Need help tuning

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jaymzz

Need help tuning

Post by jaymzz »

I have been trying to tune my vee and am having some major issues. It has a really bad hesitation at the low end of RPM's, but when it starts to rev it smooths out. It is also popping through the exhaust every now and then, but not like a backfire just a popping noise. I have been in contact with the last owner of the car on some of the specs so I will post them up plus what I have tried. Last year when I drove it once, it was popping through the exhaust and I thought it was the old leaky exhaust. Thanks in advance. I have been messing with it everyday trying to get it running good.

What I have tried:
Adjusted the valves to .008 intake .012 exhaust.
Checked all gaps on the spark plugs
checked all the spark plug wires and they seem fine
Cleaned the fuel filter
synced the carbs to 7
Made sure throttle linkage is working smoothly and the same per side
cleaned the distributor cap and rotor

What it is I am working with
duel port 1600
duel 44 Webers with 28 ventury as per SCCA rules for B mod
Stock internals
electric fuel pump
electronic Bosh 009 distributor
Dietmar
Site Admin
Posts: 650
Joined: June 24th, 2006, 11:56 am

Re: Need help tuning

Post by Dietmar »

Trying to respond to your question is rather difficult. The car that you have is a Formula Vee, but the engine is not so I will venture some guesses.

Why are the valves set at 8 and 12? VW sets their valves at .004 on all intakes and exhausts on the dual port heads.
You did not say what the gap was on the spark plugs.
The above two items would not cause the problem- just two items that needed clarification.

You did not mention checking the timing- either static or with a strobe light. A possible cause.

Since we do not know what cam is in the engine, I would check for a leak either at the manifold(s) where they enter the heads or the exhaust where the exhaust attaches to the head(s). Lastly I would suspect a carb issue. Here is where most of us would get lost as the Weber is not on our parts list! Sorry.

Hope this helps
Dietmar
jtgb
Posts: 19
Joined: December 25th, 2008, 9:35 pm

Check your Jets

Post by jtgb »

You may want to re-post your question in the tech tips category if you don't get a response. The professional builders/tuners are more apt to identify your setup compared to us FV-centric home garage guys monitoring the novice section.

Not that it necessarily applies to you, but I had a similar problem at Driver's School last year. Fred Clark, who builds the Caracal Vees, wandered over to my paddock wondering why I had my idle set so high - I explained to him it was the only way I could keep the car from stalling. He fidgeting with this & that and found a small piece of fuel-cell foam lodged in my main carb jet. After a shot of compressed air, my motor now purrs at 800rpm.

The other side of that story - you need to clean out the fuel pump after installing an inline fuel filter (my car didn't have a filter) to be sure you don't foul your carb. Silly me.
Joseph Brown
CCR, FV38
DanRemmers
Posts: 293
Joined: June 24th, 2006, 7:21 pm

Re: Need help tuning

Post by DanRemmers »

There's a chance it's a leak somewhere in the intake system. Check all fasteners and gaskets.

It's possibly running rich, or the fuel pump is dumping fuel too fast. The best thing would be to put it on a dyno and check the F/A mixture.

BTW, I adjust all my valves to 0.007". (1600 DP with single Dellorto carb)
hardingfv32-1
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: Need help tuning

Post by hardingfv32-1 »

Is this a new issue? Did it run great before?

What is the history on the carbs? Have you worked on them?

Brian
ajax
Posts: 131
Joined: July 4th, 2006, 9:22 pm

Re: Need help tuning

Post by ajax »

I'd advise getting a Weber tuning book. these are great carbs, everthing is adjustable & tunable and it takes a "system" to go through the process so you do not screw up one fuel circuit while fixing another.
I have a Datsun 280 with triple Webers (this is like 6 single barrel carbs) and during my initial tuning process found (2) key items The idle circuit has small, no tiny holes and is easy to clog. as each runs it own cyl I found one or more cyl will drop out at low RPM and shows up as a stumble when accelerating, make sure each of the 4 circuit is flowing right! Also a real key to Weber tunning is and this may sound wierd, but is ignition advance! They love ignition advance, even when cam is stock, advance needs to be greater then normal. Other wise they spit back and run rough at anything other then flat out. Keep at it, they are sweet when right!
hardingfv32-1
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: Need help tuning

Post by hardingfv32-1 »

Any idea why Webers like ignition advance?

Brian
FM4SOLO
Posts: 129
Joined: June 26th, 2006, 4:17 pm

Re: Need help tuning

Post by FM4SOLO »

I agree with looking at the carbs. Check that all jets are clear, the floats are set properly (this has a surprising effect on drivability), and that there are no vacuum leaks. I set my valve clearances at .006, intake and exhaust, cold as a stone. While your at it, check the torque on the head studs (don't ask how I know that, it's embarrasing.) Check for exhaust leaks, they can be a source of mild popping as well. I have a pertronics rev limiter that went bad once, caused all sorts of problems.

A good site for Weber tuning advice is http://www.redlineweber.com/html/Tech/T ... ntents.htm

Good Luck.
Charles
jaymzz

Re: Need help tuning

Post by jaymzz »

Thank you for all the responses. The reason the valves are set to that is because that is what the book I have says to set them at. I will go out and re adjust them. One of the manifolds has been repaired. I know this because I can see where the weld is on the outside. I don't know a whole lot about the motor, except it has about 100 miles on it. This is one of the problems about buying someone else headaches. I also was wondering if it was the fuel pump. I have an extra that I will put on and try. If that doesn't work then I will take the carbs apart and check everything out. Again thanks for all the help. :)
Bill Carroll
Posts: 72
Joined: January 21st, 2009, 8:33 pm

Re: Need help tuning

Post by Bill Carroll »

I am a novice to Vee, but ran Webbers for years on type 1 engines, all of the advice above is to be considered. I do recomend a couple things. first, only make one change at a time. This does take longer, but costs half as much. Second a good look at all of the obvious things (jets, I have removed little pieces of whatever many times to fix a poor running engine, filters, intake & exhaust gaskets locations. your repaired manifold would be suspect, try spraying either (be careful) on the crack area while running, if rpm goes up it needs fixed, if not spray it at each intake gasket. Remember this is either, very flamable, safety first. Look at the size jets you have when you check them, if they have been drilled out, take a minute to check them with clean numbered drills and record what you have, they should all be the same size(4 air and 4 fuel). then get back to us and we'll have you going 200mph in no time! :mrgreen:
jaymzz

Re: Need help tuning

Post by jaymzz »

Sorry I updated my car thread but not this one. The problem ended up being the carbs were full of gunk. I rebuilt both of them and now it runs awesome! Thanks for the advice.
jaymzz

Re: Need help tuning

Post by jaymzz »

So now that I have it running fairly well, I am going to rent a dyno and fine tune it. What should the AFR's be? I am familiar with tuning fuel injection on a dyno, but not a carburetor car. Is there anything special I should worry about?
DanRemmers
Posts: 293
Joined: June 24th, 2006, 7:21 pm

Re: Need help tuning

Post by DanRemmers »

Jim from SR Racing can help with the numbers. He tuned my solo motor, and it runs great.
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