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  1. #1

    Default 1998 C40TLRX slight surge

    Hello this is a tough one for me to figure out. I have a 1998 C40TLRX with 307 hours. Compression is 129/128/129 (T-B) and it has a clean and strong flow of water through the indicator.
    When I run the motor it will idle perfectly, hole shot well and then somewhere between 2700-3500 rpm it has a miss that makes it run just a bit off with intermittent small surges which during the 3-6 second surge it runs perfect. Also if I punch it it responds well and will run up to 5500rpm but still seems a bit off in performance. It has from time to time bogged down with a harsh vibration, when this happens I bring the rpm down to idle speed 7-800 rpm while still in gear. Give it gas and it runs fine but still has a slight miss. At idle or sub 1200rpm, in or out of gear it runs flawlessly. Starts perfect also every time. It seems to also be using a lot of fuel, while I haven't analysed it yet, an educated guess would be about 8 gallons an hour. I have cleaned the tank and filters, drained the carbs, checked the gap on the plugs and replaced the fuel pump. Ran it at night to look for dancing spark and it is good. One thing I did notice, when it started to act up I pumped the primer bulb on the tank and while it did not affect the performance of the engine, the bulb itself seemed soft and easy to pump, not rock hard and feeling full (Your welcome if that comment made you snicker) I did check all the clamps on the fuel lines and they were tight. Any ideas? I have not pulled the carbs yet for a cleaning. wanted input before doing surgery. Thanks. I always do followups for future readers when I ask a question.

  2. #2

    Default Re: 1998 C40TLRX slight surge

    Quote Originally Posted by BAS View Post
    I have not pulled the carbs yet for a cleaning. wanted input before doing surgery.
    I'm thinking you've got debris clogging 1 or more jets in 1 or more of your carbs. You've got good compression and good spark. The 3rd out of 3 systems left to troubleshoot is the fuel system. Which ironically, accounts for 90% of all outboard issues. Pull carbs, pull jets, thoroughly clean so when you hold the jet up to the light you can see through it. Verify spec height of floats, as well as test that floats are not damaged (leaking).

  3. #3

    Default Re: 1998 C40TLRX slight surge

    Rebuilt the carbs, there was some trash in the #2 HS jet. Put boat in water, runs worse! Lol. So I started trouble shooting and confirmed the proper flow and lack of leaks in the fuel system. Backed mixture screws 1.5 turns as per Yamaha factory manual. Trouble shot the ignition system and everything but the trigger under the flywheel checked out. It has at 227 and 228 ohms,highest spec per cdi is 220. Im assuming this is my issue even though all coils are firing a 3/4" blue spark. Whatcha think? Also did some searching and cant find a "trigger" is this known as a "pulser" also? Again this is the unit with the white wires with stripes colored R/G/B. The CDI unit checkes out for resistence anyway. i do have a DVA tester but stopped at the trigger when I saw it was oo spec
    Last edited by BAS; 09-25-2017 at 07:57 PM.

  4. #4

    Default Re: 1998 C40TLRX slight surge

    Got my DVA out and tested the system as per spec at crank w/ fresh battery. The CDI and Coil were in spec but the Pulser - "Trigger" was firing at 1.45-1.85v on each lead. Spec is 3.0 at cranking which calls for replacement. Will replace and report findings when installed, unfortunately I have to wait for the part so it could be a few days.

  5. #5
    Join Date
    Dec 2015
    maplevalley WA

    Default Re: 1998 C40TLRX slight surge

    Sounds like your getting close did you check/adjust engine sync after installing the carbs? Sync between spark advance and throttle pickup.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  6. #6

    Default Re: 1998 C40TLRX slight surge

    Yes, and checked to make sure the "wand" on the cdi was aligned at bottom and top of throttle

  7. #7

    Default Re: 1998 C40TLRX slight surge

    Feel pretty confident it is the Pulser. Ran in tank [email protected] 1500rpm and got 3.22v peak on DVA. Spec is 9.0 @ 1500rpm. At lowest throttle speed is 600rpm (+/- 25rpm) got 2.25v. Got 1.45 at crank, spec is 3.0 These #s are out of spec. The only thing that troubles me is all 3 leads (one pulser per cylinder = 3 pulsers), were all within .25-.50 of each other. I would think one would be bad, unless the unit rectifies the output and sends an balanced voltage to the coils on each individual lead.
    *edit for clarification*: I dont have a 3 pin adapter so I have to test each lead coming off the tested component individually, in this case the pulser has three pins. each pin was tested for ohm and voltage separately while running, cranking and off
    Last edited by BAS; 09-26-2017 at 04:14 PM.

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