2005 115 Johnson PLSOR dies at idle

[Harkonnen]

Alright, after sorting out earlier problems with the project (dying when throttling up - don't ask me how, it just started running OK after unscrewing and blowing out the jets for the nth time), here's another: dies at idle. Starts OK, idles for a few seconds at about 700-800 rpm, then sort of peters out and dies.

Other observations:
If I push throttle past idle before it dies, it catches up and runs OK.
Only happens when the engine is freshly started, cold or warm - does not matter. Idles fine after a WOT run as long as I do not stop and restart the motor; after a restart, same trouble.
Runs OK for a while at 1000 rpm.
Takes a lot of pumping to get primer bulb firm when I experience this.
Primer bulb is OEM and about 6 months old.

I suspect either a fuel pump (I tested it, it pumps, how well - no telling) or anti-siphon valve. Anything else I might be overlooking here? Is there a good systematic approach to hunt for those things?

Thanks!

 

[rowerowe101]

Well, first. You've confirmed proper spark/compression? Not sure if this model has an idle adjustment screw on carb but I would do the factory setting for that, and or adjust if it's already at factory to see if that evens it out.

 

[Crosbyman]

34 looks like idle needle try to open it up a bit .5 turn look for reactions
(at worst.. count the turns.. take it out.. blast in some carb cleaner reinstall with same turn count) were eye protection

yet...
repumping usually means bad pump, air leak suction side , dirty fuel tank pick-up, filters etc... tried a diff. tank/fuel supply ??

do you have a service manual .. how long ago were carbs serviced ??

 

[Harkonnen]

>proper spark/compression?

Checked earlier. Spark good, compression borderline, but within acceptable, and consistent across cylinders

> idle adjustment screw on carb

I did not mess with the adjustments, so I assume (or rather, hope) they are where they need to be. I'd rather try to eliminate simple things first. Carbs still scare me.

How does slurping sound from the tank when you pump the primer figure into the picture? On a different forum (IIRC) I was told this is a normal sound from anti-siphon valve, but I am not at all sure.

 

[racerone]

There may be a leak in your tank.----Simply test run with another tank.----Borrow one if you have to.----There is nothing scary about carburetors.----And this issue might be as simple as turning idle mixture screws a wee bit.-----Wonderful time to learn or pay $120/ hr at the shop.

 

[Harkonnen]

>34 looks like idle needle

It is. I am not messing with carb adjustments, though, before eliminating simple things (and for that, I'll probably take it to the shop, since I am still having nightmares from trying to balance 4-carb setups on my old Hondas/Yamahas).

>bad pump

Possible; I'll get to it after checking everything else. It pumps; how well, not sure. At least, it does not seem to give me trouble at WOT. What's the wisdom on non-VRO aftermarket pumps?

>air leak suction side

That's what I suspect; clamps look questionable. Let's see if new clamps cure that.

>dirty fuel tank pick-up

Also very possible. When I pump the primer, there is slurping sound from fuel pickup area. I was told it is normal sound of the anti-siphon valve, but I am not sure anymore.

>filters

Both external and engine filters replaced between last December and now.

>do you have a service manual

Yes, but it covers engines from 2.5 to 250 hp, 2- and 4- strokes, carbed and injected, so it is light on diagnostics. Are there engine-specific books out there? Dealer service manuals like I had for my old Samurai, perhaps?

>how long ago were carbs serviced ??

Did carb kits and bowls, together with cleaning, last Fall. Hope I did not bump any adjustments in the process.

Thanks!

 

[Crosbyman]

I did not mess with the adjustments, so I assume (or rather, hope) they are where they need to be.

actuualy they are probably exactly at the proper place the problem is the fuel crud which blocks a very small passage hence the need to just open up the idle counter clock wise to check for reactions... you can surely put it back wher is was with no harm done !! nothing to be stresse about

if you cleaned the carbs you surely took out he idle needle didn't you ?
the question now is ... did you put it back at the proper place turn count wise ???

