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2002 40 hp 2 stroke single carb Mariner conks on reducing throttle to idle.

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saoceallaigh

Member
Hi,
Have had lots of reliability issues recently with difficult starting/unwillingness to start, not giving full power.
which was put down to carb dirt.
Workshop said my tank was clean and fuel clean so cleaned the (single) carb, took loads of money and said it was A1.
Next fishing trip took about forty pulls to get it started for home and it still conked again in sight of the pier.
Went back to workshop they threw out my fuel said it had been bought at a dodgy forecourt and that they only endorse one brand of gas.
They cleaned the carb found no dirt made no difference.
Then they swapped out the coil under flywheel no improvement.
they replaced one of the coilpacks and that did seem to improve the spark for that cylinder and give more power flat out.
Keeping it running at idle was still a problem. Compression was 120 on both cylinders.
With 6.00 pm on a Friday looming they again took loads of money and said it was an old engine with (in their opinion) huge hours done and I should keep upping the idle revs if the problem persisted also ordinary TCW3 oil was no good only Quicksilver or Yamahalube would do.
The engine is usable but idle is fast and there is a bit of a clunk/crunch on going into forward.
I feel there is very little wrong with it and these guys talk a lot of BS!
Any comments/advice appreciated.
 
Advice - find another shop that actually knows what they are doing.

If we assume that they cleaned the carb correctly - twice by the sound of it, and their compression gauge is good then you will have to look elsewhere for the problem.

You said they swapped a coil under the flywheel (sounds like a Yamaha/Mariner?) and a "coil pack" (not sure if you mean switchbox or one of the sparkplug coils). In any event did they actually confirm good spark or just started "swapping stuff" guessing at what might be the issue?

You need to have the spark tested to rule it in or out as a problem.

If the ignition is ok (and your symptoms could be ignition) then there is also a number of seals/gaskets that could be letting too much air in (or air/gas out) which could also cause your problems.

And these are numerous - some being, crank seals, carb gasket(s), intake cover gasket, exhaust gasket, power head base gasket, and a few more that don't immediately come to mind.

Each has to be chased down and eliminated.

So while it sounds that you rely on a shop to do the troubleshooting for you, like I said, find a shop that knows what they are doing....
 
Hi Graham,
Thanks for reply.
Would normally do most DIY stuff myself bit while on holiday and with the kids demanding fishing trips I took the easy way out.
They changed the red stator under flywheel(no improvement), then one of the CDM modules and judged the spark by holding plug against block said it was much improved.
The motor was liberally sprayed with WD40 to detect leaks????

How should spark be objectively tested???

What is the best leak detection method/fluid???
Seán
 
Yes, you can try the idle jet (screw) if there's one there. Also, if you are "away" you can try winding in the screw a bit that controls the butterfly in the carb - turning it (in) will raise the rpms a bit (by keeping the butterfly open a little) and might keep it going until you can really get at the motor.

Most of the seals that might leak will allow (gas/air/oil) to "escape" - those on the crank, the intake cover, the exhaust cover. If those are leaking you will usually find an oily/goopy mess adjacent to them (upper crank seal would leave a mess under the flywheel/top of the powerhead), leaking exhaust or intake cover would be on the side of the engine and run down into the lower cowl just below them. Gas/Air/Oil gets "blown out" and when the gas evaporates you are left with the oil.

If it's sucking too much air that would be at the carb gasket/intake gasket - spraying a little WD40 in that area, when the motor is running will normally result in a noticeable increase in rpms momentarily (when a temporary seal is created).

To properly test the spark many discount auto places sell a (cheapy - around 5 bucks) spark tester. Shaped like a sparkplug with a little screw in the bottom portion/scale to see how far it's (screwed in/out) and an alligator style clip. You clip it to the block (somewhere convenient) and plug the sparkplug wire onto the tester (just like it was a sparkplug) and then turn over the motor.

Depending on the exact engine model you have you are usually looking for the spark to easily jump a 7/16"-1/2" gap with a good strong snap.
 
Thanks guys, but the only jet is the main jet???? just inside the fuel bowl drain plug????
Also I should have mentioned I found one of the fuel bowl retaining screws lying in the pan under the motor on inspection before our first outing,
Put it back with offset screwdriver, did not notice any consequent change in engine performance.
 
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Have a look on the right side of the carb for the idle screw.

So if you are looking down the throat, on the right hand side, near where the fuel line connects, there is a screw going through a spring.

Now in the same area is the shaft (with spring) etc that goes through the throat (holds the butterfly) so don't get them confused.

The idle screw is sitting fairly proud of the carb body and is (forward) of the fuel line - a slot type screwdriver will work here.

You can initially turn it all the way in and then back it out 1 1/2 turns. If that makes a difference but it's still groggy you can try another 1/4 to 1/2 turn. If you do turn it while the motor is running, give it a minute to adapt to the change before adjusting more.
 
saoceallaigh said:
Thanks guys, but the only jet is the main jet???? just inside the fuel bowl drain plug????
Also I should have mentioned I found one of the fuel bowl retaining screws lying in the pan under the motor on inspection before our first outing,
Put it back with offset screwdriver, did not notice any consequent change in engine performance.
Click to expand...
Just faced the same issues last week, motor would only start with stoke out, died on idle. I had just cleaned the carb a couple weeks ago and it ran fine. At first I thought it could have been the fuel/primer bulb line and changed that to no avail, changed gas no difference, finally I went and adjust the mixture screw and presto, the motor runs like a champ; that should have been the first thing to check, second by checking the main yet on the carb bowl instead of doing the same they are doing at the shop you take your boat. To adjust the mixture screw, turn it clockwise until is in just all the way ( DON'T FORCE IT), then back it counterclockwise 1 1/2 turns, try to start the motor; once started adjust the screw by 1/8s of turns until you find the sweet spot which usually 1 1/2 to 1 3/4 turns, good luck and stop giving your money to this guys at the shop, they don't sound too knowledgeable
 
Hi,
The idle mix screw is now out about 1 and 3/4 turns.
The engine does not now stop it continues to run. It still gives an occasional kick and backfire with a puff of blue smoke but where that would have stopped it before now it recovers and keeps going Its also easier to start and restart, all in all usable for the next few weeks. The idle speed is still too high which appears to be due to the throttle cable having been tightened up.
When I get it home I think I should check idle speed+ timing etc in case theres been some fiddling done there??
 
At least it should allow you to baby it through the rest of your vacation.

And yes, you should re-sync everything when you get back home. The hitch/backfire still makes it sound like you have a seal/gasket leaking somewhere but no sense trying to track it down now. Once you find the actual cause, then you can set the carb, linkages, idle speed etc back to starting spec and take it from there.
 
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