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IT QUIT RUNNIN

B

B.G.R.

Active member
The old girl just turned over and would'nt fire. Left me stranded on the lake this past Sunday. Than got a service call on top of it.:mad: Not happy at this point. Had my bud look it over and found I lost fire on #3 cyl. Plugs were near black from rich idle. So he did one power pac and replaced the charging system {40 amp}.:) Plugs today and lake tomorrow.:drool: Carb adjust on the way.:confused: All for 400 bucks. used parts of course.
 
Thanks 82. I found out a bit yesterday. The carb adjustment screws are for air not fuel, correct? This is what I was told. That being said ,standing behind the motor the lower right cyl was'nt fireing right. Sometimes good and sometimes bad. This is with new plugs in it. I adjusted the carbs all at 1 1/2 turns out from seat. That idle screw I had to turn it to 1/4 out to make cyl fire right. I took carbs apart a few months ago and made sure they were clean but didn't blow them out with high pressure air. The emulsification tubes are spotless but I feel I should have blown the passages out. I assume each barrel of the carbs feed the cyl. behind it.
Hey thanks again for the answer and link. I was useing the wrong oil as well. Now useing tc3 only.
 
Hey B G R, Which motor are you running? On some motors the carb actually feeds the cylinder opposite from it which can make idle mixture adjustment a little more interesting.
 
B.G.R. said:
I took carbs apart a few months ago and made sure they were clean but didn't blow them out with high pressure air.
Click to expand...
be careful, with high air pressure on the carbs, there are lots of small passages ways and small brass parts that can be easily damaged with high air pressure
 
All I know it a mid to late 90s 150 hp carb engine 2.5 liter. Seiral # don't
match powerhead. It has a gremlin hiding somewhere. I'm going to put another bottom carb on it next week end and try that. Have a hunch it's sucking air somewhere. The 2 adjustment screws are 1/4 turn out from seat and I know that ain't right. Only in idle do I have an issue. Once I'm on the pedal a bit she runs smooth an strong.:brickwall: Since I added a stereo and built a back seat the added weight dropped my top speed to 65 from 68 gps. So I know she is hitting on all 6. Will keep ya posted. And thanks for the advice guys! Every bit counts
Bruce
 
Hey again BGR, I'm thinkin that the idle mixture screws should be 1-1/4 to 1-3/4 out. Is this what the others are adjusted at? I'm thinkin that the mid 90's motor has WMH carbs on it and 3/4 out on the idle mixture might be lean or maybe I've already had too much Southern Comfort this evening.
 
Not really sure on type of carbs but a friend said the adjustment screws are adjusting air not gas. Yes the other carbs are at 1 1/2 turns out.
 
Hey BGR, if it has the carbs that I think it does, than the screw is for fuel not air. I think on your motor there are two covers on top of the carb as it is mounted to the motor. These covers have two screws attaching each to the carb?
 
Not sure what you mean "covers". The carb has 1 brass 7/16 (cover?) on top and a total of 4 on the bowl which is where the emulsification tubes live. I have had this carb off and apart lots of times. All 3 are spotless clean inside and out. It's sitting on my desk as we speak. I have a friend comming over today to check the reeds out. I looked at them and appear to be fine. I'm dying to find this gremlin. I have ruled out a "fire" issue due to perfect running with throttle just out of the idle circut, you can hear that cyl. hit right away. As soon as I idle again it hits on 5.
 
Hey BGR, No covers on your carbs means they're the later model. The brass emulsion tube cover is next to the enrichment fitting. The idle mixture screws provide a small range of adjustment. The idle air bleed jet and air trim screws are factory set and under the welch plugs. The idle circuit is seperate from the mid and main jet circuits so a small piece of debris could be the cause of the idle miss. Clockwise=Lean, Counterclockwise= Richen. The idle air bleed jet is next to the back draft vent jet. Any obstruction here and the motor will be very fat at idle. Also the carb placement can be very important as there may be different jetting for different cylinders. You probably know this stuff, but I'm just sayin.
 
I hate to bring this part up but..... The ignition system in your Merc motor has a low speed side and a high speed side. I have seen cylinders drop at idle when the ignition system is not happy. A spark tester on that cylinder would show if it is dropping out at idle from a no spark condition. When she is sitting there idleing with the airbox open you would be able to see if there is a lot of blowback from a bad reed. No revving without the airbox cover on because it will be pretty lean with it open.
 
oooooooooooooboy. The gremlin sounds like it's turning into an evil spirt. Just had a new (used) charging system put on. 14 plus volts at crusing speed. Brand new hi-po plug wires and new plugs. Has a 40 amp charging system on it. Did another little test today with air box off I choked off all 3 carbs with my hand. Top carb and middle carb pull hard and idle fumbled. Bottom carb didn't "pull" as hard and didn't falter the idle that much. My buddy now suspects low compression in the fumbling cyl. Will do a compression test by the week end. He stated low comp. showes up at idle not on hi end , keeping in mind this little 150hp on this 1979 20 ft. Enchanter is still knocking down 65 plus mph with big stereo amp bass tube 15 gallons of fuel and a 1200lb hull and my fat can @ 200lbs. I'm getting flusterd.
 
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