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BlackMax-ThunderToad

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1979 20HP model 200. SerNo: 5408750. Rebuilt Carb. New plugs. Electric start. Carburetor "B". Starts OK. Won't idle and tries to run away in tank (trash barrel). Won't idle meaning: WAY TOO FAST. Then runs away sort of. Right away before it's even warmed up. Mixture screw and stop screw have no affect. Has a manual choke and a choke solenoid. Motor is new to me. The solenoid choke is wired but not mechanically hooked up. I have to emergency choke it to stop the run away. Throttle and advance all seems to be working. (obviously not). What the hell is happening?
Also why does it have manual and solenoid choke?
I have a manual for it.
You guys fixed my 150. Thank you..........Please fix this little brother. I answer fast and watch my post hourly.
 
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How much carbon build up is there on top of the pistons? Excessive carbon will glow red hot and light off the fuel and redline the engine. One way to tell is if it continues to runaway after the ignition is turned off.
 
It does run after ignition off. Thought that was because it is a sort of magneto self generating system. Also would the carbon heat up right away? I will try to look into plug holes a little better. Is this big tear down fix?
 
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Teardown might not be necessary .Buy a can of engine tuner and follow instructions on can, It's a decarbonizer. If that does not cure your issue ,head removal and thorough cleaning will.
 
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What are names/brands? Outboard engine tuner? thanks. Can someone clarify the two chokes? Does having the solenoid wired harm anything or confuse the motor/fuel system?
 
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Is the carb butterfly closed all the way? those carbs when they get old can start sticking sometimes they need to be soaked.. Quicksilver power tune, BRP engine tune, and Yamaha ring free are all good. Do not follow the directions just spray it into the spark plug holes and let it sit overnite. The directions for them is to warm the motor up and spray it through the intake, can't do that on a runaway. There is no head on that motor to remove.
 
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Thank you Scott. I did soak and rebuild carb. I believe butterfly is closing but will check for sure.

Please note: as I try to not forget any info. My grandson took off the carb before he gave me the motor, so I could rebuild carb. I did not see how carb was linked. Even with a manual, my experience and common sense, I may not have correctly connected the carb throttle shaft to what I believe is the throttle rod. There is a threaded pin holding a plastic piece. The "throttle rod" goes to a bell crank mounted/pivots on a plate on the port side of motor. It seems like it has a provision for remote control cable on opposite end of where rod attaches. What else does that "Z" bar/bell crank do? Is this lever/bell crank operating something inside motor or a wasted pivot?
 
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BlackMax-ThunderToad said:
It does run after ignition off. Thought that was because it is a sort of magneto self generating system. Also would the carbon heat up right away? I will try to look into plug holes a little better. Is this big tear down fix?
Click to expand...

Do not tear your engine down.

Keeps running with ignition turned off tells me that Carbon is your problem, nothing more. The carbon heats up immediately. Pull the plugs tilt the engine all the way up and soak the cylinders with power tune or Sea foam, just pour it in the plug holes. Let it sit for a day or two. Then fire it up and let it run.

FYI, If your engine is this clogged up with carbon and unburned oil there is a good chance that this engine may not live too long. Pennzoil was probably used in this engine.
 
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Whats wrong with Pennzoil??? Been using it XLF for years in all my engines and never had a problem with carbon.
My hoseboat 14x48 Fleetwood with 950SS has run flawless with it and it never see's over 4000rpm.
 
BlackMax-ThunderToad said:
Scott, after soaking with Power Tune, do I let it blow out open plug holes by cranking..... or start motor?
Click to expand...
Start the motor and run it to clear the carbon out after it soaks. If it is a carbon problem I doubt pennzoil did it. More than likely a lot of slow running/trolling or to much oil in the first place, no thermostat on that so tends to run cold.. If that doesn't work look for an air leak.
 
UPDATE SUCCESS. I can't believe it. All that trouble: Run Away, fast idle, adjustment screw not affecting......as Scott suggested, butterfly was open a tiny bit. Could not see, took off the threaded pin on carb shaft, saw hole in shaft was off from hole in plastic lever when twist grip at max low. The misalignment was showing the carb shaft was being held open. Adjusted the screw in the plastic lever and it starts, idles, adjusts and revs up and down. THANK YOU ALL SO MUCH!! I did see black "soot" on pistons. Gently ran a screw driver over it and it did come off as soft goo, down to shinny. Probably better than being baked on? Is that still considered carbon build up?

Don't want to get too excited until lake test. Will report final results.
I still can't believe that would cause all that, but I tell you it did. A person can easily miss that. It's hard to see into carb throat. It's hard to see if lever screw is just touching timing advance pin, it's all black parts. Flashlights don't illuminate black very well. Stating this for the next guy like me. The guru's in this post know all that. As I said, noticed that hole in carb shaft had to rotate (open butterfly) to be concentric with threaded hole in plastic lever.

P.S. I have to type words over and over on this forum. The keyboard skips letters and space bar commands. Just this site. I'm on windows 8.1
 
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Empirically it does explain it. It now shuts off every time. It did not before butterfly adjust. No other repair was made. Maybe key switch is faulty. Does not a pull-start spark without battery? Maybe it will do a "no shut off" after I run it longer at lake. The total test is not complete. I understand that it makes no sense and may still point to carbon. There can easily be more than one problem happening.....but it shuts off now. That's all I know. If it shuts off after extended runs at lake, we will have to come up with a theory.
 
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That is possible I guess. Hard to remember what happened when I was in panic mode. I remember turning off switch, then pulling off connector from side of motor then choking. After that I always choked to stop.
It only took off after I gave some throttle. I remember pushing on linkage between carb and advance to hold it down to a fast idle trying to adjust stop screw and fuel mix. Then gave up and posted here before I blew it up.

Also thanks to Jeff. I'm sure you had the answer first.
 
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Docksidemarineservices said:
The open throttle plate does not explain the engine running after the ignition is switched off.
Click to expand...

If you look at post #20 it sounds like the ignition harness was pulled off the motor so it fired right back up when he did that. Don't pull the ignition harness off of the side of the motor any more.
 
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flyingscott said:
If you look at post #20 it sounds like the ignition harness was pulled off the motor so it fired right back up when he did that. Don't pull the ignition harness off of the side of the motor any more.
Click to expand...

"I remember turning off switch, then pulling off connector from side of motor then choking. After that I always choked to stop."


If the engine did not shut down with the switch, how long did it take you to get back to the engine and wiggle the harness apart?

Sounds like too much time to me.

Just saying, put some power tune or seafoam through your engine and make sure its clean of carbon.
 
Will do. Thank you very much. I have learned a lot here.
I was standing on port side of motor, turned key switch off and within 3 sec, pulled plug (dumb idea)....then within 3 sec, choke.
I don't think it ever got too near WOT.
 
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