 

[Harkonnen]

>actuualy they are probably exactly at the proper place the problem is the fuel crud which blocks a very small passage

Good point, didn't think of that.

if you cleaned the carbs you surely took out he idle needle didn't you ?

No, actually. There are 4 metering bodies with bowls/floats/valves/jets, and there are two throttle bodies (one per pair of cylinders) with butterflies; the idle needles screw into the throttle bodies. I've re-done the former. For throttle bodies, I just blew out passages with cleaner and replaced carb-to-block gaskets. What you are suggesting makes sense, though.

I still wonder if there is an internal fuel leak somewhere (from pump to pulse hose perhaps). One, it smokes on warm startup for a few seconds, then clears. Two, disconnected lines at connector after letting it sit for a day. Tank side had plenty of fuel, engine side was pretty dry. That gas must be going somewhere - I don't see how all that mix would evaporate without a trace.

Thanks!

 

[Crosbyman]

one rabbit at a time ! clean the carb's low speed orifices ...all of them & blow dry them out


or open up the idle screws .5 turns to 1.0 and TELL US what happens !!!

jmho

 

[Harkonnen]

clean the carb's low speed orifices

#9 in the picture above? Already done. Will tweak idle screws and update later.

 

[Crosbyman]

try 34 #9 is a orifice likely just to let air go in the carb and mix with the fuel from the LS needle 34

carb clean the orifice with a shot of carb cleaner and a small monofilament ( maybe 4 pound size)

 

[Harkonnen]

try 34 #9 is a orifice likely just to let air go in the carb and mix with the fuel from the LS needle 34

Yep, next step. Thanks!

 

[Harkonnen]

So I assumed wrong. Somebody did mess with idle screws: not only they were off, but all carbs were different. Returned to factory settings, major improvement. We'll see how it behaves on the water.

Thanks!

 

[Crosbyman]

take time to blow out the ls orifice in front of the needles ...then install the needles to specs . takes just a few more minutes for peace of mind

up to you

 

[Harkonnen]

take time to blow out the ls orifice in front of the needles

Did it as a part of restoring factory settings - took them out and blew the screw hole (and the orifice) with carb cleaner.

 

[ct1762@gmail.com]

could still be a slightly torn pump diaphram, or leaking pulse hose connection to pump. has it been synch n linked properly? if the cam roller is too far away from the throttle cam it will run lean in effect. too much timing, not enough fuel. to set those carbs perfectly, you really need a good digital tach or a timing light with the 2 stroke setting and tach in my experience. you cannot hear a difference of 100 rpm easily, for example. with the tach, you can adjust the rpm for it to be the highest possible, then back each out a tad

 

[Harkonnen]

could still be a slightly torn pump diaphram

That's what I am wondering about, because it smokes too much even for a two-stroke (smoked A LOT more before carbs redone), lots of smoke on startup, and when you close the throttle, a big puff comes out. Pump checks out OK per manual, but there is always some gas in the pulse hose; that doesn't seem normal to me. I suspect that there is a tear that is small enough to hold when I pressurize the system with the primer bulb, but large enough to let gas through when engine starts pulling vacuum. What do you think?

Thanks!

 

[Harkonnen]

could still be a slightly torn pump diaphram

Iiiiiiiiiiinteresting... As I said earlier, if I pressurize the system with a primer bulb, no obvious leaks. If I then give just a tad of suction to the pulse hose connection at the pump, gas comes out - not a lot, 2-3 cc's at the most. Does it look like a leaky pump?
Thanks!

 

[racerone]

In my opinion the VRO pump ( if equipped with that ) is very easy to inspect and repair.----Any other Pressure operated diaphragm pump is also easy to inspect and repair.----Have a go at it.

 

[Harkonnen]

In my opinion the VRO pump ( if equipped with that ) is very easy to inspect and repair.----Any other Pressure operated diaphragm pump is also easy to inspect and repair.----Have a go at it.

It is a VRO, but oil injection was removed long ago; I am running pre-mix. I was thinking about getting an aftermarket non-VRO rig; what's the wisdom on that?
Thanks!