Compression test varies

[miket]

1998 115 Johnson<br />Hard starting and idling. Check fuel lines and cleaned carbs and new water pump, still no better.<br /><br />Compression result 110 in three and 95 in one.<br />Engine seems hot, noticed gasket leakage in low cylnder, spark plug seems ok not washed clean by water leaking in.<br /><br />Will this variance cause poor idle and hard start after warm up? Runs good at high speed.<br /><br />Thanks for any suggestions

 

[mikeyzx2]

Re: Compression test varies

it'll probably cause a crappy idle, and that one cylinder is borderline being out of whack with the others. might wanna look into the problem before it gets worse

 

[OBJ]

Re: Compression test varies

Mike...is this a looper or cross flow....Post the model number please.<br /><br />95psi in one seems a little low....if the leaky gasket is the head gasket, that would probably be the source of the low compression. If so, change it out.<br /><br />Don't think the one low cylinder would cause the rough idle. When you cleaned/rebuilt the carbs, did you soak them out and follow up with compressed air? This should be done. At least blow through the carb passages with canned choke and carb cleaner. New carb kits installed?<br /><br />If the engine seems hot, most likely is. Would check the t-stats and replace if they have never been done.

 

[miket]

Re: Compression test varies

OBJ Johnson 115 spl<br />Model xj115hxecm<br /><br />The carbs were spotless, all passages were clear. I did not use carb cleaner because i could see clear thru passages.<br /><br />Could compression effect fuel pump performance at idle?<br />Thanks

 

[OBJ]

Re: Compression test varies

Hey Mike....it's a cross flow.<br /><br />What you can't see is the built in passages in the carb....that's why we soak them out when rebuiding and blow through with canned carb cleaner. Every carb I do has the soft plugs removed and blown through with carb cleaner and compressed air after soaking. It's just a good way to do it.<br /><br />I'm more interested in where the gasket is that you said was leaking. Was it on the exhaust cover or the head gasket. We need to address that.......darn!...english language is gettin' pretty good here ain't it....anyways....we need to find out why you only got 95psi on one cylinder. If your looking at the back of the engine, which cylinder was it?<br /><br />And no....I don't think with the compression you got the fuel pump would be affected.

 

[miket]

Re: Compression test varies

Thanks OBJ<br />The top cylinder on the right side looking at back of engine. It's the headgasket at the top which showed residue from leakage.<br /><br />The engine seems to run hot, and when water stream slowed down to constant dribble I replaced the water pump, stronger dribble.<br /><br />I have new head gaskets and plan on replacing. Is it better to remove head bolts with the engine warm rather than cold?<br />Appreicated you help

 

[Solittle]

Re: Compression test varies

Hot or cold - makes no difference. <br /><br />While you have the heads off might want to replace the thermoststs & deflectors.

 

[miket]

Re: Compression test varies

I don't see deflectors on parts list. <br />Do you need to replace all of the components when replacing thermostats?<br />Thanks

 

[Solittle]

Re: Compression test varies

Yep - it is a pain in the butt job so might was well replace everything so as not to have to go back to it. There is a related post close by - might want to read it.

 

[Solittle]

Re: Compression test varies

Yep - it is a pain in the butt job so might was well replace everything so as not to have to go back to it. There is a related post close by - might want to read it.

 

[miket]

Re: Compression test varies

Head gasket off, damaged piston and divets in head. Also divit in one exhaust port.<br /><br />Rebuild?<br />Or buy remanufactured powerhead?