Slight miss at top speed

[Mark P]

I finally got my 92 DC 25 running well. I did notice at top speed that it has a slight miss. The plugs are new. Could this be from old gas (which was stabilized)?

Thanks

Mark

[Murray]

Doubtful, with old gas the engine will start and idle okay until you apply any throttle. Once throttle is applied the engine will not rev up and run like crap. My experience with old gas.

[Mark P]

Hi Murray, you were right. Maybe it was wishful thinking on my part. I was just wondering if you have ever experienced any issue like this? When first started it seems to run fine but once warmes up it seems to miss. My son took it out today with fresh high test andhe said there qas no difference from the previous day. Thanks again for your feedback.

[Moonlighter]

Seen a number of reports lately of brand new spark plugs that had one bad one in the set. Plugs or leads can be OK cold but not when they get hot.

If you still have the old ones you could try them again, assuming that this problem started after they were replaced?

Do ypu know what rpm its hitting at WOT? Might be hitting the limiter (if those old 2 strokes have them??)

[Mark P]

Thanks Moonlighter. I wish I still had the old ones. As far as the rpm"s go it is usually at a higher rpm, but I believe my sin said it starts at a high rpm but it is a bit erratic..

[Murray]

s e l f f i x e r d o t c o m (all one word) has service manuals in pdf form should you need to dig deeper. You will find factory specifications and troubleshooting procedures. I’ve purchased service manuals from them before and had no issues.

[Mark P]

Thanks Murray
While following up on Moonlighters suggestion I ran across a video with a person with very similar issues (although it wasnt a Suzuki motor). He said if you have a grey fuel line from the tank to the engine (which I do) replace that line and your fuel filter. If the gas you are running has ethanol in it over time the ethanol breaks down the fuel line lining and plugs up your filter. Runs great after a start then the bogging starts. I will keep you posted if it works. Thanks for the advice.

[Solarman]

In most cases I've found that missing, as you described, usually relates to electrical breakdown at higher rpms. Plug wires, coils, even those little boots at the end of the plug wires. It's much easier to see them arcing if the hood is off and WOT. Flashes of light (arcing) to ground usually the culprit.

Good luck, post back.

[Mark P]

Thanks Solarman I will check that and I plan to know more by the end of the weekend. I will post results.

[Mark P]

Just a quick update. I have changed the fuel lines, prime ball, and fuel filter. When I changed the fuel lines I could see some "scaling". I wish I took a picture. I could see particles in the fuel filter on the bottom from this scaling breaking down. I plan on running it the next few days if we get some dry weather and I will post results. Thanks again for all the results.

[Mark P]

So my son had the boat out and he said it ran great. It appeared all issues solved. After a full day of running it it started to miss again but it was very slight. I am thinking if replacing the gas tank. I think the internal hose might have a crack of some sort and when the fuel gets liw its starts sucking a bit of air.

[Moonlighter]

Some tanks you can remove the pickup, inspect and replace if necessary. May be worth a try. Also those anti-syphon valves are just a source of potential problems, some its still there, be worth getting rid of it, and make sure there’s not one fitted to the new tank if you go that way.

Few years ago I picked up a contaminated load of fuel, replaced the fuel filter when it happened and then again 20 hours later, just to make sure all the contaminated fuel was out of the tank.

Do not discount an electrical issue. These engines are voltage sensitive. Therefore the other thing to check is all the electrical connections to the engine - main battery cables and white wire connections at the battery and battery main switch. A look at them is not sufficient - I recommend you undo them all, clean, inspect the crimps and connectors for signs of corrosion, reattach and tighten. Inspect and clean the large fuse in the white wire and make sure its connection is good.

[Mark P]

Thank you Moonlighter for the info.

[Mark P]

So I finally had the chance to give my motor a try. I have done the following
1-new plugs
2-new fuel filter
3-new fuel lines and prime ball
4-,new fuel tank
Ran it last night and once again when it gets warm it doesn't run consistent. It has a miss or intermittent hesitation at top speed. I was wondering if anyone has any ideas? Thanks for the help.