i-6 jetting

[lightchop]

Im breaking in my 1500. Got about 2 hrs on it. The plugs to me are on the edge of lean. I live in central fla. on the west coast. (clwtr.) The motor is board out 20 over, ecept the one(#5) its 30 over. ( im new at this, twas toooo much timming) shure jumped outa the hole good. anyway if u guys could suggest jet sizes, thier 82 now. timings at 20 btdc. 93 oct fuel, good oil.

[xskid]

.082 jets are what i use in all of my 1500s except the 1500xs which i use .084. i have a motor that i just bought that was starting to melt #1and#2 pistons, found a blockage in top carb, the motor had sat for a while,the guy that i bought it from said it was not run in a couple years and the last time he took it out it did not run good. water pump and pressure was good....i go over the motors good when i buy them, i put new timing belts on, make sure dist. is good, and i run 23deg. timing on all my inlines, and 89 oct. gas. some say 23 is too much timing, and 89 is not enough octane, but i have light boats and never had a problem. never lug the motor. when full throttle, make sure rpms are up. most all the standard inlines of the 70s were made to run on 86 octane.

[xskid]

also, i always make sure the spark plugs and top of pistons are wet and black. i check them fairly often. when the pistons look brown and dry,...its close to the edge.

[sosmerc]

I agree with XSkid...don't lug it. Make sure she can turn at least 5800 wide open. If it were me, I'd run mid-grade fuel with 40:1 oil mix. (I like Amsoil HP Injector oil OR Merc's Premium Plus) 21 degrees max advance should be safe.
You running L76V or BUHW's?

[lightchop]

Im runnin BUHW and 93 oct fuel. Should i be runnin lower grade fuel? And with it bein board out the .082 jets should be good? MY boat is a 72 mx13 and the 1500 sits on an xs mid and lower w/cmc hyd. jack plate. Got the j block and parts in the garage. THX fer the replies.

[Raceman]

I personally think its a BIG RISK to run anything less than 92 in a 1500 inline. You've gotta remember that when these motors were designed the regular grade fuel was better than ANYTHING we get at the pump now. In the 70's when these motors were new I ran Premium Leaded, which was around 100 octane and Merc oil at 25:1 in my 1500's, both 20" and XS's. Nowdays I run Klotz at 32:1 and put a gallon of race gas in 3 gals of Super Unleaded just for cheap insurance. Since the XS doesn't get run a whole lot the extra cost is insignificant. I've never burned a piston in a 1500 inline back then or now, although a lot of "experimenters" around here did. Timing over 21º is also risky too, and good waterpump condition is especially important.

[crazy horse]

I also run .084 jets in my XS with L76 plugs. Run the highest grade gas you can get. I use 100 oct gas with syn oil at 40:1 and make sure you can spin your engine to around 6 grand under normal conditions. :D

[xskid]

ive always used 89. never had a problem. the most important thing is to get fresh gas,go to a local station that is always busy. as for 100 octane, a total waste of money. the inline 6 motors including the xs were made to run on 86 octane,so 89 is plenty good enough. dont lug the motor, and when full throttle, make sure it is around 5800, give or take. mercury also says 89 is good. too much octane will cause exhaust plates to heat up, because fuel is still burning after it leaves the combustion chamber, because higher octane burns slower, and the inlines dont have a high enough compression ratio to need high octane.....period.

[Raceman]

" the inline 6 motors including the xs were made to run on 86 octane"


I've gotta disagree with you on that. When the inlines were designed, the regular gas was like 93 octane, and on top of that it was leaded, and there was no such thing as 86, at least not in this section of the country. If you want to run your engines in a risky enviroment it's certainly your perogative, I think it's REALLY RISKY and I sure wouldn't advise anybody else to do it.

I've probably had over 30 inlines, counting the 20 or so I still have. I've never burned a piston while I've seen dozens of other ones that have, most likely caused by people who wouldn't listen to simple timing, RPM and fuel advice.

