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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16102
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 115hp Yamaha saltwater series V4. It is very difficult

Customer Question

I have a 115hp Yamaha saltwater series V4. It is very difficult to start even when warm, running really rough, backfiring, stalling and now and then is not smooth off the mark when throttle is engaged.
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello my name is ***** ***** am I speaking with?The engine requires some testing in order to figure out what is going on with it. What were you looking to do here? What kinds of questions did you have for me?
Customer: replied 2 years ago.
What is the next step in diagnosing the problem? Last time I went out after driving for almost an hour I could not get the engine started for 20 minutes. I had to use the manual choke and fast idle to get it going. When I flushed it that afternoon it was running very rough, backfiring and stalling. This has been going on for over a year. I want to be able to take my family out on the boat and not have to worry that it is not going to get us home.
Expert:  Jason replied 2 years ago.
Good morning. The engine needs compression, timed spark ignition and the proper ratio of fuel to air. If you have to keep it choked that is a pretty good hint that the carbs are clogged or the gas is bad. (or both). But in the shop I would go through the motions and check compression and spark first. Here is how I test them. 1. Compression test. - Results should be about 90psi or better on that engine, all cylinders should be within 10-15% of eachother. If you get much below 90, then the engine is worn out or has mechanical problems, and you might as well stop your troubleshooting here, as there is nothing you can do to an engine with low compression to make it run better. 2. Spark test. A timing light or a spark tester can be used here. These are the testers we use in the industry. you can also get cheap spark checkers at most good autoparts stores.You need to hook the spark tool up and set the gap to 7/16ths of an inch. The spark should easily jump that gap, be hot and blue in color, and be consistant with engine rpms. Weak looking yellow spark will not cut it. If you find no or weak spark on any cylinder, the ignition systems individual components will need more troubleshooting. 3. Fuel test - Pull a sample of it and put it in a clear jar overnight. In the morning, look for any kind of dirt/debris/water in the fuel, or any kind of separation line. As contaminated or old fuel simply does not burn as it is supposed to. 4. Fuel supply test - Run the engine off of another fuel tank. If it runs better. The gas is bad. If no change, pump the primer bulb over and over, if the engine picks up, the fuel pump is bad. If not change after all the above. It's a safe bet at this point the carbs are clogged, and need to come off and be rebuilt. I think that should do it. If you had a further question on the issue by all means feel free to ask. If not, Just incase 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. 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 tomorrow or next week with follow up questions to this you still can even after doing a rating. And if I have saved you quite a bit of money, or saved you a trip to the dealer, tips are always greatly appreciated.Thank youJason
Expert:  Jason replied 2 years ago.
Hello. Just checking in. No rating has been put through yet so I wanted to make sure that all your questions were answered. Did you have any further questions on this issue?