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Dominick
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 1994 yamaha 700S waverunner starts right up idles

Customer Question

i have a 1994 yamaha 700S waverunner starts right up idles fine when i throttle it up it starts backfireing what could cause it
Submitted: 8 months ago.
Category: Boat
Expert:  RSRBOB replied 8 months ago.
Hi and thank you for your question.I need some more information to be able to assist you. Please answer the following questions.1, When did the problem show up? Were you out riding it one day and everything was fine, shut it off, then went to re-start it and it developed this problem or did the ski run fine the last time you rode it, then it sat up for awhile and hasn't run right since?2, Please remove the spark plugs and tell me what they look like on the business end.3, Please do a compression test and let me know what the results are. Remember, when doing a compression test on a 2 stroke mutli cylinder engine, you must leave the 2nd spark plug in while testing the other cylinder.4, Look at the fuel filter and see if it appears to be full. Also look for signs of water in the bottom of the fuel filter. If you aren't sure about the water, remove the filter from the fuel line and dump the gas out into something like a spray can cap and look for water in the bottom of the fuel. Water in the fuel looks like air bubbles running around in the bottom of the container.5, Has any service work or repairs been done to the ski lately? If yes, please give specific details.ThanksRSRBOB
Customer: replied 7 months ago.
I traded for it I did put in carb kit and backed out high and low jets 3/4 to 1 turn when done filter is good plugs look new have good blue spark idles good just backfires when I throttle it up could it be carb adjustments or what else
Customer: replied 7 months ago.
I did compression test front and rear did 138 and held good then put a little in each cyl. hole and got 148 lb each
Expert:  RSRBOB replied 7 months ago.
Thank you for the additional information.So it sounds like it has never run right since you have owned it. Is that what prompted you to put the carb kit in? Did you happen to check pop off pressure? The compression sounds fine. It is a little low but that could just be the gauge you are using. It is certainly not a cause for concern at this point. The next test I would suggest is putting a timing light on the spark plug lead and run the engine while observing the timing light. See if you are losing spark as you warm the engine up.If you are not losing spark, there is definitely a carb/fuel supply problem.Thanks,RSRBOB
Customer: replied 7 months ago.
ok i need to hook a water hose to start it at home. there is no fitting for hose and cant find a diagram of cooling system to know where to hook it not shure what sends water thru engine
Expert:  RSRBOB replied 7 months ago.
Your particular engine will require the installation of a flush kit. They are inexpensive and very easy to install. Your local water craft dealer should be able to get one for you.

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