1975 135HP will not idle less than 1100rpm

I've been working on this engine off-and-on for a few years now and it just won't give me 100%. Seems to work great on the high end but just does not want to run at low rpm.

Here are my current standings
Just rebuilt both carbs, even added new orifices (all eight). Carbs looked great when I tore them down as they were just re-built last year by a mechanic but I wanted to make sure everything was done 100% right, this time.

This weekend I took her out and she ran good at WOT but would not idle. Performed the Seafoam routine as described here at iBoats and brought the boat home. Pulled the plugs and they looked pretty good. It is recommended here to replace them after the Seafoam ritual. Is this a necessity? they sure looked good!

Checked compression again, I don't have the numbers here in front of me right now but if memory serves, the readings were something like 142, 155, 150, and 157. These values were comparable to the last time I took them about a year ago when all readings were exactly 4-5psi higher in each cylinder. But the engine was not at operating temp this time.

Decided to check the ignition side again.
Two years ago, I went through the ignition side and found reasonable results but did replace all four coils. This time spark was good in all four cylinders with a good spark across 1/2" gap (tested 7/16" as well but went up to 1/2" to compensate for junk spark tester accuracy).

Did not check the timing yet but all was okay last year and nothing has been changed. I did note last year that in order to set the timing, My timing stop adjustment is 100% in and I could just barely get the timing set to spec.

Sensor Coil resistances were 9.2 and 8.9 ohms at 90F
Charge Coil was 630 ohms

I am not sure if I need to go further and check voltages but if so, I lost the procedure to use my DVA to check voltages. I could use some advice on that if anyone has the proper steps.

I am worried that whatever is wrong is now going to be something really expensive and not worth fixing. Timing coil, charge coil, leafs, worse!

My 1973, 16' fiberglass, trihull, Bassboat will go 40mph, moderately loaded, with a WOT of 5250rpm. Just can't handle the 'No Wake" zone! Trailering is a real trick since it won't idle. I would really love to fix this as my clutch dog will probably be the next thing to go if I don't.

On a side note, a boat mechanic saw me at the dock struggling with the engine and came over to give his advice. He went through all the usual dockside tests, looking for the obvious and found nothing. Sorry this got so long

Thanks,
Randy

Re: 1975 135HP will not idle less than 1100rpm

Have you done a link & sync according to your manual?

Re: 1975 135HP will not idle less than 1100rpm

The idle jets are on opposite sides of each carburetor under the screws. They lead to four capillaries for each throat that enter the carburetor throat floor behind the throttle plate.

If you force the tip of the straw that comes with aerosol carburetor cleaner into the idle jet and spray, you should see the stream enter the carburetor throat through each of the four holes. Check all four idle jets this way.

Also, Make sure that the throttle plates of both carburetors are 100% synchronized with each other in their movement from closed to WOT.

The engine should idle at around 900 - 1,000 RPM on muffs because it is not under load and has no backpressure. At idle on the water under load, look for 650 RPM.

Did you follow Mr. Reeves' instructions to check your timing? The factory service manual has the timing at 20 degrees @ 4300-4600 RPM in Gear.

http://forums.iboats.com/showthread.php?t=228183

Re: 1975 135HP will not idle less than 1100rpm

ezeke said:

The idle jets are on opposite sides of each carburetor under the screws. They lead to four capillaries for each throat that enter the carburetor throat floor behind the throttle plate.

If you force the tip of the straw that comes with aerosol carburetor cleaner into the idle jet and spray, you should see the stream enter the carburetor throat through each of the four holes. Check all four idle jets this way.

Also, Make sure that the throttle plates of both carburetors are 100% synchronized with each other in their movement from closed to WOT.

The engine should idle at around 900 - 1,000 RPM on muffs because it is not under load and has no backpressure. At idle on the water under load, look for 650 RPM.

Did you follow Mr. Reeves' instructions to check your timing? The factory service manual has the timing at 20 degrees @ 4300-4600 RPM in Gear.

http://forums.iboats.com/showthread.php?t=228183

Click to expand...

I've linked and synced this bugger to death. Timing has been set. A couple of independent mechanics confirmed that these were okay. Other than the fact that the timing adjustment stop is cranked 100% in to achieve the proper WOT (per Mr. Reeve's method). Barely a turn left on the screw if I had to go any further.

I haven't run the engine on the muffs alone lately. I generally have it on muffs and submerged in a tub of water up to the vent-plate. I can check and see if it will idle at 650 on the muffs (no back pressure) without stalling. Perhaps that may offer some usable info. I realize that I will have to increase it back up before putting the boat in the water.