[crazy horse]

Well, I don't get accused of wastin money to often. So lets look at it from my end. My 76 XS has NEVER been run on anything less than 92 oct. I also have about a dozon other 2 stroke engines that ALL are run on prem. gas. Including 2 410 vertical cly. Homelite chainsaws that have the org. pistons and clys. thats after 20 years of heating with wood. The xtra money that I spend a year to run 100 oct. gas is less than 1 piston would cost to replace in my inline. I've been turning that engine over 6 grand sence it was new with no piston damage. I think thats the cheapest money I could spend. You go ahead and run that cheap gas, I've got six junk inlines settin around here for parts from guys that did the same thing. ;)

[Jeff_G]

"too much octane will cause exhaust plates to heat up, because fuel is still burning after it leaves the combustion chamber, because higher octane burns slower, and the inlines dont have a high enough compression ratio to need high octane.....period."

Xskid, could you please advise me to where you got the above quoted information. Also can you advise as to what the effective compression ratio is? Also could you produce anything from Mercury that addresses the fuel requirements in the inline in the past 10 years specifically? I appreciate your help in this. Maybe we all could learn.

[sosmerc]

The Factory service manual (90-86134--4 printed 12-91) says: "any good grade regular leaded, premium (super), unleaded gasoline, with a minimum posted octane rating of 86 are satisfactory for use in these model outboard motors".
This manual covers 75-150hp inlines starting with serial number 4112635.

I would still recommend mid-grade and I would recommend top quality oil such as Merc's Premium-Plus or Amsoil HP injector oil and I would sugguest a ratio of 40:1.

I'm servicing a stock 1985 115 Merc this week that has never been apart...and the compression is 135-140 on all and the leakdown is 4% on all but #2, which is 14% (probably has some rings starting to stick...will try some quickleen to see if that brings the numbers up).

There are two different dome height pistons available...and new pistons now have two half-keystone rings instead of the 3 square cut, tight fitting rings.
They say you can intermix the piston styles without problems. I probably wouldn't do that...but on today's fuel the low domes may add some measure of safety from detonation. If you want to see what detonation looks like on these motors, just bump your timing up abit!! I generally set them at no more than 20 degrees at wide open throttle.

Great motors, especially in their day. Always thought Merc could have taken them to the next level with lost foam casting, and fuel injection.

[Raceman]

No question that an 80's inline has low dome pistons and as such has a greater tolerance for sorry gas. As far as service manuals, probably guys at Merc that were editing/okayin' em in the early 90's were playin' tiddle dee winks in kindergarden when the motors were popular in the 70's. If you recall, Merc also first said it was okay to run the timing at 27º, later 23º, and finally 21º. For what putting a piston in an inline costs these days, and the difficulty of even finding somebody willing or qualified to do it in a lot of areas, it seems foolish to me to see how sorry a gas somebody can get by with running, no more significant the difference in cost is, given the hours of use of the average inline now. I run good gas an mine haven't broken, not once in all these years. I remember bassboaters cookin' 1500's in the 70's because they were too hard headed to buy Premium gas, AND the regular then was over 90 octane and leaded. Y'all boys risk it if you want to, but I can't figure any reason to do it just to prove a point.

[sosmerc]

"If you recall, Merc also first said it was okay to run the timing at 27º, later 23º, and finally 21º." ........and now, 18 degrees!! That's gotta tell ya something about what they think of today's gas!!

[Jay R.]

we are having simialr issues with diesels these days. more and more people come to us complaining that their motors smoke excessivly. and after checking these engines, the thing that fixes the smoke most often is cetane booster. especially with the crap diesel we get down here in florida!!

[lightchop]

THXs that was some good stuff on gas,oil,and timming. Should i be expecting to go with larger size main jets(at this time their 82) because of the over size pistons-20 over with #5 being 30. As always thxs fer the replies.

[Jeff_G]

The stock jets for a 150 are .080. The jets for an XS are .082. You should be fine with the .082 with no problem. The bore size would not make any difference to the jet size.

I would however use premium gas only and lower your timing to between 18 and 20 degrees. I agree with the 40 to 1 and I like the Mercury Premium Plus oil in the inline.

