1350 merc carb upgrade?

[rpm1350merc]

Hey ya'll just joined the forums and have found a lot of great information on this site. I was wondering if it is possible to upgrade the carbs on my 70 1350 6cyld merc with carbs from a same era 150 hp or are they the same carbs that I have only jetted down? Iam rebuilding the ones That are on this thing now but i am interested in pumping it up once I get the thing dialed in for the summer. I figured there is some way to mod it b/cause these engines are all the same displacement just timed/jetted differently? This engine is in excellent condition internally with a compression test showing 175 psi on all cylds. I am also searching for a 79 or later lower unit b/cause the skeg is damaged and i read that the 79 l/u is much better and geared better also. Any help/guidance is greatly appreciated. I really like these old engines alot and don't want to blow it up. I like to water ski and cruise the rivers in the summer. The engine will be going on an 83 16 ft Baja ski boat. again thanks in advance.

 

[yamamarinetech40]

Re: 1350 merc carb upgrade?

You think the 70 and 150 were the same engine??? You mean BLOCK, don't you? Not heads.

 

[rpm1350merc]

Re: 1350 merc carb upgrade?

No, THe 70 hp is a 4 cyld and the 135 is a 6 cyld, I meant the 6 cyld were all the same or very similiar. By the way, the block and the head are all 1 piece, the part that bolts on the top of the block where the plugs screw in is only a water jacket. I'm not that much of a newbie!!!

 

[OldMercsRule]

Re: 1350 merc carb upgrade?

"If it ain't broke don't fix it."

I would leave it alone if it werks now.

Why change the carbs? Don't worry about 135 HP vs 150 HP. Everything, (carbs, jets, timing, pistons et al), needs to werk together so leave it alone.

If yer skeg is bent see if ya can straighten it out (which can usually be done).

If yer runnin' in fresh water ya don't need the later LU which maybe in far worse corndition then yers is. Remember: 1979 is 29 years ago!!!!

The 1968 and 1969 1250 were a bit strange as they didn't have the exhaust extentions as the rest of the 100 cubic inch inline 6s do. The 1350 was much better. I would not change ANYTHING if it runs good. Enjoy it.

Those old engines were some of the very best ever made in terms of power to weight et al. That is why they were manufactured fer sooooooo long and sold sooooooooomany of 'em. If the wire nuts are still on the block LEAVE IT BE. She's a virgin and needs respect not disrespect by viewin' the green grass on the other side of the ol' fence!

Me overpriced $.02. JR

 

[Droll]

Re: 1350 merc carb upgrade?

but i am interested in pumping it up once I get the thing dialed in for the summer. I figured there is some way to mod it b/cause these engines are all the same displacement just timed/jetted differently?

Keep your exiting carbs, the engines might look identical but the extra hp on the later 150hp comes from internal differences .

The first improvement over your 1350 were the 72 1400.....this one was the first engine ( except for the 71 115 hp ) with the new exhaust system ( this block does NOT bolt on to your mid ).
Next change were the power port on the 73 1500, this bumped the hp from 140 to 150.....

Only mod on the 1350 that might help some are using the reedblocks from the later 1500, but it's NOT worth the time spent ..

The later back swept lower unit might be a good choice, you might need a new propeller too, the later lower unit got a different gear ratio ( 2:1 ).


Arne Kjetil

 

[emckelvy]

Re: 1350 merc carb upgrade?

Arne's right, a 1350 is just about at the top of its game. The 1400 was the same motor internally, the increases came from changes in the block exhaust passages and mid-section tuner.

The 1350 has HUGE ports. You're not gonna make any appreciable improvements to this motor without seriously compromising its reliability and/or overall performance.

The suggestion of a later-model lower unit is also a good one. I had a '71 1350 with Power Trim & Tilt, '79 swept-back lower unit, and a nice stainless performance prop. It was a screamer and hard to keep it under 6000 rpm on my old 16' Sidewinder SS.

The later-style lower unit looks better, and due to the improved gearcase design is less prone to ventilation, and blowout at higher speeds. Plus it's got a built-in speedo pickup so you can get rid of that ugly plastic pickup thingy on your transom!

The best thing you can do for this ol' gal is the lower unit upgrade, a decent performance prop, and optimizing the motor's setup.

I had mine 'tweaked' to the correct transom height, which made a big diff in performance. Start with the anti-ventilation plate at approx 1/2" to 3/4" above the bottom of the keel. Note of caution when you drill for your motor mounting holes, leave some travel in the upwards direction so it's adjustable if you need to move it up some more.

