sluggish 75 Horse

[the rebel]

Hi everyone, I registered a few days ago and would like to say hello and that it's great to be on board. I just had a great weekend in the Gulf of Mexico with my bass boat. I'm running a 75 Johnson (J75TLCNB), I was told it is an '82 model. Some problems are bugging me. It spits back through the top carb at idle and is sluggish(boggy) right at the bottom of the powerband. This makes it hard to load, and also trolling kinda sucks unless I speed the idle up with the fast idle bar. I have pulled all the carbs down and they are clean as a whistle, floats are set perfect and the throttle linkage is set correctly. Timing is 19 degrees, just like the manual calls for. Compression is 123-125 on all 3 holes. Spark is fat as it gets( I'd be worried about getting bit by it), Jumps over 1/2 inch. I am contemplating a set of Boysen reeds to help with both of these issues. Anyone here know how well these work in this engine? Also, I have been reading some similar posts on this subject, where can I get the idle jets to enrichen the idle mixture on these carbs? Is there a few good hop ups for this engine to boost low end performance? Top end is fine, as I'm not looking to zing it up past 5800 anyway, just for longevity reasons. Is it safe to bump the compression up on these engines and still run pump gas? By how much? I have been around 2 stroke engines for quite awhile so I'm no green horn to the technical aspects of this design. Thanks for any help you can offer. BWJ.

 

[Todd Humphreys]

Re: sluggish 75 Horse

Sounds like a broke reed and/or a reed not fully seating. <br />Sluggish on take off is classic for this motor. I have that exact engine and due to the carbs not having fixed jets its hard to obtain the correct idle. You might can try 0.002 larger low speed jets. Mine seems to idle better with spark plugs gapped at .040 instead of .030. especially for trolling.<br />All your values seem to be in order, and as for your bottom end power you can port your prop to get the rpms up into the powerband quickly.<br />I have talked to mechanics that said that the 75hp is a *******ized 70hp, and OMC almost ruined a great design trying to squeak out 5 more ponnies. Good Luck

 

[R.Johnson]

Re: sluggish 75 Horse

With the engine at idle, loosen the top carb anchor screw to the throttle link. This will let the throttle plate snap completely closed. See if this improves the idle. I have had this happen to me even when I thought I had the carb's in sync. Check and see if the primer hose to the top carb is cracked, or broken, this will give you a heck of a vacuam leak. Did you replace the O-ring around the low speed needle when you rebuilt the carbs, and is there a sealing washer under the plug screw covering the intermediate jet? You can see most of the reed plates just by taking the carb off, and using a flash light.

 

[the rebel]

Re: sluggish 75 Horse

Well, I just got in from playing with my Big White Johnson. Still running the same. <br /> Ok, in order of reply, Donkdaddy I was on the same track on the reeds cracked or broken before I pulled the carbs off. You can get a good look at them when you pull the carbs, they are in perfect shape with plenty of tension just by looking through the manifold and checking them with a small probe. Do you get the low speed jets from the dealer or is there another source? My plugs are already gapped at .042,that is where my manual specs them at. Now prop porting is a new one on me, can you or anyone shed some light on that subject? I am running a 13 3/8 X 17 al. prop.<br /><br /> R.Johnson, I have done the lock screw adjustment when I set the carbs back on. All hoses are in good shape also. I was under the impression that that was the actual fuel feed line going to each carb. Am I right in this assumption? The O-ring that you are refering to, I believe, is the one that seals the bowl to the carb body, is that correct? That is new also. If that is not the one that you are refering to, I am not sure which it is. There is a seal under the intermediate jet plug also. You are right about being able to see the reeds with the carb off, all reeds look to be in great shape with plenty of tension. <br /><br /> I don't pretend to know it all, but all of that seems to be in order, as I went through all of that before I posted my question. It is puzzling me because the top plug is darker than the lower 2 plugs. Has been since I started, even after new plugs were installed. So, getting back to the question, does anybody know if the Boysen reeds will help this quirk with the 75 Johnson? Can anybody point me toward some literature or a mechanic that has tweaked these puppies into running better at idle and right off idle?<br /><br /> Thanks for the response guys, it sounds as if you have been here with me before. Still trying. BWJ.

 

[R.Johnson]

Re: sluggish 75 Horse

I am talking about the primer hose, not the fuel feed hose. There is a O-ring around the idle needle valve, I'm not talking about the float bowl gasket. You have to be able to identify these parts before you attack the reed valve's. Get the engine running first. By the way! we are mechanics'

 

[the rebel]

Re: sluggish 75 Horse

No worries R. Johnson, I have come to the conclusion that there must be different set-ups on these carbs. I guess I failed to say that my carbs don't have primer tubes, they have choke plates. I'm not here playing a guessing game about o-rings around idle needle valves, something that I haven't seen in my carbs, and is not pictured in my manual.Are these readily accessible during the rebuild without pulling the welch plugs out to get to them ? I would know what you are refering to if they are. I didn't pop the plugs out just for the fact that the carbs looked to be freshly built and were too clean to suspect any foriegn matter under them. I have the OMC repair manual for this engine and the exploded view doesn't show an idle needle valve or an O-ring for that matter. Could this be that it is not used on all models? There is an off idle jet with an O-ring at the top of the carb that is accessible from the outside of the carb body, underneath a screw plug. Is that what you are refering to?? The ring gasket I was refering to in my previous post is not the actual bowl gasket, it is the small round one on the inside sealing surface next to the emulsion tube. I'm sure it isn't that easy to explain things in a post like you can if we were both looking at the carb in hand. Attacking reed valves is no problem R.J. . I have rebuilt several outboard engines with excellent results, so I want to clear this area of your question of my mechanical abilty. <br /><br /> The engine is running, and mighty fine if I don't say so myself. I might be trying too hard to get this thing to do something it just wasn't designed for; idle well at 400-600 rpm.<br /><br /> No questions about you being a mechanic, or assumptions, I was only asking if anyone had an opinion on if replacing the reeds with Boysen's would help this engine perform better in the idle and of idle range. And if anyone had bumped the compression up slightly to acheive this. Thanks again for the response. BWJ

 

[R.Johnson]

Re: sluggish 75 Horse

The mix-up on the idle screw is mine. I checked the parts manual, your engine takes a #59 low speed jet, and a 67 intermediate. The Boysen reeds will help the idle. They will also improve low, and mid-range punch. I apologize for the way I came across in the other post.

 

[the rebel]

Re: sluggish 75 Horse

Hey, no worries R.Johnson. Apology accepted with grace. We can't always assume the other guy knows his a&& from a hole in the ground, now can we? lol I beleive you are correct on the jet sizes. Thanks again. BWJ