Can't figure this one out... (Gotta video for ya)

[sam000lee]

I put in a GS450 engine with 4,500 miles. Long story short I put an ebay cylinder head on it. When I start it up, the left side gets hot and the idle races but the right side is cold and I pull the right side plug boot, nothing happens (i.e it's not firing). If I put it back on and pull the left boot, the engine dies. With the left boot off, and I can start the engine on choke and it seems to idle normally. If at this time I put the left boot back on, the idle starts to race again.

I thought that maybe the ebay head valves weren't sealing, so I got the original machined, put it back together with new gaskets, no difference.

It's not the carbs - I have two pairs, both are properly cleaned/new O-rings and one pair I know to be good. Same response on both.
I have UNI Pods and shorty exhaust, have tried wide variety of jet/needle settings and the behavior is pretty much the same.

I thought maybe I was setting the timing incorrectly. I've triple checked it twice and even opened up my other engine to compare. Everything checks out.

Could this be explained by a bad piston ring? Seems unlikely to me considering the low miles. Could it be something in the bottom end?

Here's a video with the original head back on and me demonstrating the L/R behavior.

https://www.flickr.com/photos/976376.../shares/W12TK8

Timing:




TIA!

[sam000lee]

I should also say that I just did valve clearances and they are in spec.

[tom203]

"With the left boot off, and I can start the engine on choke and it seems to idle normally. If at this time I put the left boot back on, the idle starts to race again."

this says that right cylinder is firing when "choke" is applied, but is not when no choke. This suggests your right carb is not delivering enough mixture,i.e. plugged idle passages or wrong mixture screw setting.

did you bench sync these carb sets?

[Steve]

Even though you have two sets of carbs that don't appear to make any difference on the way the bike runs, it does not mean that either set of carbs is properly cleaned and adjusted.

I am going to agree with Tom on this one. You say they have both been "properly cleaned", but not everyone agrees on the definition of "proper". Please spell it out to us to make sure you ARE doing it properly. You also did not mention whether you bothered to synchronize the carbs. If the right carb is not open far enough, it simply will not add anything to the power output. On "choke", it uses a separate circuit that bypasses the throttle butterfly, so it could easily run on "choke" but fall on its face without it.

.

[sam000lee]

To clean I fully disassemble, dip overnight and reassemble with new O-Rings from R. Barr. The new engine is from a parts bike I bought and the carbs that came with that bike were dipped last month.
My other set of carbs are the ones that I have been riding on for the past few years. They've always worked flawlessly and I cleaned them (with new orings) last year at the beginning of the season. I tore the bike apart in the fall so they were not stored with gas in them over the winter.

Both sets are bench synced using the `needle' method.

That being said, I'm going to disassemble one of the pairs and dip them tonight! I'll update then, thanks guys.

[Guest]

I think you need to really sync them. Like buy some gages and really sync them.
I had a similar problem with my 400 after I cleaned the carbs. One side would fire, the other wouldn't.
It was out of sync and I bench sync'd the **** out of them first.

[sam000lee]

That was it, thanks guys. To be honest I didn't dip them again but did blow some passages with carb. cleaner. Then I raised the float height of the right side and bench synced them again and it started right up and idles pretty good. I also backed my idle screw to 4 1/4 turns out.