1997 40 hp 2 stroke 3 cylinder, Help with rough idle?

[bedwar44]

New to the forum; first post. Thanks in advance for help.

I have a 1997 c40tlrv 40 hp 2-stroke, 3-cylinder motor. It has always been reliable and performed well. Recently, I have developed a problem where it will hardly ever stay running at idle. If I start it and put it in gear as soon as the advanced idle period ends, I can run through the midrange and at WOT no problem. Sometimes, after running for a bit, I can idle some and it will stay running. Usually, however, when I bring it down to idle it runs for a few seconds, gets slower and slower, and dies. Then I developed a regular pop out of the exhaust at low throttle. It was obviously missing and running very rough when it would idle.

I can run it on the muffs at the house with the fast idle lever raised about 1/3 of the way and it will stay going. Any lower and it dies every time now.

First, I replaced the fuel pump (and gasket behind it) and the motor side and fuel side ball valve fittings. I am running with a good hose on fresh gas out of an extra can at the house. It is hooked directly to the pump in case the problem was the filter. When I initially replaced the fuel pump (it was compromised), the first time I started it up, it seemed to run dramatically better and the regular pop from exhaust went away. However, it still runs rough and will not idle. Still have to use the fast idle lever to keep it running.

Checked compression. I have (from top to bottom) 95, 95, and 90 on a dry test, and 100, 95, and 105 on wet test.

Checked spark. I have 7/16" spark at all three plugs.

Next I cleaned the carbs. All seemed really clean inside, but bottom carb may have been slightly clogged. Put back on and although it still ran a little rough, I got idle back. It was late, and I figured after I did a link and synch the next morning, all would be well...

Well, the next morning I followed the service manual instructions to set the throttle linkage (pointer on cdi and full retard and advance screws). There was a small adjustment made. Next synched the carbs (closed all butterflies, tightened adjustment screws, then set roller to hit cam about 8 degrees atdc).

Now it wont stay running at idle again.

Other symptoms than what Ive described:

Seems like a bit too much oil pooled in the throat of carbs, especially lower one, since I have only run it about 30 minutes since cleaning them. There is no oil injection, so it isn't that.

If I pull the plug wires, all drop the RPMs, although it almost sounds better on two rather than 3 cylinders. If I put my hand in front of the carbs, RPMS drop noticeably on middle and bottom, but it will choke out when I do the top. The top also seems to have significantly more suction, just by feel.

So... any suggestions where to go next? I don't have a timing light, so that is the one thing I haven't checked yet. But, it doesn't seem like it could get that far off unless the CDI is just toast. I have seen a test for it in the manual. Would this tell if it was jacked up in terms of intermittent spark or timing, or just whether or not it works?

Also, what are the hoses and check valves on the starboard side of the crank case? They run behind the CDI and starter mounts. I assume these are recirculation hoses for emission purposes? They look kinda rough. Could this be the issue if there was a leak in one of those?

Does this sound like it could be bad reed valves in cyl 2 and 3? Gasket?

Thanks again in advance. Sorry about the long post... At this point any suggestions would be much appreciated

[robert graham]

When you cleaned the carbs did you remove that top plate and clean/ check the idle mixture circuit, then reset those mixture screws/needles to about 1-1/4 to 1-1/2 turns out from lightly seared?....

[bedwar44]

I did, and I have the screws 1.5 turns out from seated. I am going to re-clean them again tonight so I will do the idle circuit again really well.

[robert graham]

Do you have a fuel/water separator type canister filter installed on the boat?...

[bedwar44]

I do not have a water separator. I just cleaned the carbs again, and now it will idle again, but it is still very rough, as if there is a misfire.

[robert graham]

WalmartAttwood filter unit $28.... Great insurance against dirt/debris/water in carb jets....is your fuel fresh?...any dust in fuel filter?.... A contaminated fuel system can plug carb jets just as quick as you can remove and clean them...

[bedwar44]

I have been meaning to get the filter, but it has never caused problems before. I try to be pretty careful about getting non-ethanol gas, etc. Right now, I am running from a clean can with fresh gas, and am bypassing the fuel filter going straight to the pump, just while I try to work out the issue.

[bedwar44]

took for a test on water after cleaning carbs again so I could open up. Still no improvement in the idle really. It opened up fine at first but then started to not run well when opening throttle. Seemed like just running on 2 cylinders. Every once in a while it would kick in all of a sudden and start to run right.

I am almost certain it is not a fuel issue. Been through carbs three times, and replaced pump, couplings, etc. Am running it on the muffs with a clean, portable tank with gas I just bought now, and it idles like crap. There is a regular pop from exhaust every two seconds. If I pull the plugs while running, numbers 1 and 3 cause it to die. If I pull number 2 the rpms go up, more in line with what the idle should (and used to) be. I have the enrichment valve set to off to try and rule that out.

