Switched from Zenith to Weber carbs- now crunching noise when starting the engine?

[Chily89]

I am very very confused. I recently rebuilt my 2.7. I had been running very modified Zenith 40 tin carbs. The engine ran extremely well however only under about 3000 rpm. I also have a set of Weber IDA 3C's. I decided I would switch to the webers. Switching the carbs was super easy. I was very careful to make sure that no bolts or washers went down the intake ports during the switch.

I tried to start the engine and then I was going to sync the carbs. Unfortunately, I heard what sounded like a crunch coming from the starter area. I thought it was just a fluke so I tried it again- same issue. The engine will turn completely. I can even get the engine to fire for a few seconds. Once it is running- no crunching noise.

The sound is also similar to what it sounded like what I installed a distributor 180 degrees off- cylinder firing at completely the wrong time. Nothing has been changed timing wise so I don't see how that could be it.

I figured that maybe somehow something got into a cylinder when I changed carbs so I removed all of the spark plugs and scoped every cylinder. Everything appeared perfectly normal and I did not see any foreign bodies.

Since the spark plugs were out, I decided to crank the engine. No cruching noise. I am super confused.

Any ideas what might be going on? The only thing that I can think of is what if only one of the two carbs is firing (as if the carbs were extremely out of sync)? Could that make a noise like this?

[chris_seven]

So with the Zeniths the engine only ran correctly to 3000rpm ?

This is a very light throttle opening and depending on the venturi and Jet sizes used could be a clue that something may be wrong.

Did you try to find out why it only ran correctly to 3000rpm?

If you haven't changed the timing or the leads then it can't be firing at the wrong time as the carbs won't influence this aspect of the engine.

An engine running on three cylinders would sound like a 3 cylinder engine - the 'crunching' noise is just bizzare.

Did you check any of the functionality of the Webers before you bolted them on? Are the needle valves stuck? Are floats operating? and not full of fuel, do the accelerator pumps work ???

I take it you changed the cross bar and drop links?

The Weber and Zenith Air Boxes also differ but I guess you are a long way from these issues.

[tornik550]

Originally Posted by chris_seven

So with the Zeniths the engine only ran correctly to 3000rpm ?

This is a very light throttle opening and depending on the venturi and Jet sizes used could be a clue that something may be wrong.

Did you try to find out why it only ran correctly to 3000rpm?

If you haven't changed the timing or the leads then it can't be firing at the wrong time as the carbs won't influence this aspect of the engine.

An engine running on three cylinders would sound like a 3 cylinder engine - the 'crunching' noise is just bizzare.

Did you check any of the functionality of the Webers before you bolted them on? Are the needle valves stuck? Are floats operating? and not full of fuel, do the accelerator pumps work ???

I take it you changed the cross bar and drop links?

The Weber and Zenith Air Boxes also differ but I guess you are a long way from these issues.

I should clarify what I meant by the engine doesn't run well about 3000 rpm with the zeniths. At rest I can rev up the engine past 3000 without any issue. When driving I basically loose power at that point. I believe it is a combination of jetting an timing issues. I think it is fairly fixable. Basically I just wanted to switch to webers.

The webers have been gone over completely. Pretty much anything that is brass is new. All ports are patent and floats move freely.

[tornik550]

The noise seems to have come from the starter area. I am wondering if I might have broken a tooth on the flywheel? What are the symptoms of that? The carb change could have just been a coincidence.

[wayner]

Is the noise still,there?

If you suspect that you dropped something in a cylinder it could have fired out the exhaust, hopefully not touching any valves.

[chris_seven]

Originally Posted by tornik550

The noise seems to have come from the starter area. I am wondering if I might have broken a tooth on the flywheel? What are the symptoms of that? The carb change could have just been a coincidence.

I would have thought a starter ring noise would still be there even with the plugs out.

[tornik550]

Originally Posted by chris_seven

I would have thought a starter ring noise would still be there even with the plugs out.

I am thinking that since the engine wasn't under load- it didn't make a loud enough noise for me to head over the starter motor.

I just removed the starter and sure enough- broken tooth. So no connection to the carb change.

[chris_seven]

Useful to know

[winders]

The teeth shouldn't break off the ring gear like that. Did you recently replace it?