79 100hp CARBS

[wayneo99]

looking into a used 79 100hp used block 115-120 pis on compression tests

i have the carbs off my 79 85hp and a set off my 83 140hp
which ones would be the best option to use?
what size carbs came on the 79 100hp?
thanks

 

[emdsapmgr]

Re: 79 100hp CARBS

Not sure just which size carbs were factory on a 100 hp. Perhaps 1 3/16" throats. What are the throat sizes of the two sets of carbs you have? If you use the 85 carbs, you'll get 85 crank hp. If you use the 140 carbs, likely it will run, but you will probably have to rejet them (should run rich) to run on that 100 block- but you certainly will make more than 100 crank hp out of the block. Maybe 115+. A stock compression figure for a factory-fresh 85 would be around 125 lbs. Your current compression is solid. 1 5/16" throat carbs would be ideal.

 

[wayneo99]

Re: 79 100hp CARBS

the carbs off the 85hp are 1 inch with 48 and 25 jets

the 140 carbs are 1/5/16 with 3 jet sizes 68c being the largest. i have to check the rest.

i think it was 24 and 36???

 

[emdsapmgr]

Re: 79 100hp CARBS

I think those 1 5/16" 140 carbs will work for you. Some of the 140's came with the really large 1 3/8" and those are just too big for your block and porting. The 79 carbs came with .065 mains. Those carbs will probably run out ok as they are, till you get towards top end, when they may overfuel somewhat. Probably a little jetting required to get them really dialed in. I run a set of 74 135 1 5/16" carbs on my ported 79 85 hp block. Runs really strong. I've rejetted the original .069's down to .068 and it still overfuels a little. One of these next hot summer days I'll decide to do some further jetting on it.

 

[wayneo99]

Re: 79 100hp CARBS

I plan on using the 140 intake with the filler blocks and reeds, upgrade to the choke primer system and the recirulation system from the intake to the side of the block too.

do i need to rejet will anything happen if i dont?

 

[emdsapmgr]

Re: 79 100hp CARBS

Run it and see how it performs. You'll want to chart the max rpm's versus max speed to create a running baseline on your powerhead before you make any additional changes. (including different props and engine mounting heights.) Overfuels are most noticeable at WOT. Engine will run great up to higer rpm's, but won't make full rpm's potential. Won't hurt anything to leave it that way, as I have with mine. Dialing it in perfectly might involve a further gain of 200-300+ rpm's. The intake filler blocks are a good idea, good for 3-5 hp.