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+--- Thread: Huge flat spot - Zenith 26VA (/showthread.php?tid=7621)
Huge flat spot - Zenith 26VA - Ivor Hawkins - 13-06-2022
Hello fellas, I don't know what I've done, but the old box saloon is as flat as a witch's whatsit and I can't seem to fix it...please can I have some bright idea as to what to check?
I've fixed the sticking valves, put the motor back together, starts right away on the choke and that's it, it will only run on choke (very nicely actually!) and as soon as you touch the throttle it almost dies until you take your foot off the throttle and with the choke out it whizzes back up again.
I've had the carb to bits and cleaned it out very thoroughly including all the jets and the the one that's hiding underneath, triple checked for air leaks, plenty of new petrol getting through and it was running perfectly before I pulled it to bits, the only think I've changed is the plugs from NGKs to Champions, but its running great on choke.
I'm beginning to think I've missed something really obvious but I can't think what...if I had someone local to Brackley with a spare carb, I'd try that, but I only know of a few Chummies locally and a few others running on SUs!
What can I be missing?
I think I'm going to head for the cocktail cabinet...
RE: Huge flat spot - Zenith 26VA - GaryCullen - 13-06-2022
Ivor, Rebuilt my A10/4 engine and refurbished its Zenith 26VA, new plugs and had the same result as you are getting now.
The short story after redoing carb and distributor again was that plugs 2,3 and 4 had very low internal resistance. should be close to infinity. Brand new NGK's so took them back to supplier and got a new set. engine ran fine for about 30 minutes then no pick up on the throttle. checked the plugs and same problem. got my money back and purchased another brand.
my advice is to put back your old NGK's and see if that fixes the problem.
With NGK's in our neck of the woods in Aus/NZ, rumours of Chinese knock offs are rife. Maybe the same thing is occurring with Champions where you are.?
The simple test I did was to run the engine at idle speeds and use a long screwdriver and short out each plug to the adjacent head stud nut and see what effect it had on the engine.
For me, shorting out #1 killed the engine, where shorting out 2,3,and 4 did nothing.
Holding each HT lead to get a spark to the plug terminal doesn't show if the plug has low resistance.
RE: Huge flat spot - Zenith 26VA - Ivor Hawkins - 14-06-2022
Thanks Gary, that’s the first thing I’ll check, I’m supposed to be going on an old car run tonight, but at the moment I’ll be lucky to make the end of the drive!
RE: Huge flat spot - Zenith 26VA - Charles Levien - 14-06-2022
Hello Ivor,
It doesn’t 1/2 sound like a blocked main jet to me - - could it have picked up a bit of dirt despite your cleaning it? Do you use a fuel filter?
RE: Huge flat spot - Zenith 26VA - Howard Wright - 14-06-2022
Hi Ivor
Just my twpence worth. I had a similar problem with a SU carb a while back. It turned out to be a small bit of dirt that flowed back and forth in the fuel line. Put your foot down and the dirt would flow up the pipe and block the jet. Foot off the dirt dropped back and it ticked over OK.
Cheers
Howard
RE: Huge flat spot - Zenith 26VA - Ivor Hawkins - 14-06-2022
Thanks Charles and Howard, two more things I’ll check, I have put in a glass inline filter in the fuel line under the car, so I’ll check that, I’ve cleaned the carb out so many times, and blown it through with a high pressure air line, but I will check again. Thanks fellas!
RE: Huge flat spot - Zenith 26VA - Ivor Hawkins - 14-06-2022
Sorted! Changed the plugs to NGKs, no change.
Checked the filter, all clear.
I remembered Tony Betts sold me a batch of old fuel bowls for spares, so in desperation I took the existing one off, screwed one of Tony’s on and hooray!
So despite all that cleaning, there was obviously some dirt in the jets or transfer tubes somewhere along the line, I’ll strip it again, together with the emulsion block and go through everything with a fine tooth comb.
What a lovely day for a drive around the lanes in the Seven, I may even put a pound’s worth of five star in it!
RE: Huge flat spot - Zenith 26VA - GaryCullen - 14-06-2022
Glad you found the cause Ivor.
Chasing these types of problems can be frustrating.
Gary