1985 90hp dead cylinder

[TBarCYa]

Hello again. While trying to figure out why my engine won't accelerate past half throttle, I pulled the plugs and noticed that the #1 spark plug came out clean as a new plug. Since the engine has been run and there is no fuel/oil on the plug, I have to assume that there is no fuel getting into the cylinder although there was some raw fuel in the exhaust port.<br /><br />My question is, am I correct that the clean plug means that there is no fuel getting into the cylinder, or does it mean that there is no combustion in that cylinder?? I have 125psi compression in that cylinder.<br /><br />My next question is that if there is no fuel in the cylinder, but there is compression, where do I look for the cause?? I'm very familiar with 4-stroke engines but am clueless with things like reed valves and their function.<br /><br />Thanks.

 

[Goodoleboy]

Re: 1985 90hp dead cylinder

You will need to do a spark test on the engine. Should jump a 7/16 gap. You can get spark tester at auto. parts store. Or you can make one really easy. Just do a search here on sparktester.<br /><br />If you have good strong spark to this cylinder,Then you know its a fuel related problem.<br /><br />Good Luck!

 

[TBarCYa]

Re: 1985 90hp dead cylinder

I'll definitely do the spark test first thing tomorrow. If it passes the spark test, would the reeds be the next place to look?? The carbs were rebuilt yesterday and all of the fuel hoses were replaced so I'm confident that fuel flow is good everywhere except the #1 cylinder. <br /><br />Thanks again.

 

[Goodoleboy]

Re: 1985 90hp dead cylinder

Reeds are seldom a problem. My guess is that you have an ignition problem.<br /><br />When you are certain you have good spark to all cyl. But you still have a miss in engine.<br /><br />Take a squirt bottle and spray some premix into carb throat that you suspect cyl. is missing. If it picks up and starts to act like uh good motor orta.<br /><br />When you rebuilt carbs. Did you remove the welch plugs and clean all passage ways with cleaner and compressed air. {Extremely important}.<br /><br />After you have done all this to your satisfaction and it still dosent sound like it should. Rough idel, No get up and go.<br /><br />Then Idd do a decarb on it. Seafoam, Read instructions in FAQ,s on this forum.<br /><br />If none of this works.....Well then Id get out my 12 gague shotgun and fixer good, once and for all.<br /><br />Just kiding...Ha..ha!<br /><br />Good luck!<br /><br />Good luck.

 

[djzyla1980]

Re: 1985 90hp dead cylinder

Maybe thats what I need to do... the shotgun that is ... I thought about takin her to the lake unboltin her and take it for a spin... my luck though she would get me 1/2 way across lake and then go.... NO WAY am I gunna paddle that far...<br /><br />or at least run REALLY REALLY GREAT and as I'm trying to grab the 250 lb beast she falls in

 

[TBarCYa]

Re: 1985 90hp dead cylinder

Does each carb throat feed a particular cylinder or do they combine in the intake manifold?? I had made the assumption that they combined but I haven't taken a good look at the manifold yet.<br /><br />If it is one barrel per cylinder, does the top starboard barrel feed the top starboard cylinder?? Sorry for all of the questions, I just don't want to go taking the entire engine apart if I don't have to.<br /><br />Thanks again.

 

[TBarCYa]

Re: 1985 90hp dead cylinder

The engine has passed the spark test. I haven't tried spraying fuel into the carb yet because I'm waiting until I get home to see what the manual says about how the carbs feed the cylinders. I removed the head and the cylinder looks like it's never fired because it is perfectly clean so I'm not planning to decarb the engine just yet. When I get the thing home, I'll check the manual and see what else I should look at.<br /><br />In the meantime, if anyone knows if each cylinder has it's own carb barrel or if the barrels for each carb combine, that will help me determine what my next steps will be before I get elbows deep in the manual.<br /><br />Thanks again.

 

[DJ]

Re: 1985 90hp dead cylinder

A "perfectly clean" cylinder is indicative of an H2O leak. Most likely the head gasket.

 

[Solittle]

Re: 1985 90hp dead cylinder

Put a new head gasket in it & give it a good run & recheck.

 

[Joe Reeves]

Re: 1985 90hp dead cylinder

Each carburetor throat feeds one cylinder. There are two brass fixed high speed jets in each carburetor, located in the bottom center section of the float chambers.<br /><br />If the HS jet that feeds the non performing cylinder is clogged bad, it normally will not come clean simply by soaking in carburetor cleaner and/or using compressed air. It would need to be manually cleaned with a piece of solid (single strand) mechanics wire.<br /><br />Note that fuel needs to flow through that high speed jet before it can gain access to any other fuel passageway, including idle.<br /><br />Yes, the top port throat feeds the top port cylinder (#1 cyl). The other carb throats follow suit.

 

[TBarCYa]

Re: 1985 90hp dead cylinder

Is the high speed jet in the carb body or the float bowl?? I've removed the orifaces in the float bowl by removing the screws on the outside and removing the orifaces. If these are not the correct ones, should I look at the ones that have the brass covers on them or are the high speed jets the narrow tubes that go thru the carb body and into the area in front of the throttle plates??

 

[Joe Reeves]

Re: 1985 90hp dead cylinder

In the float bowl. The ones with the 1/4x20 thread.

 

[Goodoleboy]

Re: 1985 90hp dead cylinder

Joe...Ill tell ya what, you just taught me uh good lesson...And ats hard tu do to.<br /><br />Thats to take uh wire and see.... if it passes thru. <br /><br />Then ya know!..no guessin...no I hope so!<br /><br /><br />Thanks!...I needed at!

 

[TBarCYa]

Re: 1985 90hp dead cylinder

Ok so it looks like I'm good on the high speed jets then. I removed the float bowls and the two screws on the outside of the bowls and the orifaces inside which I was then able to see thru and get quite clean. I can also spray cleaner thru the oriface so it seems like it's okay there.<br /><br />I'll spend some extra time with that carb when I get home tomorrow. I have a set of carbs from a 1981 115hp... I know they'll bolt up, but should the engine run if I put those carbs on this engine just to test that bad cylinder??

 

[TBarCYa]

Re: 1985 90hp dead cylinder

Today I removed the intake manifold and checked the reeds and replaced the gaskets on the reed blocks and installed a new manifold gasket. The engine ran great for a while and then went back to misbehaving. When I removed the carb cover (black plastic) I noticed that the carb for the #1 cylinder had gas spraying out instead of going into the cylinder. <br /><br />I spoke with someone about it who suggested the head gasket or cover gasket may be bad and need to be replaced and someone here suggested the head gasket as well. It looks like I'll be replacing the head gaskets and bolts and possibly swapping the heads with the ones from my 115 to see how that helps. I had thought that it was wierd when I bought the engine that one head was a different color than the rest of the engine and I guess I now know why. <br /><br />Thank you to everyone for your help.

 

[Joe Reeves]

Re: 1985 90hp dead cylinder

Fuel being sprayed out a carburetor throat indicates that a reed plate (leaf valve) is stuck open or broken. Your next step is to remove the intake manifold in order to inspect those leaf valves (Reeds).<br /><br />The head gasket would have nothing to do with that type problem.

 

[TBarCYa]

Re: 1985 90hp dead cylinder

When I removed the reed block for that cylinder, it passed the flashlight test but I will check it again when I replace the head gaskets. I'll be removing the carbs and intake manifold to check the reed blocks plus replacing the head gaskets and checking the block and heads to make sure they're both flat.