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Poorly xflow


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GCP17

Any recommendations please for mechanic in Sussex  who knows their xflows ? Mine suddenly started running on only 3 cylinders and misfiring/ popping. 

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Head is off - broken valve spring caused loss of compression. Apart from leaking core plug, there’s a leaking water pump, build up of sludge in waterways and garage says worst head gasket they have ev

What carbs please ?. Also is it still running a dizzy, is the cap clean inside, have you swapped leads to eliminate a duff lead, same with spark plugs.

I've had a venturi come loose on a Weber carb. The locating grub screw falls out and it allows the venturi to rotate and shuts off the main jet to that choke. Easy to spot if you remove the filters an

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OldStager
10 minutes ago, GCP17 said:

Any recommendations please for mechanic in Sussex  who knows their xflows ? Mine suddenly started running on only 3 cylinders and misfiring/ popping. 

What carbs please ?.

Also is it still running a dizzy, is the cap clean inside, have you swapped leads to eliminate a duff lead, same with spark plugs.

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GCP17

It’s on twin Weber 40s and electronic ignition. Haven’t swapped spark plugs or leads yet - good suggestion. Had the carbs balanced last year. Compression tested too and all was well. 

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OldStager

OK same carbs as me then, make sure the jets are all still tight in the body of the carbs ( remove the wingnut to gain access to most of them) but I doubt its that.These things are generally electrical for most faults. Sometimes mine runs on 3, no faults other than a flooded plug, take it out dry off and refit ( you can use a blow torch carefully to dry it properly) As long as the igni is in tip top condition and all is clean it should run. One other thing , are you getting enough fuel to both carbs, hard to test but removing a pipe or two will tell you that.

ETA

May be worth blowing through each jet to clear anything that maybe blocking them, if you take that cap off.If it runs lean , it will pop and bang.

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GCP17

The only thing I did today was wash it - maybe water has got into the electrics somewhere. Really need to have a good look. The car did get me home - loss of power and loads of popping - so hopefully something simple. 

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OldStager

Ah well, yes water isn't good for electrics in general, check the dizzy is dry then or the leads, although I can't see how they would get that wet , unless you had an engine bay wash as well.

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OldStager

What filters do you have, has it  soaked the filters and  thus sucking in water ?.

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GCP17

Just the standard Weber ones - was careful not to get water on those. I should add I had been driving for an hour or so with no problems - then all of a sudden I noticed a change in exhaust note and it started popping. Poor acceleration and misfire under load. Got home 30 mins later taking it slowly. Please Lord let it not be a dropped valve!

 

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OldStager

You would be very unlucky to have dropped a valve, a compression test would show that up without removing anything, although the simple one is whip the rocker cover off and have a look, if it had dropped a valve I would have expected lots of odd noises at the same time as the loss of power, I have had a rocker arm snap in the past on a triumph engine and that made a dreadful racket Try a comp test first then , got to be worth doing and then swap leads , plugs try another dizzy cap or arm. Let us know anyway.

Richard.

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Mighty Mart

It sounds as though something simple to me - as above, plug or lead, or water somewhere - possibly displaced during the run?

 

Mart.

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GCP17

I replaced the plugs, leads are nearly new, dizzy all clean, fuel pump working, no leaks from carbs or fuel lines - still the same. No white or blue smoke coming out of the exhaust.  It overheating and healthy oil pressure. No problems starting. Engine pops and misfires at 2,000 rpm and sounds like it’s only on 3 cylinders. The only other noteworthy thing is that the exhaust note sounds ‘different’ to normal. Can’t really put my finger in it. Anyway, booked in with local garage which has vacuum gauges to test the carbs. 

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OldStager

Is this misfire 2000k and above or below?. To be honest these are really simple engines ( that's why I have one !) and issues can be found fairly quickly. You shouldn't need a garage to diagnose an issue with a Xflow.

If the misfire is below 2000k, I would be looking at the pump jets, remove air filters and see if there is a 'squirt' of fuel being forced into the inlet manifold and check the  idle jets for no blockages. The idle jets controls the first 25% of throttle travel.

 

If its above 2000k then a possible blockage in one of the main jets, so it runs lean and pops and bangs.

All of the above assumes the timing is correct and all electrical systems are working correctly .

Richard

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Andrew
16 minutes ago, OldStager said:

If its above 2000k then a possible blockage in one of the main jets, so it runs lean and pops and bangs.

 

I've had a venturi come loose on a Weber carb. The locating grub screw falls out and it allows the venturi to rotate and shuts off the main jet to that choke. Easy to spot if you remove the filters and check the "bars" across the chokes are aligned. 

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