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Discussion Starter #1
I have an 89 head and 89 pistons in a long stroke engine. Here is what I have so far:
1-150lbs
2-135lbs
3-135lbs
4-120lbs
 

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I dunno what the #'s are for the 750, but for the `89 1100, the book says 170-199psi is "standard" 142psi is the low limit, and there should be no more than 28psi difference between cylinders. ie, the book says an overhaul is due of pressure is less than 142psi or if there's more than 28psi diff between any two cyls. Make *certain* that your valve-lash is set properly... You can pour a little oil on top of the pistons through the spark-plug hole and if the #'s jump up a lot, it indicates worn rings; if the numbers don't change much, it's a prob with your valves.

I don't have the manual for the 750; but the 30psi diff between #1 and #4 doesn't sound good...
 

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I have almost the same readings, My number 1 cylinder is 150 and the spark plug is a lot cleaner on that cylinder than on the rest. The rest are showing about 130. I was wondering if mine is bad as well. If I pour a teaspoon of oil on top it jumps a little bit up to about 150. I've got a 91 engine in mine though. The manual shows the same as the guy before 142-199, kinda scares me. Let me know what you find out.
 

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A compression check won't tell you as much as a leak down check, if you are worried about the state of your bores/valves/pistons/rings.
Rather than using the piston to provide the pressure, a leak down check uses an external source to pressurise the combustion chamber at TDC. Depending how much of this pressure is lost, the test equipment will give you a readout in % terms of how efficient your combustion chamber sealing is. I believe 95 - 96% efficiency is about the lowest you want to go. I had to go to specialised car racing workshop to have mine done, bike workshops don't tend to offer this facility, in the UK anyway. As far as your compression test readings go, they do appear to be a little low.

Steve.
 

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As stated above be sure that the engine is warm and be sure to hold the throttle wide open. You need to allow each cylinder to receive the same amount of airflow for good readings.

A leak down test is a good way to pinpoint what is wrong but you can do almost as much with the compression guage. The only difference is that the leakdown can tell you which valve is not sealing, a compression test will only point to the rings or the valves.

Also make sure your battery is in good condition and fully charged so that the cranking speed is equal when testing each cylinder.
 

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Discussion Starter #7
I think the problem is the rings. I put a little oil in the cylinder and compression went up some. I am going to tear down the top end and see what I find. The rings are new but on old pistons, I fear they might be sticking to the piston and not expanding like they should. I will let you guys know what I find.
 

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Originally posted by suzukiltd:
I think the problem is the rings. I put a little oil in the cylinder and compression went up some. I am going to tear down the top end and see what I find. The rings are new but on old pistons, I fear they might be sticking to the piston and not expanding like they should. I will let you guys know what I find.
<font size="2" face="Verdana, Arial">you have new rings? did you hone the cylinders?

did you run the engine for a bit yet?
 

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Discussion Starter #9
The cylinders were honed by Suncoast. The bike did run but only on 3 cylinders. I am getting nothing out of #4. I have spark and gas so I have started to look elsewhere fir problems.
 

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Just to confirm. My 86 750 had 165 psi and my 91 1100 had 185 psi. After a rebuild and a thinner copper gasket it had 225psi. 120 sounds weak to me but it should still fire. Was that cyl dead cold? Did you check for heat in that header pipe?

CT
 

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Originally posted by suzukiltd:
Dead cold. No heat on the header and the plug is clean, like new.
<font size="2" face="Verdana, Arial">As Yosh said.. Swap that plug AND swap the #4 for the #2 plug wire. They fire the same time so you can swap. I have had brand new plugs that would not fire. It should run on 120 psi. Plus. I bet the second it warms up its 150+

CT
 

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Discussion Starter #13
I checked the plug and it fires from the #4 coil wire. now what?
 

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Originally posted by azgsxr11:
</font><blockquote><font size="1" face="Verdana, Arial">quote:</font><hr /><font size="2" face="Verdana, Arial">Originally posted by suzukiltd:
Dead cold. No heat on the header and the plug is clean, like new.
<font size="2" face="Verdana, Arial">As Yosh said.. Swap that plug AND swap the #4 for the #2 plug wire. They fire the same time so you can swap. I have had brand new plugs that would not fire. It should run on 120 psi. Plus. I bet the second it warms up its 150+

CT
</font><hr /></blockquote><font size="2" face="Verdana, Arial">Um, actually... #1 and #4 are the same coil, and #2 and #3 are the same... do NOT swap #4 with #2 ...unless, of course, you have a fire extinguisher handy. (Don't ask me how I know this).

...and Oh yeah... compression checking an engine that isn't broken in yet will give low and erattic numbers... I didn't realize you had new rings in the thing.

[ 06-11-2002, 11:37 PM: Message edited by: FastCat ]
 

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Discussion Starter #16
Dead cold. No heat on the header and the plug is clean, like new.
 

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Discussion Starter #17
...and Oh yeah... compression checking an engine that isn't broken in yet will give low and erattic numbers... I didn't realize you had new rings in the thing.
<font size="2" face="Verdana, Arial">I figured on that. I have been using two sets of carbs. First I used a set of Mikuni 36 flatslides then switched to Mikuni 33 (stock carbs) and I get the same problem with both. When I put my hand over the carb I don't get a lot of suction on #4, I thought that maybe because compression was so low it was not pulling enough gas into the champer to fire but everyone says it should run on 120lbs. It just dosen't make any sence. Now what?
 

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I like to use a can of that quickstart stuff

if you shoot a blast of that into the bad cylinder and it still won't run then you are fooked
 

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suzukiltd, before you tear your engine down again, pull the spark plug your having problems with and with a insulated pair of pliers, hold the wire with the plug in it to the block and turn the motor over to see what kind of spark you are getting. you may have already done this, but if not, it doesn't hurt to try. if the plug is clean in that cylinder and the header is not getting hot, it can be only two things, no gas or no fire. i have seen many bikes with tons of miles on them with low compression still fire.
hope this helps!


[ 06-12-2002, 11:21 AM: Message edited by: cide ]
 

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Discussion Starter #20
I did check the spark and it was a nice bright blue, so I know it is firing. I know it is in time because it will run on 3 cylinders and its not backfiring. I didn't even think of the starting fluid, I will try that and see if it comes alive.
 
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