Help, finally started 520 conversion, issues

Aircraft powered airboat discussion.
fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Help, finally started 520 conversion, issues

Postby fletchster76 » Sat Nov 15, 2014 7:15 pm

I blew up my 220 a few months ago so decided to build a 520 gpu conversion. Finally finished and got it started. Starts and idles but after 15 seconds it starts spitting and sputtering then dies. Rev it up to 1500 rpms, runs good but after a little it starts running rough but cleans up if I feather the throttle a little, after I drop down to idle it spits and then dies. Tops out at 2700 rpms, tired gpu was turning the same prop 2750. I've played with timing and jets buts can't find issue. Any thoughts or theories would be appreciated. In case this would make a difference, only running the one mag I had on the gpu and using the same holley 500. Lastly, when I adjust the mag while engine is running at higher rpms, mag body shocks me a little, could mag be grounding out? Once again, thanks for any insight.
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Sat Nov 15, 2014 7:52 pm

Call me, 786 227 4204
I never finish anyth,,,.

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Sat Nov 15, 2014 9:40 pm

Called earlier, will try again tomorrow. Making the neighbors mad while trying to figure it out tonight.
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Sun Nov 16, 2014 8:41 am

Saw missed call this morning, sounds as if the o ring on needle and seat has shrunk and you are flooding out.
I never finish anyth,,,.

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Mon Nov 17, 2014 8:36 am

I believe you were correct. Rebuilt the carb and now she idles. Thank you sir. Still not as many rpms as I was expected. That makes me think that the 500 holley isn't enough carb. I've got a predetaor but I don't think it will fit under the seat without some serious modifications. Wonder if I should just buy a 650?
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
Bruce
Site Supporter - IV
Site Supporter - IV
Posts: 4793
Joined: Tue Feb 27, 2007 9:43 pm
Location: orange county fl
Contact:

Re: Help, finally started 520 conversion, issues

Postby Bruce » Mon Nov 17, 2014 8:40 am

id get another mag and put some timing into it and it outta run good and id have at least a 76 jet in it
12 foot Mamba "The Underdog"
Tired Gpu 520,Whirlwind Razor X

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Mon Nov 17, 2014 8:54 am

Take it, get it hot, run it full throttle then shut it down as soon as it comes to idle, pull plugs read the color if white, bring it up in jet size till plugs read light brown to beige.
I never finish anyth,,,.

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Mon Nov 17, 2014 9:19 am

Thanks for the help guys, I've got to find someplace to get points and a condenser for my 2nd mag. Once I do, I'll get it on there and see what she does. I'll post what I find out. Thanks again.
13'6" Laser, 520 conversion, 72" 3 blade ngh

SthrnStyle3
Southern Airboat Member
Posts: 510
Joined: Mon Apr 06, 2009 6:41 pm
Location: Sanford, FL

Re: Help, finally started 520 conversion, issues

Postby SthrnStyle3 » Mon Nov 17, 2014 3:12 pm

I don't know much of anything about aircraft, but I'll throw an idea out there for ya anyway.. I have a small block that i just got done fixing a similar issue today. It would rev up but shortly after start dying down and losing rpms. I noticed air bubbles in my fuel filter, so I checked for air leaks everywhere in the fuel system. With no luck there, I threw on a new fuel pump and problem solved. Just something for u to check. It may be the jets, too small of a carb, timing/ mag issues or bad fuel pump. Start with the cheapest and simplest first. Definitely read plugs to give u a direction of too lean or too rich. Good luck.
12' aluminum hull, 350 sbc w/ flattop Pistons and camel hump heads, side by side seating w/ double in front, 2:1 gearbox and a 78" whirlwind whispertip 2.0

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Mon Nov 17, 2014 10:35 pm

Thanks for the help. I'm gonna try and find points and a condenser to rebuild my 2nd mag tomorrow. Seems like someone told me points for a gm 327 work in a bendix mag. Anyone know any truth to that.
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Tue Nov 18, 2014 12:44 pm

I doubt it, unless it had a dual point distributor, even then I can say that it isn't the same.
I never finish anyth,,,.

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Tue Nov 18, 2014 12:49 pm

Ronnie Shears Jr is in Inverness, might have a set, don't know any contact information on him though.
I never finish anyth,,,.

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Mon Nov 24, 2014 8:30 am

Got my 2nd mag on it, definitely cleaned up the idle and runs smoother. Still not turning what I thought it would, so I put a big ole predator carb on it. Gave it another 150rpms. Better but not what I thought I'd get. Noticing that my intake crossover hose in the back of the motor is collapsing when I give it throttle. Is that normal? Was thinking about getting a hydraulic hose that will stay stiff. Anyone have any ideas on how to stop that from collapsing or if it even matters?
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Tue Nov 25, 2014 9:46 am

What is it timed at? What pistons are in it?
I never finish anyth,,,.

