Difficulty cold starting

[JonB]

Hi

My car is laid up while I overhaul the front suspension, but I thought I'd do an oil change so tried to start it. I have Dellortos, but I've always used the "pump throttle once before starting" approach, even though it's given variable results. I did read that this is the way to cold start a Twink with Webbers and that the Dellortos need choke only.

Last night I tried till the battery was pretty well flat. Today, same thing, except I had a look at the plugs. Wet, the engine is flooded. Hmm. I took each one out and dried it, then tried again to start. Eventually it puttered into life.

Strange thing here that I have never experienced before. When cold, it will misfire and with too much throttle (meaning, more than a tickle) it coughs and dies. Very hard to get the revs up. I suspect it is running very rich indeed. Once it is warm it runs beautifully.

All this is pointing to a problem with the carburettors when cold. Any ideas (or am I starting it wrongly)?

[billwill]

Maybe that thick oil you put in is restricting starter motor RPM. As it is cold in the UK at present.

We have snow here in North London, I don't recall when it last snowed this early in December.

[Orsom Weels]

Hi Jon,
Apparently the reason behind not recommending pumping the throttle with Delorto's is that some have accelerator jets that just squirt the fuel vertically straight down into the venturi, & not down the throats as would be expected. This can lead to fuel running back out into the air box if there is no air flow through the carb to draw it towards the engine. Should you then have a back fire, this could lead to a fire in the air box.
That said, I've always found full choke & no throttle pumping works best with Dellorto's, but if it doesn't fire up within a few cranks, give it a pump or two while cranking. Others will have their own favoured way/recommendations.
First port of call for a reluctant starting twincam, especially when damp, is always plugs for me. Cheap & easy to try, & nine times out of ten has the desired effect. The other well documented problem is fuel draining back, requiring a lot of cranking to lift it back up, there have been loads of posts on here discussing this, & lots of owners have converted to electric pumps or added some sort of primer system to overcome this. If the diaphragm & one way valves are good in the original mechanical pump, & all fuel lines & their connections are well sealed & leak free, this shouldn't be an issue though. After that, it's just the usual checks you would do on any other classic, points, cap, rotor arm, leads etc.

Regards, Tim

[vincereynard]

I second Tim. My twink totally refused to fire after a few test starts when doing the gear lever mods.

A new set of plugs and it started immediately.

[JonB]

Hmm, interesting. My plugs are only a year old. Probably the gap's not set right though.

[Orsom Weels]

Age doesn't make much difference, if they've been flooded a time or two, or got fairly damp, the insulation seems to break down & the plugs performance suffers. They aint wot they used to be , time was when you could give em a good clean, warm em up & away they'd go again. Not any more it seems, I've had virtually new plugs go dead after suffering the above. Stick a new set in & see what happens, worst case scenario, you have a spare set of plugs .

Regards, Tim

[vincereynard]

Jon,

I don't understand now.

I thought you stated in your oil change post (submitted a few minutes before this thread) that you had fired it up after the change and it "purred".

[JonB]

Yes, but only after it had warmed up a bit. While cold, it ran lumpier than a bag of spuds.

I'll try again this morning with just choke.

[jimj]

My experience is that different engines behave differently. Assuming that, after the car has been standing quite a while, you`ve churned the engine over enough to pull fuel through, you`ll find a particular routine that suits yours. Our S3 with a Sprint engine on Dellortos has always fired up easily with 2 pumps of the accelerator pedal, smooth running immediately. Our Sprint, identically equipped, needed no pumps just choke then slip the choke away as you catch the revs. on the accelerator pedal, but much more churning.
However, there`d always been a tiny unevenness at light throttle openings that defied expert balancing etc. so I booked the car in with a highly recommended rolling road wizard. He thought the car needed jets somewhere between the standard options and soldered up, and redrilled my standard Sprint jets. The car now runs perfectly and to start from cold needs no choke just 4 pumps, then it fires up immediately and it`s as smooth as can be.
No matter how competent and well equipped owners may think they are, you can`t beat having an expert with a rolling road set the carbs. up properly. Then DON`T fiddle with `em.
Jim

[miked]

A little heat beneath the engine makes quite a difference. I have a few tube heaters and at times have sat one of them under the sump overnight. It takes the chill off the oil and hence the viscosity. Also takes away a bit of that dampness as the heat rises into the engine bay. In terms of starter current it makes a difference.
In addition I have sat a 12 inch or even 24 inch one in the car on a time clock. Keeps everything nice. Stored a plus 2 in someone's garage over winter. No problems with damp.
Mike

[JonB]

Interesting, but I don't think I'll be preheating my engine (inconvenience). I can see it would help reduce wear!

I tried to start this morning with choke and no throttle pumping. Much better. Engine caught on the second attempt and ran (a little stumbly) but very soon started firing on all cylinders. So that's sorted, thanks!

Regarding tuning, I agree it is a specialist job. Those Dellortos look intimidatingly complex. I do have a Gunsons Testune and flow level meter so I can try them to see what the mixture looks like. I'm guessing "very rich" if the condition of the exhaust and plugs is anything to go by. I read on here that one should adjust the mixture to a blue flame, then wind back a little to the edge of yellow (slightly rich, in other words). I need to review those tuning threads, once the old girl is back on the road.

[RichardHawkins]

With reference to plugs, I read a monthly contribution by Dave Walker (Emerald ECU) in Practical Performance Car. His view is that fouled plugs seldom recover. When he is setting a car on his rolling road, the starting mixture is often considerably wrong. He uses cheap plugs to get close, then installs good plugs before returning the car to the customer.

Richard Hawkins

[jimj]

That sounds a bit unlikely, how much cheaper are cheap plugs? Does he mean old plugs?
Jim

[JonB]

(Tuning Dellortos)
..on the other hand. The service manual says this (paraphrasing because I don't want to retype it all) in section L page 66 "Synchronisation" (balancing Dellortos):

• Disconnect throttle cable, unscrew idle speed screw
• Set butterflies to close fully
• One full turn on idle speed screw so it contacts the lever
• Fully close mixture screws then back off 2 full turns
• Reconnect accelerator cable
• Start engine, allow to reach normal operating temperature
• Adjust idle screw so engine runs at idle speed
• If engine runs irregularly, "adjust mixture screws on each barrel to obtain regular running on all barrels". Turn inwards to weaken mixture, outwards to richen.
• Readjust engine speed

I'm a little bemused by this. They are effectively saying you should adjust the idle mixture screws blindly. How are you supposed to ensure they are all at the right setting if you aren't measuring the result in some way? All very empirical!

[alan.barker]

Jon,
if your car starts and runs it's not too far off.
All you need to do now is the balance and then after a drive when the engine is hot fine adjust mixture.
If you can't take your car for a run to warm up the engine then imho leave the carbs for the moment untill you can drive it.
Alan