V8 won't accelerate

I had this on my 97 RR V8.

I changed the coil and it seemed to cure it,

Check if that is OK?

check oil level in the dashpots of the carbs . check that the vacuum advance diaphragm is working .

check all rubber hoses for splits .

if youre engine runs fine under light load but it missfires after you give it a real hard full throttle acceleration from a standing start then it may well be the fuel pump .

ie the pump is not delivering enough fuel volume under acceleration .

if you have a facet electric pump this should be ok for the job and shouldnt really cause any problems, but check just in case .

also check fuel filter especially if its a cartridge filter .

i suspect it may be the vacuum advance thats the problem, or lack of advance under acceleration .

i presume the choke cable is connected right and that the cold running fuel enrichment works ,ie linkage movement .

i think the older rover V8 engines need more advance on the ignition timing , so perhaps something like 10degs adv is more in line with an old P6 engine .

. running retarded will cause lack of performance and affect acceleration under full throttle .

look in a manual for ignition timing relevent to a P6 rover 3500 . i think the dwell is 28degs or so .

other than that if the engine gradually starts missifiring and eventually wont run at all look towards oil pump pressure or lack of it .

lack of an air filter will also lean the mixture out and make engine pop and bang .

do you have a vacuum ADVANCE & RETARD distributor , if so timing is different for these and idle revs have to be correct for setting timing .

you may have a 10.5-1 compression engine in the P6 rover engine, so need to be carefull if using unleaded fuel . octane booster would benefit this comp ratio .

farther down the check list would be to see what cam the engine has, just in case its a long duration cam , i doubt it has one but is allways worth a thought , youd soon know anyway if it had due to engine revving a lot higher than standard spec 4500rpm touch .

you really do need to make sure all youre plug leads are good and remember these engines used different spark plugs between years , i think short reach in older engines .

check the inside of distributor cap > terminal posts for oxidation, just clean them off with a sharp knife if corroded . make sure rotor arm makes contact with pin in centre of dizzy cap .

. hope this helps .

That all sounds to me like a fuel starvation problem, either the fuel pump isn't delivering enough fuel, the floats are incorrectly set or the carb breather pipes are blocked (which effectively airlocks the carb. As the engine load increses so does your fuel requirement so you are getting enough fuel for light loads but not enough at high loads.

It is also possible that the return pipe has no restriction in it which can sometimes lead to a situation where the fuel effectively bypasses the carbs and heads straight back to the tank. My challenge team mate ( still on carbs) uses a small pipe clamp on his return pipe to ensure that the carbs are getting as much pressure as they can hold. Too much pressure and the carb valve is forced open which floods the carb !

If you have a fuel filter inline (you ought to have really) then make sure that is clear too.

The breather pipes are easily checked, just take them off at the carbs and see if the problem goes away - they are attached to the carb with a rubber "elbow" joint.

cheers

Dave W.

I had the same symptoms after my 110 was converted to lpg. The fitter had knocked the ball joint off the link between the two carbs.

AJH

In message , danny writes

Check that the mechanical advance is actually working by reving up with the timing light connected and check the timing advances. If it's been standing the bob-weights could have seized in the dizzy and you'll never get a good result. I assume that the points have been checked for cleanliness and security? Next comes my particular favourite, the condenser. I took a fortnight to find my faulty one ... and the faulty one in the complete replacement dizzy!!! Replace it (it's cheap) and make sure connections are clean, secure and not shorting to the dizzy body as the advance plate moves

Only one carb's working is what my money goes on.

To work out which, pull the elbows off and see which one!

Regards

William MacLeod

Thanks for the replies and suggestions.

It looks like weak mixture. It starts with virtually no choke (rich initial mixture) and if I pull the choke out progressively as the speed increases above 50mph it pulls like a horse and runs fine. So currently I'm using the choke above 50mph. I assume this means that the mixture is weak at higher revs/speeds?

Does anyone know if overhaul kits are available for 175CD carbs? I have the original set from the replacement engine and I will probably recondition/service these to swap out with the existing carbs. I can't adjust the mixture on the current carbs, since one of the adjuster screws has been broken.

By the way, does anyone have hints for starting a warm V8. Both this and the last engine wouldn't start 10-15 minutes after a shortish run. Turns over for ever then gets faster and starts. I was told that this is common on these engines? Maybe I also have a weak fuel pump....

Thanks again.

Yep, if you've got backfires once its warmed up it's probably the coil.

