What to do

Neilr

Neilr

Member
After completing refurb of carbs ignition and camshaft and followers plus timing chain I am still having running problems. I am now contemplating removing cylinder heads to check valves. There is a popping noise in the exhaust note. Anyone else had similar problems.
 
I am going to put my money on too rich a mixture and/or timing out of spec. Do you have access to an exhaust gas analyser?
Before jumping in and pulling the heads, do a compression test. That, while not being definitive, will give you an idea of the general state of affairs, so you have an idea where to look and proceed from there.
 
Long shot, but based on my recent and frustrating experience which had a simple fix, it may be worth checking the vacuum control on the brake booster.

Clamp off the vacuum line from the manifold to the booster to see whether the idle changes and the engine smoothes out.
 
good advise so far. removing heads may be needed but we ought to start checking the easy stuff first. HT leads correct to each cylinder in foreign order? is any plug wet? sotty? ( faulty lead.connection etc then basic timing. and of course compression test. have we tried the carb(s) lifting pins to see effect? plus check for air leaks .( spray around gaskets/joints etc) as any air leak will interfere badly with idling. hence advise to temporarily block servo take off on manifold or crimp line etc.
the popping sound may indeed be a sticking valve .faulty tappet but this can also be due to poor fuelling .timing. if we have a strobe? balanced carbs? have we tried colour tune ? where we can also see not only the 'blue' flame in each cylinder but if its firing ... good luck . know the issues as my own V8 is very poor on idle and starting despite carb rebuild. tuning. balancing .timing check new plugs. leads .dizzy .compression check etc
 
I agree but by the virtue that I have completed these checks already albeit before the cam change I am going to go through it again. I am unable to use colortune due to lack of idle. Timing is also difficult to check with strobe as it only runs at around 2000 rpm.
 
You would need to set the timing static and take it from there. I have had timing that is out and you get a lot of popping. What you can do is if you have it roughly timed with the marks on the crank and line up the rotor arm with the HT lead. Then with the engine running rotate the dizzy clockwise or anticlockwise and see if it helps.

What you should do is also check that No 1 cylinder is at TDC, you can have the dizzy 180* out which really doesn't help. if it is, turn the engine over until you line up the timing mark again and check No1 for TDC.

firingorder.gif


Also check that the rotor arm locates and doesnt have any movement, I have on where the plastic broke and it would retard the timing.

You should be able to put the colour tune on each cylinder in turn. some of them must be firing or you wouldnt even get a rough idle. when you know the ones which are firing you might be able to work something out.
 
Okay it runs better and revs if I nearly completely cover carb air inlets. I did have 5 and 7 leads round wrong way. So Its definitely an air issue. How ever still doesn't idle. I cant hear any air being sucked in anywhere though.
 
Please take the top off of one of the carbs and remove the air slide piston and photograph the bottom of it showing clearly how the needle is located in the bottom of the piston height wise.
 
Spray carb cleaner carefully around all the intake joints. If the revs pick up, that's where your leak is.
 
cobraboy said:
Please take the top off of one of the carbs and remove the air slide piston and photograph the bottom of it showing clearly how the needle is located in the bottom of the piston height wise.
Click to expand...
Couple of pics of one of the carb pistons.
 

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Something just occurred to me.

Are the pistons handed? I think that the will fit in either side but with the air holes prevent correct operation.

Colin
 
Neilr said:
Couple of pics of one of the carb pistons.
Click to expand...
The needles seem to be located correctly. The info on needle height can be confusing namely the sintered bush holding the needle being level with the bottom of the piston. This is not true as the bush needs to be flush with the slot in the bottom of the piston as you have yours.
Having the bush flush with the bottom of the piston puts the needle too low and gives poor weak running, I was hoping that this might have been your problem, but alas it does not look like it.
 
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All now running with replacement carbs. Don't know what is wrong with my ones. I'll send them away to have them rebuilt properly now. Thanks to all who offered advice.
 
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