Cold vs. Hot compression numbers.
#1
09-21-2018, 09:47 AM
Cold vs. Hot compression numbers.
1997 FLHR, screaming eagle airbox, slip on mufflers, EV13 cam.
Cold compression: 150 front, 160 rear
Warm: 135 front, 150 rear
I was expecting to see these results reversed... higher compression with the warm engine.
The carb was recently rebuilt and I’ve been waiting since Tuesday 9/11/18 for a new slide needle. (USPS slowed due to Hurricane Florence.)
The spark plug on the rear cylinder is loading up, very black and a bit oily. The plug on the front cylinder has one spot near the electrode that’s a bit black, the rest of the plug is a nice dry cream color. WTF?
Cold compression: 150 front, 160 rear
Warm: 135 front, 150 rear
I was expecting to see these results reversed... higher compression with the warm engine.
The carb was recently rebuilt and I’ve been waiting since Tuesday 9/11/18 for a new slide needle. (USPS slowed due to Hurricane Florence.)
The spark plug on the rear cylinder is loading up, very black and a bit oily. The plug on the front cylinder has one spot near the electrode that’s a bit black, the rest of the plug is a nice dry cream color. WTF?
#4
09-21-2018, 10:59 PM
Join Date: Aug 2008
Location: Lafayette, Louisiana
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Originally Posted by Kingglide549
When you talk about carbs here and AFR ratios we all have to stop guessing, or continue dwn the same path.
People as devoted as they are top helping you will be just guessing too.
People as devoted as they are top helping you will be just guessing too.
#5
09-22-2018, 03:40 AM
I was really looking for some input on the odd compression numbers.
The dramatic difference in the color of the plugs can be explained by an intake leak on the front cylinder. I replaced the manifold seals last week, but I could still have a leak.
I checked for leaks using a propane torch and didn’t find any. I’ve never used a torch to check for leaks before, but thought it would be a bit less messy... I’ll check again using starting fluid.
I’m fairly sure I have an issue with the slide needle, so I’m waiting on a new one from CVP and I’ll be changing the main jet to a 180 when the new needle arrives. I’m not too concerned with the carb being rich or lean at this time, I’ll get this right soon enough.
I’m planning on taking off for a few days of riding on Tuesday, surprisingly she’s running okay.
I’m concerned with the compression going down when the engine warms up. I just don’t know if I could have something going on that could cause damage, beyond a fouled plug, and hopeful someone could explain this condition.
Sorry for muddying the water by including the carb issue with the compression question... but I’m not sure they couldn’t be related.
The dramatic difference in the color of the plugs can be explained by an intake leak on the front cylinder. I replaced the manifold seals last week, but I could still have a leak.
I checked for leaks using a propane torch and didn’t find any. I’ve never used a torch to check for leaks before, but thought it would be a bit less messy... I’ll check again using starting fluid.
I’m fairly sure I have an issue with the slide needle, so I’m waiting on a new one from CVP and I’ll be changing the main jet to a 180 when the new needle arrives. I’m not too concerned with the carb being rich or lean at this time, I’ll get this right soon enough.
I’m planning on taking off for a few days of riding on Tuesday, surprisingly she’s running okay.
I’m concerned with the compression going down when the engine warms up. I just don’t know if I could have something going on that could cause damage, beyond a fouled plug, and hopeful someone could explain this condition.
Sorry for muddying the water by including the carb issue with the compression question... but I’m not sure they couldn’t be related.
Last edited by GOGOBECK; 09-22-2018 at 03:41 AM.
#7
09-22-2018, 04:56 AM
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#8
09-22-2018, 05:07 AM
Banned
What is the problem?
If the AFR is being suspected one has to start somewhere with real facts.
Use a meter with two inputs and it becomes a process of elimination.if suspected.
That is my natural inclination, as I hate guessing carburation when it is not necessary anymore.
It is just caveman!
.For this case I would start with an leak dwn test.
Last edited by Kingglide549; 09-22-2018 at 05:12 AM.
#9
09-22-2018, 08:54 AM
Seasoned HDF Member
#10
09-22-2018, 09:40 AM
I’m at 98k miles and never been into the motor, just the cam change 21 years back.
The two plugs showing different things is totally new... Just happened after installing a carb kit. Prior to this both plugs were a bit black and sooty, but not overly so and no wetness.
I don’t have the equipment to do a leak down test. But I’m not opposed to purchasing one... any recommendations for an economical and effective tool for this?
The two plugs showing different things is totally new... Just happened after installing a carb kit. Prior to this both plugs were a bit black and sooty, but not overly so and no wetness.
I don’t have the equipment to do a leak down test. But I’m not opposed to purchasing one... any recommendations for an economical and effective tool for this?
