Carb? problem

[Caterman7]

I've had my 7 for a couple of weeks and have had 500 trouble free miles. It's a Wenz built Cross Flow that I was told would not be very street friendly. Yesterday when I was halfway through a 70 mile trip the engine suddenly started acting up. The carbs were popping and snapping and the car was backfiring. Rough running regardless of RPM. It made it home but it was ugly. I was wondering if anyone has any thoughts or suggestions. I can do a lot of mechanical but not carbs. If someone could point me in the direction of a good resource or knows of a shop in CT qualified to work on it. Thanks.

[xflow7]

I don't know what spec your engine is built to, but mine is also a Marcovicci-Wenz engine and is very streetable. Having said that, mine is only ~135HP.

 

If the car was running fine for so long and then suddenly started running poorly, I wouldn't really guess a carb problem - at least not in the sense of jetting, idle mixture, etc.

 

Did the engine start acting up while in motion at speed? While at idle? pulling a way from a light? etc.

 

Obvious things might be:

 

- pull the plugs and see if any of them look strange

- make sure you didn't have a plug wire come loose or something

- check that throttle linkage between the carbs is still hooked up correctly.

[Ian7]

I think it was me that predicted unsuitability for street use; sorry!

 

Best guy in your area is probably JR Mitchell at GMT Racing, give him a call. Tell him I said Hi.

[TheDingo8MyBaby]

Pull the air cleaners off as well as the trumpets. Make sure the venturi tubes are secure.

 

If they're secure, pull out all of the jets and clean with carb cleaner.

 

So it's missing no matter what you're doing? Idling, accelerating, or cruising? Is there any difference if there's a load or not?

 

We also need to keep in mind it could be ignition too and not just carb.

[MHKflyer52]

STOP and check the timing first to see if it moved as that will cause what you have described before you tare into the carbs on your car.

 

Carbs will not usually cause it to back-fire unless they are so messed up that they are dumping raw fuel into the cylinders.

 

If you have points in your distribuator then check to see if they did not colse up or burn and pit as that will also cause what you have described.

[lowflyer]

I agree with the last posting. If it came on suddenly, I would suspect a timing issue. Perhaps the distributor has moved slightly or more likely something inside the dizzy is causing the problem.

 

You don't mention what kind of ignition you have, whether it has points/condensor or a Petronix type of pickup or something else. I had a very similar problem years ago with a car equipped with a dual point ignition system when one of the sets of points became loose.

 

If the car is equipped with Weber 40's the only thing I can think of there would be a stuck float, perhaps caused by some dirt/debris in the fuel.

 

The timing is easiest thing to check.

 

Good luck, and don't overlook the really simple things - like a spark plug wire burning through or coming loose.

 

Ken Edney

Chandler, AZ

[Kitcat]

Yes, carbs tend to go off-song slowly and this was sudden.

 

When mine did what you describe, my radiator hose had sprung a leak which blew coolant back onto the distributor, which soaked it and eventually shorted things out inside. As you say, it was ugly (first and only time in 12K mikes of driving my se7en I ever needed a tow).

 

Mike

[catracer]

Believe I'd be looking at fuel filter and ignition first. Rule that out b4 going into carbs.

[BusaNostra]

Is this a weber sidedraft?

 

If popping, it's rich... the adjustment went off --->as usual.

Use a colortune.

[lowflyer]

I've been playing with Weber side drafts (40 DCOE's mostly) on and off for about 40 years and have never seen the "adjustment go off".

 

How exactly would that happen?

 

Ken

[BusaNostra]

air/fuel mixture screw adjustment.

Also check the synch.

 

I played the weber for just a month, I know there is a mixture screw.

 

40 years in weber?

Edited July 27, 2009 by BusaNostra

[lowflyer]

There are a number of screws that can be adjusted, but once adjusted they don't change their setting by themselves.

 

About the only thing that could effect the running (assuming that the carbs are set-up right in the first place) is a piece of dirt coming through the fuel line and either blocking the float needle open or blocking off a jet somewhere in the system. A good reason for an effective fuel filter somewhere in the system.

 

BTW, I've done this (on and off) long enough that I can use a stethoscope that was made from a pair of airline earphones to listen to the airflow through the carbs to balance them, when I don't have a Unisyn. The last guy I lent my Unisyn to never returned it, and that was in the late 1990's! The sound is quite easy to hear, changes are obvious so getting the individual mixture screws adjusted is easy.

 

On a similar note, a lot of people try to balance the carbs without disconnecting the linkage between the carbs first. If the linkage is wrong, the balance of the carbs will almost never be right.

 

Still betting on an electrical problem.

[Caterman7]

I'd like to thank everyone for their input and ideas. Today I finally had a chance to work on the car and found 1 plug not firing. After checking the plugs and wires it turned out the magnetic pick up for the Pertronix electronic ignition was starting to separate at a seam. I tried to cheap out with a little super glue. It looked good enough and ran much better but not under load. I replaced the pick up and all is well. Thanks again to all.

[xflow7]

Very glad to hear you've got it sorted. Now, time to drive the snot out of it!!!! :driving:

[lowflyer]

Someone smarter than me once said, " About 80% of all carburetor problems are electrical".

 

I guess we can make that 81%.

 

Glad you found the problem.