In the water anything below 1000rpm, it just quits and must be at 1100 for longterm idling. That puts my boat at about 6-7 mph and of course makes for rough shifting. Carbs have just been cleaned but I will confirm the 4 holes are not plugged as you suggested. I do not have the carbs in front of me so I can't picture where each of the four holes are located. Can you please describe, that way when I get home tonight, I can check this out and won't have any questions to worry about then. Do I have to take the carbs off or can you see this through the throat? Thanks for your replies ezeke and bhile

Re: 1975 135HP will not idle less than 1100rpm

you can see complete diagram of your carbs here, follow prompts. http://shop2.evinrude.com/ext/index.aspx?s1=bf6ad09c53cead335fcfd8a6471c0f7f

Re: 1975 135HP will not idle less than 1100rpm

Something is fishy if you've got the max timing stop adjusted all the way out. You sure the timer base is the correct one?

Re: 1975 135HP will not idle less than 1100rpm

not trying hijack your post, but im reading this intently as im am having the same problem. i hope someone can help with this for both of us.

Re: 1975 135HP will not idle less than 1100rpm

I have not pulled the flywheel. That is one nut I really didn't want to have to crack [pun intended]. I have suspected a possible sheared key but not an incorrect timer base. Is there a way to check which timer base I have without pulling the flywheel off?

Re: 1975 135HP will not idle less than 1100rpm

You do not have top take the carbs off to check the idle capillaries.

Take the cover off the carburetors.

Take the screw off one side of the carburetor body (not the bowl); the idle jet is right behind and aligned with the screw.

Open the choke and the throttle so that you can see through to the back bottom of the throat of the carburetor. Spray the cleaner through the jet and you should see it spray into the carburetor throat from the four capillaries. The holes are so small that a lot of owners don't even know they are there after rebuilding the carburetors, but if they are clogged you won't have idle on the cylinder that it services.

Protect your eyes. Repeat for all four jets.

Re: 1975 135HP will not idle less than 1100rpm

Sheared key is more likely than an incorrect timer base. But, you got me wondering if someone tried to fit a later model timer base on it. That era of timer base is adjustable. Each coil is fastened to the rotating base by a through-bolt and nut, then epoxied over. You can scrape off the epoxy and adjust the clearance between coils and flywheel. Later model timer bases are not adjustable. Should be easy to figure out what you've got.

Re: 1975 135HP will not idle less than 1100rpm

ezeke said:

You do not have top take the carbs off to check the idle capillaries.

Take the cover off the carburetors.

Take the screw off one side of the carburetor body (not the bowl); the idle jet is right behind and aligned with the screw.

Open the choke and the throttle so that you can see through to the back bottom of the throat of the carburetor. Spray the cleaner through the jet and you should see it spray into the carburetor throat from the four capillaries. The holes are so small that a lot of owners don't even know they are there after rebuilding the carburetors, but if they are clogged you won't have idle on the cylinder that it services.

Protect your eyes. Repeat for all four jets.

Click to expand...

I will confirm those are working properly. I did spray some cleaner into those lines but I did not monitor for assuring all four holes were open. Cleaner went in, cleaner shot out!!!! I'll put the goggles on, thanks for the reminder. Hope the cleaner doesn't taste too bad. I assume for the venturi effect to work, these holes point backwards. Will it be easily evident that they are functioning properly? Thanks again ezeke.

Re: 1975 135HP will not idle less than 1100rpm

I did not see any comments about the idle timing, as it is the primary way to set idle timing on the enigne.. Will it respond to lowered timing?

Re: 1975 135HP will not idle less than 1100rpm

emdsapmgr said:

I did not see any comments about the idle timing, as it is the primary way to set idle timing on the enigne.. Will it respond to lowered timing?

Click to expand...

Not sure what you mean by "respond to lowered timing". I did set the idle timing per OEM manual (somewhere around 4-6 BTDC, don't recall right now). Are you asking if I retarded the timing to a lower setting? If so, I did not.

Re: 1975 135HP will not idle less than 1100rpm

I had similar issues with an older v-4 did all the things you have done, it was the intake manifold gasket leaking or for a better term the reed plate gasket, i did not mess with the reed valves at all, just cleaned the gasket surfaces and the oil drain screens, put it all back together and had 100% improvement.

Re: 1975 135HP will not idle less than 1100rpm

Idle timing per the factory manual is a starting point. You can vary idle rpm's by adjusting the idle timing. Idle in gear rpm's will depend on how low the boat sits in the water, and what pitch prop you have. For that reason,they make the idle timing adjustable. The factory idle timing spec a starting point. Try turning the idle timing screw and see if you can get it to idle down to the 650-750 in gear.

