Continued problems with Yamaha 70TLR

[by0609044]

Hi everyone,
Long time lurker here but after continued problems with my 2 stroke Yamaha 70TLR, I feel compelled to make this post hoping someone will be able to help me with this problem. Here is the rundown:

My Yamaha 70TLR loves to violently shake at rpms lower than 1700, so bad that it makes all the screws in my hull come loose, even with 5200. It runs amazing at higher rpms and at WOT and doesn't have any problems getting up onto plane. It is extremely uncomfortable *****ing and going idle speed however, and I try and avoid bringing passengers since my motor is a tooth breaker. Here is a list of everything I have done to it to try and solve the issue:

Fuel
- Replaced all fuel lines and connections going from the tank to the motor
- Replaced fuel pump
- Replaced fuel water separator
- Stripped and rebuilt carbs with ultrasonic cleaner
- Have replaced fuel/air mixture screws
- Flushed gas and ran ethanol free fuel
- Ran seafoam

Electrical
- New spark plugs (gapped)
- New spark plug boots and coils
- Timing adjustments with gun
- Cleaned grounds
- New batteries
- Multi-meter tests on everything stated in the workshop manual

Other
- New propeller
- New lower unit
- Good compression

As you can see, I have pretty much replaced and tested everything on this motor that I can think of and it still runs like garbage below 1700 rpms. I am almost at my wits end trying to solve this and am about to scrap the motor. I know 2 stroke 3 cylinders run rough, but I have been on boats with the same motor and they definitely don't shake bolts loose. Any suggestions are welcomed and I appreciate any and all advice you guys have to offer. Thanks so much and I look forward to potentially solving the issue!

[Keithbaja]

Installing idle screws ?? How about fine tuning them ??

[99yam40]

pilot screw settings ,jets, or passages still have a problem if there is good spark and timing at idle
is this severe shacking coming from lean sneezing on one or more cylinder?

did you follow the link and sync procedure in manual when re installing the carbs?
if all carbs are not opening exactly the same it will cause a problem

[by0609044]

Installing idle screws ?? How about fine tuning them ??

manual calls for 1 1/4 turns out +- 1/4 so tuned according to the manual. I’ve messed with the mixtures a lot and nothing seems to help

[by0609044]

pilot screw settings ,jets, or passages still have a problem if there is good spark and timing at idle
is this severe shacking coming from lean sneezing on one or more cylinder?

did you follow the link and sync procedure in manual when re installing the carbs?
if all carbs are not opening exactly the same it will cause a problem

I wouldn’t say it’s a lean sneeze, I have had the screws out making more rich than it ever should be and it still behaves the same. Ever since I rebuilt the carbs with new parts, I have ran ethanol free fuel. Didn’t make a difference before and after I double dipped the carbs in the ultrasonic cleaner. My next angle of approach are the reeds.

[Keithbaja]

Lunch break for me.. U might try the plastic bag or hand trick over each carb and sea what the results are....

[99yam40]

I wouldn’t say it’s a lean sneeze, I have had the screws out making more rich than it ever should be and it still behaves the same. Ever since I rebuilt the carbs with new parts, I have ran ethanol free fuel. Didn’t make a difference before and after I double dipped the carbs in the ultrasonic cleaner. My next angle of approach are the reeds.

if there is a problem with jets or passages, the screws in or out have no effect

I have never seen a motor that will vibrate that hard without it lean sneezing.
normal miss firing does not cause that kind of vibration.

can you post up a link to a video?

[ausnoelm]

Check spark on ALL cylinders, make sure it has spark all the time (especially the middle cylinder) then clean the carbs properly, don't "fiddle" with stuff.

[brian3006]

Have you syncing the carbs? one could be allowing more fuel than the other one causing a cylinder imbalance