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Herald 1200 running rich?


geoff121
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Hi, I have just bought a 1966 1200 Herald Convertible and have a problem with it. It starts OK but misses at low revs, as the revs build it pulls lovely but as the revs drop it is back to missing again. The car did this even worse when I bought it. Since then I have replaced the entire ignition system and fitted a Simonbbc electronic distributor, also I have fitted a new Solex carb. Every time I work on the car it is slightly better, but only slightly. Right outside my front door is a main road with roadworks in both directions, a nightmare with poor slow running.

Can anyone tell me what is wrong, please? Geoff

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Have check the slow running jet in the side is clear,

 

then fuel pump full of debris

 

partial blockage at the back of the float needle valve

 

loose pipe and hose connections especially of the tube from the top of the tank

 

have you reset or checked the timing since fitting the electronic unit , as this will differ from when on points

 

pete

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Thanks for that Pete, have checked all of that and intend rechecking tomorrow. Checking the timing is a little more difficult as I cannot get the engine to run slow enough and run to check it without the bob weights advancing the timing, so think it is way to far retarded at the moment. It's bloomin' frustrating!

Cheers, Geoff

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with any down draft the throttle plate position has a lot of effect if its open too far to geta afaster idle you cut off the idle circuit and will never get any adjustment on the volume screw.  it has to be slowed down

 

the fact yours wont idle is probably nothing to do with this idea, but ???

 

 

is the base of the carb flat, its a common place to suck air as the flanges get distorted by over tighening on a soft gasket

 

are you sure the slow run jet has nothing lurking inside the jet body its only about a 0.45mm hole and the crap can also be in the airway down to the throttle plate zone or inside the brass body of the jet.

 

checked the tappet clearances ??   all 0.010"  cold

 

we may need a cam timing check    explain that if and when  ..its easy.

 

for now ignore the timing marks and turn the dizzy to get the fastest idle and just back it off a little

 

but if it revs but wont idle its still looking at the slow run circuit as a contender there could be  valve /HG problem 

 

can you get a compression test done  ????   to check the fundamental basics 

 

Pete

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Tried all that and it is running a little better, found 2 air leaks, carb to manifold and manifold to engine. Will have a compression tester that I can borrow next week. Now I have messed up my throttle cable so I have ordered another and knocked it on the head for the day and as I am going away for a few days tomorrow that is it for this week.

 

If it's OK I will contact you next week to pick your brains again, Cheers Geoff

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buy a push bike brake cable  a long ladies type will make two for peanuts and are better spec, than most of the dedicated ones available

 

may need a solderless nipple to make it connect as it will have a 'bare' end inner  once cut to lenght.

 

 

and the left over keeps in the boot for another day

 

enjoy a few days holiday ,    

 

Pete

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Hi Pete

Well, the compression figures are interesting. All 4 are the same but they read as 200psi, as standard is only 133psi it has had a huge lump taken off the cylinder head.

Probably explains the poor slow running. All I can think to do is fit a second head gasket to lift the head a little and reduce the compression pressure thought it won't drop it to standard. Either that or a new short engine, and I don't suppose one of those is available.

Oh well, out with the spanners and away we go!

Cheers, Geoff

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 All I can think to do is fit a second head gasket to lift the head a little and reduce the compression pressure thought it won't drop it to standard. Either that or a new short engine, and I don't suppose one of those is available.

 

 

I wouldn't fit two head gaskets, recipe for earlier failure if it works at all. There is a company that sell specially made plates to reduce compression ratio but can't seem to find them on the web at the moment, will keep looking. Higher compression will be down to the head being skimmed heavily over the years, so it would be that what would need changing not the short engine. 

 

Any good engineers should be able to measure the depth of the head to give an indication of how much has been taken off in the past, you'd need to take it off of course.

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have you checked the gauge on a known engine? they are not usually accurate, and do get knocked about. 

 

Have a measure of the head depth, as in from bottom to top faces. Then see if you can find the original depth. That will be a strt point. If it has been massively overskimmed, best bet would be another head. Often available for not huge sums (they seem to sell for £10-50 at jumbles)

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Yes, checked gauge against another. Got head off and ordered another plus new gaskets etc. The old head gasket is solid copper whereas the new one is composite, interesting. Just got to wait for new head to arrive, should be the week after next, all this lovely weather and I cannot drive my convertible.

Thanks for all your help and comments. Geoff

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From the Owners' Repair Manual:

 

Choke                           21.5

Main Jet                     112.5

Air correction jet         175

Pilot Jet                        45

Pilot air bleed               85

Econostat petrol jet    100

Econostat air bleed        1.2

Accelerator pump - set on short stroke (outer slot)

 

Chris Longhurst did an article in the Courier years ago (about 1985) giving different jet listings for the different versions of the engines and the later ones used a 115 Econostat jet, although he didn't think it made much difference.

 

In case it matters, and for what it is worth he also says:

""One point should be made about floats in PSE1 carburettors.  If a plastic float is fitted, the washer under the needle valve should be part number 512658; if a brass float is fitted, use washer 510742.  The washers are a different thickness"

I've no idea how thick those part numbers are, but obviously this could be a problem if the bowl is overfilling.

 

C. 

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