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220 won't idle ?

jopete

jopete

Well-known member
Hey, my old faithfull 220 gpu is running great on top and has no miss that I can tell, but won't idle but for a second then kills. fires right back up, just won't idle. I've had this boat for 5 years or so and I can crank it up and after it's warm, will usually idle all day long. I ran some hard marsh this morning and it runs normal all except for it won't idle.

I've got a holley 500 on it, other than that it's stock. had the same d16 spark plugs in it for at least 2 years with no issues. I did change the mech fuel pump in the spring. I haven't been running the boat a lot the last 3 months, I am thinking I got junk in the idle circuit.
anyway, I changed the sparkplugs today with new d16's gapped at .025'' the old ones were tan in the center, but carboned up pretty good on the sides. I frog/idle a lot. and cleaned the spark arrester real good, and it fires right up and will run great above idle. I have a racor fuel filter with a clear bottom. I drained some fuel into a container and the fuel looked clean/good. unless my tach is lying, the motor dies appruptly under 800 rpm's. it usually idles 450-500 rpm's. it turns 2750 on the water no problem, and throttle response is normal.

only thing I haven't done is jack with the throttle stop. it hadn't moved in 5 years, idk why it would move now.

I wanted to check all these things before I go into the mag. the gap on the mag should be .015'' if I remember right. might put some mechanic in a bottle in the gas tank and go run the heck out of it and see what happens.


any opinions would be appreciated.
 
Sounds like a small intake leak to me. Those rubber seals on intake tubes rot out and if sucking small amount of air will do what you are talking about. When throttle down the leak is not big enough to affect engine up high.
 
Check the pcv port plug, if rubber cap, they split over time, suck air and idle circuit can't keep up.
 
the idle circuit was clogged. one can of carb cleaner later it will idle all day. thanks for all the helpful advice, I have checked everything that was advised, ready to go run some more marsh!

this is not the first time that the Braintrust on Southern Airboat has helped me out with a airboat problem. I genuinely appreciate it !!!
 
well, it started doing it again yesterday. cut my workday in the swamp short cuz I was worried about all the starting I was doing was gonna kill my battery. boat wouldn't idle. on the way back to the landing the motor seemed to clear up. when I got home I ran the ide screws [both 1 turn out] in and then back out to 1 turn. then I checked everything on the carb, the 4 bolts holding carb onto the high rise intake, and all intake boots. I made a half to 3/4 turn on the 4 bolts holding the holley 500 onto the intake.
not loose. but not tight either.

cranked up and the boat set and ran at 450+- rpms for 10 minutes. lol

I sprayed a half a can of wd40 into the atlinator and it started working. I will change it when I figure out what kind it is. it's just a 1 wire altenator, but I hadn't got a # off it yet.
I usually run this boat every week, but I been a poor bastage lately and been putting the fun stuff like airboating on hold so I can pay the bills. looks like I shoulda just ran the boat instead. tach wire is getting jumpy now too. probly from non use.!!!!
 
I got the alt redone. works great now.

the last 3 or 4 times I have taken the boat out it will idle great for while then I have to screw the idle needles in then back them out 1 to 1 1/4 turns out and it runs fine for a while then wont idle. one of the idle screws will bottom out, then It feels like the seat is tore up and it will make a 1/2 turn before it bottoms out. I ordered a renew kit and a redress kit with new idle screws/seats and I got a podna that can do the work for a handshake next week or so. he thinks it may just be a float adjustment, but we will put the kit in and see whats up. the carb was last touched a couple years ago when I got a new mag from GMAC76. heck, I ran the same plugs since then and only recently changed them when this idle issue started up. I have checked numerous times for a vacuum leak and hadn't found one.

btw, carb is a holley 500 #4412-3 carb renew kit is #37-474 and I got another kit from amazon that's supposed to have the idle screws in it.
 
check to make sure that the idle screws still have the little cork seal around them...if they are gone it can make a constant good idle hard to set....the renew kit will have them in it ....just a thought
 
Sounds like a classic case of tank full of crap and filter issues. With fuel issues, I always start at new filters and work from there. Won't cure what already is, but maybe the next issue.
 
I agree with the junk in the tank thing, but I am pretty sure the fuel is legit and my racor filter with the clear bottom has been drained a couple times and I can't find any debris in the fuel. unless a hose is coming apart between the filter and the carb.

the idle screws fit loose, I bet when I change them out and the seats it will fix it, at least that's what I am thinking.
 
jopete said:
the idle screws fit loose, I bet when I change them out and the seats it will fix it, at least that's what I am thinking.
Click to expand...
those little seals are what keeps the screws in place and seals the needle when ya find that sweet spot....I think your on the right track man....good luck
 
GMAC 76 said:
jopete said:
the idle screws fit loose, I bet when I change them out and the seats it will fix it, at least that's what I am thinking.
Click to expand...
those little seals are what keeps the screws in place and seals the needle when ya find that sweet spot....I think your on the right track man....good luck
Click to expand...
I agree, the next step after filters is to make sure the pump is pumping, then it's take the dam'n thing apart, clean it good and put new stuff in it. Cures' 90% of my issues.
 
Pull the bowl and metering plate, the idle circuits are in the same slot as the power valve feed circuits, a small brass jet per side pressed into the block, most likely you have some corrosion bouncing around in there, I would soak the block in ospho, if you have a pin vice, (tiny drill type torch tip cleaner) I'd open the little brass jets up a little bit.
 
thanks guys for the tips. I've got the rebuild/renew kits in, but since I played around with the carb settings this week on the deer lease, the boat is running great. It may have passed some trash or not, we will see. I was running around with me and 10 sacks of feed like I owned the place! lol that north wind dries up my swamp and it's a blast running the cypress swamp with just mud!!!!!!

I've got my buddy who is a carb savant waiting on me to bring it by if it acts up again. lol
 
well, guess it's running better now, musta passed the trash. still idleing around 700 rpm's, I just hadn't slowed it down yet.
ran to feed on deer lease last night with 11 sacks of corn/rice bran in the boat. stepped on a mud flat and never checked up till I was where I needed to go.
my old 220 is by far my favorite motor I've had on a airboat. and I've had 2 lycomings and a BBC. it's just simple.
 
update... boat is running fine, but if u let it idle for more than 10 or 15 min it floods out and kills. been running it back and forth to deer stand and it does fine. got my carb guy lined up to tune up / rebuild carb, sheck mag in a couple weeks. got to get it running right so I can make some money with frogs here shortly.
 
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