Cheers guys,

I have had the exact problem with both the original points dizzy and the new one, the current dizzy is a accuspark 4D54.

After I wrote this post, I thought about the possibility that someone may have changed the cam at some stage, it does have a smooth idle when adjusted properly but I see most of the cam upgrades say to time the cam at 107 degrees, do you think maybe the cam timing could be out rather than the ignition timing?
I believe it may have had the engine rebuilt at some stage because it leaks absolutely no oil and blows no smoke lol

Maybe the timing device is bad. I have a 65DM4 electronic ignition and an old fashioned (1960s) timing light would not give a clear flash on the marks- was a blur. Buying a modern timing gun solved the issue, nice sharp lighting of the marks as they wiz by.

I've had a slight 'buck' at low rpm on mine for awhile.  Put a timing light on it yesterday and at 1000rpm it was 18 degs.  Turned it back to 13 degs and now it's smooth.

To me it sounds like an ignition timing issue. (Or maybe a vacuum leak)
If you advance the timing to get rid of the bogging, you lose upper speed power. That suggests the timing curve is wrong and/or the spark advance is not working, or going to extreme.

What kind of electronic ignition system is installed? Does it have vacuum advance and is it working properly? If it has a selectable timing curve (e.g. the 123 electronic ignition), do you have it set to an appropriate curve. When I put a 123 into my Mini, the guidelines from Marcel Chichak, who developed the system for Minis, said that the choice of curve (there were 16 set curves available) may not go according to the printed selection chart, but to experiment and the engine would tell you which curve it liked best. Later 123's are programmable so that's anybody's guess (and beyond me!).

Have you tried going back to a points distributor? That might confirm whether the problem lies in the electronic ignition system. The original spec would have you set idle timing with the vacuum advance disconnected and plugged at the carb port (to avoid vacuum leak).

If you are using vacuum advance, is it ported properly at the intake system? If not correct it may be pulling constant vacuum advance, giving you good advance at lower speeds but going way too advanced when the curve comes in. Vacuum advance should recede as rpms climb, allowing the curve to take command.

Vacuum advance is mainly an "economy" feature, allowing the engine to run leaner at low rpms. Try disconnecting the vacuum advance and setting the timing and then see how it runs without the advance. Alternatively, the vacuum advance may be stuck full on.

Hey everyone,
I am new to this Forum, but have joined in search of HELP!

I have a 1979 1100 Clubman with a severe bogging issue. I have read a few forums with similar issues but this one seems a little different.

When accelerating from idle, the engine bogs like a standard carb with the accelerator pump removed.
Any type of light or hard accelerating causes a bog so bad it is dangerous, it stays down until the engine reaches 1500rpm and then drives fine after that.
It is good up in the revs but does lose power near the top end.

It has had this issue since I bought it and I am desperate to get it fixed so my wife will drive it!


*Headers with standard intake and electric fuel pump all on when I bought it

Modifications and things I have tried;
*Standard exhaust (had no mufflers when I purchased, now has standard single muffler
*Changed dizzy to electronic
*Compression around 100psi
*Valve clearances checked and adjusted
*Standard Carb rebuilt by a specialist
*Tried 7 different weights of oil in dash pot
*Tried a 1275 Carb
*Tried 4 different needles
*Tried 2 different springs , double spring and no spring!
*Tried air cleaner off and on
*Tried changing plug gaps
*Checked carb and intake for air leaks
*Tried adjusting position of needle in piston
*Tried fixed and floating needles (floating standard)
*Fit new timing chain
*Checked air filter housing is sealed to carb
*300 different idle mixtures


Things to note;
If I adjust idle mixture to smooth idle, the bog is severe
If I richen mixture to the point of chugging and black smoke, bog mostly disappears but runs terrible through the revs and looses power quickly
I can replicate symptoms without driving by accelerating in neutral swiftly
If I remove plunger and hold piston down, revs up perfect with no hesitation and forces my finger up
**When trying to check idle mixture with lift pin, piston is sitting high enough that lift pin does not touch when lifting (does this no matter how low the revs are.
*Lift pin lifts piston correctly when engine is turned off
*Bogging can improve when advancing the timing but runs out of power in mid range

I know this is a bit of a Novel, but as I am a qualified Mechanic and own my own shop, this is getting really embarrassing!!

Any help or suggestions would be greatly appreciated

Regards

Mike