Compression Test

NRA223

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May 20, 2015
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A few months ago Injector #7 was showing a -5ish balance rate and i was getting intermittent smoke on start up, hard cold starts, and occasional hazing. This is on a set of new Exergy 30 overs that were installed in February. I started getting paranoid about my rods, but was told it was most likely a sticking injector. I replaced the fuel filter and started running 2 cycle in every tank and after about 2 tanks the rate was back with in 2.0. Fast forward a few months, the intermittent smoke on start up is back and injector rate is back to -5ish and i am nervous about a bent rod again. Should i get a compression check or is there a better avenue to check first?
 

Awenta

Active member
Sep 28, 2014
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No amount of 2 stroke would straighten a rod. A rod usually maxes out the balance rate.

Are you using ashless 2stroke? I would recommend a diesel additive instead. Did you just run it then or regularly?

Swap that injector with another and see if the rate follows it.

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Harbin_22

Active member
Dec 4, 2010
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Southern Indiana
I ran a compression test on my stock engine when I was having cold start smoke. All were right around 390#. 2 days later blew a rod out of the side of the block.
 

NRA223

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May 20, 2015
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The 2 stroke oil was used based on the suggestion that it could be a stuck injector, and it seemed to work for a while.

So Harbin, you think the compression check wouldn't tell me anything since yours checked fine until failure?

Ne-max, i am running the same tune as i was then, would it still change it?

Is cylinder #7 the driver side rear cylinder?
 

Ne-max

I like turtles
Nov 15, 2011
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The 2 stroke oil was used based on the suggestion that it could be a stuck injector, and it seemed to work for a while.

So Harbin, you think the compression check wouldn't tell me anything since yours checked fine until failure?

Ne-max, i am running the same tune as i was then, would it still change it?

Is cylinder #7 the driver side rear cylinder?

7 is driver side rear. I would say yes on tuning if you went bigger.
 

NRA223

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May 20, 2015
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After the Manifolds and up pipes were installed i started noticing a ticking sound that sounds like an exhaust leak that sounds like it is coming from the rear driver side cylinder. I have had 2 shops look at it and nobody can find an exhaust leak. Could this be a related issue?
 

Bustedknuckles

Honey Badger
Sep 25, 2010
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Hagerstown MD
Where are you located? A good tech can do a compression test without even getting his hands dirty using a amp clamp. It won't work if all cylinders are low but will tell you if you have a bent rod or 2. It does sound like an injector issue though.
 

Ne-max

I like turtles
Nov 15, 2011
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Lincoln, Ne
I would personally start with a compression test. Will take little time to do. If that checks out good then swap that injector with another.
 

Bustedknuckles

Honey Badger
Sep 25, 2010
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Hagerstown MD
After the Manifolds and up pipes were installed i started noticing a ticking sound that sounds like an exhaust leak that sounds like it is coming from the rear driver side cylinder. I have had 2 shops look at it and nobody can find an exhaust leak. Could this be a related issue?
Tape a shop vac to the exhaust and set it to blow. Listen for leaks or dump powder of some sort around the manifolds and watch for being it being blown around. Works like a charm! I had a tick like that and it turned out to be an injector copper washer not sealing btw.
 

Awenta

Active member
Sep 28, 2014
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CT
Turn off that stick and see if goes away

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Awenta

Active member
Sep 28, 2014
4,090
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CT
What I meant with the two stroke is that if it was a bent rod then adding two stoke wouldn't have make the balance rate better.

Assuming you used new coppers?

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TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
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You could still be leaking slightly at an uppipe flange. it happens.

Really like Busted's shop vac idea. Ingenious. You've got to describe the amp-clamp compression test, though.

2stroke doesnt "cure" a bad injector, it just helps give you more time. I think you've got one on the way out is all.