Poor starting

I fitted a new SU carb years ago and had similar probs to yours turned out float chamber vent was blocked.

It sounds like your engine will run from fuel pumped in by the Acc pump, ie squirted when you operate throttle but stalls when this runs out which points to the possible causes previously listed.

Is there any restriction in the fuel line from the tank? might be worth blowing it back just in case.
 
mixture screw

Hi Russ

I have just had another look at the second picture

I think I can just see the tip of the mixture screw in the circular recess between and just below the butterfly's



Tim
 
I have zoomed in on the pics, the idle screw could be behind a sealed plastic plug, it will be on the side of the carb.

No carb can be factory set, every engine is different depending on wear etc as to how it breathes its mixture.

It also has an electric choke, make sure it's not staying on choking the engine of air.
 
Russ, VolvoPaul is the expert on these issues.

I would have a bit of a recap, and think about what the problem is not.

So, what have you replaced and what do you know definitely works? And if you have changed somethng, and the outcome is no different, then move in to the next issue. A bit of a plod through this might throw something new up.
 
Does this engine have TKS?
Sounds very like symptoms I had albeit on a 3.0L with a TKS.
The problem was the connection to the oil pressure switch.
You can clean up the terminals on the pressure switch to see if thats the problem, but on mine they would corrode enough to loose the connection again after a week or two. In the end I soldered leads to the pressure switch and used a better, tighter connector. problem fixed for good.
Worth a try!
 
could be

low fuel level in carb once its warmed up the fuel expands
or
angle of engine / boat means the carb is running weak as fuel level iffy
or
air being drawn in causing a weak mixture
or
carb was set up for a warm climate and wrong jets fitted for uk temp
cant see it being a blocked jet or choke as once warm fine

cheers
mick
 
When petrol engines have starting issues and only seem to run OK once warmed up, it's a sign something's not quite right.

It's impossible to say without being there that it's one thing or another as a methodical approach is needed. FWIW my approach is to sort out the ignition first, then go on to the fuel.

Here's what I would do if it were mine. Not sure on your experience so feel free to disagree but don't be offended, as none intended:-

1. Remove and check the plugs. What colour are they around the centre porcelain electrode? Black? Nut brown? Or white? This gives you an indicator about fuel mixture later on. See 6 below.
2. Clean and regap the plugs before refitting.
3. Remove the dizzy, check inside cap for cleanliness, and the electrodes around the edge are clean not pitted and crusty. Ensure the centre carbon brush is clean and moves freely in and out and protrudes far enough out to be pressing on the rotor arm when put back in position. Rotor arm should be clean, shiny brass all over - use Brasso or Duraglit. Particularly at the trailing edge where it touches the dizzy electrodes.
4. Clean & gap the points and replace the capacitor (aka condenser) if it has one. If electronic ignition, check there is a decent spark at the plugs by removing one and turning the engine over a couple of times.
5. Check the timing. This is critical to starting, smooth running, efficiency and power. But should only be done after 1-4 above. Get a timing light, identify no.1 plug lead and fire it at the front pulley at idle speed. There should be a clear fixed mark on the block, and a groove on the pulley. With the engine at idle the two marks should be roughly in line. As you manually rev the engine, the pulley groove mark will move as the timing advances. Note which way it moves when the engine revs, and allow the engine to idle again. Now look again the the timing at idle. Is the groove slightly advanced relative to the fixed mark, directly in line, or after it? It should be about 1cm before the fixed mark (rule of thumb), i.e. advanced. If retarded or exactly in line it won't run well or start easily and will drink fuel. Ideally refer to manual on precise info but this will be near as dammit. If not, adjust (rotate) dizzy until it's right.
6. NOW you can look at the carb. The plug colours from earlier will give you clues here. If they were black, it was too rich and another clue is that the engine will be hunting. If nut brown, perfect, leave it. If white, it may be OK but probably a touch too lean - depends if you want power or economy. Refer to manual for which screws to adjust - or posts above give guidance on this.
7. Once the mixture is sorted out then adjust idle speed so engine ticks over smoothly and evenly.

The order of doing the above is important to get the right result, otherwise you can end up going round in circles and replacing random parts needlessly.

As VP says above, the carb will need setting up to suit the engine, but unfortunately that's the bit that's hardest to explain in writing as it all depends on sound and feel.

Good luck :)
 
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Sounds like the choke may not be working correctly, mixture needs to be rich to start and run ok cold. Is the tickover speed ok? Is there is something to increase tickover speed when cold?
 
As Trundlebug has suggested I think my first port of call is to check the plugs to see how the engine has been running and work from there.

A pm and phone call from another forumite has advised the HT leads could be breaking down especially in cold damp conditions where they could be arcing and having a weak spark. When warmed and dried out they start to perform and thus letting the engine tick over. A cheap fix and would be best to change to copper core leads.

Also the oil and temp switch wires mentioned by dpd are worth a look.

After that if needed I will get the carb adjusted.

Thank you to all for your advice. Will let you know how I get on.
 
Sorted, well mostly.
Started up the engine today after fitting new HT leads. It started much easier and ran for a while at 1/4 throttle and when at half way to normal running temp I throttled back to neutral position where she began to tick over without cutting out as it had been doing.
The old leads had tags on them dated 2005 so I guess they are the originals.
Shame I went the costly route first with the new carb.(anyone for a used one)?

