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MG Midget and Sprite Technical - misfire on strat up which then clears

Sprinted the frogeye on Sunday and everything was fine once the car had been running for about five minutes.
On start up, it just isn't revving properly, then once I've been driving for about 5 minutes, it runs as usual.
Left if for 45 minutes, then same thing again, so not really enough time for the engine to get completely cold.
Not checked anything yet. Running 123 dizzy. 97 ron fuel and not changed anything. Any ideas?
G Lazarus

That bloody damp garage of yours Gary

Moisture inside the cap

Out with the Vaseline to insulate the joint between cap and body after WD40ing the innards. Close it up after smearing the base of the cap in it after you take outthe damp already in there.

Anything ELSE will be darned expensive to fix, so hope it is THAT
bill l

May be that Bill, but I didn't get it when I started the car yesterday morning (after not driving it for two weeks). It ran fine with no problems. It was only after I started it again an hour after after arriving at North Weald.
I will do what you say though.
G Lazarus

It sounds like the plugs are fouling - either with rich mixture or oil.

It could be valve guides/stem seals allowing oil to run down, although this is normally more of a problem when left for longer time, like overnight!

Possibly a spark plug on its way out.
Dave O'Neill 2

Yes, I've been running the engine a bit rich since the burnt piston damage earlier in the year. I'll check the plugs and replace if needed.
Ta
Gary
G Lazarus

That's a good point Dave and Gary I misread the problem anyway

I made the fatal assumption that I knew wot I wos talkin abaht

Too rich mix sounds like the reason if you have been working its little socks off

How did you do?

How was our mate?
bill l

Our mate was a no show I'm afraid, and I couldn't be bothered to call him.
I was outclassed by some rather special minis (one posted the same time as Porsche GT3!). But I had a great time and Gaps dun good :0). I'll try to post a video or two this evening.
G Lazarus

I forgot to ask...which plugs are you using?
Dave O'Neill 2

I can't remember which ones they are NKG bp6es or NKG bp7es (whichever is the cooler one). Also it's the R version for electronic ignition. They've been working fine for the last six months.
G Lazarus

The only time I've had anything similair was on a Nova SR which was weeping coolant into 1 of the cylinders.

Would take a minute or 2 to clear that cylinder in the morning when started.

Not overly helpful I know

Any hint of whether its 1 cylinder not revving...or all of them ?
Dean Smith ('73 RWA)

Bp7es is the colder plug

Whats your plug gap?, if your running a tad rich, and a stock plug gap, on cold running plugs. it could just be a build up of crud on the electrodes... clean them up, plus a wider gap, (.030 - .035) may solve some issues

Prop
Prop and the Blackhole Midget

And rear wheel off the ground!

G Lazarus

And a few more here halfway down the page.(C) Nick Cook, Harrow Car Club.
https://www.flickr.com/photos/ncstriker/page1/
G Lazarus

Good grief gary,

If there werent gaps before, there are now... any idea what happened to the left front wheel and tire ...hahaha

Prop


http://www.flickr.com/photos/ncstriker/page1/
Prop and the Blackhole Midget

Here's an update on my rough running on startup.
I started it this evening and it fired up immediately but rough running while i pulled out of the garage
I've checked and cleaned the plugs which were nice and dry BP7ES R and plug no.1 & no.4 were sooty, no.1 being slightly blacker, but more around the rim of plug rather than the electrode. no.2 & no.3 were lovey light brown colour. Cleaned them all up, WD40'd the dizzy cap (which was nice and dry anyway). Vaselined the rim of the dizzy cap just for good measure.
Then started it up. Again, the same slightly rough running which cleared after five minutes of running.

Thinking back to the other day, It ran fine when I started it (after a two week break). Ran fine as I drove down the motorway, 30 miles at motorway speeds, but when i restarted it an hour later I felt this few minutes of rough running. I then really thrashed the hell out of it all day, but had the same rough running for 5 minutes every time I started it.
I'm now wondering if it could be the carb (single Hif 44)?

Your thoughts would be welcomed.
G Lazarus

Im not sure what would be the culpret in the carb that would get better after 5 minutes of running rough

Fuel related, id probably look to the fuel pump, if SU pump id suspect the diaphrm wear or the points needing cleaned or replaced

Prop
Prop and the Blackhole Midget

It could be an idle problem, Gary.
Gaps is basically idle.
Nick and Cherry Scoop

Just curious gary,

What about the carb do you suspect is the issue at play

Prop
Prop and the Blackhole Midget

Oil?

Dashpot oil, how is it for level?

I wouldn't expect the HIF to go much out of tune if it's still running OK normally

I wouldn't expect the HIF to go much out of tune

bill l

Just theorising now, but the HIF carb has an "0" ring on the inner end of the shaft thing that acts as a choke. If that were split, it might cause an upset to the running until fully warmed up?

That said, my first thought was that a valve was sticking, and only freed up with higher revs and when the engine was fully warmed up so that the valve guide expanded to free off the sticking valve stem. Not sure how you would test for that, or why it should suddenly develop such a fault.

Sorry Gary - this isn't being much help is it!
Guy Weller

Gary

Have you done a compression check?
Bob Beaumont

Good idea Bob. That would reveal my sticking valve theory!
Guy Weller

I'll see if I can get time to do a compression check tomorrow and also check the dashpot oil.
G Lazarus

I wanted to say sticking valve also, but didnt that get ruled out...if not, count me in on sticking valve also...but im going with one of the 4 exhaust valves

Id also like to add my name to sticking dog legs/rusty dissy centrifical springs inside the dissy

Prop
Prop and the Blackhole Midget

"Id also like to add my name to sticking dog legs/rusty dissy centrifical springs inside the dissy "

Prop, it's a 123 dissy.

That smoke has really gone to your head!
Dave O'Neill 2

Gary, when you say slightly rough running, what actually happens when you put your foot down? Can you get the revs up eventually, or does it dip, and splutter along at 2 or 3 thousand?
Nick and Cherry Scoop

I'd say probably through the rev range rather than a mid range flutter.
G Lazarus

Just to give feedback. I started the car early on Friday morning (without topping up the dashpot oil), and there seemed to be no hesitation or splutter, so I can only assume that it was mucky plugs. I drove down to Dover from London at a rather swift pace (having woken up at 05:35 when I should have already been on the road at 05:00!) No dramas. Topped up the dashpot with 3:1 oil, which was actually a bit low, then drove about 700+ miles over the weekend, mainly at speed.
No problems whatsoever and the car started on the button, even parked outside the hotel on a very damp morning.
I'm not 100% certain if it was the dirty plugs, low dashpot oil, slightly damp dizzy or a combination of all three. Either way, it seems to be back to its normal good self.

Two minor problems were;
1. The passenger side bonnet hinge bolt fell out (into the passenger footwell) on the way down to Dover. Which was very easy to put back, as it's a bolt into a captive nut.
2. The bonnet stay came loose on the way back. Not a difficult job either, but will have to be sorted next time I open the (frogeye) bonnet).
Thanks for all the feedback and advice

Gary
here's an image waiting for the ferry home (early evening) at Dunkirk.
G Lazarus

here

G Lazarus

Great job gary,

Its a midget... sometimes they just hold there secrets...id guess its a combo ...its almost never one single issue.

Prop
Prop and the Blackhole Midget

This thread was discussed between 22/09/2014 and 30/09/2014

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