Re: 1975 135HP will not idle less than 1100rpm

a70eliminator said:

I had similar issues with an older v-4 did all the things you have done, it was the intake manifold gasket leaking or for a better term the reed plate gasket, i did not mess with the reed valves at all, just cleaned the gasket surfaces and the oil drain screens, put it all back together and had 100% improvement.

Click to expand...

I've suspected an intake leak. Before putting my carbs back on, I decided to check the intake manifold bolts for tightness. Lo and behold I found a loose one. A couple of quick turns with a small box wrench and it snapped right off. It wasn't a hardened bolt. I had to drill and use an Easy-Out. Got it out with no damage to the engine. I replaced the bolt. this was the only one I found that was loose and it was on the top corner by the starter. I did not see anything else that caused alarm. but after I did this, I noticed no change in the idle issue.

Re: 1975 135HP will not idle less than 1100rpm

emdsapmgr said:

Idle timing per the factory manual is a starting point. You can vary idle rpm's by adjusting the idle timing. Idle in gear rpm's will depend on how low the boat sits in the water, and what pitch prop you have. For that reason,they make the idle timing adjustable. The factory idle timing spec a starting point. Try turning the idle timing screw and see if you can get it to idle down to the 650-750 in gear.

Click to expand...

But the only way to adjust the idle speed is with the timing adjustment, is it not? and if I try to lower the idle past 1000 it just stalls.

Re: 1975 135HP will not idle less than 1100rpm

ezeke said:

You do not have top take the carbs off to check the idle capillaries.

Take the cover off the carburetors.

Take the screw off one side of the carburetor body (not the bowl); the idle jet is right behind and aligned with the screw.

Open the choke and the throttle so that you can see through to the back bottom of the throat of the carburetor. Spray the cleaner through the jet and you should see it spray into the carburetor throat from the four capillaries. The holes are so small that a lot of owners don't even know they are there after rebuilding the carburetors, but if they are clogged you won't have idle on the cylinder that it services.

Protect your eyes. Repeat for all four jets.

Click to expand...

I submitted a photo of one carb throat and I am assuming these are the holes you are talking about. The ones in the brass tubes sticking up behind the choke plates. Please let me know if I am wrong. 'Cuz if so, I just wasted a lot of time.

I tried this with two jets. I couldn't reach the other two with the carb-cleaner tube. It was to short. Very difficult to plug the ends of those brass tubes enough to stop the flow of carb cleaner out the ends. Looking at the photo I submitted, when I sprayed the carb cleaner into the jet orifice on the left side (as looking at the photo) the cleaner just shot out the top of the right brass tube in the throat and the right brass tube pointing directly out of the carb (and into your face). So I had to plug the top of the tube in the throat (the one with the four holes) with a fingertip and plug the tube sticking out the front with another fingertip and then still try to see in the throat to examine the four holes in the brass tube. It appeared that each hole was fine as carb cleaner was spraying out quite well in each direction. But my hand block any chance of getting a good view. Whew!

The holes look very clean as you can see in the photo. well...okay you can't tell a lot from the photo but I could see them quite well and they looked open. Couldn't see the back ones, of course, lost my dental mirror.

Re: 1975 135HP will not idle less than 1100rpm

Not the correct holes. These are capilaries on the top of the throat just behind the front butterflies. They are drilled directly into the carb body - no bronze. You won't be able to see them clearly w/o very close inspection.

What you actually tested there are the mains.

Look for something coming out where the red arrows are pointing. The idle jets (and caps) are located in the top half of the carb, the mains in the bottom.


Edit: Ok darnit I messed up. The capilaries are on the bottom not the top of the throat. I'm thinking of a different carb body entirely, and I'm almost too embarassed to say that it's not even a two-stroke OR an outboard. Anyway, they're _right_ behind the front butterfly when closed. I think there's even one about 1/2 mm in front.

Re: 1975 135HP will not idle less than 1100rpm

iwombat said:

Not the correct holes. These are capilaries on the top of the throat just behind the front butterflies. They are drilled directly into the carb body - no bronze. You won't be able to see them clearly w/o very close inspection.

What you actually tested there are the mains.

Look for something coming out where the red arrows are pointing. The idle jets (and caps) are located in the top half of the carb, the mains in the bottom.

Click to expand...

Now there's an a-hah moment!
Am I shooting the carb cleaner into the correct orifice? I was injecting the carb-cleaner tube into the orifice at the bottom of the carb (61C). Is this correct. Are you talking about the small holes found directly below the Core Plugs? "Cuz that would mean I'm in the wrong place. And those looked fine when I had the carbs apart but one was damaged with a screwdriver (it appears) from someone punching out the plug. Not me! If anything, the hole may be a bit more opened up now. And I re-read ezeke's instructions and he said "on the carb-body not the bowl" Dooooh! I didn't read it well.