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Join Date: Sep 1999
Location: Dallas, TX
Posts: 4
"tuning" single weber HELP!

I have a 1.8 with a single Weber (32/36 DFAV) that came with the car. I am very experienced w/ F.I. but no little about carbs. The car runs okay right now, but hestitates on full throttle acceleration --( when the second butterfly opens)and I think it might be running rich.
My questions: 1) does changing the "jets" help any ?
2)what size jets do people recommend for this application (I'm just cruising around town, not racing)
3) should the jets be the same size? (mine arent -- I think the secondary is bigger )
4) anybody know the "default" number of turns for the idle air screw after rebuild? (in case I decide to rebuild)
any other helpful advice for "tuning" this carb -- or just getting a nice reliable ride out of it would be nice.
Thanks from Dallas.
Old 01-24-2000, 12:30 PM
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Join Date: Dec 1969
Location: Dade County, FL.
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See what dizzy you have. The 009 is famous for a "flat" spot. Also see if the accelerator diaphram is shot. I think you can see fuel squirt out when it is floored. For Pete's sake do this with the engine off! I know 2 people who lost eyebrows adjusting carbs on running motors. Funny? Yes, but also dangerous.

The Haynes webber carb manual is pretty good on how to identify and rebuild these carbs. As for jets ask CB performance if they have any recomendations (besides buying dual webbers) on what jets to buy.
Old 01-24-2000, 01:44 PM
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The hesitation on full acceleration can be a couple of things. First, check the accelerator pump (after you have made sure that there are no ignition problems). Try to measure the volume. It should be consistent and smooth. I can look up the exact volume if you need it. Second, Yes the jet size makes a big difference. Weber's are famous for being tunable, but that also means they can be overy sensitive. If the hesitation starts only when the secondary is opened, and if the accelerator pump is o.k, I would pull the secondary main and try one a size bigger. If it gets better, you know your on the right track. If it gets worse, go the other way. But always go richer to start when you are not sure.
The idle adjustment screws depend on the size of idle jets, and how many vacuum leaks you have :-) Seriously, warm the engine, and screw the idle screw in until the engine just starts to stumble. Then back it out until it cleans up, and give it about another 1/4 turn. This may be anywhere from 1 1/2 to 3 turns. If the carb is set up right, I would expect to see about 2 to 2 1/2 turns out. I would also recommend buying the Weber book by Bob Tomlinson. Good info, from basic theory to troubleshooting. Good luck.

Last edited by turbo2.0; 01-31-2008 at 12:06 PM..
Old 01-24-2000, 01:49 PM
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on a similar note...

I'm running Dual 40 IDF's on my 2.0, and do believe it's jetted wrong. I've troubleshot it down to the carbs and this is my problem:

#1 will not fire. about 100 miles ago (when I got the engine) I tested compression with result 125 all around, except #1 123 psi. swapped plugs with no change. Carbs were cleaned out, Blown with an air compressor, reassembled, and tuned as per Haynes manual. All of the plugs except #1 are sooty, which leads me to believe the improper jets. #1 plug is gas soaked, and obviously not firing. When I take a look at the exhaust pipes (with muffler off), 2-4 are sooty, 1 is clean and wet with fuel.

Also, when the engine is warm, I get an occasional backfire through the carb (only while driving) from #1 cyl.

will rejetting fix my problem or is it in the head (valves)?

running 372G heads, 050 dist.

Kokanee
'64 Manx 2.0L
Old 01-24-2000, 03:12 PM
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Kokanee,
Check your float level on the #1 carb. Sounds like you might be flooding. Also check your electrics, verify #1 is firing.
neil
Old 01-24-2000, 03:59 PM
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I guess you checked and have a good spark at all four plugs with them all out? If not check that to see if they are the same, at night in the dark so it is easier to see. If spark is good and timming is set correctly and dwell is okay (no electronic stuff?) then I would check the valve adjustment. I checked the valves on the 914 race car last weekend and #1 exhaust had NO clearance which can mean the valve is sinking into the seat or that the stem has stretched due to over- heating. At any rate the backfiring I was getting went away after the adjustment! Good luck.
Old 01-24-2000, 05:02 PM
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Yes, I grounded plugs and got an a-ok on spark all-around, no electrics.

I checked the valves and had some odd results: the tolerances that I set 005 and 007 grew to 007 and 009 over the interval that I drove the car. Except for #1's valves, which stayed consistent. Screwy I thought, but may be useful here

the bubble float air-flow "p", is way high on #1 (checked recently, balanced when I tuned the car, which coud be due to the tighter valve clearances now that I think about it), and when I put the bubble on #2 the engine almost dies. Could this mean that the 1-2 is running so rich that restricting it with the sync. richens it to the point that It doesn't fire? In a similar question what is the upper limit of gasoline's flame point (about)?

Also, after running for a while the 1-2 head was only warm, not hot as compared to the 3-4. This also suggests a float problem, right? I will tear the carb off and check that next. Got any ideas on those valves?

Kokanee
Old 01-25-2000, 05:19 AM
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AIR. Regarding both of the problem carb situations mentioned above, I think it is common to focus on the gas jets, but air jets are commonly overlooked. For example, it is very common for the emulsion tubes and air jets on Dellorto carbs to get clogged with dirt, resulting in a rich or very rich condition.

If your number one cylinder is not firing and the plug is wet, once you have completely eliminated electrical considerations (always start there), then I think you should pull out, check and clean your air jets.

Regarding stumbling at high throttle check to see if your carb is sized correctly. For example, the main venturi limits the total air flow and thus the maximum RPM of the engine. Also, the air jets have a big effect on what I would call the crispness of acceleration. On my Dellortos, I found a huge difference in accelleration characteristics by going up two sizes on the air jet. This cut out any stumbling on acceleration. But be careful you are not getting too lean.

Other considerations: At what altitude are you driving? There is less O2 in the air and the air is less dense as you go up. Up here at 5280 ft above sea level, the jetting formula is quite different than at sea level. You have to compensate for BOTH O2 content and air density.

Also, as noted above, the distributor curve makes a big difference. I found a big improvement in the smoothness of acceleration by going from an 009 to a 205AA (stock 1.8L dizzy) with vacuum advance.

Good luck and stick with it.

Old 01-25-2000, 06:11 AM
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Thanks for all the help -- sounds like I need to do some reading. BTW: I am running a 009, and dont suspect any problems w/ spark. Like I said, the car actually runs strong, its just a very off-and-on throttle, and hesitation at full accel.
Now the other big problem is that the car runs way too hot....(I was hoping that would trace back to mixture probs -- we'll see.)
Old 01-25-2000, 06:50 AM
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THOSE CARBS WILL NEVER WORK RIGHT.EVEN THE VW GUYS WONT USE THEM
Old 01-27-2000, 09:07 AM
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