P700 700 Won't Start [SOLVED]

[fmjnax]

This is actually on a 2011 Big Red, but I understand it shares the same engine as the P700 and this forum is more active so I'm cross-posting here.

I picked up the machine as a project. I had to split the case and clean (replace) the oil screens. Also rebuilt the clutches. Installed a new piston/rings into a new jug (it was supposed to be OEM, but I'm starting to think it is overbored). Broke down the water pump and oil pump to clean/refurb. Cleaned the fuel tank, lines, and injector. The only thing I didn't mess with were the valves (I don't currently have the tools to do the job). Checked and confirmed all of the internals at that time and everything else seemed to meet specs.

In addition to the bottom-end rebuild, I have installed a new starter (twice, actually), new solenoid, new battery (3 times now), new air cleaner components (they were ALL missing when I got it), new spark plug (twice). After the rebuild and the new parts, the machine would fire up and ran perfectly fine. A couple of weeks later, it started becoming hard to start. Now, it won't start at all. The starter engages and can turn the engine over once, but then can't muscle it past the compression stroke. If I stop cranking, wait a second, and bump the key again it will do the same thing; turn it over once and stop. If I remove the spark plug, it will turn over until the battery dies (if I let it go that long). I can turn the flywheel via socket and could turn it from the cam chain by hand (already a bit hard) when the top-end was off. I don't believe anything is seized up internally. Oil pressure and level good.

Yesterday, I replaced the cam thinking it was the decompressor. Exact same symptoms with the brand new OEM cam. The decompressor on both the old cam and the new cam seemed to function just fine when pressing by hand. I made sure the valve clearance was on-spec. I checked compression and it reads 130psi (which I understand is higher than spec, but maybe it's because the new piston and jug are actually overbore and not OEM). I have spark and I have fuel. I disconnected both the intake and the exhaust to make sure I didn't have a blockage. I also installed the 2nd brand new starter and 3rd brand new battery.

At this point, I'm not sure what else to look at. I'm going to give it a shot of starting fluid today when I can go out and work on it, but I don't suspect that will make it fire. Even if it does, that doesn't fix anything. I'm also going to take a closer look at the wiring and make sure I don't have a bad ground or something. I've looked it over a time or two and it seems fine, but I'll look more closely this time. I lined up the new cam at TDC on the compression stroke (both cam lobes down and vertical play in the rocker arms) as per the manual, but it's possible I have either advanced or retarded the timing by a tooth or two. I'll probably take a closer look at the alignment and move it +/- 1 tooth either way to test. I did notice that when I fully retracted the chain tensioner, it didn't immediately snap back in to place. However, as soon as I backed it off with the screwdriver just a fraction of a turn, it snapped back like it should have so it was only sticky at full tension release.

I am open to any and all suggestions here. I'm running out of thoughts for what could be wrong.

 

[Admin]

 

[fmjnax]

I didn't get enough time this afternoon to look at everything I wanted, but I did get to do some diagnosing.
- I drop-tested the starter; both ground and hot was in the 100-200mV range, so should be good there.
- Confirmed voltage to the starter was right at the same as the output terminal on the solenoid, which was right at the voltage of the battery, so should be good there.
- Checked resistance on the ground wire from the battery to the engine body. I picked up 10ohms there (though I don't know if that's good or bad).
- Shot starter fluid in the intake (no change) and also directly into the combustion chamber (no change)

If I turn the key and then keep holding it after the starter has turned it over as far as it can, it will eventually turn it over past the compression stroke (and I can hear a "pop" from the exhaust) but it still won't turn past the next compression stroke without still holding the key. I only did this a couple of times because it really gets the battery leads and starter HOT. This also causes a backfire, I suppose it is (blowing out through the intake/throttle body)

Thought maybe it could be too much oil pressure so I removed the dipstick and bumped the key. Same result.

Still getting 130psi consistently (and the gauge was confirmed accurate against a regulated air supply).

If I pull the plug and let it turn over, I'm not getting any "spay" out of the plug hole like I think I would expect. It looks slightly wet in the chamber, but definitely no spray out.

When I pull the plug, it is never wet. It is dry and slightly black (when working, the machine idled a lot and never really got opened up full as it was used on the farm).

I pulled the fuel line from the throttle body and hit the key to prime. It pours gas out like it should. When I had the connecting sleeve between the TB and intake off, I could see the mist being sprayed out of the throttle body.

Hopefully tomorrow I will have more availability to tear down the top-end again and do more inspecting. I'll try to hook up the starter to some jumper cables and see if it will turn over directly off the fully charged battery, but I don't think that's going to work. I'm leaning towards a valve problem or a timing problem, though I'm not sure how to narrow that down (you know, being a 2-stroke guy).

My thought (and I'm no mechanic, just a tinkerer that mainly works on 2-stroke outboards) is that if the intake valves are stuck/bad, that could explain why no spray-out through the plug hole when it's removed. If the exhaust vales are stuck/bad, that could cause extra compression in the cylinder that the starter can't overcome (though that doesn't explain how the decompressor on a brand new OEM cam doesn't relieve that extra compression).

If the timing is off, that impacts the position of the valves, which could also explain the no spray-out and/or the extra compression right? But would being off +/- a tooth or two really be that much difference? What about if I was 180 degrees off? Again, the timing was aligned at TDC with the cam lobes facing downwards and vertical play in the rocker arms so I'm pretty sure I had it right, but maybe not.

Still open to any thoughts, ideas, suggestions, etc. I have no clue what is going on here.

 

[allgm1]

It sounds to me like your cam timing is off. which way its off I'm not sure but when its set correctly the valve timing will have some over lap and reduce your compression some. I havent had to work on these engines as of yet, but I started rebuilding the engine on my ct-70 when I was 15 and have rebuild a lot of honda engines through out the years. It seems to me that there should be a dot on the cam sprocket that needs to be lined up with another dot or mark somewhere. I have the service manual on my computer but it won't let me save the pages for the proper cam set up. I'll take a pic and post it in another post

 

[allgm1]

 

[allgm1]

Sorry about the double pics, first time doing that on my phone

 

[fmjnax]

Thanks for chiming in allgm1. Much appreciated! No problem on the double-pics.

That is currently the avenue I'm chasing now. I pulled the top again today and finally broke down the valves for a good cleaning and spec'ing (all good according to the manual). After pulling the head, I took a better look at the timing from multiple perspectives and it does look like I missed the mark, quite literally. LOL We'll see what it does tomorrow when I bolt it all back up. Might have to give it a few tries to get it right. It seems so easy to be off +/- a tooth or two.

 

[fmjnax]

Looks like we were right, allgm1! At least for right now.

After confirming all of the electrical components were good, I took the top-end back apart. I broke down the valve assembly and made sure it was all in spec. I then cleaned all (98% of it, anyway) of the carbon up.

On that teardown, I took a look at the timing from various angles and really scrutinized it. It looked slightly off so I realigned that. It was 2 teeth off (retarded, I think it was).

Bolted it all back up and turned the key. Fired right up. I'm pretty sure it was the timing being off, but the valve cleanup and re-adjustment certainly could have helped.

I need to top off the oil (will probably do a full change, actually) and put new coolant in it and then I'll make sure it wasn't a fluke start before I fully button the machine back up, but I'm optimistic that it's all good to go now.

What a headache this has been for me, but now I can say I understand valves and timing. I still prefer working on 2-stokes. LOL!

 

[allgm1]

Glad you got it figured out. Valve timing and adjustment can definitely reek havok on engine performance. I have never dabbled in 2 strokes, I understand how they work and all just never had the need.