Rough Running at Steady Speed

[cegerer]

Well, my Weber problems have returned - I think. Last year, they began to run rough at low steady speeds. When accelerating it ran fine. This was traced to the idle circuit. After cleaning the idle jets and running Techron thru the system, the car ran perfectly. Until a few days ago.

The same symptoms re-appeared, only they seem to be worse. No changes have been made to the car/motor. The idle jets have been cleaned 3 or 4 times and I've run some Techron, but probably haven't done enough miles yet for it to be effective. Again, if I put the throttle down it runs like a banshee with no missing, popping, loss of power, unusual noise, etc.

This weekend I will be rebuilding the carbs because it has been 10 years or so since they've been taken apart. My question is: are there any other motor problems (i.e. ignition, valves, etc.) that would cause these same symptoms? Thanks. -- Curt

[porsche74]

Hi:

IMHO, your symtoms returned due to plugged idle passages. These are some of the most sensitive parts of Weber carbs and really underscore the need for near-perfect fuel filtration.

Simply removing the idle jets and blowing those out does little; the drivabilty problems you are having are due to foreign matter stuck in the idle passages.

Now,....you do NOT have to disassemble the carbs to clean these effectively. All you need to do is remove the idle jets (careful of those O-rings). Then, remove the main jets and drain the float bowls. Using a rubber-tipped blow gun, blow air through the idle jet passage and though the main jet passage a few times to dislodge the very tiny pieces of material that is causing your grief. Reinstall everything and you're ready to go.

The root cause of these happenings is a combination of dirty/rusty fuel and insufficient air filtration. Any slightest dirt in the aircleaner housing migrates into the float bowls through the bowl vents or air corrector jets and winds up stuck in the idle passages. Once you install an effective fuel filter, and resolve the air cleaner issue, you will no longer battle this problem. Sometimes the engine compartment insulation pad sluffs off tiny bits of foam material and this will cause this very problem, too.

I've not need to touch my Webers in over 20 years; Runs perfectly, too.

I sure hope this helps, these things can run so well when they are setup properly and looked after.

[cegerer]

Excellent information. It is most helpful and I suspect you are spot on. I took the car out for a ride this afternoon and the Techron worked its magic again. After about 10 miles, the car ran perfectly! Then, after another 5 or so, the rough running occurred again.

I've got 3 issues related to your suggestions:

1) my fuel tank was replaced 15 years ago. The new tank replaced the original 15 year old tank. Is 15 years the average life span for these tanks before rust becomes a problem?

2) I have K & N watershield filters. I've read all the debates on these, but is it possible that either they are letting particles thru or that maybe they are not oiled enough to be trapping particles.

3) Apparently the stock fuel filter is not sufficient to remove particles that can clog the idle passages. Is there a filter available with greater filtering ability?

Thanks in advance for any assistance. -- Curt

[cegerer]

I've found the answer to Q3:

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=56945&highlight=fuel+filter

For Q2, short of installing a factory air cleaner system, I am going to wrap my K&N filters with an open-cell foam precleaner or this new K & N wrap - http://www.knfilters.com/wraps.htm

Also, I dissected my old fuel filter and nothing unusual was found, so maybe a rusty tank is not my problem.

[Reg]

Nice post Porsche74!

Curt, did you ever get my funny money?

[cegerer]

" did you ever get my funny money?"

You mean that Monopoly money? Yup, I got it. Thanks! -- Curt