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  HELP! 40 HP Yamaha is running like a trolling motor.

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Author Topic:   HELP! 40 HP Yamaha is running like a trolling motor.
adaps4 posted 09-22-2001 10:55 PM ET (US)   Profile for adaps4   Send Email to adaps4  
Well, Fall is here, and unlike most of you my boating season has just started.Snook season just started, and I went fishing for the first time in months. Problem is, I think my carb got gummed up over the summer. When I push the throttle, I hardly get a response. Has anyone ever had this problem?
I just want to avoid a very expensive bill at the yamaha dealer.
If you know how much I am looking at, I would appreciate it.Also, if it sounds like any other sort of problem, please mention it. I will be checking the spark plugs tommorrow.
Thanks for the help, and thank you for this message board. It has been a wealth of knowledge.
P.S.- The boat in question is a 1972 Sourpuss- just for your information.
JBCornwell posted 09-22-2001 11:43 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy, Adaps. You are probably running on one cylinder, though fuel starvation is still suspect.

Pull your plug wires, one at a time. If there is a drop in rpm or the engine dies that is a good cylinder. If there is no change that cylinder is making no power. See if that plug wire will arc at least 1/2" to the block.

Good spark? Try pumping your primer bulb when the engine is misbehaving. Picks right up? Check tank, anti siphon valve, fuel hose and fuel pump for air leaks or obstructions.

Dead cylinder that has spark? Two Carbs? Clean the offending carb.

Good spark to both cylinders, both make power at idle? Overhaul fuel pump.

Let me know what happens.
Red sky at night. . .
JB :)

Dick posted 09-23-2001 12:04 AM ET (US)     Profile for Dick  Send Email to Dick     
Check the vent on your fuel tank. Is it open?
andygere posted 09-24-2001 12:22 PM ET (US)     Profile for andygere  Send Email to andygere     
Check your fuel filters: On the motor and in-line if you have one. A little bit of rust and gunk can really restrict fuel flow. Also, some dirt or rust may have plugged your carb jets. That may or may not be a job for the dealer depending on your mechanical ability.
Bigshot posted 09-24-2001 03:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
that is a 3cyl with 3 carbs and my $$ is the needle and seat stuck on the bottom carb(common). try tapping the float bowl with a wrench while running. Also you can remove the black cover and put a rag in front of each carb. If it dies, carb is good. If it does nothing or even picks up speed, bad carb. I am having the same problem with my 90 but I am gonna do all 3 just for S$G.
adaps4 posted 09-24-2001 08:03 PM ET (US)     Profile for adaps4  Send Email to adaps4     
Thanks everybody for the help.
I have tried the spark plug trick- good spark, top plug when unplugged- slight variation in sound, middle plug when unplugged- engine dies, and bottom plug when pulled- no noticeable difference.
Big Shot- would this be similar to the "covering up the carb trick"? If so, the top and bottom carb are not functioning correctly. Also, could you describe the "float bowl", I am not much with engines, but always willing to learn. Hope y'all made it through Gabrielle OK on Longboat, and hope the fishkill is over. I am local in Tampa- Harbour Island area.
Cheers all.
Bigshot posted 09-25-2001 09:26 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Do a compression test just to be sure. Then pull the carbs and have them rebuilt. A lean carb will blow an engine. Do NOT chince in this area. All three will be less than $150.
adaps4 posted 10-06-2001 12:08 AM ET (US)     Profile for adaps4  Send Email to adaps4     
Thanks all for the help- I brought my baby to the Yamaha dealer, and had them rebuild all three carbs. $170 later, I have a sweet engine. Compression test was fine, so I didn't do any damege(thank god). If there is a moral to this story, it is to use gas stabilizer on a regular basis. I know I will never forget. The boat only sat for about 2 months, but it was enough.
Anyone know the best stabilizer to use?
Again, thanks.

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