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Power Band Understanding


Davo

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If after changing the filter it still struggles it might be stuff in the tank floating about and blocking the fuel feed. Its tricky to seal the fuel gauge assy and sometimes people use silicon which swells massively in fuel. As previously said check the basics before spending money.

Edited by Peter Bell
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  • 2 weeks later...

Ok. Just a little update if anyone is interested.

 

Not finished yet but here is so far:

 

New fuel filter put in. Its only a cheap inline one but seems to do the job.

 

Removed the carb. The second throttle jet was definitely blocked so I cleaned that out. I can see it now squirts both throats on throttle. I also took each of the other jets out and bathed them in brake cleaner until I could pass a bristle through.

 

Its definitely running a lot better now but still dies at 3000. Ive tried powering past 3000 but it stutters on off on off power and cannot progress.

 

I guess the next task is timing

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Sounds like you have an understanding of carbs and ignition.

As said its about being systematic.

The car has been standing for a while then its clean clean clean to get the carb back in good shape.

You can check ignition timing and advance with a strobe to check if there is any obvious problems at 3000 rpm.

I have in the past I have swapped a complete inlet manifold and carb with a know good one loaned from a friend, this is a simple way of pinpointing or eliminating a carb problem.

Back to the condenser issue you mentioned, if that has been removed then perhaps the distributor and coil are mismatched and that is the root of the problem

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The dgav has a power diaphragm....if that is bugg**ed it can cause those symptoms.

It has a rod about 1" long inside a spring that is fixed to a bras disc that is fixed to a rubber (like) diaphragm.

IIRC it is attached to the carb top casting and projects into the float chamber (not sure about this & I cant

get to my weber manual at the moment.

http://www.carburetion.com/diags/3236DGAVDiaginfo.asp

its the part between 90 & 91 its on the parts list as 93 but i cant see that on the diagram.

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Snapper, Im a complete newb but I can read manuals and work out diagrams so thats where my knowledge is lol. All makes sense so far.

 

I got the strobe put last night, warmed it up a bit. Put my finger over the vacuum advance and checked the timing mark. A bit tricky with only two hands but it looked like at idle the mark was about 5cm away from the blade. That seemed way out to me. I twisted the distributor until it was much closer. Instantly sounded smoother. I then reconnected the vacuum tube and gave it throttle. The mark seemed to move which Im assuming is the correct behaviour; regarding the firing to account for the faster revs. Ive not driven it yet due to weather but Im rather hoping my theory might be correct in that because the timing was so far out when the vacuum advance really kicked in at 3000 the sparks were firing at completely the wrong time meaning there was no combustion.

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You could well be right.

As a rule of thumb, a problem with the carb wil usually cause rough runnin and or misfiring.

When the timing is out, retarded,, the engine will usually run smoothly, but lack power.

If it is advanced it will kick back when using the starter, and sound mechanically "harsh".

Good luck, keep plugging on!

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I would set timing at tickover, vacuum line to distributor removed from distributor and blocked, at 10deg Before Top Dead Centre (BTDC). That's ten degrees of advance. It's a reasonable starting setting which will be very close to ideal ignition timing. There is a pic below of my old pinto crank pulley (but there are two types of pulley). In both cases the first deep groove is TDC. I can't remember why I chopped part of the blade off. When using the strobe it helps to put a little tippex on the blade and the 10degree groove so they show up well. Slightly loosen the distributor clamp bolt so you can turn it with some resistance (but its not loose) as the engine ticks over and you align the marks. Beware all the twirly rotating bits of engine which can seriously damage you while you do this. When you are happy it's aligned, switch off the ignition, clamp up the distributor and run the engine again to double check. Then test drive. Be carefull both carrying out the procedure and driving. Rear wheel drive, more power and slippy roads will easily have you in the hedge or worse.

 

Nigel

post-21-0-75935500-1513207521_thumb.jpg

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Hmmm; despite having more power after timing adjustment, there still remains a problem at 2800 revs. Tried powering through but just at the point of 2800 power comes off power comes on.

 

Back to the carb I guess.

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Guest lotusPaul

Do you know what fuel pressure you are getting to the carb?

 

And on that thought, is your fuel supply line completely clear and free flowing from the tank to carbs, with no obstruction?

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Alan, didnt know there was a filter there. Ill get on it.

 

Paul, the metal pipe from the tank Im unsure of but the rubber pipe onward I would completely replace.

 

How would I check for the pressure?

 

I wonder if it would help diagnose the issue if I got a passenger to video the issue.

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I think I got a fuel pressure gauge off ebay when I originally reset my carb's up. It was fairly cheap and I just connected it in to the pipework directly before the carbs while I adjusted the fuel pressure regulator then took it out afterwards. I had quite a long pipe run from regulator to the carbs and wanted to make sure that the pressure was correct at the carbs, 3 or 4 psi at the regulator was quite a lot less at the carbs so I adjusted accordingly.

The smaller the bore of the pipe, the greater the frictional loss.

You could try running with a separate fuel container like a drinks bottle and a short piece of larger pipe just relying on gravity feed to see if that makes any difference. That would at least eliminate your existing pipe work from the equation. Be careful with loose containers of petrol though.

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