Cold Starting Problem

[SoEazy]

Hello again Gents.

I've got another carb problem on the 400, I'm hoping to get sorted out quickly. After cleaning and rebuilding the carbs the bike will run great but is very difficult to start cold. It appears to be flooding evening when I attempt to start with no choke. Usually, I can push start the bike after attempting to use the starter but sometimes even that won't do the trick. Usually after running it starts warm no problem.

I'm guessing it's my pilot screw setting? It's currently at 2.75 turns out. I have a Micron slip-on exhaust but that's currently the only engine modification. It looks like stock pilot setting is 1.5 turns out, so I'm guessing I'm too rich. Anyone have any thoughts? 

[TJS]

What makes you think it's flooding? Do you see gas dripping from the carbs? Do you think gas has by passed the float needle and now in your oil? Is there a very strong smell of gas?

Flooding is not too many or not enough turns on the air mix screw. Answer the questions above and we should be able to help.

[yoda]

I've had trouble with my petcock vacumn link. Its always on now, and if its stood a while it seems to hydraulic lock on a couple of cylinders. runs ok after though. It might be worth checking your tank and tap, and make sure the vacum hose off the inlet to the tap is clear.

[SoEazy]

It turns out my mixture was far too rich. I dialed it back to 2 turns out and that cured the problem. I have a Pingel fuel valve, so I knew it wasn't a petcock problem.  Alas, the bike is dead again with no spark. Bah.

[ventYl]

in wiring loom somewhere between cylinder head and carbs there is insert connection which is easy to disconnect. result is no spark at all without anything else looking bad. otherwise you'll need some gear to diagnose what is bad and what you have to fix.

[SoEazy]

New CDI fixed the no spark problem. I've still got a couple major issues...

• The engine will not idle correcty. I have rebuilt all the carbs,  cleaned all jets and attempted to balance but the carbs do not want to sync properly. It will run as long as I continue to rev the engine but if I leave it to idle, it dies.
• The engine suddenly loses power. It will run perfectly from mid throttle to upper range for 20 or 30 minutes and then go into a state where the engine will only rev up to idle speed, even at wide-open throttle. Usually after sitting for a bit it will run properly again.

On a side note, I was limping the bike home at idle speed (at WOT), when I hit a bump and the engine kicked back in. Almost like something became unstuck. Anyone have any ideas? 

This bike is truly lucky I enjoy riding it. I would absolutely love to ditch this thing but my pride will not allow it. 

[ventYl]

Do you still have spark after engine starts running rough and barely idles? This looks like something overheats and then there's no spark. Either new CDI isn't that much new or your coils are near dead too. Check ignition performance by two nails. Exact process is described in workshop manual.

[SoEazy]

Do you still have spark after engine starts running rough and barely idles? This looks like something overheats and then there's no spark. Either new CDI isn't that much new or your coils are near dead too. Check ignition performance by two nails. Exact process is described in workshop manual.

I assume there is still spark when the engine gets hot because it does continue to run but will not rev past 2K RPMS or so. I am getting the exact same behavior with the brand new CDI as I did with the repaired CDI, so I don't think it's the culprit. I suppose it could be the coils. The lack of revving generally happens when I'm sitting in traffic or after running the engine fairly hard. I thought maybe it was a fuel problem, but a Pingel fuel valve and clean carbs should have fixed that. I suppose if I am testing the coils, it would need to be when they are hot to get an accurate measure?

The project continues...

[ventYl]

Spark power test is performed by two nails separated by 8mm gap. One nail is connected to HT coil wire, another one is grounded to engine. Under all circumstances, there should be spark. If no, maybe HT coils are overheat and lose their parameters. If they run ok when cold, try to test spark power when engine refuses to rev over 2k RPM. Btw how does it idle then? Is idle still OK or engine tends to stop?

[SoEazy]

Spark power test is performed by two nails separated by 8mm gap. One nail is connected to HT coil wire, another one is grounded to engine. Under all circumstances, there should be spark. If no, maybe HT coils are overheat and lose their parameters. If they run ok when cold, try to test spark power when engine refuses to rev over 2k RPM. Btw how does it idle then? Is idle still OK or engine tends to stop?

I suspect you may be on to something. The engine will run fine when cool. It's usually when hot that the engine will no longer rev. So I assume if one of the coils were the culprit, it would measure correctly when cool but defective when hot. I suppose I'll give that a try. I'm not sure if this would have anything to do with the idle being erratic.

One problem at a time I guess...

 

[ventYl]

with overall good condition of engine (valve clearance, compression, carbs clean and at least after basic setup) fail of single coil should still give you ability to rev engine until rev. limiter. But engine sound will be rough and it will sound more like two cylinder engine and throttle response will be much slower than when running on all four cylinders.

but i doubt that any mechanical engine parameter can change so dramatically that engine will no longer rev only due to heat. Of course this assumes you have engine coolant filled and thermostat is not locked in closed state. Locked down thermostat should cause excessive internal friction and refusal of rev but cycle would also more regularly run radiator fan and/or overheat lamp would be lit probably.