300 Mountainview Roughneck (same as 300 Linhai) Won't idle

[PKR]

I have had this machine running and put about 4 hours on it but it would not idle great. Would fluctuate between 700 & 2000 rpm and usually quit at the low rpm. Spark plug would carbon off and have to be cleaned. Throttled up nice and ran good in mid and high range. Machine then quit and wouldn't restart, couldn't get it to fire. Checked everything, had spark, gas, etc. Thought spark may be weak so ordered a new coil. Machine sat for 3 weeks waiting on new coil. Installed coil and machine fired right up. Idled nicely until it warmed up and then rpm's were all over the place. It quit after about 20 minutes and then would restart. If I let it sit for a few days it will start but won't idle. 

Fuel/air mixture screw does nothing, can be screwed out or in and no change in idle. Only way to keep it idling is to turn the throttle screw way in and have it revving over 2000 rpm.

As this unit sat for close to 14 years I have replaced the pulse pump, carb, CDI, spark plug and now the coil.

What am I missing? I have done all the ohms checks on the stator, pulse trigger, etc and they are all good. I've took the carb apart to ensure it was clean, reset the float to be leaner as plug was indicating it was running rich. Didn't make any difference. Don't know where to look next?

Also can anyone tell me what these wires are for that come off the bottom of the carb (see pic).

Thanks for the help

PKR

 

 

[Mech]

I've just added a service manual that should help. It'll appear in here shortly I think, otherwise it's in the "other ATV" section of the manuals.

I think that's an auto choke. If the idle mixture won't adjust then it must have a dirty jet I think, or blocked drilling..

[Gwbarm]

I had this happen to a Honda once, I cleaned carb a multitude of times never had such a problem, changed jets and needle, no help, never got it to idle correctly, like you said over 2000 RPM I could use it barely, but annoying, I ended up replacing the carb and it ran perfect, still don't know what was wrong with the old carb.

I would double check the jets again make sure there's not one down in a hole you missed, I have done that before, and make sure you take out the emulsion tube and clean it.

As far as the wires go it appears to me to be a carb heater, can't really see it good, if it is you might try unplugging it , sometimes they can cause a grounding issue.

[PKR]

Thanks for the comments, I'm going to take carb apart again. It's a new carb, I've cleaned it twice but have found nothing.

I think the extra wires from the carb are what they call a warming resistor and work with the electronic choke.

[Gwbarm]

I know, you have done a lot of work, hopefully it end up being something simple, but it does seem carb related.

[Mech]

Might pay to check the valve clearances, and for vacuum leaks. If it has a rubber inlet manifold it might be split, or be missing a gasket or O ring.

Other than that check the carb again. If it's sooting up the spark plug it's either too rich, or the plug is misfiring..If the idle is too rich i might be the jet is loose or missing(yes it happens), or the idle air jet near the air filter end is blocked.

[PKR]

Hey guys

I've stripped the carb and cleaned out again, didn't make any difference, unit won't start. Pulled old carb apart and cleaned and rebuilt it, didn't make any difference. Unit is getting gas and I have spark but it will only fire about once every 20 seconds of crank and then it is only one fire, no start.

Started thinking maybe the timing was off, Checked the valve clearances and they were right on spec with the manual, so I'm assuming the timing is good.

I think that leaves me with 2 other options to look at, the CDI (this has a new CDI in it) and the pulse trigger.

I did the ohms tests for the stator and pulse trigger and they are all in spec with the manual.

Took a acv reading on the pink wire at the coil (comes from the cdi) showed 26.3 acv with key on. Got no reading on the black and green wire at coil (this also comes off the cdi)

Is there some way to voltage test the stator and trigger coil without a peak voltage meter or adapter, all I have is a simple multimeter. I'd also like to test the 2 wires at the coil for voltage while cranking. The manual has no specs on doing this so I'm not sure what I should be seeing for readings, I am assuming these should all be acv readings.

Thanks again for all your help and insight.

PKR