Couple of engine issues - Moved my gas tank & spark plug...

[lugoismad]

A couple questions I'm hoping someone can help out with.

25 hp 2-cylinder 2 stroke Johnson. I think its an 83' with an 84' lower unit.

I moved my gas tank to the front of the boat, and now have about a 15' long fuel line. I used 3/8" fuel hose from a local hardware store. From the fuel pump to the carb, the motor had 1/4" fuel hose, so I assumed 3/8" would be plenty for that long of a run.

I've noticed that since moving it, when I accelerate, the motor will briefly drop in RPM, then come back about a second later. The rest of the time its fine. And it only seems to do this after we've sat for a while.

Is my fuel line run too long and the pump can't suck fast enough to keep up?

I'm wondering if with this long of a run, so I need to add in a helper pump?
I just rebuilt the fuel pump with a kit at the beginning of the season.

like this one? - https://www.amazon.com/W8sunjs-Universal-Heavy-Electric-Petrol/dp/B00L8IHM9K


finally, one other question.

I'm running NGK sparkplugs that are labeled for marine use and are on the compatibility chart for the OEM plugs for the engine.

However, I read that because the NGK's have an "R" in the model number, that means they are "resistor plugs", and could damage my coil packs?
I don't want to throw away $10 worth of plugs, because I have brand new ones in there, and I have a new set in the dry box just in case. I've been running it all season on them (just replaced them after about 10 hours on the engine to see what they looked like) without issue. Is there any truth to this? Should I switch to the OEM Champions?

 

[JMichael]

Yes the R indicates it is a resistor plug. Resistor plugs, just like spark plug boots/caps, and resistor wires, have resistance built in to them, and were designed to eliminate RF (radio frequency) noise. RF noise use to be a big deal back when we only had AM radios. Now days (as far as I know), the only good reason for running them is to eliminate possible RF interference with sensitive electronics, although those electronics would have to be pretty close to the source of the RF noise in order to cause any issues. If you inadvertently install multiple resistor items in an ignition system like resistor wires and resistor plugs or boots, you could potentially weaken the power to the spark plug and cause a weak spark. But to answer your question about damaging your coils, I've never heard of that happening or being a possibility, but since we're all human, and subject to making mistakes, I won't say it's impossible to damage the coil if you install too much resistance in the ign system.

 

[Siguz]

I've got my fuel tank up front too and also had concerns with the 15 feet of hose. I've no issues at all.
My motor is an 89 and it seems to run best with NGK surface gap plugs (can't remember # but I can get it for you).
I've experienced the same hesitation as you described. Turned out to be a bad spark plug wire on cyl1.

 

[lugoismad]

I've got my fuel tank up front too and also had concerns with the 15 feet of hose. I've no issues at all.
My motor is an 89 and it seems to run best with NGK surface gap plugs (can't remember # but I can get it for you).
I've experienced the same hesitation as you described. Turned out to be a bad spark plug wire on cyl1.

Could you get me the NGK model number?

And where did you get new plug wires? Do they make short universal ones?

 

[Pappy]

You should probably never need to change out a spark plug wire during the service life of an engine. Ever. Damage excluded.

Any surface gap spark plug for two stroke application is designed primarily for engines that spend most of their life at high rpm.
They typically exhibit reduced idle quality comared to a J gap spark plug. Unless you have plenty, you will be wasting your money.

Spark plugs in a two stroke that sees any idle time will appear wet and oily. This does not mean in any way shape or form that it is fouled.
The engine, all the way from the drawing board to production was built and tested using Champion Spark plugs. They typically are great running plugs in your engine.

 

[lugoismad]

You should probably never need to change out a spark plug wire during the service life of an engine. Ever. Damage excluded.

Any surface gap spark plug for two stroke application is designed primarily for engines that spend most of their life at high rpm.
They typically exhibit reduced idle quality comared to a J gap spark plug. Unless you have plenty, you will be wasting your money.

Spark plugs in a two stroke that sees any idle time will appear wet and oily. This does not mean in any way shape or form that it is fouled.
The engine, all the way from the drawing board to production was built and tested using Champion Spark plugs. They typically are great running plugs in your engine.

Pappy, this motor sat for a decade next to a barn. I had to replace the entire wiring harness already. So the plug wires may be bad, I wouldn't be surprised.

I will switch to the champion plug and report back.

 

[Siguz]

I've got my fuel tank up front too and also had concerns with the 15 feet of hose. I've no issues at all.
My motor is an 89 and it seems to run best with NGK surface gap plugs (can't remember # but I can get it for you).
I've experienced the same hesitation as you described. Turned out to be a bad spark plug wire on cyl1.

Could you get me the NGK model number?

And where did you get new plug wires? Do they make short universal ones?

Attached is a photo of the ngk box.
The universal wires that I used are too long but they're doing the job.

My motor spends most of its hours at WOT. I rarely troll and primary anchor when I get to where I want to go.

 

[lugoismad]

I think I found the issue. Accelerated at the lake this evening and the fuel filter filled with air. I have an air leak in the fuel system somewhere.