Unpredictable transition from low speed to high speed

[gogordy]

Hi

First post here, I ‘m hoping to find a solution from some of the more experienced enthusiasts here:

I’ve got a ’65 Simpson Sears 35 HP outboard (made by WestBend) That runs great at high speed, idles poorly and just won’t make a good transition from low speed to high speed.

I assumed it was the jetting in the carb, so I cleaned the carb (it was quite clean anyways), set the air screw to factory specs, fiddled with it as much as I could and decided it was something I couldn’t find with the carb, or that I had cleaned it wrong. So I was lucky enough to find a brand new tillotson carb for this motor and installed it…same problem.

The motor runs just great at high speed

Here’s a youtube video of it running

https://www.youtube.com/watch?v=R8dGVCoR9uc

The trouble is, it will not make a smooth transition between low speed and and high speed. From idle, i can put it full throttle and it will just speed up a little bit…spurt a little after a while (like about a minute) spurt a few more times, then finally kick in at full blast.

I was so sure it was the low speed/high speed jets, but both carburetors act exactly the same, so it must be something else?

Looking forward to some ideas/solutions or help with troubleshooting.

Thanks

Gord

[fleetwin]

Your video shows the engine running great at WOT, but doesn’t show it running poorly at low speed. You swapped out the carb and it runs the same.
You mention that it idles poorly, then sputters before finally getting to high speeds.
So, my guess is that it is running on one cylinder while idling, maybe only getting spark to one cylinder until the throttle is advanced to WOT. You may want to try those inline neon testers while the engine is idling, or do a cranking spark test.
Did you try new plugs?

[billw]

As I read your post, my feeling was leaning towards the same conclusion as Fleetwin….possibly running on one cylinder at ilde and below transitional speed. If it were me, I’d run the engine where the problem is the worst. Then, stop it dead immediately and remove the plugs for inspection. Is one drier than the other? is one more wet than the other? At idle speed they should both be the same and kind of moist. Not dry and not soaked, either.

One the other hand, the relationship to where the mag is, as opposed to how open the throttle is, is critical and usually adjustable.If no one else knows, I think I can look up how to check this very important "synch and link."

It would help in trouble shooting to do a compression and open gap, cranking spark test, as a baseline. Spark should jump at least 1/4".

I’m not familiar with this exact motor but West Bend engines usually run very well; so I am sure it can be worked out.

Long live American manufacturing!

[Mumbles]

Hey Gord, that video looks familiar. Was it posted on the old MLC site once?

As stated, ignition is the probable cause. Something as simple as a bad plug will cause missing on acceleration.

By the way, nice motor! I have a ‘Made In Canada’ one here to which sat in storage since the late seventies and runs like a charm!

[frankr]

My gut thoughts are the same as fleetwin, running on one cylinder at slow speeds, then it starts firing after you open ‘er up for awhile. Could be ignition, but consider the possibility it may be ingesting water into a cylinder at slow speeds. Certainly doesn’t sound like a fuel problem, unless possibly a leaking fuel pump diaphragm dumping extra gas in the cylinder it is mounted onto.

[gogordy]

Thanks Fleetwin, BillW, Mumbles and FrankR,

Great advice, I’ll have to give it a try tomorrow. Sheesh if it is only a set of spark plugs, I will be grinning from ear to ear.

I was thinking in terms of the fuel pumps as the next thing to check out, but I’ll go the easier route first with the plugs. As far as the "link and sync" goes, I get the concept, but it sounds like a magical undertaking…I’ll have to leave that one to the last.

Mumbles, yes, I had this one on the Maple Leaf Chapter forum as well last fall. Still agonizing over the same problem this spring. The MLC forum is offline at the moment. I’ll bring it to the wet meet in Hastings later this year, hope to see you there.

Anyways, I wanted to thank those who responded, your input is very much appreciated

Gord

[gogordy]

I’ll see if I can get a video of the transition, rather than at wide open throttle…but I may not have to if the plugs do the trick 🙂

[gogordy]

EXCELLENT diagnosis guys. Changed the plugs (found the correct ones) and the magic happened! Thanks thanks thanks

Big grin from ear to ear.

This old simpsons-sears OB runs perfectly now, what a thrill.

Commendations and medals for all who responded, thanks.

Gord

[gogordy]

http://youtu.be/JKV-Qd2C7j0

video of the simpson-sears outboard making the transition from low speed to high speed. Well done boys!

[Mumbles]

It sounds great and I’m glad you got it running good in time for summer! 😀

This should prove once again that new plugs and other expendable ignition parts are part of a thorough tuneup.

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