You should also install a water pressure guage and make sure your water pump is in good shape. Alos if your motor does not have a tell tale off of the top of the block I would install one there to stop a steam pocket from forming.

[sosmerc]

Very GOOD advice from Jeff G. !!

[lightchop]

Does't have a tell tail nor guage-ill do that.Im using the 93 oct., quicksilver preamium pluse,and ill back the timming to 18 its 20 now. The intake side of pistons as follows 1,3,5-carbon but cleaning up at port.2,4,im beein lazy on six-no carbon and brown, exhaust side are all black-dry. plugs have verry slight tanning. As allways thanks fer the input.

[sosmerc]

Since sticky rings has always been an issue on the 3 ring square-cut rings, you might also want to run 1 ounce of Merc's Quickleen for every 6 gallons of gas. It's a very good product.

[lightchop]

Im using the 2 ring wiesco's.

[sosmerc]

High dome or low dome??

[lightchop]

not shure what a high dome or low dome would be. the block is a 1975 (year)i would think that would be a high dome. how high are the diff. domes. i can get the # if i have to. Thanks for the responce. Also thiers no place to put a tell tail at the top of the block, there is a place on the clnder cover between 3 and 4. The j block has one though on top. but its not runnin.

[sosmerc]

If you used what Wiseco called for then they will be high domes. No big deal...you could have used their low dome (like the 84-88 calls for). There is less danger of detonation on today's fuel with the low domes. But with the fuel you are running and the jetting and timing...you should be fine.

[CrayzKirk]

Just my $0.02 worth...

The aftermarket pistons call for low domes even though the motors called for high domes originally. The Mercury parts list calls for low domes as well even though the 1500s all came with high domes. I think the Wiseco parts are 3123Px (x=S, 2, 3, 4 for std, 0.020, 0.030, 0.040) for low domes and 3109Px for high domes. The difference is 0.010 in the deflector height.

Or at least this is how I understand it...

Kirk S.

(Guess I can't type anymore either)...

[Raceman]

Actually the difference is .100. .010 is only 10 thousandths, high dome to low dome is 100 thousandths.

[sosmerc]

Side by side they are easy to tell apart...for what that is worth.

[Forkin' Crazy]

Keep 'em straight RM! :)

Do these actually have a dome (like my CF OMC) or a deflector? Compression increase? Sorry for the highjack, but I do have an '84 115 I6. :D

[sosmerc]

I'd call them a deflector. Merc called them "direct charge" pistons and the later ones also had round holes cut in them called "power ports". Your 84 should have the power ports.

[lightchop]

So anyway-whats the dam piston supos to look like if its getin what it needs. thanks fer the replies.

[lightchop]

Im also interested in sellin this thing. believe me i don't whant to but got a 24' SRV searay thats totally gutted,whant to get goin in the stringers.

[sosmerc]

They should stay pretty clean and wet looking on the intake side, you'll get a thin layer of dark brown carbon on the exhaust side. I look for sharp defined original shape on the deflector part of the piston....if that starts to round off on the edges you have a problem coming! The polar gap plugs should always come out looking pretty wet with a tannish-brown appearance to the porcelene. The plugs will last a long time, but always check for cracking of the porcelene...I've seen that followed by the center electrode ejecting itself into the cylinder messing things up.

[xskid]

there are some people that think the higher the better, but the fact is ive had many inlines in the past 25 years, always used 89 gas,never had any type of engine failure. i think that says something. also raceman if gas was so much better in the 70s, explain why the inlines were burning pistons like crazy back then, even at 21 timing, they were burning pistons during a time when gas was supposed to be so much better,burning pistons did not start happening in the 80s or 90s,it was happening all through the 70s. dont you remember thats why they lowered the deflecter height in 1977 to try and stop them from burning? i think the reasons for burning pistons is lugging the motor, poor water pressure,stale gas,clogged carbs. octane was NEVER a problem. the gas of today is formulated different than years ago, but octane was not, and is not a problem. the inlines will run forever on 89, as long as carbs are clean,keep rpms up,etc.etc.etc. but the bottom line is the design of the motor. pistons with a deflector are more vulnerable to damage from heat.

