My 1850 is playing silly games

[Bumpa]

Lots of things to try when I can find a dry day. Roger, thanks for the info on Strombergs, but my 1977 car has SU carbs.

[MIG Wielder]

Its a long shot, vac advance not working?

I'm thinking along the same lines of the problem being associated with vacuum advance plus centrifugal advance. Under the conditions where you are running along the dual carriageway at say 60 mph there will be 10 - 14 degrees of vacuum advance plus 17 -22 degrees of centrifugal advance. It's round about the maximum you can get. Under these conditions the L.T, wire to the points ( and also the baseplate earthing flexi; lead ) will be at maximum stretch, so I'd be checking these for breakage etc. ( see photo above ). There again I would have expected that giving the car some welly would reduce the vacuum and the problem would go away. And the rev; counter would be jumping around which it isn't.
Tony.

[dollyman]

Lots of things to try when I can find a dry day.

I think you might be in for a long wait Mike

Tony.

[Bumpa]

Its a long shot, vac advance not working?

I'm thinking along the same lines of the problem being associated with vacuum advance plus centrifugal advance. Under the conditions where you are running along the dual carriageway at say 60 mph there will be 10 - 14 degrees of vacuum advance plus 17 -22 degrees of centrifugal advance. It's round about the maximum you can get. Under these conditions the L.T, wire to the points ( and also the baseplate earthing flexi; lead ) will be at maximum stretch, so I'd be checking these for breakage etc. ( see photo above ). There again I would have expected that giving the car some welly would reduce the vacuum and the problem would go away. And the rev; counter would be jumping around which it isn't.
Tony.

I've got a decent strobe gun so will check out the advance and vacuum next time I can get under the bonnet. As Tony Dollyman said, it might be a long wait. Meanwhile the garage is occupied by my Z3 which has a broken front spring. Grrr. And the spring punctured the new tyre. Double Grrrr.

[marshman]

According to the XC weather site there is a dry sunny spell coming in your neck of the woods for an hour or so around 9am on wednesday, we expect answers then

[Bumpa]

Hello all. Some of you may remember my thread from way back before lockdown about how my 1850HL was losing power in a big way when travelling on main roads at 70 mph, but only when the engine was fully up to operating temperature - you can read all the grizzly story above here. It was dire and struggled to maintain 40 mph flat out.

I had a lot of good suggestions and implemented some of them. For example, I swapped the points for an electronic ignition trigger (much smoother running and better starting but not the cure), checked plugs, cap and HT leads, fitted a fuel filter, checked and rechecked the dynamic timing with my strobe gun, fitted a new fuel pump, all to no avail.

Thinking about it one night it suddenly dawned on me that it was to do with heat. If the engine was only recently started from cold it ran nicely until it heated up, typically once I had done in excess of 5 miles. What changes because of heat? Ahaha, the waxstat jets on the SU carbs. So I dismantled the carbs and with the jets on the bench I used my heat gun to watch what happens. Sure enough the waxstats lift the jets up by a substantial amount, more than you might think, so weakening the mixture. Maybe, with modern fuel this is overkill.

I ordered a pair of non-waxstat jets from Burlen and they duly arrived, only to find that I had ordered two the same instead of a handed pair. Doh! One went back with a request for the other one as exchange, only Burlen messed it up and just refunded the money. More delay while that was sorted out. Put them in and retuned the carbs from first principles.

Today I took it out and ran it up the Irvine by-pass at a steady 70 mph, covering at least 15 miles. Ran beautifully. Plenty of power right through the range. Hoo-bl**dy-ray. If you have waxstat jets think about ditching them. Use the two one penny coin trick or buy solid jets. You won't regret it. I didn't use the two penny coin trick as the jets were pretty old anyway.

I hope this update is of use to someone.

Mike

[dollyman]

Well done for sorting it Mike It's a great feeling when something has gone right for a chage

Tony.