weber and electromotive help

pu911 · 06-14-2003, 07:55 PM

Gentlemen,
I have a 3.5 L rsr "spec" twin plugged motor, it has 46mm webers and a electromotive HPV-1 twin ingnition set-up. The car ran very well until recently when my mechanic switched to a different set of carbs. He swears all parts (mains, emulsions, idle jets) were either the same or switched from the original carbs. The problem is this the car hardly runs anymore, it pops and backfires through the exhaust and carbs, it runs OK at wide open throttle but not at any other condition, it idles ok when cold but not when warm. My mechanic thinks something is wrong with the crank fired ignition, but put new plug wires and went completely through all the electical conections and I can't find any problems. Can the carbs cause the symptoms I have described above. I went through other threads, these problems seem more severe than the issues others were having.
Thanks as always,
happy fathers day all
Phil

Nitrometano · Nitrometano's Garage

The problem that you have no are the webers because you only are using the webers like a throttle for control the air flow and no like a carburetor. The problem like the one that you discribe can be the pickup coil that reads the distributor to send the signal to the capacitor and then to send the signal to the coil and to the distributor cap. That explosion that occurs maybe are a wrong ignition timming or a static distributor. You hace a double ignition distributor system. I think that they run in a timming sequence. Check it. I'm not expert in this electromotien systems in combination with webers. I'm in planning to add one of this combination to my Porsche. I will question your problems to my friends. They are familiar with this electromitive system in their drag racing mazda rotary car. One on them have the world faster rotary car in the world. Him are the guy that programs this vehicles. I will try to help you. For know check this things.

Nitrometano · Nitrometano's Garage

You are using the carburetors in the manner or no?

911pcars · 06-14-2003, 08:24 PM

Runs well with old carbs.

Doesn't run well with new carbs.

Doesn't this mean something is going on with the new carbs? Can you try the old carbs again to verify?

Perhaps an idle circuit is blocked. Check jets for foreign objects, then blow air through all fuel passages to verify they're open.

Check float bowl fuel level as well.

Sherwood Lee
http://members.rennlist.org/911pcars

pu911 · 06-15-2003, 05:42 AM

Sherwood,
Thanks, it does seem simple. We have pulled carbs apart blown everything out, unfortunately I sold the other carbs, I may have to through myslef at the mercy of the buyer and see if I can get the old ones back. My wrench who is extremely experienced says all is well with carbs, that they could not cause the symtoms I am experiencing. I am not buying it at this point. I now if it ain't broke don't fix it.
Take care, enjoy your fathers and kids,
Phil

rs911t · 06-15-2003, 06:50 AM

Sounds like clogged idle jet(s) or passages. Won't be a problem at WOT and otherwise can be intermittent. Try another set of carbs.

pu911 · 06-15-2003, 07:14 AM

We have pulled the carbs apart and blown out all these areas, very starnge problem, would the carbs be causing all the backfiring problems or would that have to be in the ingnition.
Phil

pu911 · 06-15-2003, 07:20 AM

Another thing is the car starts right up and idles fine, but as soon as you crack the carbs open under load, things seem to go to pieces. The problem kept me off the track this weekend, it's killin me.
thanks all,
Phil

West · 06-15-2003, 08:08 AM

Since your mech. is so sure it's the carbs, ask him to prove it! Have him put the carbs on another car in his shop and see if it runs correctly. Just my 2 cents.

WERK I · WERK I's Garage

Phil,
Sounds like an over-rich condition. If it runs fine cold, then stumbles when warmed up, sounds like too much fuel. Was the fuel pressure adjusted when the webers were installed? I seem to remember reading somewhere, that webers are very sensitive to fuel pressure. I thought they ran better with lower pressure settings. You might want to do a search on this forum or the Rennlist forum on the subject.

rs911t · 06-15-2003, 12:20 PM

Quote:

would the carbs be causing all the backfiring problems or would that have to be in the ingnition

Yes, a clogged idle jet makes for a very nasty running car. Have had this problem first hand. Misfiring and/or dead cylinders dumping raw mixture into the exhaust. A local mech told me "99% of the time it's a clogged idle jet." Sure enough, we pulled them all and found gunk in two. Note - I'd recently rebuilt both carbs. I figure I'd simply loosened the varnish without actually getting the passages clean.

Start the car and let it idle (crank the idle adjustment if you have to or get someone to work the throttle). Remove one jet at a time, pull the jet out of the carrier and inspect.

david c. · 01:53 PM

I'd bet there is something very small stuck in the idle circuit somewhere. Even a small piece of dirt roughly the size of a pepper flake causes my Webers to run poorly and manifest the same symptoms you have described.

Here's another wild guess... you said that most of the parts from the old carbs were transferred to this new set. But, you also might consider measuring all the jet sizes with a jet gauge to make sure NONE of them were from the old carbs.

Some people will ream out jets rather than getting new ones. Maybe you think you've got the right size jets somewhere but they really aren't if they came from the used carbs?

Paul Thomas · 06-15-2003, 04:11 PM

I am curious, if the car ran well before, why make the change? I run the same twin-plug HPV-1 setup that you do and have never had problems that weren't from the induction.

BTW- Please tell me what advance settings that you are using. I have been experimenting with mine and comparison would be great.

Dual plug 3.5L MFI

Paul

pu911 · 06-15-2003, 05:36 PM

Guys thanks for all the input, we did measure all the jets before the install, they are sized as indicated. I'll look harder at idle circuit. Paul I'll pull the covers off the electromotive controls and let you know the set-up. I thought this electrmotive stuff was fairly bulletproof myself. What do you use as a redline. I bought the car from someone who did not know much about it unfortunately, I am going to try and run down previous owner who had work done. I could see that car was nicely contructed and boy did it run. In hindsight never should have switched carbs, I had an extra set that mechanic thought were a little nicer, bet I spend more money getting it to run correctly than I got for carbs, I.R.Pissed.
Phil

clr2cont · 06-16-2003, 06:44 PM

I feel your pain. i have a 76 2.7 with webers on it. i bought it and it ran like poop! It would Pop through the intakes and backfire on a regular interval. I checked all my timing, and it was all right on. I then removed the crabs and cleaned them as Best I could, and would you beleive it cleared up alot but not all the way. I then spent the money and had the carbs professionally cleaned and adjusted on a flow table. they run great. It was told to me this way, If they pop through the intakes then the mixture is too lean. If they backfire through the exhaust the mixture is too rich. The carbs could be clean, but you may be drawing air in theough the intake gaskets.

pu911 · 06-16-2003, 08:00 PM

I took your guys advice, pulled carbs, blew out everything, saw some schumutz here and there. I'll fire it up again tomarrow.
Phil