Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

[Manoj77]

Thanks to the help of many of you on this forum Ive tweaked out the minor initial issues I had with my recently-purchased used 2011 Tohatsu 6HP 4 Stroke. I had a great weekend fishing with it BUT I did notice one remarkable change in performance that I am guessing is due to the alitude of the lake Iwas fishing as compared to where I was first using the motor. I initially used the motor on the mouth of the Fraser River in Delta, BC , Canada (elevation =0). I could get it to plane my 12 foot Jon boat and I was more than impressed with the power.

Last weekend I took it to a lake in the BC interior of an altitude of 3700 feet.The motor would start first pull but I did notice a notable drop in power; difficult to estimate quantitatively but as a guess I would say 15% perhaps? The engine also was no longer purring as it did at elevation 0 but instead sounded like it was simply running at a slower rpm at any given throttle position. 3700 feet is not that high so I am wondering are the changes I noticed due to altitude or possibly some other issue in this 'used' motor?
Thanks

 

[TOHATSU GURU]

Re: Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

Your engine is drowning in fuel. It requires high altitude jets above 3200 feet.

 

[fishrdan]

Re: Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

HP will drop about 3% per 1000', so you were down on power about 11%. The only reasonable way to get performance back is to use a prop with less pitch, though 3700' isn't really all that high. There are other things that can be done, but not recommended for occasional trips to high elevation due to difficulty, carb and timing.

 

[Manoj77]

Re: Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

I dont mind tweaking the carb if you have any suggestions. Im heading back there this next weekend so please let me know your suggestions. I doubt if I would be able to get a high altitude carb kit by then though.

 

[TOHATSU GURU]

Re: Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

They are available from any Nissan, Tohatsu, Mercury or Evinrude dealer. So, you either replace the jets or live with a powerloss.

 

[pvanv]

Re: Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

For high altitudes, you would run:

3AU044680M MAIN JET #68, F3.5A/B/6B $7.56
3R6032540M PILOT JET #35 $7.44

Some people who travel frequently between high and low altitudes will buy a spare carb, and jet it for high altitudes. Then it's just a matter of a 5-minute carb swap to change over.

Or... they just pitch a little less, run hard, and after the weekend trip, change out the sooty plug.

 

[Manoj77]

Re: Altitude affects on Tohatsu 6HP 4 Stroke - elevation 0 vs 3700 ft?

The lake I fish is around 3700 feet. I guess I will just go with the power loss rather than swap out jets each time I am back fishing at sea level. I will bring an extra plug just in case. Not sure how fouled up my plug will get. I just put a new one in about 5 running hours ago so as a precaution I will clean before I go to the lake this weekend. Hopefully that will suffice.