1972 V4 100HP low speed Idle adjusting screws

[wireready]

On my 1972 V4 - my carb has 4 screws marked low speed idle adjusting screens located behind the air silencer. I can't find anything mentioned about these 4 adjustment screws in my evinrude service manual.

My motor is idling fine, but I'm curious what the correct setting for these 4 screws are. There is an idle speed adjusting screw next to the throttle arm that the manual cites for setting the correct idle speed RPM. I'm familiar with that one and understand how that operates and I set my idle speed with that screw according to the service manual.

But the 4 screws behind the air silencer puzzle me. My experience with other carbs is these low speed screws would simply control an orifice and thus regulate the fuel mixture at low speed, but this V4 motor has fixed high and low speed jets, no? Or maybe these screws intersect with the low speed jets somehow.

I've acquired two motors of this vintage over the years, and in both cases all 4 low speed adjusting screws were jammed tight (full clockwise until stopped) when I examined them. I also bought a spare carb on ebay recently and sure enough it's 4 low speed adjustment screws were turned all the way CW until tight as well. Shouldn't these be kept open at least 1 turn CCW like typical carbs? My concern is on both carbs (and I have a spare) that anytime these screws are loosened even a 1/4 turn, there doesn't seem to be any resistance at all, so I'm worried that if I don't leave them shut tight, they will just spin around with vibration over time. Maybe there is a grommet that is supposed to be in there that is long ago worn away. Currently, I do have all 4 low speed screws opened about 1 rotation, but I'm worried they will spin freely over time since there is little to no resistance on them. Maybe they will stay put. But on oher carbs, the fuel mixture screws always seem to have a little more resistance so they stay put.

I haven't fully cleaned a carb in a few years, and hek if I took the time to figure out thier function on the bench a few years ago, now my aging brain has forgot already.

 

[Joe Reeves]

Re: 1972 V4 100HP low speed Idle adjusting screws

The single idle speed set screw is simply a mechanical stop as you state. Knowledge of the actual function of the carburetors is really not important, what's important is that they are absolutely clean, including the four brass high speed jets located in the bottom center portion of the carburetor.

That model engine's carburetors has fixed jets, BUT if the slow speed jets are adjustable, earlier model carburetors have been installed. If so...................

The four adjustable needle valves control the flow of fuel in relation to the set air flow, adjusted as follows (if needed).

(Dual Carb V/4 With 4 (2 each carb) Slow Speed Adjustable N/Valves)
(J. Reeves)

The adjustment procedure of the carburetor slow speed needle valves follows. NOTE... if the needle valves turn too freely, replace the nylon bearing retainer (the nylon item at the front of the carb that the needle valve goes through first) with the newer type RED retainer #315232. If your engine has that weird linkage that connects all four of those needle valves, the newer RED retainers will enable you to discard that linkage. The RED retainers make it impossible for the needle valves to vibrate out of adjustment.

(Carburetor Adjustment - 2 Slow Speed Adjustable Needle Valves, each carburetor)

Initial setting is: All (4) Slow speed valves = seat gently, then open 1-1/2 turns.

Facing the carburetors, start with the top left needle valve, then the top right valve, then the bottom let valve, then the bottom right valve. It may be necessary to redo these steps to get the adjustments ideally set

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Do not attempt to gradually adjust all four of the valves at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[jbch]

Re: 1972 V4 100HP low speed Idle adjusting screws

I know this is an extremely old thread, plus let me say, I don't want to contradict the experts, but I have this exact engine, and have been working on getting it restored and going. I just came from the local boat shop, and the owner has been working on these boats for many many years, he's very knowledgable and plus he has the service manuals to all these old motors.

I mentioned these four screws to him, and the fact the factory service manual (I have one) has no reference to adjusting these screws. I also mentioned the fact that the carbs have fixed jets, a high and low speed, and asked how is one supposed to adjust or tune these carbs. I told him that I had seen an article on the web about adjusting these screws to 7/8 of a turn to 1 1/2, but that they spin freely. He pulled up the service manual, same as the one I have, and he was somewhat surprised... He said that some of the older carbs of this period had long needle valves in these holes and he even pulled up some other manuals of similar time period that did show long needles and retainers. He said that Johnson used the same bodies as these older carbs, and that these screws needed to be bottomed out and tightened, that they were not designed to be adjusted. I mentioned the plastic plugs in the front of the air silencer, and again, he said they used the same parts across different years.

So this might explain the different/conflicting reports people have regarding these carbs. If anyone can tell us otherwise or show evidence to the contrary, please do, as this subject has had me confused for some time.

 

[bigpoppakdog]

Re: 1972 V4 100HP low speed Idle adjusting screws

well my 1970 115 evinrude came with the same stupid linkage. My manual made reference to these screws. You can certainly "bottom out" these, but I will bet you whatever $$$ you want that your engine will not run. You can unscrew these idle screws and look at them yourself. They will look like a skinny pencil. That linkage makes it very tough to adjust them individually. I replaced it with the nylon retainers indicated in previous post. Makes it easy to adjust each one according to the manual. I guess I could scan the page in my manual that addresses these screws to show you if you wish, but then again my manual is for a 1970 not a 1972 so I won't say it's not possible that your manual left that part out. The manual of course didn't make reference to the nylon retainers. My guess would be this part was not available back then otherwise they would have come with these retainers instead of the linkage system.

 

[F_R]

Re: 1972 V4 100HP low speed Idle adjusting screws

Old thread has to be put back to bed, but now it first needs to have the confusion cleared up. The 1972 100hp DOES NOT have adjustable low speed jets. Those are plugs behind the air box cover and must be screwed in all the way, tight. There should be gasket washers on them so they don't leak. The air box cover has the reference to adjustments and plastic plugs because OMC in their infinite wisdom decided to use the cover from earlier years instead of spend a thousand dollars or so for a new die casting mold.

The only way it could have adjustable needles is if somebody swapped carburetors. Furthermore, older motors with adjustable needles are not the "same motor".