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Discussion Starter #21
did you say if the bike has ever had the valves adjusted? low compression doesn't automatically mean it's a bad motor. stuck open valves etc can let all of the compression out.
I just checked the valves and 15/16 were in spec, and one of them was just ever so slightly too large. (max of 0.2mm, able to just fit 0.203mm feeler gauge in)

Intuit - the bike has 26k miles...Although my title lists the miles as 0, as did the previous owner's. Is it possible the bike had way more and the previous owner bought a new lower mile dash for it?

Thank you!
 

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The other thing that can cause low compression, is the engine timing being off. It's something to check, but it wouldn't address the 30 PSI variance between some cylinders.

Re title, maybe there's some other reason like it's not required and/or the title agency clerks can be too lazy to go out and perform an inspection. Regardless, gauges are easily swapped and the overwhelming majority of bikes in the rust belt and northward, do a lot of sitting with far less mileage. If they swapped it, the could've done better.

It may have been modified and/or beat to death. A lot of people don't realize that more power, more especially when not properly tuned, is not free. The cost is additional or even rapid engine wear.
 

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Discussion Starter #23
Hello!

I did a leak-down test. Not sure the percentage but it was lower than anything on the chart that came with the tester. Cylinder one was leaking very badly from the intake valves, and also through the piston rings. The other three cylinders seemed okay through the valves but leaked bad through the rings.

Good call, Intuit - I think my timing was off by one tooth! With the cam timing marks perfect, my pickup rotor (?) had it's timing mark pointing about 1/4" above the line where the case meets.

My timing chain tensioner seemed to be in decent condition, along with all chain guides. Maybe it was put together incorrectly by the previous owner and I've had improper timing the last 6000 miles? Do the timing chains ever slip on these bikes?

Started digging into the motor and got some pics for ya guys. There is still crosshatching visible on the cylinder walls. Overall it's better than I was expecting it to be.

Considering that my timing was slow, could that have caused the rich looking buildup on the plugs and in the ports? Apologies if that's a dumb question, can't say I really know what I'm doing hehe!

I'm planning on lapping the valves and putting in new piston rings. Put together a parts order of everything that the service manual said to replace. Came out to $550. Heck!

Should I replace crankshaft bearings? Also, are the OEM piston rings the way to go or should I look elsewhere?

P.S. Dropping the engine out without any sort of lift is a damn tricky one person job hehe. Motors are heavy!
 

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Discussion Starter #26
Hi all!

It took me a bit more than I month but I got the engine rebuilt. New piston rings and seals. Also replaced the timing chain. I then sent the head off to a machinist to do a pro valve job and clean out the ports of all that carbon. He also resurfaced the head as well!

Got the engine put back together and after 100 miles it seems to ride exactly the same, and now my compression is at 85, 90, 85, and 90 psi over the cylinders. More consistent but almost exactly the same as before. Those 100 miles later and two plugs came out very sooty, and two of them came out fairly black but lighter on the tips.

At this point I'm quite out of ideas.

(Also unplugged the power commander after rebuilt, no major change and left it unplugged to simplify things)
 

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At this point all assumptions are out the window. If that was the compression readings post rebuild and before running it, something's not right. Have to go back to the absolute most basic things. Have someone else run the compression testing using their own tools. I'd look at exactly how the timing marks line up, and consider whether it's somehow possible that the intake and exhaust cams were switched during the install. We can't even assume that the cam lobes and valve stems were measured.
 

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Discussion Starter #30 (Edited)
At this point all assumptions are out the window. If that was the compression readings post rebuild and before running it, something's not right. Have to go back to the absolute most basic things. Have someone else run the compression testing using their own tools. I'd look at exactly how the timing marks line up, and consider whether it's somehow possible that the intake and exhaust cams were switched during the install. We can't even assume that the cam lobes and valve stems were measured.
As for your suggestions, I did take pics of the timing marks before I sealed it all up. T with line on pickup rotor pointing to case split, then the I and E with respective marks on the outside of the top of the head. The exhaust cam has the extra ring in the middle, visible in picture 1.

I think you're certainly right that something is not right. You're correct that I did not measure the cam lobes, and I also did not measure the valve stems. The cams seemed to be in reasonable enough condition but I could certainly be mistaken. As for the valve stems, I did buy some shims and adjust the valve lash as I was putting it together if that covers the valve steam measurement? Or are you referring to the diameter / runout of the post?

Probably a good call on letting someone else do the test. I looked up some price estimates and for $200 I could probably buy a snapon compression tester, but it could be that I'm the problem. The compression test is fairly close between my two different testers and I am holding WOT with all the plugs out and a charged battery.

The bike does certainly start, run, and easily pull up to 100mph. My compression, at less than half the spec, I'm curious if it would even run if that's actually the compression.

In the next couple days I'll do another leakdown and see if that turns anything interesting up.

Thank you for the responses!

Hunter
 

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Discussion Starter #31 (Edited)
Gosh, one other thing I noticed. I had the power commander plugged into my laptop.

The RPM reading while the bike was sitting at idle was jumping all over the place. It would flash even 5000 rpm and then go back down to 1300.

My idle is not particularly steady but could these power commander numbers be an issue?

I've since disconnected the power commander but could my pickup rotor be faulty?

Here's a video where you can listen to the idle speed and see the power commander freaking out: https://vimeo.com/351737772
 

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That's a good microphone.
Well, first thing's first. What should the compression be at post rebuild, versus where it's at now?
(>200 PSI?) Make sure the unit of measure matches though, if that were kPa you'd have virtually no compression at all.
Getting compression within spec doesn't even require running the engine... it's just pure mechanics.
Ask someone who rebuilds engines whether this is normal and supposed to improve and over what time frame.
https://forums.anandtech.com/threads/rebuilt-engine-with-low-compression.2456881/
Once that's figured out, then focus should turn to other things... like the fact that it seems to be missing a cylinder. Wire harness should make it nigh impossible for an out-of-order fire. Flashing ECU back to stock if such a thing applies.
But I think as long as there is low compression, there is going to be fowling due to incomplete burn.
Timing marks at the crank as well as the In/Ex cams looks good.
 

