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My engine never fails to start, however once started it spits and spews soot and black smoke. Then it will not respond to increased throttle. She sits and idles at 900 rpm and I "nurse" the throttle to finally get it rev'ed up to 1500 to 2000 and all is well. The black smoke clears, the large patch of exhausted soot floating astern drifts away and the little 1GM runs like a tiger. Full rpm (3400) or so and clear exhaust in other words no sign of the 3 or 4 minutes of anguish I'd just gone through while trying to get her running.
Once underway, there are no indictions of problems. No smoke, no overheating, no skips, bangs, or hesitations she runs fine, in fact impressively.
Has anyone experienced this? If not are there any suggestions; my starting technique, not enough or too much throttle while starting? I've used both.
My 1GM does the same thing. When I first start it up, it "THUMPS" OR "KNOCKS". I just let it idle as is until that noise goes away and gradually increase the throttle and as you say all is fine.
Do you have a floating mat of soot during that wait?
I'm not exaggerating it's as big as a beach towel, so at the very least I'm wasting fuel, at the worse I've got a more serious problem.
My 1GM does the same thing. Somebody on this board said that these one-cylinder engines need a lot of throttle to start up. That seems to help quite a bit.
The engine is a real workhorse, but it does produce a lot of smoke at startup--and my transom carries a diesel "mustache" for most of the season.
--Joe
Former Commodore, CDSOA
Former Captain, Northeast Fleet
S/V Crème Brûlée, CD 25D, Hull # 80
"What a greate matter it is to saile a shyppe or goe to sea."
--Capt. John Smith, 1627
Thanks for the input. The PO had advised using a lot of throttle. And the manual says the same, so maybe I'm wrong in my thinking that the more I open the throttle the more fuel that will be left un-burnt in the combution chamber.
I've been doing the exact opposite, that is leaving the throttle shut.
When I get a chance I'll open it up before starting next time.
I've found that my 1GM doesn't need much throttle at all to start. I usually advance the throttle lever just about an inch, and the engine cranks 2 to 3 seconds and fires up, then I put throttle in vertical position and let engine warm up, and wait for the KNOCKS and BANGS to lighten up as the oil hits all the necessary spots.
Just small white wiffs of steam from the tailpipe along with the cooling water as it heats up. The only time I've seen the Dreaded Floating Black Beach Towel is when the engine has full throttle and won't come up past 3200 rpm.. (probably have just a little too much prop on it).
One item that helps with the transom 'moustache' is the oil level.
Check your engine manual, but the recommended quantity of oil (and for the life of me, I can't recall it while at the computer) that Yanmar gives only comes up to the halfway mark on my dipstick!! I had always filled to top of dipstick mark and had the BlackTransom. Started using the recommended amount of oil, and don't have the problem much anymore. RC
On the GM series they do tend to carbon/crud up and will produce "carbon blankets". I have had success in removing the water hose and cleaning the inside with a jewlers screwdriver and a small diameter stiff brush. If the inside is too far gone it would need replacement.
Replacing the exhaust elbow made a huge difference in how my engine starts. I was worried about all sorts of fuel delivery issues that might have been rather expensive to repair. When the exhaust elbow finally cracked and I was then aware that it needed to be replaced, I was rather amazed at how blocked up it had become. Between the carbon build up and rust the engine was having a very hard time voiding itself of hot gases. Sounds like a chile fest before church! Anyway it is something to take a look at. The mechanic told me you should only expect about five years out of one, Steve.
The problem sounds familiar, because I had it for some years. The solution was a new head and exhaust elbow. Total cost including labor about 1200 +/-. Funny that after replacement the rpm under load doesn't exceed 2700-2800 rpm but boat performance is the same. I decided that I didn't want to screw around with an incremental effort to fix problems on what was then a 20 year old 1 GM (rated at 6 hp when you actually read the plate). I am thrilled with the results. Fast smooth starts, an adolescent mustash, and full utilization of all 6 hp. There are earlier threads in this - search on 1 GM.
Dick K
CD 25D Susan B #104
Mattapoisett, MA
Fleet Captain - Northeast Fleet 2014/2015
Tempus Fugit. And not only that, it goes by fast. (Ron Vacarro 1945 - 1971)
Thanks for all the input.
Just to update, The exhaust elbow and injector replace by PO about 2 years ago, in running time maybe less than 100 hrs.
Head gasket is possible but no other symptons present, for example water in oil or noise or loss of power.
She runs great, always starts, but spews out the soot upon start up. Not always so I'm thinking or fuel delivery, or start up proceedure.
I had my 1GM's head rusted through at the exhaust pushrod galley because the exhaust elbow had rusted through and allowed seawater to enter the head's exhaust port. This can go on for years and you'll never know unless you take th exhaust elbow off and look. I've even heard of 1GM's getting so much seawater in the engine via the valves that it locks up. I now know why Yanmar lists thje 1GM's exhaust elbow as a spare item.
My 1GM will blow black smoke on start up IF I open the throttle too much. I start it with just a tad off idle throttle.
After I bought Seraph I got a terrible sooty transom till I started running the 1GM more. They really don't like to be run with little or no load.
Well here's an update. I had a noted diesel mechanic check out my engine. He reported no problems found, with the exception of max RPMs underloade are only 90% of rated. He suggested either a fouled or oversized prop were the cause, but added, 90% isn't bad for a 26 year old engine. The smokey start was due to running under no load condtions, just charging batteries and short runs to the dock and back to the mooring, over the last several weeks.
onboard the YOLO 1983 CD25D
