150cc Crossfire Hard to start, does not stay running and bogs down
 

Here is what I have done so far / know of as of now:
Replacement carb (Which was included when I did an engine swap in 2011)
5 Month Old Wiring Harness
Replacement CDI
2 Day Old Fuel
Adjusted Valve Tolerances to .005

Here is where I am lost: Being a Honda clone, I am familiar with it from working on it from ATC 110's. However, following everything that I have found online, I still can not get this to run right. Basically, it is very hard to start, and will not stay running when started. If I do get it to run, it generally bogs down after a few minutes. I do have a choke resistor on order, and it will arrive soon (Hopefully). In the mean time, what am I missing? I highly doubt that it is an electrical issue, as I have went over the harness several times trying to find any loose/bad connections.

All assistance is greatly appreciated.

Thanks in advance

Check your compression. Should be around 135-150. Sounds like it may be low.

I think ur intake is an .003 & ur exhaust is .005?

Well, I tightened the valves to almost zero tolerance, where I had found it before, and it ran slightly longer. It seems to be in the adjustment. Saturday, I have a range of adjustments that supposedly work that I will be trying. Hopefully, I can solve my problem.

Good luck "k" keep us posted!

Had these symptoms with a leaking intake manifold and bent intake valve.

Replaced the intake boot and off idle improved.

Ported head and found the real problem a slightly bent intake valve causing hard start and running concern.

Could get it to start but if I opened the throttle slowley it would die and was hard to get started.

I found before the valve was fixed that if you would flat foot the throttle it would take off but ran like junk untill warm and still ran like junk.

I hope this will help.

Hard to start
 

Funny, I seem to have a similar issue.
Hard to start, and can't open the throttle more than a little until it warms up.
Idle gets progressively faster as it warms up.
I assume it is a leaky/cracked intake, but the valve issue could come into play.

Well, I ran a compression test - 65 Pounds. The highest rating that I could get was 110, with the intake and exhaust at .008. Would I be correct in saying that this gap's too big? Also, is 110 too low for the motor to run? I tried to fire it off, but it was in the 30's and was getting dark, so I did not do much else with it. Tomorrow should be warmer, so hopefully I can get something worked out.

Valves should be around .004 - .005 on both valves. And was the throttle held open when compression testing?

110 psi is pretty low. 150 psi is about average.

The throttle was open during the test. So I am assuming that, if it does not run tomorrow, I should look at pulling the top end?

I would make sure your cam is timed properly and valve clearance is correct before you go tearing anything down.

Well, you're right.

I got it to run for about 45 sec., and it ran horribly. Backfiring, no power, etc. So, I did check the timing, and it's off. I'm off tomorrow, so I'll look into getting it reset.

Good luck

Make sure theres not alot of slack in your cam chain.

I always set my valves at .003 both sides. I hate yakity valves however you do need to know that these valve seats will sink in over time and when they do it will run like crap because there will be no lash.

Timing off? Is there a reason that the timing may have been physically modified?

Well, the timing was off, but I still only have 105 pounds. So, it's coming apart tomorrow to find out what went wrong. The bad part is that this motor was new 2 years ago, and has less than 20 hours on it.

Well, I tore it down yesterday
http://i1225.photobucket.com/albums/...ps84cf086a.jpg
http://i1225.photobucket.com/albums/...ps29e93ee5.jpg
http://i1225.photobucket.com/albums/...psb31684ca.jpg

Unfortunately, it has big problems. The cylinder has been worn completely smooth. You can see the line where the piston stops, the crosshatching is still visible below it.

http://i1225.photobucket.com/albums/...psf1cbbd42.jpg

The rest of the cylinder looks like this

http://i1225.photobucket.com/albums/...ps1e6fb7d8.jpg

Onto the piston, which had had the coating worn off of it; I am assuming that this is how the piston began to eat the cylinder.

http://i1225.photobucket.com/albums/...ps876317f6.jpg

Last, the head. As you can see, the exhaust valve is warped, and does not seal when liquid (Super Clean, in this case) is poured into the chamber.

http://i1225.photobucket.com/albums/...ps51e357b5.jpg

So, I need an entire top end. What do you guys recommend?

If you think the cylinder is trashed, then a big bore kit would be the way I would go, depending on your budget, of course. The head may be usable, but be sure to check the guides and seats, I am curious why the valve would be warped, unless it being out of time caused it to touch the piston just enough to put a slight bend in it.

You may be able to just replace the cyl and piston (Big Bore kit would be a nice upgrade) and maybe replace the valve. Get a gasket set and you should be in business for around $120 unless you go with performance parts.

Bent valves worn cylinders,,,,, normal operation, repair and buggy on. The cool thing is you dont have to pay for labor.

Replace the valves and cylinder. I recomend the 60mm or 58.5. The 62mm big bore is cool that I did last summer but not a big game changer.

Some cases can run the 60mm srp piston kits without boring. I bored the case and added a cylinder spacer, messed with cam chain being too tight from the 3mm stroker crank and the 62mm cylinder and it didnt run that much faster than the 58.5 high compression set up in the red buggy.

More is better when it comes to ice cream but not always with buggy motors.

If you wanted mods now would be the time to do them. If your happy with the stock performance then by all means go back stock. From the looks of the cylinder it appears it was washed with fuel. I just done a customers buggy this past weekeng and his cyl looked the same. His problem was the vacume operated pump went bad and fuel was flowing therough the vacume side of pump directly into the intake. If your oil smells like fuel this is why. Also sometime if the choke is not working the engine will flood when warm. The bigbore alone will not make a performance difference unless you upgrade the head and cam, mainlt the head. If eng. was washed with fuel you will probably also have badly worn guides, timing chain and oil pump. So while its down check it all out. Crank should not be a problem since it rides on roller bearings.

Well, the choke was not working. I'll check tomorrow, but I thought something smelt odd when I tore it down.

The new top end parts arrived yesterday. I ended up going with the stock pieces; it was just more cost effective. The motor is in, and should run tomorrow. As of about 2 hours ago, the exhaust is drying in my garage. I did get the electric choke worked out. Turns out, the resistor was at fault. So, I should avoid having to do all of this again.