[lightchop]

Yall keep mentioning rpm that they should spinn at,and about not luggin the motor. Could yall explane that please. Theirs alot about 2 cyc, i don't know.

[Raceman]

XS, I've gotta disagree again. I do agree with your contention that lugging (causes detonation), low water pressure, etc. but to say that octane was never a problem is pretty out of touch in my opinion, and it's one shared by a lot of Merc employees at the time who I had a lot of contact with (and still do, although they're retired now).

Gas in th 70's had a MUCH LONGER shelf life than today (ask anybody knowlegeable with fuel) AND it had lead, which has some good protective qualties in itself. The guys I knew in the 70's that were runnng high test gas weren't burning pistons. The guys that were blowing powerheads were the regular gas/50:1 know it alls. I also disagree with the statement that the higher octane causes excessive heat in the exhaust plate because of slow burn. I ran it by one of my old Merc buddies the other night who alternated between service school instructor and warranty at Merc for over 20 years and he just laughed. He said that "too many people in the dealerships now weren't even around when these motors were really used hard and regularly, and now that they're basically dinasaurs the new school of mechanics think they know everything about what was wrong back then." It's true that "the higher the better" isn't what's needed with octane, with an engine only requiring what's needed to control detonation and also, excessive octane can inhibit performance, BUT, I'VE NEVER SEEN OR HEARD OF A CASE OF EXCESSIVE OCTANE DAMAGING OR LOWERING THE LIFESPAN OF AN ENGINE and I don't think it's likely. No question that borderline or lower than necessary octane is a risk.

The deflector/direct charge combustion chamber design was basically done in the late 60's with the 1250Super BP, which carried over into the 70 model 1150/1350 production engine. My '69 L88 Corvette has a factory installed sticker on the console that says "minimum 103 Octane gas must be used or serious engine damage will occur". Decent gas was available at the pump at most any station, and all the Sunnocos offered 103 or 104. I doubt that it ever dreamed on the GM or Mercury Marine engineers of that time frame that 30 years later we'd be dealing with watered down crap for gas with low octane, and all the stabilization additives removed which made it significantly deteriorate in 6 months. Nowdays the bandits that run the oil companies are only concerned with wringin' every last cent out of us that they can, rather than delivering a quality, long lasting product. Removing the additives that made gas have a decent shelf life was only about economics, NOT quality or emissions improvements.


I don't really care about winning this debate, but what does bother me is the possibility of somebody running crap gas in an inline and hurting it, based on poor advice obtained from THIS website, and my big question is, WHY TAKE THE RISK when there's NO downside except for a little extra money, and since these engines are rarely in heavy service, cost is insignificant. Again, the regular and midgrade today is inferior in every way (except emissions) from what was at the pump when the engines were designed, and today's Super Unleaded ain't even as good as the leaded regular of the old days. The enviro-nazis won, we lost, and now it's just a matter of compensating.

[Raceman]

Yall keep mentioning rpm that they should spinn at,and about not luggin the motor. Could yall explane that please. Theirs alot about 2 cyc, i don't know.

My opinion is that the older inlines, especially the higher horse ones are happier in the 5800 to 6000 range at wide open throttle. Luggin' em causes detonation. If you take a manual transmission car and put it in a high gear goin' up a hill sometimes you'll hear "spark knock". Same thing is occuring in an outboard when it's lugged at full throttle, but you don't hear it. The two strokes don't have the tolerance for it that a four stroke does, and engine damage happens quickly.

By "luggin" I don't mean part throttle operation, but rather full throttle, but loaded (too much pitch for the load in the case of a boat) where the engine can't reach optimum RPM.

[lightchop]

Thanks raceman,So luggin is luggin, 2cyc.-4cyc. I was startin to worry that i shouldn't operate at part throttle,which is a little scarry to think about. :eek: About the gas debate-Bills outboard here in town.(bin here forever) thay also say to use low grade fuel in the inlines, I don't know eneogh to side up. But im using 93 oct.http://forums.screamandfly.com/forums/images/icons/icon6.gif THX for the info., all of u.