Ok.. I'm no mechanic and it's obvious I need some help. I just got everything together for new rig and want to try and run engine this weekend. Had her on trailer and was going to adjust WOT to 4300 Out of water and idle to 1100-1200. The problem I've run into is once I get over 2500rpm's it starts running like shit. It's smooth all the way to 2500, but then goes to making popping sounds kinda like a small backfire.

The only thing I changed out was the exhaust.. Went to a MM double barrel. So is this a Carburetor issue? Do I need a carb kit? If so, can you get a kit with bigger jets? Or, could this simply be an AIR/FUEL adjustment on the tabs? Am I to understand I need to break or cut the limiter tabs on these to set things correctly?

Any ideas guys?

exhaust alone won't make that big of a difference. Check carb, bad gas, plugged main jet or I've seen it run on one cylinder either by bad plug or no fire to that cylinder. Carb still dumping fuel into cylinder but not burning.

Banded... I forgot to mention to everyone .... brand new tank and brand new non-ethanol gas yesterday... could be some of the other issues.

I would still pull the carb, very easy and check the jets. Get a small piece of wire of a torch tip cleaner kit qand rod them out. It really doesn't take much if any to plug those jets. Thats the easy part. then go from there.

Have you tried pulling one of the spark plug boots of while it running? Maybe a bad coil?

Will attempt to clean carb first and see what happens... thanks for the advice.

Could be flash over too. Spark being robbed from one cylinder by arching from the boot to the air dam.

Ok.... I think txmudcutter is on to something. I can pull the starboard side spark plug boot off of the plug and hit 3500 rpm no problems sounds clean. I put the boot back on the plug and it goes to shit.

I pulled the plug out with the boot attached and when I roll engine over I do see it sparking. Sooooo....

WTF? CHUCK ... somebody help!

liquid electrical tape your whole spark plug boot

wait are you saying the spark plug is sparking?

or there is a spark by your engine and spark plug boot?

The spark plug is sparking while removed from the engine. There is not a spark from the engine to the boot while everthing is hooked up normal. Is this bad?... fuck dat.... how bad is this?

If you are serious that it is sparking while you turn the motor over with the spark plug removed, I need you to very carefully reinsert the spark plug(don't over tighten hand tight plus 1/4 turn). Then hook your boat up and bring it to the shop. BECAUSE YOU KNOW WAY TO LITTLE ABOUT ENGINES TO WORK ON THIS. IMMEDIATELY PUT DOWN THE WRENCH BEFORE MORE HARM IS DONE

You're fine, he's saying he is getting spark on the plug with the plug in the boot but out of the motor.

You are getting "flash over". The spark is coming out of the boot and jumping to the metal beside it robbing it from the plug itself.

I highly suggest pulling the factory boots off, clipping the silver metal crimped on fitting off the end and installing some NGK LB05EP boots. Simple to do, they literally twist into the end of the wire.

http://www.ngk.com/product.aspx?zpid=20061

http://www.ngksparkplugs.com/docs/resistor_covers.pdf

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This......

I will try some new boots and let you know Will.

Thanks everyone for helping me with this... I hope that's all that turns out to be an issue.

Ok... That was not the problem but we are narrowing it down. I tried boot covers on the plugs and it's doing the same thing. I thought originally it was only the starboard side plug so I didn't ever pull the other one. Here's the situation.

I can pull starboard boot off of the spark plug and the engine runs fine all the way to 3500rpm. I put the starboard plug boot back on and pull the port boot, then the engine completely dies.

Suggestions?

Isn't that the side that the plug sparks while out of the motor but iin the boot?

yes Will... If I completely remove the starboard side spark plug but leave it in the boot... it is sparking when the engine rolls over. The entire starboard side cylinder is not firing correctly. Is this a coil issue? Or maybe the carb is stopped up to one side of the engine? Anyone have any insight? This motor is about to be FOR SALE quick if this thing frustrates me anymore. I can't stand working on shit like this.

So you're getting fire, either wrap the shit out of the wire and the boot or take the air dam completely off of that side and then try it. I'm still thinking the same thing...

Im thinking a bad coil. Ive had one spark when you take it out of the motor but in the boot and turn the engine over. I changed the coil and it was fine. I came to the conclusion it was getting weak fire or almost like it lost fire the more you went up in the rpm range. Just my .02

If you don't like working on engines, better get out of the mud motor game.

Sent from my SM-G900V using Tapatalk

I thought a bad coil from the first post but went ahead and read whole thing.

Todd I cant remember if this is a CDI motor or not, if so and If you are replacing coils go back with the hi rev coils.

Guys, I can't tell you all how much I appreciate the input and help. I ended up taking the carb off and breaking it down last night. Apparently there are 4 jets in these carbs...... I'm assuming two for each cylinder and one is idle and one is high.. Anyway. I found a stopped jet on the starboard side of the carb. I cleaned everything up and put it back together. It ran like a top today. Me, Dad, 2 batteries, 16 gallons, yeti of beer, trolling motor, and a few tools... 25 mpg at 3500rpm all day long in deep water which I thought was pretty good for a stock motor on my 19ft tank.

starboard hi flow carb jet.jpg

Pete, I'm glad it turned out not to be the coils but I thank you for your advice in going back with hi revs. Either way.... I can't say that I'm entirely sold on the MM game... I'm still thinking this GTR might be sold in the near future. A skeg and Yamaha might be more suitable to my needs.

Glad you got it figured out man.