One last thought, don't forget the basics: must be properly synched & timed; 18 deg max spark advance; use quality fuel and oil; mix at 50:1.

HTH...................ed

 

[rpm1350merc]

Re: 1350 merc carb upgrade?

wow guys I guess I really do have a gem!! I really appreciate the info. I hope to fire it up this week after finishing the carbs. I have a 14x26 "cleaver" stainless prop that a friend gave me , but he said that engine might not turn it? He use to work on old race boats and this is one he had left over from his old days racing. Is it true that I have a 1.78:1 ratio l/u, and what exactly does that imply? 1.78 crank revolution to 1 prop or vice versa? thanx alot for your help and I will post pics as soon as my girl quits yellin at me to git off tha computer!!! ha ha

 

[mthieme]

Re: 1350 merc carb upgrade?

That's a whole lotta pitch on that prop.
A friend of mine has a 140 on a 16' Baja with nowhere near that much pitch.
Baja is fairly heavy boat for what it is. You can try it, but you may not get what you expect.

 

[OldMercsRule]

Re: 1350 merc carb upgrade?

I would start slowly and show the old girl the respect she diserves.


Don't fix unbroken things!!!!!!!!!!!!!!


Put it on the boat with a lower unit you decide on with a fresh water pump and prop it for 5500 RPMs with a light load with an aluminum three blade prop BEFORE ya get too cute.

Make sure ya follow the linc n' sync instructions and pay attention to the advice on maximum spark advance, (or Ed can tell ya what to set it at).

Once ya have a stable situation that runs good you can start to play with the props and combinations. Ya prolly want to be careful about sustained running above 6,000 RPMs due to the age of the engine. Power trim is a real asset on these engines to dial things in.

If you prop this thing toooooooo steeeeeeeep and lug it you may not like the result! She maybe a virgin but she's not young.

Me overpriced $.02. JR

 

[rpm1350merc]

Re: 1350 merc carb upgrade?

Yeah, I had another guy tell me that about that prop yesterday when he came by my shop to pick up a car that i was working on, just so happens he renovates old skool Allison boats. I don't want to hurt that engine at all. I guess I'll try the 2 blade prop that came with it for starters? and go from there. I also would like to track down some trim cylds for it that will work with my onboard trim pump(old skool merc style) Anyboby got some reasonable ideas on where to get good used at other than ebay? Thanx for all of y'alls insight on helping me resurrect a true classic!!!

 

[OldMercsRule]

Re: 1350 merc carb upgrade?

Yeah, I had another guy tell me that about that prop yesterday when he came by my shop to pick up a car that i was working on, just so happens he renovates old skool Allison boats. I don't want to hurt that engine at all. I guess I'll try the 2 blade prop that came with it for starters? and go from there. I also would like to track down some trim cylds for it that will work with my onboard trim pump(old skool merc style) Anyboby got some reasonable ideas on where to get good used at other than ebay? Thanx for all of y'alls insight on helping me resurrect a true classic!!!

I would try an aluminum three blade 19 pitch (maybe the 17 if yer runin the 1.78 to 1 stock LU) to dial it in first, (5500 rpms with light load) before messin' with the two blade stuff (which is fer very light hulls where ya don't need much of a hole shot). JR

 

[daveswaves]

Re: 1350 merc carb upgrade?

I run a 75 1150 and am rebuilding a 75 1500. Things I have learned: 40:1 not 50 :1. 19P 3 blade is about perfect. Later model gearcase is a definite plus. 2 blades suck, poor balance,poor holeshot. Link and sync is critical, timing must be "ALL IN" before the carb butterfly starts to open. Retard timing to 21 degrees for todays gas. Minimum fuel pressure at WOT is about 4.5 psi. Fix all the rotted wires, if you cant find the rotted wires look closer and fix all the rotted wires.Don,t lug it, prop according to your use. If you are pulling skiiers, prop down. If the idle is poor check for missing restrictors. (look behind intake port plate, they are not there...trust me). The carbs are not the limiting factor. Enjoy your classic.

 

[tashasdaddy]

Re: 1350 merc carb upgrade?

the 1350 set up properly, tuned properly, you would not notice much difference between that and the 1500. that pitch is way too high. here is some great info for your motor.

http://forums.iboats.com/showthread.php?t=168855