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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16206
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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Maybe. have a 1999 sea ray with the 305 chevy motor. runs

Customer Question

Maybe. have a 1999 sea ray with the 305 chevy motor. runs good till it get a load put on it and then backfires trough the carb, I put new distributor and coil on it and still does it? when it does it the tack goes to like 6000 rpm when your only at 1800 to 2000.
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.

Hello my name is ***** ***** am I speaking with?

The tach needle is just a bad tach, and not related.

Popping back through the carb indicates what is called a lean fuel condition. Lean means not enough fuel, and it can mean a few different things.

1. Bad gas/old gas/water in the fuel

2. Engine is starving for fuel because of a restriction in the fuel system, or a weak fuel pump.

3. A leaking intake valve is pushing compression pressure back into the intake.

4. Carb is clogged up and now flowing enough fuel.

That being said, have you done any testing on your own yet? Run the engine off of another fuel source? How old is the gas?

Customer: replied 2 years ago.
Gas should be good we have ran 50 gal this year. it runs good until you try to pull a tube or get people in the boat. to me it seemed electrical cause the tachometer goes crazy when it starts doing it?
Expert:  Jason replied 2 years ago.

Well.... if the firing order was wrong, or the plug wires were so bad to the point they were cross firing that would also do it. But other than that jumping tach would just be a fluke. You can get a spray bottle and mist down the plug wires and see if you can induce a misfire that way .

When was the last time the engine ran correctly? Has it been sitting a long time?

Customer: replied 2 years ago.
Its runs fine a lot of the time, just starts acting up from time to time. I have ran it for 20 or 30 minutes with no problems then it starts doing it. seems like it even does it more when its warm. had thought it could be a sticky valve. idk .boat get ran pretty much every year.
Expert:  Jason replied 2 years ago.

A sticky valve wouldn't do it.

Here is what I would do if you brought it to me.

1. I would mist the plug wires down with water and see if I could get it to misfire or not.

If no change

2. I would hook up my own tank to the engine, and run it off of that and see if it clears up. Because the problem is intermittent, that would rule out a bad pump (they either work or they don't). If the engine runs better on my tank then I know there is either a fuel issue, or there is a blockage issue in the tank.

If no change

3. I would go ahead and rebuild the carb.

Plug wires are easy enough to rule in or out. But after that, if it is intermittently, that would point towards fuel being the issue. Be it bad gas, a blockage in the tank, or a clogged carb. Those would all cause a lean fuel condition to engine, which gives you the popping. Does that all make sense to you?

Expert:  Jason replied 2 years ago.

I think that should do it. But I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the start and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you

Customer: replied 2 years ago.
yep, that does, Gives me some things to try anyway? other then i don't understand why the tach goes crazy and always seems to be when it starts doing this.
Expert:  Jason replied 2 years ago.

A misfire in general can cause the tach to do crazy things. But mist the plug wires and see what happens, as that would actually explain both symptoms.

Expert:  Jason replied 2 years ago.

Was there anything else?

Customer: replied 2 years ago.
No, gives me things to try.
Expert:  Jason replied 2 years ago.

Very good. Feel free to reply back at any time. And please do not forget to put through a rating for me. The website will not credit me until a rating is done.

Thanks again,

Expert:  Jason replied 2 years ago.
Hello, just checking in. I see that no rating has been put through yet so I wanted to make sure I got all of your questions answered. If there was anything else on the issue feel free to ask.
Thank you,