05-18-2014, 03:40 PM #1
- Join Date
- May 2014
93 Polaris 750sl odd compression and running strange
Would first like to say its nice to have a board around like this to help out newbies like me this is my first post here and I would like to say thanks in advance for the help.
I bought 2 skis about a month ago, a 93 750sl and a 96 1100 zxi. Both were sitting for three years so first on the agenda was drain old fuel, rebuild carbs and drop in new fuel and plugs. Zxi is oil injected the polaris is premix. Got that all done....dropped in new batteries and got them running. The polaris ran but seemed a little off. The zxi seemed to run great....this was out of water of course. I finally got them to the lake this past week and it went as expected. The zxi ran awesome, the polaris not so much. The polaris started right up but wouldnt get past 5 mph and die under just about any throttle, then for some odd reason I decided to pull the choke and seemed to get up to 25-30mph depending on where I had the choke ( 1/4 out 3/4 out). I figured this was a fuel starved issue, we loaded the skis up and came home. I checked the air/fuel mixture settings and the screws were turned almost all the way in, maybe 1/4 turn out on both hi and low. I adjusted them to 1 and 1/2 turns out which is stock if I'm correct? The polaris now (out of water) seems to run ALOT better! I tested the compression today and got the following results: pto 85 cen 80 mag 85.....these immediately seemed low being as 120 is the norm but would my elevation play a role in this? I am at 6500 ft. My zxi was 85 across the board and it runs perfect so I'm assuming its the elevation making the compression lower. Thanks in advance for the help!
05-18-2014, 04:46 PM #2
- Join Date
- Jul 2007
- near Toronto, Canada
Is your compression gauge accurate?
At 6500 feet elevation there are special specifications for the carburetors. Somewhere on here you can find the standard carb settings for that engine. And somewhere are the high altitude carb settings.
When you rebuilt the carburetors did you check the jet sizes? Was this Polaris previously owned and used at your altitude?
Did you verify carb arm height while they were open?
And verify carb pop-off pressures after re-assembly?
Correct spark plugs installed?
BTW, have you looked through my signature links? Lots of useful info there.
05-18-2014, 05:13 PM #3
- Join Date
- May 2014
Thanks for the fast reply! The original gauge we used to test the compression was a little rough so I got another and it gave the same readings. I havent verified pop off pressure yet, im still in the process of getting a pop off gauge. The skis were used at this altitude before and the previous owner stated it was running lean on the polaris. I did take all the heads off and inspected the cylinder walls and head gaskets along with the top of the pistons really well, all looked good. When rebuilding the carbs I tried to match the pop off springs exactly when i swapped for the new ones. Im using ngk br8es .032 plugs. I forgot to look at the jets when I had the carbs apart, kickin myself in the butt now. I will look through your links for compression info thx.
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