My engine has got the ADHD!, Can't get my engine to idle at less that 1000 Options

[tornik550]

On my dual weber 44idf, 2258 engine- I cannot get my engine to idle at less than 1000 rpm. I have backed out both idle speed screws all the way. I unhooked the linkage. I played with the timing (which will slow it however it runs like crap). I adjusted the mixture. I even put new throttle plates in the carbs and synced them. I made sure the throttle shafts were not bent.

My old throttle plates were worn which I feel let too much air in. I replaced the plates with new ones which I thought would correct the problem. I was able to get the idle to go down from 1200 to 1000. I shined a light under the plate after installing them- I can see a very slight amount of light from between the plate and barrel wall.


Any ideas?

[rhodyguy]

perhaps it's time to bite the bullet and send them out to Air Cooled Engineering (ACE) 801-747-3347. you will have to provide them with the engine build and operating parameters. displacement, cam specs, comp, etc. they will rebuild and set the carbs up according to your needs. you're running a pretty darn big T4 and there may be some special tricks required.

is the 1k rpm reading from the tach or your dwell meter? what do you consider acceptable idle rpm?

k

[tornik550]

I think sending my carbs off to get them rebuilt is an excellent idea. Any idea of the general cost of something like that? I probably won't send them off til winter.

Also, are butterflies supposed to close 100% if the carbs are unhooked? Mine are not visibly open however you can fit a thin piece of paper between the throttle plate and the barrel wall when the carb is not hooked up- is normal? Is it possible that the plate simply don't close enough (even though they are visually closed)?

[Valy]

Check for air leaks between the carbs and heads. Probably just a bad gasket.

[cgnj]

Hi,

Intake air leak below the throttle plates or throttle plates not aligned in the bores properly.

Were you pulling the same amount of air when you reinstalled the carbs? Was the idle air way off? Did you pull the manifolds? If not the they should be ok. New base gaskets when you put the carbs back?

Getting the plates back in the bores and to work correctly is the hard part of the job. I ended up getting full motion of the shaft, then killing the lights, shining a light from the bottom of the bore, and confirming that the plate was square in the bore. With the idle screw all the way out, woun should see no light. You need to make sure the first progession port is covered by the plate. Swedge the the throttle plate screws, they will fall into the head. Ask how I know.

I contacted Art about a month ago about rebuilding my drla 45's. I heard his quote and decided to do it myself. Maybe the price for webers is less. Just need the throttle plates to come over from the Italy.


Hope this helps,

Carlos

[rhodyguy]

re throttle plates. when you have the/a carb off, turn one up side down and open the throttle plates. you'll notice a slight bevel on the plate edges and when closed a number with a degree mark on the bottom side. the bevel is illustrated on p.31 the CB manual. a 40 weber i'm looking at has 76*, which i presume is the degree of bevel on the plate edge. the plates need to be installed with the 76* marked side visible on the bottom of the plate and facing what would be the center line of the engine. if the bevel is in the wrong orientation i think the contact edge could be holding the throttle plates slightly open with contact on one side of the bore and a slight artificial/built in premature opening on the other side of the plate that will effect the idle circuit that you can't adjust out.

if the throttle shaft bushing are spent that's a whole dif factor. owning a serviceable set of webers or dels and having them rebuilt is far cheaper than purchasing a NEW pair of carbs. i seem to remember postings about there being manufacturing/qc issues with new webers.

k

[tornik550]

Thank you to everyone for your ideas. The past two nights, I have been trying to get my throttle plates to line up perfectly. As I mentioned, they are brand new and they appear to line up perfect however if you shine a bright light behind them, there is an extremely fine line between the butterfly and barrel. I have an extra set of new throttle plates so I decided to try to shape the plates better to make them so they would close completely.

It took a very long time of tedious trial and error sanding and checking my work by sticking a shop vac in one end of the barrel and putting a snail gauge in the other. Once I was able minimal readings (1.5 or less) on both barrels, my work was done. I installed them and now the car runs great. I am able to get the engine to idle as low as I want. If I back the idle speed screws all the way out, the engine will stall. Guess that was my problem.

[VaccaRabite]

Alright!!

[rhodyguy]

good fix. trimming the throttle plates prob allowed them to fully seat, covering the lowest progression ports. not seated they were letting some fuel in even with the idle air needles fully closed. i imagine your idle a/f ratio cleaned up.

k

[rhodyguy]

good fix. trimming the throttle plates prob allowed them to fully seat, covering the lowest progression ports. not seated they were letting some fuel in even with the idle air needles fully closed. i imagine your idle a/f ratio cleaned up.

k