Engine Juddering 1098 Traveller!

[pertwoodpie]

Symptoms as follows:-
Coughs, splutters and judders when under load eg going up hills but only when the engine is warm then you can smell exhaust fumes, if you slow down a bit it settles down. push it towards 50mph even on a flat and the same thing happens.
so we took the head off and found gasket a bit suspect and a broken valve spring. so we replaced all the springs, plugs head gasket. cleaned and re seated all valves, cleaned all surfaces up and put the whole lot back together.
Did 60 miles in it no problem got beyond 50mph still good then today the problem returned.
All HT leads checked, put another coil in and even tried a different distributor, we adjusted all valves and the timing all to no avail.
help would be appreciated
thanks
Marcus and Charlotte

[bmcecosse]

As we all know - it's NEVER the coil, as you have proved. Neither can it be the dizzy - since you have tried another (great to have a spare!) . Assuming the gasket has not failed (how does a gasket 'look suspect' ?) and the valve gaps are all correctly set - I would assume fuel flow is the issue. I would do a flow test - getting the pump to deliver say two pints (without a break) and time how long that takes. Also check the carb piston rises and falls well, and the air filter is not blocked -in fact - try a good run without a filter in the casing - is that any different? If nothing obvious shows up - then a compression test is required... The 'exhaust smell' is a bit ominous. With engine hot and idling - take the oil filler cap off and rev up...is there a plume of fume/smoke from the filler hole?

[katy]

Was the head retorqued and valve lash checked/reset after the first heat cycle?

[pertwoodpie]

yep all torqued valves reset, tappets adjusted went like a rocket after all this, the fault seemed to have gone as could take him over 50 plus and no problem. Will take a look @ bmcecrosse's list in the morrow.

[pertwoodpie]

since we have skimmed the head as was found to be a bit concave and the problem persists HELP!
thanks
Marcus

[bmcecosse]

Fuel flow ok ? Carb piston rising/falling ok?

[pertwoodpie]

yes good pump. carb piston seems good, no evidence of it sticking.
But what concerns me is the exhaust fume build up before and after it happens!

[bmcecosse]

Is it possible the exhaust system is choked ?? The silencer may have collapsed internally...

[pertwoodpie]

Oh that's worth a look, may be blasting some air through it will give us a clue or even an answer! Thanks

[simmitc]

Although you have done the work, have you run a compression test? I verge towards an exhaust problem (could just be a leak) but would like to rule out any other issues too, and the compression test is simple and gives good data.

[pertwoodpie]

Have carried out a compression test and all good.
Its the loss of power before this happens you can smell exhaust fumes it does this loss of power and juddering and you slow down smell more exhaust fumes and it clears only to start all over again if you go towards and over 50mph!
Thanks Marcus

[bmcecosse]

Hmmm - if it 'clears' then I doubt it's blocked exhaust - but worth checking I suppose. When you changed the dizzy - did that include different cap and HT leads ?

[pertwoodpie]

I say it clears but as soon as you increase speed it returns again with all these fume smells.
In answer to your question re dizzy all was replaced except HT leads

[bmcecosse]

Well -I suppose you could try different leads... although I rather doubt that's the problem.. So it possibly IS an exhaust blockage - above a certain flow it chokes back.... Is the system old/new ???

[MarkyB]

Have a look at the exhaust and make sure it hasn't been crushed or bent by someone jacking the car up on it.

[pertwoodpie]

fixed now thanks for all your input, replaced the carb with an over hauled one and bingo!
the old carb was not quite sitting properly the bit that the needle goes into at bottom and the spring to the damper/piston was double the length and was causing the whole thing to do this petrol starvation thing!

[bmcecosse]

Double length spring ? Can we see a picture please ? More likely the 'overhauled' carb has had the spring shortened.... This can be done to try to improve throttle response - but is then likely to allow the piston to jump up too easily causing flat spots.

[pertwoodpie]

its now with a friend who is writing an article for Dorset MMOC and I think it will be in their next issue!