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Discussion Starter #35
That's a good microphone.
Well, first thing's first. What should the compression be at post rebuild, versus where it's at now?
(>200 PSI?) Make sure the unit of measure matches though, if that were kPa you'd have virtually no compression at all.
Getting compression within spec doesn't even require running the engine... it's just pure mechanics.
Ask someone who rebuilds engines whether this is normal and supposed to improve and over what time frame.
https://forums.anandtech.com/threads/rebuilt-engine-with-low-compression.2456881/
Once that's figured out, then focus should turn to other things... like the fact that it seems to be missing a cylinder. Wire harness should make it nigh impossible for an out-of-order fire. Flashing ECU back to stock if such a thing applies.
But I think as long as there is low compression, there is going to be fowling due to incomplete burn.
Timing marks at the crank as well as the In/Ex cams looks good.
That was a helpful link and a good read. I think I've covered most of the initial suggestions there.

My leakdown tester is at my parents house as I don't have an air compressor, but I'll try to get on that in a bit here. My neighbor may have an air compressor.

Reading a little bit it seems the consensus is that the compression will go up a bit it breaks in, but certainly not as drastic as 100+% gain.

Yes, the spec is 190-250 psi, and I am measuring in psi as well :smile: Gosh, I wish this was just a unit conversion error on my part!

As for the low compression causing poor burn / fouling - I sure do hope that's the case.

Here's a picture of my plugs that were new at the time of rebuild. Cylinder 4 on the left, 1 on the right. The second plug from the right looked a bit wet with gasoline.
https://imgur.com/cryhLcq
 

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Discussion Starter #37 (Edited)
Did the valve job include checking or redoing the valve seats?
Intuit - yes it should have. I honestly can't verify that he actually did the valve seats but I asked for it.

Today I had the best results I've ever had with this bike.

Tried to synchronize the throttle bodies with a homemade manometer.

The service manual calls for leaving the adjustment for cylinder 3 alone, and making the others match.

My issue was that cylinder 3 was so out of sync that it was pulling fluid up towards the engine within a second or two of starting the bike.

The other three had no where near enough adjustment range to get into the ballpark.

I decided that maybe the previous owner had messed with the #3 control, and adjusted it myself.

With new sparkplugs and the engine warm (but radiator fan off, as someone said this was the way to do it, though I'm not sure the reasoning) I adjusted it to the best I could manage.

I also have the idle set (as close as I can surmise from the tach) to the called for 1,300rpm.

I have the screw for TB #3 as far out as I can without it nearing falling out, and the screw for TB #4 as far in as I could manage.

#3 is still pulling much more vacuum than #4.

I estimate the difference in fluid level between them to be maybe 24 inches / 0.6 meters. Given my fluid density, I have a pressure difference of about 5 kPa. The manual calls for a maximum difference of 1.33 kPa.

I did some research and was not able to find much other than bad coils or improper valve clearances - both of which should be fine in my case.

I can still swap coils around and see if the pressures change, but I've never seen anything change by swapping my coils around before.

The service manual does not seem to say anything if the adjustment is unable to be properly set with the adjustment screws. (Or at not least that I can find)

Could this be a vacuum leak issue? All of my TB's vacuum hoses look to be in decent condition. Also, would a vacuum leak induce more air into the system and cause the bike to run lean?

The bike DOES feel a bit better after honing in the TB's a bit. This is the first thing I've done that's actually addressed the issue of the hesitation!!!!

Here's a video of the manometer. It was fun to make :) Cylinder 1 is on the left, cylinder 4 on the right. This is with the vacuum of 3 set all the way low, and the vacuum of 4 set all the way high.

https://vimeo.com/351916935


Update: I took my propane torch and went around the vacuum lines with it and was not able to discern any changes from that
 

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.............decided that maybe the previous owner had messed with the #3 control...............
In such a case, it may be that 3, disconnected from the others, would be set by vacuum gauge. Verify that the other three cannot influence 3 (at idle) as a means of confirming that theory.

Unrelated, there was a person that had used four vacuum gauges, and steadied them using a ball valve to attenuatively restrict airflow. I don't think they were in any way operationally linked to one another.
 

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Discussion Starter #39
I'm not completely sure I understand what you mean!

Tomorrow my plan is to get a vacuum gauge and connect that to #3, setting that to the specified 24ish kPa of vacuum and then starting from there.

I can't really check if 1, 2, and 4 effect 3 with my current setup as it only measures the pressure difference between all the cylinders!
 

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Discussion Starter #40
Oh gosh, I think I may have found the problem.

I ended up buying a harbor freight vacuum gauge, and starting with cylinder 3 it was spot on.

The other three cylinders I was unable to get up to the 18 cmHg vacuum that the manual calls for.

One of them I could not even get half the required vacuum with the adjustment screw turned all the way in!

Prior, I had checked for vacuum leaks with my propane torch, and brake cleaner. I just noticed that the brake cleaner says non-flammable so I tried it again with carb cleaner.

Now, I can consistently make the engine die if I spray carb cleaner on the throttle body boots, and also where the airbox connects to the throttle body.

As I'm getting into the videos, here is how it sounds with carb cleaner sprayed on the boots: https://vimeo.com/352105732

I presume this is a vacuum leak and that I will need new boots?
 
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