zazza

I'm a hooked up newbie and have a G260PUM in a 54" Scarab, with a 257carb, clutch, pump and a pipe.

I’ve fitted everything myself and I was very happy with the setup ......now it sort of rhythmically losing power on WOT!!
It cycles from full throttle to half in a rhythmic manner....

I noticed also that it is not shutting down when I fully close down the throttle; it stays at very slow smooth idle!
Checked the carb for correct operation and I can see nothing wrong.

Took out the isolator block and re skimmed it to make sure it's flat, but had no luck!!

Reset carb to factory settings and still the same if not a bit worse!! (L2/H1)

lost now....still thinking it might be sucking air but I don't know how to proceed??
What the correct way of checking things because I’m lost. I don't have access to water often so if there are any checks I can do in the garage its better!!<o></o>

glennb2006

Might be an air leak.

But looking at the photos, check your carb isolator, I think you have it mounted upside down, the tapping for the water pump normally comes of the bottom pulse line.

Also, if running a lid on the model make sure you have enough air getting in (Run with lid off to prove this one). Do you have a clear breatehr on your fuel tank, if using a hard tank. IE can air get in when petrol is drawn out?
Is your radio / servo OK and not doing anything stupid at range when on the water?
Some things to check there.

Glenn

zazza

Thx Glenn

w3bby

Really basic on the idling issue (not meaning to insult your intelligence), have you removed the idle needle from the carb? Sometimes we forget the simplest things (like the transmitter at home[:@])

To check your tank fittings remove the one way valve and try without, could be it is not working properly and causing a vacuum in the tank.

zazza

i appreciate starting from the basics, but yes the idle needle was removed as soon as i had the engine!!

rcguy1411

as far as the not shutting off with the TX could be your end point adjustment or just not enough servo travel and if carb is closing all the way tou have an air leak somewhere (bearring case jug or carb) an air leak will cause the serging on the engine check to see if all bolts are tight replace gaskets check fuel lines a small pin hole will draw air in

zazza

welcome to my rescue rcguy!

Dan S

if butterfly is fully closed than there is an air leak somewhere like the others mentioned.
could be from the ISO block (make sure she is nice and tight),
could also be from a bearing even if you haven't had much fuel put through it, very rare but it can happen.

what is your oil/fuel mixture ratio (just for fun).
Check the butterfly again just to make sure, remove the velocity stack and see if you can close the butterfly even more by hand, if it is seated all the way than you know that is not the problem.
You can reinstall the velocity stack if you want but you don't need it, there is no gain in power using one or any loss of it if you don't.

Dan.

zazza

done the buterfly test,. It's sits perfectly.

ISO Block i resurfaced on glasee with 2000 grit wet sand paper to be extra sure and i've put in new gaskets....( i oil the gaskets before fixing them...is that bad??)
I mix 40ml to a liter - should be 25:1 an even a drop more....as explained i try to be safe with the engine.
Carb set 2 low 1 high - exhaust 12" 3/4 out....

Is it worth opening the carb and check the filter??? will it compromise the performance of the carb once opened??

It's been nearly a year i've been working on this boat.........and this one is busting my nerves.....ahh if i knew......

Joe Petro

My Feedback: (1)

It sounds like your pulse line or water pump may be leaking.
Plug the fitting at the engine and see if it shuts off.

Also, change the diaphragm in the carb. Once they start to get stiff you will start to go lean...

Let us know...


Joe

arrowshark

My Feedback: (1)

put a stock 257 carb on the engine i have had a lot of issues with carbs lately mostly due to ethanal in the gas as stated possible air leak thru the bearings or the case gaskets or possible warped case not seating properly also check the gasket at the cylinder base for possible leaks all of these will cause issues of idiling poorly or surging

glennb2006

It is worth checking the filter within the carb, though this will have nothign to do with the idle and not shuttting off problem, but a partially blocked filter might well cause it to lean off at high revs, which can create the surging you describe.

While there check the carb diaphragms, and might as well replace for the cost of them.

Glenn

blizard05

Iff your not using the stack,the stock bolts will be too long,and bottom out forcing the block away from motor causing an air leak when tightend

BMAD01

Zazza, You bring back memories! You said that you resurfaced the iso block. That's all good, but there is something I discovered way back when. The stock iso block has steel inserts inside the mounting holes. You can crank that sucker as tight as you want and all you are doing is tightening the inserts to the cylinder! Air can leak everywhere else! The very first thing I do on a new motor is take the stock iso block off and replace it with an aftermarket aluminum block. Never had a problem after doing this. I tried to upload pics, but kept getting an "internal error" msg!
Good luck, Brian

zazza

at least i'm having some comfort, that these are common issues!!

zazza

couldn't stop thinking....

zazza

any suggestions from where i could get an aluminium ISO Block!!

arrowshark

My Feedback: (1)

gizmomotors.com they have what you are looking for and fast shipping if you have any ? give bruce a call great guy to deal with

glennb2006

For Malta you are probably best off with someone like Dave Marles, Prestwich Model Boats. He lists them on his web site.

You can take a pulse line from your crankcase if you want to continue to run the pump.
Sounds like you made some progress, lets hope you solved the problem.

Glenn

ByronRC

My Feedback: (2)

Sometimes it could be the throttle servo as well. I had a delayed shut down today with my Rico v hull. Long linkage and a cheapo throttle servo can be an issue. Its not always your end points and linkage throw. Low battery and or bad/ cheepy servo can be the case. The throttle servo doesn't have to be high end but it shouldn't be bottom of the barrel either. Not saying this is your case, but it's something to think about.

rcguy1411

here is a little trick that will also help finding an air leak spray WD-40 aroud the iso block, cylinder gasket, or bearings if the RPMs rise then you have an air leak the serging i refered to was the changing of the RPMs(rising and falling) without changing the throttle position

zazza

Fixed it Guys!!!1

zazza

w3bby

Good you sorted the other problem out.

For spark plugs here's one that I have found useful over the years:
[link=http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp]NGK[/link]

Me I tend to go a 1/2 turn first, better or worse, if worse back off 1/4, then adjust 1/8 at a time.

zazza

so that's a maximum of a half a turn either way...on both needles?