Classic symptoms of a severely worn camshaft. Insufficient vacuum signal at carbs when cranking, so mixture richened up in an attempt to correct idle. BTW, the drop-off in power you mentioned earlier is partly due to the cam lobes not fully opening the exhaust valves and this acts like a lorry retarder when you floor it - by creating a back pressure in the cylinders. Opening the choke simply enrichens the mixture to the point where you develop a bit more power to overcome the pressure, and correcting the weak mixture due to the previously mentioned low vacuum signals.

Bin them and fit SU's. Strombergs are unreliable and problematic, end of story.

Sounds like fuel evaporating in the carbs or the lines vapour-locking. I take it the return line is plumbed in properly? Not common, whoever told you that is giving you bull5hi7. Pump could well be weak, or filters partially blocked.

Badger.

Badger, I'm confused now. This engine has done less than 35k miles (although it's very old) and sounds as quiet as a very quiet thing :)

I have documented evidence of the mileage and the previous owners' use of the vehicle. It doesn't sound at all worn. The mechanic hasn't touched my carbs (they are off the old engine). He swapped them after the original carbs on the replacement engine fired it up once, then never again (I suppose due to something sticking and flooding the engine on the first start and press of the throttle). This engine had been stood for at least a year.

The last engine had a very badly worn camshaft (that's why I changed it). It rattled and knocked but still pulled up to 85mph. The replacement engine is far quieter and smoother.

OK. I'll look for some.

Yes, the return line is plumbed in. I'll check the filters. Is there a way of testing the pump, ie: by way of measuring the output in a given time. On espresso machines (which are what I know about), water debit is measured to check for pump function.

Like the Government - 'tis easy to spend someone else's money!

Yep - normally you disconnect the fuel line from the carbs and put it into a bottle, then run the engine (which will run on what's in the the float bowl) for 15 or 30 seconds and measure how much fuel is in the bottle. The green bible or even the HBOL should give an output figure.

Yep, valid point Dougal, but those damn strombergs are a PITA, IMO. And there are many who will agree with me. It would be my first "improvement", as the SU's are more reliable, easier to tune and keep in tune and there are a wider choice of needles for the inevitable fitting of different cams / air filters etc. etc. Badger.

Danny, it may be that your cam isn't knackered at all, it's just that what you describe does point to worn cam lobes. It all depends what lobes wear first, inlet or exhaust, as to the symptoms. If the cam followers are operating properly, then there won't be any noise as the cam wears - any wear will be taken up by the self-adjusting nature of the hydraulic followers - until the wear becomes really excessive.

If it was that noisy, then I'd bet there was more than just the cam worn. Cams don't knock in general, crankshaft bearings do though.

If you have a pressure gauge and a "T" piece, rig it up to the fuel supply line and go for a drive. As you maintain full throttle (up a long hill in

3rd, say) watch the fuel pressure. If it drops below 2.0psi then the engine will be emptying out the carbs quicker than the pump can keep them topped up. This will either be due to the flow rate being reduced by a partially blocked filter or line, or the pump being u/s. If the pressure is below 2.0psi at idle, then either the pump is shot or there is no restrictor in the return line. My last carburettor-fed V8 had the supply pressure to the carbs set at 4.5psi (via a return-line restrictor) with no carb flooding problems.

Badger.

They've actually given me no trouble other than diaphragms (and that only when rather old). That's on two Volvo B18s and two Rover V8s. I must have a sainted life!

Oh THAT Danny, Landy fan and famous espresso nut, welcome ;-) You got me interested in commercial espresso machines some time ago and I now have a Visacreme FCX1 currently in bits, slightly higher tech than a Landy but similarly built!

Is there anything a relative non-mechanic like me can do to get an idea of the engines' likely mileage? I have a 3 month warranty on the engine and would like to get an idea before the warranty runs out...

OK. I can test that, thanks.

Hi Ian, I hope your machine doesn't stay in bits for as long as my

110 did whilst I waiting for the mechanic to swap the engine :)

Let me know if you have a problem with parts - I have a couple of sources.

Remove the rocker covers and turn the engine over slowly by hand, monitoring the valve movement. Look for 1 or more valves not opening as far as the others - this is either the cam lobes worn away or the hydraulic cam followers knackered, only further confirmation of either one would be dismantling (inlet manifold and valley gasket to allow visual examination of cam). You'll quite often find one or more that just don't appear to be moving at all. As to general condition, you could carry out a compression test (all plugs removed, crank on full throttle - remember to isolate ignition first, you don't want any sparks igniting what may blow out of the plug holes!!) but this will only prove that there is a fault, it won't really tell you whether it is bore wear or the valves simply not opening wide enough for long enough (cam).

Good luck. Badger B.H.Engineering, Rover V8 engine specialists.