97 Intruder 150 barely idles

[62ChevyII]

1997 Intruder 150 (E150GLEUC). Over the course of six months the engine would run great until the heat of the day, then stumble above 4000 rpms. It got progressively worse (lower peak rpms) until it didn't have the power to get on plane. Pumping the primer bulb would help some. I found a tear in the fuel pump diaphram and rebuilt it but it helped only a little, still seemed to starve for fuel or spark. What has been done: new fuel pump installed/switched out with rebuilt unit to no difference, all carbs cleaned/rebuilt, all fuel lines/worm gear clamps replaced, fuel filter/gasket replaced (no debris), VST/choke bypassed with fuel directly to pump then fuel rails (no difference), no visible overheating/melting of stator coils/rectifier/powerpack/ignition coils, tach has always functioned perfectly, spark is good and even to all cylinders (based on observing several times with a 3/8" gap, with a timing light and observing individual plugs), two different sets of plugs tried. I have run the engine on a portable tank (no difference) and without check valves and with/without several different primer bulbs. I have only had this engine for about two years and it has >120 psi on all cylinders. I don't have a manual (yet) for this one so I haven't tested voltages/resistances yet. The engine will start and idle ok (not smoothly) for 5 -10 seconds then idle like it is missing or starving for fuel but the spark seems even and consistent and fuel flow appears good by all measures (engine bogs worse and carbs spew fuel when each carb is momentarily blocked while running.) Pumping the primer bulb or holding the choke after all the above work now does not affect the engine. It barely can push the boat at idle and dies if you give any throttle. The only odd observation is the external temp of the heads. I noticed that with running the engine in the water, on muffs or even dry (for about 15 seconds) the surface of the starboard head is uniformly 40 degrees cooler than the port (IR measurement.) That is a might much and usually the opposite. Ungrounding the shift switch had no effect but all cylinders are firing anyway. I lean towards a powerpack or optical sensor issue but would rather not throw money away just yet.

[62ChevyII]

Just checked the idle timing (6 degrees ATDC) and noticed something else. When I gave a very quick shot of ether into the bores, the port carbs either gave no change or choked the engine. The shot into the starboard bores really picked up the engine. So it does appear to be starving on the starboard side which makes the cylinder heat temps make sense. However, given what I've done, what am I missing?

[mactlman]

vacuum leak reed issues? carb issues?

[omcforever]

Never use ether!!!!!!!!! Use a spray bottle with 50:1 fuel mixture.

[62ChevyII]

Never use ether!!!!!!!!! Use a spray bottle with 50:1 fuel mixture.

The carbs have been rebuilt, adjusted, removed, checked and readjusted again just to be sure. The bowls (slightly warped) were replaced along with all lines/clamps. I've used ether (only with lubricants) as a diagnostic tool for decades. Old mechanics use it for vacuum leaks, carb checks, etc while the engine is running outside. Very short blips can easily show you a lot of information. Auto mechanics used to use propane with a small tube to check for vacuum leaks (or sometimes use pressurized air.) Complete safe? No, but when done outside and in tiny quantities the risks are small if you are smart. Do I recommend it to anyone, NOPE. Use ether to start a 2-cycle? Only as a last resort and then most people use way too much.

[ChampioNman]

When you rebuilt the carbs did you install the nylon washer under the needle valve seat? If you did you need to remove it as it isn't used on your motor, you said your r/r'd the float bowls did you move the high speed orifices over to the new float bowls? They don't come with new ones. Ether will wash away the protective coating on the cylinder walls on a 2 stroke motor. Fine on a 4 stroke but not on a 2 stroke.

[62ChevyII]

The washer was not in the carbs so no it was not used from the rebuild kits. The orifices were installed into the new bowls and I checked the depth they went in. I've found the replacement plastic bowls for several engines either weren't tapped or weren't tapped far enough. You can wash out 4-cycle cylinders as well it is just harder with oil behind the skirts but possible (saw it once.) I see many people squirting liquids into cylinders and bores in ridiculous amounts to start engines. That is why I only use a blip of ether with the engine running and make sure as little liquid goes in as possible. You only want the gaseous state sucked in and it only needs a tiny amount to hear the engine respond better, worse or not at all. There is still oil/gas mix going in as the engine is running. Not arguing with anyone over personal methods. I do appreciate any ideas as this sucker is being harder to diagnose than any in my family over the last 30 years.

[ChampioNman]

When you buy any parts on Amazon or Ebay it is a crap shoot. OEM parts are available the part number is 0433000. If you suspect an issue with the starboard side fuel delivery You may want to check the intake manifold and seals. What are the head temps?

[62ChevyII]

I ordered gaskets for the intake manifolds a few days ago. Those are my next target for this weekend when I am home during daylight. The carb bowls are OEM. OEM parts aren't always up to snuff either but are a better chance (its the OEM plastic bowls that always warp with time, aluminum ones are outrageously priced.) I only buy auto/boat parts from a few dealers I trust online (some are on ebay but I know those guys.) Amazon sucks, lots of counterfeit stuff. The head temps (external surface around the plugs measured by IR) were port = 130-135 and starboard = 95-100 after running on muffs for about 3 - 4 minutes (50 degree well water running through it.) I didn't check the water psi as I was only running for a few minutes and had a modest flow squirting out. I'm cautious with muffs as I once blew a seal turning on the hose too much (not this engine.)

[ChampioNman]

Sounds like the starboard thermostat may be stuck open or missing. I use three main parts suppliers all with OEM parts and have never had an issue with them. I also get parts from the ATL parts warehouse and they are identical. But good luck to you.

[62ChevyII]

Update: I finally had time to remove and clean out the throttle bodies. I did see one or two specks of debris while cleaning. Reassembled and it ran nicely, for about 5 min. It then would barely idle. A check of spark showed a strong but intermittent spark on all cylinders - hadn't seen this up until now. Idle timing dropped to 3 degrees ATDC but after a minute on the muffs the engine began to cycle between two modes every minute or so. One mode = intermittent strong spark on all cylinders, stable timing at 3 degrees ATDC. The other mode = regular quick (less than a second) switching between timing of 3 degrees ATDC and 6 degrees BTDC with a strong, consistent spark on all cylinders. The timing had been at 6 degrees ATDC (several checks over the last few weeks) which I have never adjusted on this engine (literature values suggest 5 - 7 ATDC for these engines.) A few love taps on the powerpack had no affect. I fried my DVA multimeter a while back so I can't check the stator output but I'm leaning towards the stator and the fact that this engine had multiple issues making this a pain to diagnose. The optical sensor was clean with no cracks or missing plastic up top.