Engine sounds rough

Post by **Cam** » Mon Jun 23, 2003 5:39 pm

Tony,

If there is no difference when you remove the two middle plug leads, then that would suggest that you are running on two cylinders!!

I would say that on two cylinders it would be virtually impossible to reach 70 mph. Something is not quite right there.

check to see if you are getting a spark at all four plugs by putting a spare plug in the end of the lead while holding the body of the plug to the engine while someone cranks the engine over.

Also a compression test might be in order, to make sure that everything is OK in the cylinders.

Post by **Willie** » Tue Jun 24, 2003 8:12 pm

It doesn't sound as though there is much wrong with your
engine at all! Except at tickover! it would be worth borrowing
someones 'Colourtune' kit so that you could actually see what
is going on in each cylinder during tickover. (That is a GUNSENS
COLOURTUNE kit). If you have servo brakes try disconnecting
the pipe on the manifold and blocking off the hole temporarily.

Post by **Cam** » Tue Jun 24, 2003 9:59 pm

Yes, if you have a lumpy tickover then you could have a non-standard cam fitted (if you don't know much about the history of the engine).

What concerns me is that nothing happens when you remove two spark leads???

Could there still be a problem with compression when the car accelerates and maintains its momentum so well?

Usually lack of power can point to poor compression, but it depends on what you regard 'lots of power' to be like! It may be running OK but I don't like this running fine on two cylinders lark!

Best to do a compression test anyway just to make sure.

Also, try revving the engine with the two leads disconnected (it should sound really rough) then try revving the engine with the centre two the wrong way around (it should possibly backfire).

Have a mess about and get back to us!!

Post by **67trav** » Wed Jun 25, 2003 10:19 pm

I agree with Willie's comments re: servo brake line. It could well be an air leak. This could perhaps be through the inlet manifold gasket (usually where it meets the block), or if servo brakes the car should have a valve fitted on this line (I found one hairline cracked on a car I once owned; A Sierra(!!)- an absolute pig to trace that leak. That caused a very similar problem)

Post by **67trav** » Wed Jun 25, 2003 10:28 pm

don't forget the vacuum acdvance line from the inlet to distributor; another common point of leak; split unions

Post by **grainger** » Wed Jun 25, 2003 10:34 pm

hi

ive got a 1098 traveller with servo brakes and similar problems to whats being described here. i cant seem to get it to run smooth on low revs yet when its above 45 mph its smooth as it could be.

did someone say there should be a valve on the line from the carb to the servo ? this was a diy job by the previous owner. it stops the car well though.

doesnt the servo interfere with the vacuum in the inlet manifold ?

cheers
grainger

Post by **67trav** » Wed Jun 25, 2003 10:49 pm

yup, I think there should be a non return type valve (I guess that is what you would call it) on a reinforced vacuum hose running from the servo body to the inlet side (manifold). I'll check the postion of the set up of our (new) Trav and let you know the set-up. If it is a true non-return valve this should help prevent interference from the servo to manifold. I'll let you know ASAP

Post by **jimbo** » Wed Jun 25, 2003 11:35 pm

Hi,

Check your valve clearances and also your spark plugs.

I had a similar problem the other week during the trip to the National Rally. The car ran great at 60-65, but was poor at low revs. In the past I've been told by other MM owners that Champion plugs give poor results. I had N5's in mine (I think these are the original ones used in the MM), and changed them for NGK's (or NKG's - whatever). Problem cured.

I'd be interested in what other owners think of Champion plugs.

Jimbo

Post by **Cam** » Thu Jun 26, 2003 12:08 am

My experience:

Champion: Poor
Bosch: OK
NGK: Excellent

Read David Vizard's book on 'tuning BL's A-Series engine' and look at the section on spark plugs. He seems to have had poor results with Champion plugs too. Massive power drop offs on tuned engines. He recommends NGK plugs, so if they are good enough for him, they're good enough for me!!

Post by **67trav** » Thu Jun 26, 2003 6:13 pm

Grainger
on checking postion of the servo line valve, sits between servo vacuum reservoir and take off point on the inlet manifold. It does seem to function as a one-way valve, presumably to retain constant vacuum at servo end when the inlet is not creating high vacuum. Might be worth taking professional advice on(?)
Regards
Ben

Post by **Willie** » Thu Jun 26, 2003 10:55 pm

Remember,Think simple! if you remove the servo hose from the
inlet manifold and block up the hole and it cures the lumpy
tickover then you know where your problem lies. If it doesn't
make any difference then you won't waste time on a red
herring

Post by **Cam** » Thu Jul 03, 2003 10:10 am

Sounds a similar type setup to mine. Do you know what number the Kent camshaft is?? I suspect that from the rest of the engine's description it is probably a 276 / 286. In which case it will not like ticking over at all. If I set mine to about 800 RPM it is REALLY rough and un-even, so I have my tickover set to about 1200 - 1300 RPM so that it does not cut-out easily on its own.

That is your problem!! you have a tuned engine!!

No wonder you said it accelerates incredibly well!! It probably has literally twice the power of the standard Moggy engine!

Post by **Cam** » Thu Jul 03, 2003 1:35 pm

Tony,

No, you don't have a problem!! quite the reverse if you like quick cars!! A lot of people would be glad of such an engine!!

The Kent 600 has a 278 / 274 duration and is roughly equivalent to mine (276) so this is the reason that you have a lumpy tick over. Nothing to worry about!

the reason it is lumpy is that your (and my) cam is optimised for maximum power further up the rev range than the standard cam. This means that due to particle inertia and gasflow, the valve opening and closing times are altered to give the maximum cylinder filling volume at these revs. Unfortunatley, this means that at tick over there is a slight overlap between the inlet valve closing and the exhaust valve opening, which is why it runs rough.