Lumpy running

Side valve, 803, 948, 1098., 1275 and Vizard mods
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John_James
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Posts: 11
Joined: 1 year ago

Lumpy running

Post by John_James »

Taken me a while to get round to this as I actually broke down on new years day :raz:

Problem started new years eve, whilst driving along and very occasionally there was a slight loss of power but then carried on fine. Driving home on new years day it was getting more and more noticeable so pulled over to have a quick look and wouldn't start at all after that and got relayed home.

I've checked, cleaned and re-gapped all the plugs, replaced HT leads, distributor cap, points and rotor arm. The funny thing is I was trying all sorts of things and when I wound the advance screw right up it did run a bit better so moved the distributor very slightly round. I also checked the points gap when brining up the first cylinder to compression stroke and this seems fine.

Fuel is getting to the carb and the fuel pump is working fine. just wondering if I should take of the head and check the valves yet?

At the moment, it will start and tick over fine but as soon as I press the accelerator down it really struggles and am at a loss as to what to look at next.

Any ideas would be greatly appreciated.



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timb02
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Great Britain
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Location: norfolk

Re: Lumpy running

Post by timb02 »

I would first check that the timing is set accurately. Was the distributor loose at all as it seems odd that winding in the advance adjustment and turning the dizzy "a bit" has helped.Set at 5' btdc as a starting point. Do you get a good spark? is there any signs of arking at the points? Always start with the simple/cheap solutions before getting into engine strip territory. A compression test and valve gap check will give you all you need to know about the state of the engine without taking off the head. Good luck.



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Mecanglais
Formally known as chesney
France
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Joined: 9 years ago
Location: France

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Re: Lumpy running

Post by Mecanglais »

Piston moving freely in the carb?

You've forgotten the consensor, common to break down and overheat under load. Worth investing (and changing for) a Distributor Doctor set with yellow wire.

I once had a Moggy that ran like crap, it would just about idle, but touch the throttle and it would die. After hours of going round everything, I noticed that at the base of the piston (against the jet) there is a small brass washer, while doing ordinary checks to lift the piston etc the washer stayed where it was supposed to, when running it transpired (either under Venturi/suction from inlet or pressure of incoming fuel, or both at a guess) that this washer was raising with the piston with revs, which was sending the carburettor into haywire, unless you were looking for it, and directly at it, you wouldn't have seen it, a new jet and it was good as ever.

Agree that a compression test might be worth doing though, if it is a head gasket gone between two cylinders, better to know about it before wasting time with things it isn't. You can get away with removing all plugs and spinning the engine on the starter while shoving your thumb over the plug hole if needed, if the gasket has gone the compression should be poor enough for you to gauge that way.



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