Thanks to Lensman for his pm advice and others that contributed.

Just got to find out what the clackling noise is when I first start up which then disappears after warmed up. Had flappers changed so don't think its that. Not a tappets noise as mentioned before.
Could it have something to do with the thermostat as the noise goes away at operating temp? Could it have broken lose from its seating as water is trying to pass and then clears when it opens?
 
russ said:
Sorted, well mostly.
Started up the engine today after fitting new HT leads. It started much easier and ran for a while at 1/4 throttle and when at half way to normal running temp I throttled back to neutral position where she began to tick over without cutting out as it had been doing.
The old leads had tags on them dated 2005 so I guess they are the originals.
Shame I went the costly route first with the new carb.(anyone for a used one)?

Thanks to Lensman for his pm advice and others that contributed.

Just got to find out what the clackling noise is when I first start up which then disappears after warmed up. Had flappers changed so don't think its that. Not a tappets noise as mentioned before.
Could it have something to do with the thermostat as the noise goes away at operating temp? Could it have broken lose from its seating as water is trying to pass and then clears when it opens?
Click to expand...

possibly an electric choke adjustment. from recollection, adjust so that the plate over the carb inlet is just closed. have you checked for blow back around the rocker cover too (gap in the valve guides when cold). that said, could be completely normal as my 5.0l mpi use to 'tick' on first start up and it ran sweet for a couple of years. Time to go and enjoy the boat now you've found and resolved the main problem.

Well done btw for digging in to the root cause, whilst the other changes may appear a waste of time, you at least know your engine a whole lot better now which has to be a good thing
 
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russ said:
Not sure what the box is on side of elbow, could be an ECU.
No contacts in the dizzy, I'll look to see if there is a capacitor but are they only
fitted if it has points?
I have filled up 3-4 times this year so should be OK although only showing 1/4 tank at the mo.
Just cant think why once warmed up for 20-30 mins she runs fine.
Click to expand...

the box on the elbow is prob.a ignition modual that helps control the timing from the dizzy.
i have the 5.7merc with the thunderbolt ignition and that's what it is on mine.
glad you've got it sorted with the leads.
 
I use to check HT leads using a jump lead with one end earthed to the engine block and the other following each lead, if it was the insulation breaking down, you would see the spark jump. Also used on the distributor cap to check for cracks, better to check in the dark. This does not check the core conductor but an uneven idle should ID that.... Lots of good advice given by the experts as usual and now the OP has a spare carb as a service spare to boot!
 
Which model 5.7 do you have? It definitely has electronic ignition as the module on the riser is the ignition module, but does it have a knock sensor same as my 5.7. If so you can not adjust the timing or idle or mixture without putting it into service mode first.
If it has a knock sensor it will have a wire going to a sensor screwed into the block just in front of the starter motor down on the starboard side of the block under the exhaust manifold.
If it has this version of ignition system then locate a purple and white wire at the rear of the carb near the distributor, remove the plastic bung and connect it to an earth, you will hear the engine note change as it is now in service mode allowing you to adjust idle speed and mixture, when its running smoothly at 650rpm 'in gear' remove the earth wire and the ignition module will lock onto the new idle speed and maintain it.
The mixture screw is under the metal cover at the bottom of the carb as others have described, you have to carefully remove it with pliers so you can get at the screw.
Make sure the choke isn't staying on too long and flooding it also.
 
Can I piggy back on the thread....I was following this as I had similar probnlems, my 2000 mercuiser 5.0 was serviced in July, ran like a dream, didn't use for about a month and then took her out towards end of Nov and had exactly same symptoms as described here.

Started her up last week ( like a fool, hoped there would be a half decent day soemtime over the 10 days holiday to take a spin around the bay with the christmas houseguests) had same symptoms along witha strong smell of petrol coming from exhaust, my assumption that there was imperfect combustion.

I needed to keep revs well up ( about 2000 rpm) with throttle pushed welll fowrard, if I tried to throttle back it would start to run very rough, strong smell of petrol and it was clear it was about to stall. It took almost 10 mins for gauge to reach the line for normal operating temperature then right on cue the engine ran Very smoothly, unburnt fuel smell fell away and I could drop throttle right bak to idle and it burbled away completely happily at about 900 rpm.

So despite similar symptoms not convinced it is HT leads on mine.....any ideas?
 
Your choke is staying on too long by the sound of it, remove the flame arrestor and check if the flap moves freely. If its an electric choke check the wire is connected and it has 12v when the ignition is on, and that the terminal goes to ground through the bimetal heating strip as if it broken the choke will go off very slowly as it gets warmed by the engine instead of more quickly by having 12v going through it.
If its not electric then it is heated directly from a hotspot on the inlet manifold on the starboard side of the carb, you will see a metal housing with a rod coming from it up to the choke flap, it also has a bimetal spiral in the housing which is heated where its screwed to the manifold, sometimes the screws work loose so it doesn't get direct heating from the hotspot so it will take much longer for the choke to go off.
Hope this isn't too confusing!
 
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