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1998 mariner 30 hp jet misses at high rpm

D

Danield174

New member
Hi all. I have a 1998 mariner 30 hp jet motor that misses at high rpms. It is a 3 cyl. I have changed spark plugs and put new mixed gas in it and it didnt help. seems to idle fine with a miss really. It just wont open up the whole way with out missing and caring on. Any help would be wonderful.
Thanks,
Dan
 
Re: 98 mariner 30hpjet misses at high rpm

Always include the serial# when asking questions.
A low speed miss could be a dirty carb,a bad fuel pump or the carb air screw not set right.
High speed miss is the same without the air screw adjustment.
Ethanol is messing with a lot of things.
It's delaminating the older hoses.Swelling the o-rings.etc.The fuel line could have a leak.The squeezie and the inline quick connect could be bad.J
 
Re: 98 mariner 30hpjet misses at high rpm

Put a timing light on it ---------see if you have an ignition miss on one cylinder or all three.
 
High speed misses are NEVER fuel related except with EFI motors. I suspect you have a coil going away. Buy ONE new and start swapping it out, one cylinder at a time.

Jeff
 
Some " jet " equipped motors come with a different CDI unit ( rev limiter )that starts to cut out cylinders to prevent engine damage.-----------------------------So use the timing light to see what is happening.----Once you know what is happening you can take corrective action.
 
Hook up the timing light--------use it as a scope. look at the light------------------Intermittant flashing of the light indicates an ignition problem----------------check all cylinders.
 
The 30 Jet was basically just a 40/50 horse Merc 3 cylinder with a jet unit in place of the standard leg. I agree with Jeff that a high speed miss is almost always the result of an ignition component. Since the T4 ignition on these is almost legendary in it's durability, the coils would be the logical first thing to troubleshoot. And as he suggests, since aftermarket versions can be picked up for about 25 bucks, a simple swap out is an easy way to isolate the problem.

If the coil doesn't fix it, then you can look at the other components - but that's for another day - try the coils first...
 
where can i find coils for mine for $25, and does this model have a coil or is it a cdm or are they the same thing. The cdm are almost 60 on here.
 
My bad - was thinking of the slightly older models that have the generic Merc coil. You are correct - Andrew (this site) sells the CDI version for about 60 bucks - in my opinion, every bit as good as OEM and in some cases a little superior..
 
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