Sprint misfire at lower rpm, especially under load.

[GrahamFountain]

I've got a problem with the sprint I don't understand. It started okay yesterday on choke, but seemed to need it for a bit long: more than the few hundred yards that seems normal. But, at this stage it was just a bit lumpy at lower rpm under load. But after about a mile or so, with the temp gauge at about 1/4 it started to really misfire, popping and banging and refusing to tickover, with the choke having no real effect. I thought I was running out of fuel, but the gauge reads half and the low level light only comes on if I brake hard. There is, of course, oil and water in it.

I checked that there was fuel pressure at both carbs, fuel in the float chambers, and not overflowing, etc., and could find nothing. I also checked the point's gap and that the dizzy looked secure and not like it had slipped, but couldn't see a problem. I managed to get it home, during which time it did not smoke, overheat, or make any unusual noises, other than the misfire. I let it cool overnight and tried to start it this morning.

It didn't really start, and coughed, popped, spat, and kicked-back. I checked the fuel pump at both outlets to the carbs, pumping into a coke bottle on the starter. That seemed to be fine. I looked in both float chambers, and they're filled ok. Both carb pistons are free and the dampers are filled (now). So I pulled the plugs and checked the static timing. The plugs were rather sooty, but I'd been playing with the choke trying to get it to run, so that might not be a general mixture issue. I admit I've not checked them for a couple of months - the last time after I fitted solid butterflies. But it's been running really well, apart from needing the point's gap opening up a few thousand miles ago. Anyway, I swapped them for some others, not actually new, but they were clean and dry. That made no difference.

I also checked the timing, both at the flywheel and cam. The mark on the cam lines up with TDC on the flywheel with the engine going forward. I should, perhaps have checked the slack in the timing by seeing where it lined up with going backwards, but I forgot. The static ignition timing was about 8-10 degrees before, again going forwards. I should actually set it correctly, but my low profile 7/16ths socket has done a bunk, and I'll have to get another re-ground. But I think I'm sure the dizzy's not slipped anywhere.

Anyway, none of this has made a ha'porth of difference, and it still misfires and pops and bangs under about 2000rpm. Get it over that, and it seems to run smooth, though there's a clear shortage of power. It feels like fuel to me, but I can't find a problem there.

I though I had a spare set of new points and condenser, but, if I did, they've gone walkabout. But I've another couple of dizzys here and there, and one should have a good set. I'll do some checking of the condenser tomorrow. I don't have a spare coil to hand, and I haven't yet done anything to look at the spark, but I'll do that before I look at the condenser tomorrow. Think I've a spare for the herald that might fit.

Anybody think of anything obvious I've missed or can try with what I might have to hand?

Graham

[Carledo]

There are a couple of things that come to mind here, all relatively simple.

1) Condenser

2) Condensation or a crack in the distributor cap

3) Damp in and around the plug leads, especially down the tubes.

99% of all running faults like this have causes that are electrical in origin. Carbs, however fussy, don't just go out of whack for no reason.

Look at the electrics carefully, then look again!

My money is on damp in the cap!

Steve

[misterp]

Air leak somewhere?

What do the plugs look like?

[tony g]

As Carledo says but also check the rotor arm carefully for tracking.

Tony

[trackerjack]

I have just had this very same issue with a Toledo that I am looking after for a friend.
It drove me nuts and in the end I put another earth lead on the points plate and used one of my coils that I had kicking around for years and it runs fine now.

[GrahamFountain]

I had a good look at the cap and rotor already, and can't see anything. I replaced the cap a couple of months ago cos it had a crack. Wasn't as bad a problem as this tohough.

It's the way the problem came on overnight and got worse as I drove the first mile that has me a bit non plussed.

I intend to look at the condensor today.

Graham

[Jon Tilson]

Generally not a bad idea to move away from condensors these days as they are not good quality.

A maplin kit lest you keep the points and will have you up and running for sub 20 quid.

Anyway seems to me that if you go through the electrics and find nothing amiss a blocked carb jet is a possible culprit.

Jonners

[Carledo]

It's the way the problem came on overnight and got worse as I drove the first mile that has me a bit non plussed.

Graham

This is what makes me suspect condensation shorting is the culprit.

Steve

[GrahamFountain]

Think I've found it. I swapped the arm, inner cover, cap, and lead set for another, and it seems to have fixed it. I haven't got it warm or driven it, but it seems fine on choke on the drive. I will need to do more because I know that cap has a small crack that tracks when it gets wet, though it's all right else. Took the cap I'd removed and looked at it with some overpowered reading glasses I have, and there is a crack from the center to one of the plug lead terminals. Must have cracked in the frost over night.

Glad it's not the points, as I hate doing them with the dizzy in.

Anybody know a source of Snap-on low profile 1/4 drive 7/16th sockets in the UK?

Graham

[sprint95m]

Anybody know a source of Snap-on low profile 1/4 drive 7/16th sockets in the UK?

In the UK, Snap-on Tools only sell through franchises.
(The Franchise only buys the franchise from Snap-on.
There was such a vacancy advertised in the local press a couple of years ago explaining this, hence the reason I know.)

You can find your local franchise from this link (menu at the top):
https://buy1.snapon.com/catalog/catalog.asp


Alternatively, Snap-on tools are sold through ebay, Amazon etc
and furthermore, maybe more easily obtained, from experience I know that the 1/4" Teng Tools sockets are suitable for this task.




Ian.

[GrahamFountain]

the 1/4" Teng Tools sockets are suitable for this task.

Like this one?
http://www.ebay.co.uk/itm/Teng-TENM1401 ... SwiylXBueq

Graham

[GrahamFountain]

Has anybody tried this set?
http://www.ebay.co.uk/itm/BLACK-8MM-PER ... 1750992858

Graham

[MIG Wielder]

This was my solution to Sprint distributor removal. You need to turn down a 1/4in drive socket on hex length ( just long enough to cover the bolt hex ) and on total length then turn down the excess metal around the 1/4 drive square orifice to clear the bulge on the dizzy body. You then use it with a 1/4 drive "wobble bar" to get the ratchet up at an angle somewhere near where you can use it.
I had our machine shop turn up half a dozen of these about 10 years ago and the extras went to Club Spares. They have all probably been sold by now though.
Tony.

[GrahamFountain]

There are swivel sockets that look like they may fit. But they ain't cheep.

Graham

[mahony]

Has anybody tried this set?
http://www.ebay.co.uk/itm/BLACK-8MM-PER ... 1750992858

Graham

I bought a set of these initially to keep as spare set for the boot of my sprint, i ended up using them when i had some running issues as a matter of elimination and they have been fine, i mislaid the rotor arm supplied and just used the original, i will use the one supplied if i ever locate it , personally i would switch to electronic ignition also as it's a more reliable system.