What are possible causes of that one symptom, other than fuel?

[zenoahphobic]

You mentioned earlier that the top cylinder appears to have more suction.

If that really is the case, clearly that carb is slightly more open than the other two. i.e. not synchronised for some reason.

I'd carefully look at the butterfly and it's contact with the throttle body where it gets close to. Compare with the others. A bright torch at various angles helps. Check the play in the shaft and its bearing looseness. Its very small changes at idle that ruin perfect running. I'd move the throttle slightly to see how the linkages pick up. Sometimes throttling back, the butterflies are pushed rather than sprang back and it takes a little time for them to settle; this is important on how you actually sync them and verify that that is how they will be under running conditions.

[bedwar44]

Well, I have cleaned the carbs again since the original post, so I did the link and synch according to the manual. The problem is not so much rough idle anymore rather than it will die at idle. Sometimes will stay running.

I am almost 100% it is not a fuel issue. I have been through and through the fuel system from tank to carbs.

Anyone have any ideas what would cause the rpms to go up when I pull the number 2 (middle) spark plug? Am I wrong in thinking it must be an electrical/spark/timing issue? It is almost like the number 2 cylinder is working against the other two when all three are going. When I pull it, the rpms go up and it idles fine, at least as fine as you would expect with just two cylinders working.

[99yam40]

do you still not have a timing light to test with?

I found my C40 TLRX CDI was retarding the timing too far at idle.

Had to replace to fix

Timing light can also show the timing on all cylinders if you index TDC on the flywheel, to see if one of them is different than the others.

does you motor have 3 pulse coils to tell when to fire plugs?


oh yea, I believe the re-circulation lines/ check valves take the puddled up condensed fuel/oil mix that settles out in the crankcase sections and moves it to a place it will be burned.
I found them bad on my 1999 C40, had to replace them when I had it apart

[bedwar44]

I borrowed a timing light yesterday and just tried it out. Have to admit I don't really know what Im doing with the electronic stuff but here is what I did:

Set dial on back of light to 0 advance. This should show in reference to the flywheel marks when number 1 is firing, right? If this is not correct please let me know.

Started up. At idle, Number 1 was showing past the 10 ATDC mark on flywheel. Maybe about 15 or so? No marks past 10 so hard to tell.

It should be at 7 plus/minus 1 ATDC according to manual.

Disconnected link rod from magneto lever to timing pointer and moved pointer down. With it about halfway between the idle (7 degrees) and WOT (25 degrees), it looked like it was at about 7 ATDC, or close. It is kinda hard to tell in the daytime. Backed off a good bit on the idle adjustment screw (guess it was way open too when I was setting it to try and keep running with bad timing?) and motor sounded smoother than has in long time.

Also, I swear I was seeing alternating TDC and TDC2 and TDC3 (2 and 3 are marked on flywheel) going under the light, but again really hard to tell in daylight.

I am going to check again tonight in the dark, but I am guessing if I was seeing all three flash through the viewing window that I have a short/arcing somewhere, or my CDI is fried. Seems like if it was fired it just wouldn't work at all though.

[bedwar44]

I should update saying I do not have a dial gauge to index TDC but visually, it is pretty close to the TDC mark.

[bedwar44]

update

Couldn't lay off it till night... Constructed a shade shelter, i.e., towel, and checked again. By moving the pointer a little bit I was able to get it in line as far as correct timing and it runs, but.....

With the light on number one, it does alternate between TDC and TDC2 (and maybe TDC3) marks when the light flashes. Unplug number 2 wire and bam it goes away and just shows the TDC mark and numbers.

Put light on number 2 cylinder and it shows the timing marks for cylinder 1 in the window, so something definitely off there...

Put on number 3 and it alternates TDC 2 and TDC3 in the window. Unplug number 2 and bam goes away again.

So the problem seems to be leaking spark or a short, etc from number 2 to other two cylinders.

Anyone have this happen before and can suggest a likely culprit?

I will check all the wires and ohm stuff out and will update when I isolate the problem.

Thanks everyone for all of the suggestions. This is a fantastic resource for folks like me that just cant afford the shop in most cases.

[bedwar44]

Solution

Ignition coil two tested bad. Primary resistance seemed ok. Secondary resistance did not give any reading. So, I am going to replace and hopefully all will be well.

Just out of curiosity from the more experienced guys, why would that cause cylinders 1 and 3 to spark at right time AND when 2 is supposed to spark? That is what timing gun test indicated. When I would pull the plug wire from number 2 this would go away. I am not really that good with the electronics side of things; if anyone could explain why that would be, my thanks.