Proper RPM at idle??

[calh22554]

so I took the carb off, looked at the throttle plate, it's closed where I have the idle set screw at. I put it back on, can't fire it up - have to open the throttle a bit. I can get it to run at 900 and it will stay there, but If I go below that it dies. I've checked for air leakage - none. I took the gov arm off the throttle and ran it by hand, but each time I adjust the set screw or the mixture screw to get it to go below 900 it will die every time. I can get it to try to hit 700, but only for a few seconds and it dies. It feels/ sounds like it's just starving for fuel and dies out.
It's is a new carb, new fuel line, new tank - so everything is clean. I do find it odd that the new carb has a small drip on the bottom of the fuel bowl (main jet access screw - not the bowl drain plug). And the gasket between the upper carb body and bowl gets wet and seems to wick fuel outside and gets the edges of the carb wet. Not sure any of this matters, but it seems odd. Could the float level be too high? Cbrown and Soundguy asked about checking the float level and I have not done that. What does that impact if too high or too low?

 

[Soundguy]

if float is set wrong you can starve for fuel or flood.

yer flooding....

 

[calh22554]

I think you are right! In going to set that and get back to you guys on the outcome. Very much appreciate all the help from everybody here.

 

[Cbrown9064]

Could the float level be too high? Cbrown and Soundguy asked about checking the float level and I have not done that. What does that impact if too high or too low?

Like Soundguy said, too high of level and you will flood and too low and you will starve for fuel. Sounds like you are too high or have a stuck float.

While not exactly "our" carbs, this is a good discussion of basic carb principles.

Carburetion - The Carburetor Doctor

Report back...curious to see what the "deal" is.

 

[calh22554]

OK, so here's an update. I took the carb apart and checked the float level - it was set to 1/4" - I changed that to 5/16 and reassembled. I still can't get the tractor to idle below 850-900. I did a compression test thinking the compression may be too low to idle well - that reading was 110 psi on average. The FO says need a minimum of 90 psi, so I assume this 110 reading is ok. Not sure what a solid or new motor compression reading would be. I then double checked for leakage - none. I took the linkage off the governor and ran the throttle by hand - still won't idle below 900. I'm going to rebuild the old carb that was on it and see if that one works better and send this carb back. And looking inside the carb body everything looked open and clean - no blockage.

 

[jeff pk]

You should get a good carb or brake cleaner and shoot a stream through all the passages and jets. When you replaced everything with new items you could've dislodged something that's blocking a passage. When I brought home my 881 it would not idle at all---it died when I brought it down under 1200 rpm. Cleaned out the idle jet and it works fine now. Some folks say you should use wire to roto out the passages, but the cleaner with the skinny red nozzle thingy has always worked for me...

 

[Soundguy]

your compression is fine.

you'l notice harder starts and low power with lower compression.. however once running.. it SHOULD idle fine.

if you disconnect carb from governor and back idel set screw out so you can manually close off throttle butterfly.. if it dies under 800 rpm.. it's not getting fuel onthe idle circuit. idle needle is an air needle. so IN to enrich. if the circuit is clogged you can be in 100% and not help any.

i usually soak em.. then set em on the bench with guitar string and spray cleaner with t he straw. i blow thrut he ports till i see em bubble on the 'otherside' etc.

 

[calh22554]

Update for you - I returned my new carb and got a replacement carb. This solved the problem - it will idle, not at 400, but around 600, and the idle mixture screw does change the idle rpm, so I know it's on the idle circuit now. I do notice that the oil pressure really drops at idle - under 10 lbs, is that anything to worry about?

 

[Soundguy]

not uncommon for the older N series to get real worn and have single digit hot oil pressure.

here are a few things to do / check.

1, if it's the oem oil press guge.. replace it.. an old gauge can be off a few psi. and .. well 3 psi when you are under 10 is significant. can mean the difference in 6 or 9.. etc.

2, i seldom reccomend a light weigth oil like a 10w30. in fact. I like the 15w40 oils. best of both worlds. thiiner at cold startup.. but heavier when hot like the 40w recs for hard workers / high temp areas.

3, remove the oil pressure reilief plunger and spring. see if the spring is intact, or weak. measure it. there should be a spec int he book. many are worn. some people stretch them a bit to get back some pressur ethat MIGHT be lost by a weak spring.

cheap options.. might get lucky.

on the other hand. here is a rule of thumb. 6 psi per 1000 rpm and you should be keeping oil on journals and not metal on metal..

I've seen plenty of old worn N that start cold throttle at 18 rpm and hot idle are 6-8 psi.. and they still run.

not ideal.. but works.

when it and or compression get low enough.. sometimes a poor mans upp and lower will get you another 10ys work.

IE.. re-ring.. ream the ridge ont he liners.. crosshatch them.. hand lap the vlaves. roll in a set of main and rods same size as it had. guaranteed to fit.


not as good as new liners and cam inserts and a oil pump rebuild. but wont hurt and is super cheap and can be done in a day if you have the parts and tools in hand.