Johnson 70 misbehaving at high altitude

[jhotch]

Been working on this all summer. Engine surges at wot. I am trying to understand the mechanics of the carbs behavior. I can eliminate the surge by pumping the primer hard. Engine is from sea level and brought to '6500 feet. Could the carb jets be allowing so much fuel to leave the bowl at wide open throttle that the fuel pump cannot keep up at wot which is causing the up and down surging? ignition system is good, fuel system is good, carbs are clean and delivering fuel equally, link and sync is good.
My kids and I started with an abandoned whaler from the woods and an old engine, so close but this last inch has been the longest mile.

 

[racerone]

Any pictures of the fuel pump ?----At 6500' you need to make carburetor jet changes.----Your local boat shop should help.

 

[jhotch]

[No message]

 

[jhotch]

Racerone, one more piece of information. The guy I bought it from in Bullhead City was using an electric fuel pump

 

[racerone]

These pressure operated fuel pumps are very good / very reliable.-----No idea why someone would go to an electric pump !

 

[oldboat1]

need a shop up at your elevation -- will know what you need before you even ask. Flagstaff? Trouble is, you will need to change out jets if you go boating at a lower elevation,

An abandoned Whaler is quite a find -- sure nobody is looking for the guy who discovered their high country camp boat?

 

[jhotch]

lol, not found like that. It was lying in the trees on a property a friend purchased. Sat there for years and he begged us to haul it off. Turned out to be a 1990 mischief ‘15 My kids stripped it down and we repainted an restored everything. Turned out beautiful! I will find the right jets and sure appreciate the feedback.
I guess I am trying to understand cause and effect. With the jets too large, is the carb bowl being emptied at wot which is causing the up and down surging?

 

[racerone]

I do not believe it is an issue with the jets being too large.------Do more trouble shooting on the fuel pump and crankcase PRESSURE that drives the fuel pump.

 

[Sea Rider]

Carbs intended to work at sea level won't perform good at high elevations, at 6500 feet will need to re jet the carbs for smaller size jets from current installed ones. Don't know if Jonyrude has them, Merc used to have them in 1K increments, aside from smaller jets will need at least to go down 1 pitch size to increase the wot rpm range, won't run as a champ, but much better if doing nothing. The bummer is that will need to install back the original jets when at sea level or risk damaging the motor...

Happy Boating

 

[racerone]

Talk to any good boat shop and they can find the carburetor jets you need.-----Yes BRP factory manuals have the part # for the size you need.

 

[jhotch]

As far as the fuel pump and pulse, fuel pump should be good, not sure how much farther I can dig into it, are there simple tests I can do? The pulse line is a little long because of my fuel pump placement, 6 inches or so, and I’m not sure how to test that either... I bought a 4-7 lb electric pump to try and see if that is able to deliver enough fuel, I don’t want it to be my primary pump, but will have it as a back up.
I read about a guy putting guitar strings ,which have a fixed small diameter , into the high speed jet to test for different jet sizes efficiency. Anybody heard of this? He says he just leaves them and then pulls them when he heads to mexico in the winter.

 

[Faztbullet]

That Chinese Amazon pump will live about 1 hour before it becomes usless as the rubber check valves (yes rubber) swell and dont seal. The Phillips heads screws give it away. Only use the EMP or Serria replacements.

 

[racerone]

Just installed a fuel pump repair kit on a 1970 model 60 HP Johnson.-----Beautiful stainless check valves.----Who needs pumps from the ------HOOFLUNGDEDUNG-----Company in a far away land !!

 

[jhotch]

ok does anybody have a part #? I will replace that pump with a sierra and I think I’ll experiment with the guitar string method to get an idea on the jets. As far as propping down a pitch, how do you know what pitch you have? Are they stamped somewhere?

 

[racerone]

If you can not find a number on your prop then perhaps you need to visit your friendly boat shop for help.-----The " on line " part sellers may not have the boat knowledge to help you !!!

 

[jhotch]

Thanks for all your help Racerone and all, truly appreciate it!