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4.3L idle and running probs

D

dessie

Member
Hi from sunny Scotland. Due to some unseasonal sunny weather I decided to fire up my boat for the start of the season. On the trailer the engine started well and after the fogging oil burnt off idled quite happily for around 15min when I shut it down.

I took the boat to the loch the next day and again it fired up and idled great. However after a while it started running rough and would not idle (after the choke had come off perhaps). I took the boat out for a run and had great difficulty getting her onto the plane as it felt as though it was only running on 3 or 4 cylinders. After a little while it appeared to run on 5 and later on there was a small bang, perhaps a backfire,and it ran perfectly on all 6.


Today I checked and adjusted the plug gap but the engine still starts great and idles fine for a short while then struggles and stalls.

Engine is 1990 4.3L with 2BL Mercarb.

Any suggestions welcome.

Thangs for reading ;)
 
Is the fuel pump failing? Look at the fuel pump's clear drain tube running to the top of the carb...is there fuel going thru it? Pull the end off at the pump and spray some carb cleaner into the nipple on the pump...it may be plugged w/varnish and not allowing fuel thru it from a ruptured diaphragm. Did you look under the distributor cap?
 
Ayuh,.... I agree with Guy,.... 'n the Carb might need rebuildin' to...

Seein's it's a New Season,.... Maybe a Tune Up, 'n Full Service is in order...
 
Carb rebuild and clean all jets out, I had this problem on an outboard... after I did a rebuild she flew like a bat out of hell!
 
Hi, sorry for not replying sooner (work calls). Weather been a bit rubbish so have been unable to get a look at the boat. I was thinking about rebuilding the carb so this is on the list for sure. In the immediate future I will check all the other items suggested and report back. Unfortunately it still gets dark quite early and by the time I run kids about etc etc.
Guy, is fuel in the clear drain pipe a sign of a ruptured diaphram or normal condition?
Sure do appreciate all the help:D
 
...is fuel in the clear drain pipe a sign of a ruptured diaphram...
Click to expand...
Yes...that is the purpose of the hose otherwise the fuel would dump into the bilge and the next engine start is KABOOM! The Mercarb 2 BBL requires a special base gasket. I have two of them in a 2 pk, PN 27-807982 is the one w/2 separate holes. I don't have the oval type. I'll send you one for nothing just send me a PM with your address.
 
Hi Guy, that would be really good of you, as long as you are sure you have no need for it. I am concerned as to the postage costs to the UK and do not want you out of pocket.If I can Paypal the cash to you or something please let me know. I have been reading your posts re said gasket and was planning to source one when I was getting the rebuild kit and new float. I have been studying hard on carb rebuilds as I have not really had much experience in this area, but nothing ventured nothing gained.

Thanks again

Dessie
 
The Mercarb is simple to rebuild. Use a digital camera and take pics. as you disassemble it. Soak the parts in carb cleaner overnight or at least 4-6 hours to dissolve old varnish. I never submerge the carb bowl in cleaner...just fill it up w/cleaner and lay the top cover over it and let it soak. Make sure to remove the venturi assembly and soak it well. Blow all parts dry w/100 psi compressed air. Make sure to replace the accellerator pump and the float if it is heavy or fuel logged. Take as many pics. as possible and view them on a television during reassembly.
 
Had a spare few mins so started the beast and guess what, started 1st turn off the key and idled quite happily for a good 15mins until I shut I shut it down :confused:.

I did have chance to check the clear pipe from carb to pump for fuel and there was a small drop about the size of medium size raindrop of petrol smelling liquid, I'm not completely convinced it was pure petrol as the smell was not that strong.I have not been to the shops to get some carb cleaner to spray into the pump yet. Looked under the distributor and all looked ok (cap and arm replaced mid 2010).

What carb cleaner do you guys recommend?
 
...a small drop about the size of medium size raindrop of petrol smelling liquid...
Click to expand...
fuel turned varnish. Use what's available from an autoparts shop or Seafoam if you can get it.
 
Can get Seafoam on Ebay, around $30 delivered:mad: Is it worth adding it to the fuel or going straight for the carb strip down. Another stupid question - where do you get 100psi of compressed air in the house. Do you have your own compressor or nip round to the local garage?
 
My own compressor...do you have access to a portable tank of air? Fill it up at a gas station and you have compressed air at home...just need a hose and nozzle. $30 is alot for Seafoam...$8.50 - 11.00 here. Is there an auto parts shop nearby to get some solvent? If you are extremely careful you can use lacquer thinner outdoors only since it is flammable and extremely dangerous to breathe...it will kill you or use paint thinner, just soak it longer. Lacquer thinner is a potent solvent...it will dissolve anything non metallic.
 
Hi, most auto shops stock Cellulose thinner, I'll give that a try. I do have some Acetone in my shed from cleaning GRP tools. Any use? I'll have wee think about the 100psi problem.
Any thoughts on trying Seafoam in fuel or not bother and just rebuild?
 
Acetone will dissolve fuel varnish as well as lacquer thinner...use it outdoors...extremely dangerous to breathe...it will kill you! It will also dissolve any paint on the carb.
 
How old is the gas in the tank and do you have a fuel filter in line ? ...... run a 5 gal. can of fresh gas to the carb via the fuel line to the carb.

I'am William Wallace
 
Hi Guys, update! Got myself some Seafoam( bargain $21 delivered) and put some into the fuel pump and left it overnight. I added the rest to the tank at a ratio of 2oz/gallon. I fitted the base gasket that Guy kindly sent me and headed off to the loch.
The boat started off the key and ran all day with no problems what so ever, ran it upto WOT 4800 rpm 47mph and not a stutter. No sign of fuel in the clear pipe, I will keep an eye on this though. Happy days!:D
 
Make sure the clear pipe nipple on the fuel pump is open and not gummed up w/fuel varnish...stick a carb cleaner spray nozzle into it and blast away. Glad it's running.
 
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