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  1. #1
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    Inline 6 Carb swap

    I have a 1976 Merc 1150 ELPT and am wondering what WMK series of carbs will work well with this motor. I ended up finding out a set of '79 90hp will not work because they are way different and choked down. Any help will be appreciated, Thanks!!


  2. #2
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    I was wondering about putting 115 hp carbs on my 90 hp after the rebuild. Any Pro's or Con's to this carb swap. I hope to increase the air/fuel flow to boost the HP.

    1987 90hp inline 6.

    Durwood

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    I-6 carbs

    These engines are choked down at the reed blocks and also the porting is more restrictive in the lower hp. models. So going to a larger carb will hurt your bottom end response and give little or no improvement on the top end. jmo Glen

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    Quote Originally Posted by baldad45 View Post
    These engines are choked down at the reed blocks and also the porting is more restrictive in the lower hp. models. So going to a larger carb will hurt your bottom end response and give little or no improvement on the top end. jmo Glen
    I agree.
    Membership upgrade options: http://www.screamandfly.com/payments.php

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    So what is a quick and easy way to boost the power? Will it require opening the ports? My reed block are the same part number as the 115 hp.

    Thanks, Durwood

  6. #6
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    Quote Originally Posted by Turbinedoctor View Post
    I was wondering about putting 115 hp carbs on my 90 hp after the rebuild. Any Pro's or Con's to this carb swap. I hope to increase the air/fuel flow to boost the HP.

    1987 90hp inline 6.

    Durwood
    Hey Durwood.

    In 1982 Merc rated the inline6(s) at the wheel, (prop), instead of the crank, (as in 1981). The 1987 inline6 90 HP is very similar to the 1976 1150. Soooooo as the big guns say: don't mess with it!!!! N' be happy with what ya have.

    Me overpriced $.02. JR
    Last edited by OldMercsRule; 12-01-2009 at 01:40 PM.

  7. #7
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    There is no way to boost the power on an inline Merc that is easier than just finding a bigger motor

    The time and effort to change the porting (major work, this is not a 2 cylinder dirt bike, but still has to be done as precisely as eye surgery) and finding and changing out the140/150 reed cages and carbs is not worth it compared to just finding a running 140/150 that has the parts you need anyway.


    If you can find a 140/150 donor motor that needs work, it is much better to just fix it correctly rather than transplanting the parts into a lower hp version - that is the real killer on "souping up" one of the lower hp versions ... the only parts source is used motors with the desirable parts and porting.

  8. #8
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    As OldMercsRule said the late 90 hp version is basically the old 115 hp ,which has great lower end responce and as Mark75H said getting 12 intake ports and 18 exhaust ports opened up and matched for 10 -20 hp isn't likely going to happen.Plus the 140-150 blocks get their extra boost from the extra piston boost port.Having said all this I'm planing on trying to open up the ports on a 76 115 that I bought for parts just to see what happens. It's still stock bore so I can drop the crank assembly from another I-6 I have to test it out.

  9. #9
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    porting

    Quote Originally Posted by baldad45 View Post
    As OldMercsRule said the late 90 hp version is basically the old 115 hp ,which has great lower end responce and as Mark75H said getting 12 intake ports and 18 exhaust ports opened up and matched for 10 -20 hp isn't likely going to happen.Plus the 140-150 blocks get their extra boost from the extra piston boost port.Having said all this I'm planing on trying to open up the ports on a 76 115 that I bought for parts just to see what happens. It's still stock bore so I can drop the crank assembly from another I-6 I have to test it out.
    My post count on this board may be low but I have taken apart a few inline sixes and have considered doing just what you are considering. Growing up in Manitoba I understand its a long cold winter and you have to do something.....a few things to keep inmind:
    the port height on the cyl is different from a 1500 to a 1150. The port size is different too but is not the only thing making power on the 1500. As mentioned, the pistons have the power port and the sleeves have the corresponding finger port for the fuel mix trapped under the piston to short cut to the intake. The reed stop gap is different, the 1500 used WMK 14 carbs. Most reeds on the 1500 were banjo style reeds, your 1150 are more like a beaver tail (couldn,t resist). The pistons on the 1500 were high dome, the pistons on your 1150 may or may not be. I have a 1500 block in the garage right now and an 1150 block, both 1975/76 I will see if I can take some comparison pics of the ports.

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    My 2 Cents

    If the block has good bores just place on a Bridgeport and mill the port hights. This old stuff is worth=less so ya not gunna be killing anything worth much. In my way of thinking port hight is not as critical on the old L6s as we all think. O'boy I think I opened a can of .......

  11. #11
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    Dave, what about the reed cages with fewer reeds?

  12. #12
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    porting

    Quote Originally Posted by Dave S View Post
    If the block has good bores just place on a Bridgeport and mill the port hights. This old stuff is worth=less so ya not gunna be killing anything worth much. In my way of thinking port hight is not as critical on the old L6s as we all think. O'boy I think I opened a can of .......
    No, and a Duntov cam never made a difference on a vette either

  13. #13
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    apples to apples

    Quote Originally Posted by daveswaves View Post
    No, and a Duntov cam never made a difference on a vette either
    Chevys can have the compression ratio increased to compensate for overlap, dirt bikes and jet skis can have their compression increased too

  14. #14
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    I-6

    I posted pics of both the 1150 and 1500 ports a short while back and they are quite differenent . What is amazing to me is all of the following engines opened the intake port at 115*- 115 to 72,1250BP,1350,1400,1500,1500xs,T-II and T-IIX .With only the 1500XS ,T-II AND T-IIX opening exh. ports earlier at 94* vs 97*for the rest. Not much timing variation here . Wildest was on the 1000BP at 114* int. and 94* exh. The early 80 4cly [69-70] was mild at 118* int and 106* exh..My take on this is their must not be much to be gained beyond the timing of the early blocks. More to be found in larger ports and reed block work.Looking at the transfer port covers their may be something there.One thing I did notice with the 115 [76] the tops of the pistons have a definate sweep pattern matching the ports that is absent on the 150. The smaller ports must have more charge velocity, plus it isn't broken up by the piston port. The charge pattern with the larger ports and piston port must be completly different than the small port engines.

  15. #15
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    I pissed around and pissed around with inlines when I was bored one winter. And everything I did that should and I thought would help did'nt. From boring reed cages to porting, to tuners to dry stacking to carbs to reeds to having a crank swirled to blah. The late 140/150 blocks are as good as it gets for production wise motors that will run from bottom to top end. I did make a set of carb spacers I never tried how ever. Maybe I'll mess around on that with the vixen.

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