2004 Merc. 9.9 2 stroke caughs at very low speed

[Rifflerunner17]

Sound and feels like it looses spark or fuel for a second or so and then recovers. It does this of and on at a low trolling speed, runs great at high RPM. I just got this motor and when I did I changed plugs from BPZ8HS to BP8HS. Could that cause it, I'm puzzeled. Anybody got any good info?

 

[Don S]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

Yes having the wrong plug could cause it. The BPZ plugs have an inductive resistor in them. Could confuse the ignition system without it.
Put the correct plugs in and try it.

 

[Rifflerunner17]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

Thanks much Don!!! I'll give it a try.

 

[achris]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

I don't usually do this.

You have the right plugs in. As Don said, the Z in the plug indicates an inductor in the plug, but it is only for radio interference suppression. The rest of it is the same, so don't bother with the plugs. Instead, richen the idle mixture by 1/8 to 1/4 of a turn. What you are experiencing is a 'lean pop'.

Chris.............

 

[Don S]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

I don't usually do this.

No problems there Chris, and I have never changed that way on the Mercs, just my experience with the older JohnRudes with the Q77 and QL77 plugs. On some (even of the same year and hp ratings) they would idle rough, run rough and some wouldn't run at all because that inductor in the plug was missing.

But, like you, if the plugs aren't the problem, the mixture is probably lean.

 

[Rifflerunner17]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

Thanks to both of you, I will try both remedies. Is the idle screw the recessed screw on the top front of the carb?

 

[Don S]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

Is the idle screw the recessed screw on the top front of the carb?

Yes, just above the throttle bore.

 

[Rifflerunner17]

Re: 2004 Merc. 9.9 2 stroke caughs at very low speed

Thanks again! I meant the Idle mixture screw, glad you knew what I meant.
Thanks, Rifflerunner