Frustrating overheat issue...(bit of a long post)

[mamm7215]

This is a bit of hold-over from last season but I got an '81 90hp for my boat after the 140 it came with blew up (broke rings). I had great plans to rebuild but after tearing it down, the crankcase needs to be sleeved and the crankshaft is scored so it's not worth it. The 90 ran but had been previously overheated badly but thought it would be a part motor anyways so no biggie. Thing is it runs pretty good and has great compression...118-120 all four. I put a new water pump kit in and replaced the cylinder heads, water diverters, thermostat kit, and cleaned the carbs and put in carb kits as well. It ran pretty good for the most part with the only issue being a weird hesitation mid-throttle. I also noticed the top crank seal was warped (had the flywheel off) so I just replaced that today.
The issues I'm still having is overheating in the driveway on the muffs (the warning horn comes on) so I shut it down. Last year just before I stopped boating it did this but I would wait till the alarm went away, restart and it would be good after that. Now it continually overheats.
The other issue is #1 cylinder is running lean. Or at least I think it is. After idling in the driveway for a while and I stop it to check the plugs, 2,3, and 4 have a slight oil coating but 1 seems dry. Not bone dry, but not coated like the others.
I know a lean cylinder can cause overheating but it seems like there's more than 1 thing going on.
The telltale stream is strong while running but the stream goes cold/warm/hot and when I shut it off steam comes out. That almost seems like water's not getting through the head. I haven't pulled the hose to the stat housing off to test yet but will, likely tomorrow. I don't want to start pulling things apart until I can get another head gasket and thermostat kit. I'm most concerned about the lean cylinder.
So here's my to do list...
Put in new stats.
Pull head and check diverters (they were new last year so don't think this is it).
I got new carbs for the 140 (originals were damaged-cracks in the throats of all things).
The E-bay dealer sent me the wrong ones for my motor year, the 90 is an '81 and the carbs I got are '85 115hp carbs. They fit but the new ones have hosed coming off the top middle and I don't know where to attach them, otherwise they'd work I think. I just didn't have the time to send them back. They're in almost new condition.
I have the intake manifold from the 140, it's in good shape and the reeds are perfect, haven't had the 90 manifold off, don't really want to but if I can't lick this lean cylinder thing, I'll have to.
So this is me thinking out loud, feel free to chime in. I read a lot of posts about overheating and lean conditions so this is what's driving me in the direction I'm going. And I REALLY cleaned the carbs that are on it so I'm almost sure it's not a dirty carb.
BTW the 140 and 90 are both '81 motors so just about everything is interchangeable.

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

Just a bump and wondering if anyones put a later than '81 set of carbs on an '81. Fuel primer hoses are a bit different, no hose attachment on early carbs, attachment on top middle of carb on later ones...

 

[DargelJohn]

Re: Frustrating overheat issue...(bit of a long post)

I bought a '96 Johnson 88SPL last year that I wound up totally rebuilding. But, the initial problem I had was overheating. I found that port (left) side was overheating due to a cylinder head gasket leak. Leak was between the water jacket and cylinder which allowed exhaust gases into the waterjacket, pushing the water out.

A very useful tool is an IR Temp gun. You can determine which side has the problem. Harbor Freight has them for cheap $$. Good Luck

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

Thanks, it's definitely the starboard head, cylinder 1. I replaced the head gasket as well. The only thing that's consistent is the set of carbs at this point so I'm putting the other set on this week when I get a chance.

 

[Jayrock]

Re: Frustrating overheat issue...(bit of a long post)

I had a similar issue a while back. If I am not mistaken the starboard head is a little higher than the port head on your motor. It sounds like low water pressure is not allowing the water to fill the block while the motor is idling on the hose. Are you sure the Impeller was the correct size? The impeller is secured to the driveshaft? Might be worthwhile to check it, even though you put a new one in. Or a bad t-stat. Take out the T-stat and leave the cover off. While on the muffs,Start the motor and see if water comes up and out of the hole. This will rule out a bad impeller. Heat some water in a pan and drop the thermostat in. Should open a good time before it starts to boil. If all this checks out, then I personally would do a leak down test on all cylinders on that bank. This Would expose a leaky head gasket, among other things.

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

Yeah I'll be testing all this hopefully this weekend, not sure how to do a leakdown test, though.

 

[emdsapmgr]

Re: Frustrating overheat issue...(bit of a long post)

When you install the new stats on the 90, check the valve body inside the thermostat housing. Should be two pinholes in it. (newer bodies have a single oval hole) They must be open-the holes permit warm water to get to the back of the stats to cause them to open. If one/both is plugged, you will get an overheat. The intake manifolds are the same throughout all hp engines-unless one has the recirc system on it. Usually no need to change the manfolds. Your old 140 carbs have choke plates and mechanical choke linkages. The 85 carbs with the hose barbs on top don't use the choke plates. The newer carbs will work, but you will have to change the fuel primer (choke) solenoid to the new style, and get a new plastic fuel manifold which has a fuel feed for the new fuel primer. You may actually improve your performance with the larger 85 carbs-they probably have larger throats than the original 90 carbs. Lean conditions can be caused by fuel restrictions inside the carb passages. Hard to tell if there is dried fuel residue inside a passage when cleaning the carbs. You really need to blow out these passasges with an aerosol carb cleaner-comparing flow rates between carbs while using a Gumout type carb cleaner.

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

Could I not T-off of the existing primer lines to the bypass covers to the primer barbs on top of the newer carbs? It's only for priming during choke/starts so is it that critical? And thanks again, emdsapmgr, you helped me before with all my carb questions...
p.s. If these install ok, I assume the link n sync is the same as my '81 manual states? And the valve body for my t-stats has the oval single hole. New last year.

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

/\ quick bump to see if anyone knows if I can just T off the existing primer lines as per the above question. Sorry for the repetition.

 

[emdsapmgr]

Re: Frustrating overheat issue...(bit of a long post)

Not sure what year your 90 is. Some crossflows have the recirc system that is plumbed from the intake side covers to the intake manifold. Different system. In other years, the cold start fuel primer system went from the new style fuel primer directly to those intake side covers because they had not designed the carbs with the fuel barbs on the top of the carb yet. Bottom line is that if you plan to use the carbs with the brass hose barbs on top, you need to either plumb the new style fuel primer direct to those barbs or cap them off and plumb the fuel primer to the side covers. You need to be able to choke the engine to get it to start.

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

Sorry, it's an '81 with the choke primer going to the bypass covers. This answers the other question I had, could I just cap off the brass hose barbs on the carbs? Sounds like I can do either, T off the existing hoses to the bypass covers and add a primer hose to each carb primer barb or just cap off the primer barbs leaving the existing choke system as is. I'll likely start with capping them to see if the new carbs get rid of the lean cylinder issue.
Thanks again.

 

[emdsapmgr]

Re: Frustrating overheat issue...(bit of a long post)

Your call on which to do. I'd do what is easiest. Same difference. At least you already have a newer style fuel primer. There is less plumbing if you cap off the barbs in the bypass covers and only use two hoses-one for each carb. FYI, the even newer (early 90's) fuel primers have a schrader valve added to that red lever on yours. Really easy to direct inject fogging oil or engine tuner. A handy feature. Pretty easy to convert to the new style red lever. 175158 about $8.00.

 

[mamm7215]

Re: Frustrating overheat issue...(bit of a long post)

Cool, I'm noting that down for later once I get this thing back to running good. Thanks again for the info.