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Tue Nov 25, 2014 7:30 pm

Timed at 22 degrees before TDC. I think I have 8 to 1's. Just stock 520 pistons. I picked up a braided hose for the cross over today but got home too late to see if it helps.
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
Bruce
Site Supporter - IV
Site Supporter - IV
Posts: 4793
Joined: Tue Feb 27, 2007 9:43 pm
Location: orange county fl
Contact:

Re: Help, finally started 520 conversion, issues

Postby Bruce » Tue Nov 25, 2014 7:32 pm

fletchster76 wrote:Timed at 22 degrees before TDC. I think I have 8 to 1's. Just stock 520 pistons. I picked up a braided hose for the cross over today but got home too late to see if it helps.



whew theres your problem crank that baby up to 27 or 28 itll come to life
12 foot Mamba "The Underdog"
Tired Gpu 520,Whirlwind Razor X

User avatar
John Fenner
Southern Airboat Member
Posts: 2557
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: Help, finally started 520 conversion, issues

Postby John Fenner » Wed Nov 26, 2014 1:01 pm

Too high, set it at 25° max, any higher than that you will gain snap and rpm, but you will hammer the ring lands as well as bearings due to the spark knock at high rpm.
I never finish anyth,,,.

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Wed Nov 26, 2014 8:19 pm

Just checked it, It's at about 25 to 27 on my impulse. I put that braided line on there. Doesn't collapse but now it's missing when over 1200 rpms and spitting black smoke. Front 2 plugs are black as night like now its getting too much fuel and air. Gonna play with it tomorrow morn before the festivities start. Put the hose that was collapsing back on and see if the miss disappears. Thank all of you for your help. Thing is driving me nuts
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
breastquest
Site Supporter - II
Site Supporter - II
Posts: 119
Joined: Wed Jan 17, 2007 6:37 am
Location: ORLANDO
Contact:

Re: Help, finally started 520 conversion, issues

Postby breastquest » Wed Nov 26, 2014 9:54 pm

When doing the conversion did you collapse the lifters and cut the push rods to length?

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Wed Nov 26, 2014 10:17 pm

I kept the lifters in a gallons of oil while I did the rebuild so they wouldn't collapse. Didn't cut any push rods because I understood them to be the same because the stroke is the same. Are they not?
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
breastquest
Site Supporter - II
Site Supporter - II
Posts: 119
Joined: Wed Jan 17, 2007 6:37 am
Location: ORLANDO
Contact:

Re: Help, finally started 520 conversion, issues

Postby breastquest » Wed Nov 26, 2014 10:24 pm

No sir I thought the same thing but I was wrong and similar problems occured. Pulled lifters collapsed then cut push rods to length on each and they were all different. Jc stanley showed me how to do it in seconds and it was very easy. May not be the problem but it was mine

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Wed Nov 26, 2014 10:37 pm

Wow, always thought they were the same. Issue is I can't pull these lifters without splitting the case though. Not looking to go that far. Motor runs, but has issues and just doesn't have the uuumph I expected.
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
Bruce
Site Supporter - IV
Site Supporter - IV
Posts: 4793
Joined: Tue Feb 27, 2007 9:43 pm
Location: orange county fl
Contact:

Re: Help, finally started 520 conversion, issues

Postby Bruce » Wed Nov 26, 2014 10:43 pm

fletchster76 wrote:Wow, always thought they were the same. Issue is I can't pull these lifters without splitting the case though. Not looking to go that far. Motor runs, but has issues and just doesn't have the uuumph I expected.


yes you can you need a pick to remove the clips that hold them in its a bitch but its doable drop the intake and exhaust and remove all the pushrod tubes then pull the covers from over the lifters to give yourself room to work then take a sharp pick and pluck the clips out then use a magnet and pull the guts out of the follower then deflate the lifter by sticking a paperclip in the hole and pumping them til all the oil comes out then put em back together and you dont need to put the clips back in
12 foot Mamba "The Underdog"
Tired Gpu 520,Whirlwind Razor X

fletchster76
Southern Airboat Member
Posts: 120
Joined: Fri Sep 12, 2014 5:57 pm
Location: Pasco, FL

Re: Help, finally started 520 conversion, issues

Postby fletchster76 » Wed Nov 26, 2014 10:48 pm

These are mushroom style lifters. I've never thought you could or can I imagine how. I've got extra lifters and an extra case. I'll see if I can figure it out tomorrow.
13'6" Laser, 520 conversion, 72" 3 blade ngh

User avatar
Bruce
Site Supporter - IV
Site Supporter - IV
Posts: 4793
Joined: Tue Feb 27, 2007 9:43 pm
Location: orange county fl
Contact:

Re: Help, finally started 520 conversion, issues

Postby Bruce » Wed Nov 26, 2014 10:49 pm

breastquest wrote:When doing the conversion did you collapse the lifters and cut the push rods to length?


good call
12 foot Mamba "The Underdog"
Tired Gpu 520,Whirlwind Razor X


Return to “Aircraft Power Only”

Who is online

Users browsing this forum: No registered users and 5 guests