the throttle, not really a hesitation; more like it needed to clear out the excess fuel. I had the idle set too lean on the 1100 once and it would sneeze and die. Haven't had that problem.

I had the inner water jacket surface on the block professionally welded and machined before I replaced the jacket. A prior 'repair' consisted of using lag bolts and busting several cast bosses on the block.

I could have bought a 2L V-6 for what I've put into this. I've learned a bunch however at this point, I'm getting very frustrated. The original jets are about my last chance. I've got a set of WMK-4s that I can rebuild and put on to try. Just as easy as replacing the jets in the KC-7s on it now.

Kirk S.

[sho305]

I set my '73 1500 on a timing gun, all plugs out on the starter at 19-20 if I remember right. Anyway, I later turned it up some and it certainly came out of the hole harder with the 20p laser prop. I turned it up more and it made no difference so I put it back to previous. It also ran a little maybe 100rpm more on top. That was a 17' 930lb checkmate vee. I knew enough to run premium and 40:1 oil, but didn't know to keep the timing down back then. Maybe because my lake is not that big it didn't ever get run wot that far. I now know to set it under load at the ramp too, not sure how much the belt changes it if any at high rpm with me setting it that way, so I don't know where it is at now. Next time I run it I'll reset it. It would be on plane in close to a boat length and a few seconds.

My idle is set rich to start better. When it gets hot weather here and makes it richer, it will load up after trolling 5 minutes. It will miss, I gass it, it misses more and cleans out. I can smell the gas. Usually only a problem above 90F. Runs great at 65F after a minute or so, before it was real cold blooded and would sneeze all the time until completely warm at 65F. My pistons are dark with stock jets, I would think richer ones would slow it down but don't know how yours compares there.

The vented laser prop helped my holeshot no doubt. It didn't make a huge difference(the vents), maybe 400 rpm extra. I go about 5-6 boat lengths at wot holeshot and I feel it lock back up. I have no planing aids on it, no setback, just raised two inches. The real difference is how I can trim the laser up for 5800-6K rpms. The 21 aluminum ran the same exact speed/rpms, but will only run 5400. Part of it may be the 2" lift on the motor, as I can't trim the aluminum up far and it blows out. Obviously it likes tons of trim, and runs fastest just before I lose water pressure. I had to adjust the trim so it went out more

Don't lose heart, you just have a little tuning to do to get it running right.

From what I know about 2 stroke jetting...lets say you compare it to a chainsaw. The saw you adjust rich and it runs smooth and makes power cutting a log under load. If you run it free it misses (four cycles) like crazy with no load. With an outboard you are under load all the time, so you don't see that miss when it runs less load. I think piston reading is the only low tech way, since those flat plugs don't read well.

[CrayzKirk]

Changed the jets to 0.0785 and no change in rpm.

Moved the tilt pin out one hole and gained 100 rpm.

Moved the tilt pin out another hole and gained 300 rpm.

I was turning a corner at low speed and after that the motor would not rev over 3000 rpms. Inspection of plugs and pistons showed no signs of damage. Compression test was even on all cylinders however seemingly pretty low; 90 psi. Of course, it could be the gauge. The motor is on a fresh rebuild; pistons, rings, seals, etc. I haven't yet changed to 50-1 from 25-1; manual states first 30 gallons should be 25-1. Just don't run it enough; I seem to be tinkering all the time.

No rpm problem turned out to be one of the jets came loose in the carb. They aren't easy to get to on the inlines at all. Now, both of my t-bolt tachs quit working. Changed the switchbox and still nothing. Both tachs worked and now they don't. I have an older wiring harness (pre-67) that I drilled a hole in so the tach connection would fit; I then ran a separate wire to the switchbox. I'll remove the inner harness wire from the switchbox and see what that does.

Also, I seem to have to set the idle speed screw in pretty far to get it to idle in gear at the designated speed. In fact, I'm almost to the primary throttle pickup. This just can't be right.

What am I doing incorrectly on the idle? Will the compression increase as the motor breaks in?

Kirk S.

P.S. Speed is up to 37 mph with 16 pitch prop. Better power pulling skiers with people in boat as well... Time to put together a trim system. All of it is 30+ years old and probably need a bit of work to get going.

[sho305]

My '73 has the factory paint on all the block bolts, unknown hours. It shows 120-122psi in all holes on my old gauge, on starter @wot. I would be 99% sure you are not broke in yet, and not running right until then. I was told 125psi would be better on mine. Low compression could hurt idle maybe, cause adjustment to be off?

My tach didn't work when the rectifier puked, and no more battery charging either. Had no increase in DC running and had lots of AC in my DC power. I changed to a teleflex on the alternator, found and fixed rectifier but never tried stock tack on switch box again.

Go burn up some gas in that thing!

Yes, a power trim would be a high priority! In fact I kick myself as I had a trim plate on a boat I sold, should have kept it. That would give you some free setback to boot. It was on an old 80hp inline Merc.