Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 Engine Rebuilding Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: May 2015
Posts: 2
Switched from Zenith to Weber carbs- now crunching noise when starting the engine?

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?
Old 10-12-2016, 05:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: Feb 2004
Location: UK
Posts: 2,231
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.
Old 10-12-2016, 06:39 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Feb 2008
Posts: 98
Quote:
Originally Posted by chris_seven View Post
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.
Old 10-13-2016, 03:51 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Feb 2008
Posts: 98
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.
Old 10-13-2016, 03:52 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
wayner's Avatar
 
Join Date: Apr 2007
Location: I live on the road, I just stay here sometimes...
Posts: 6,372
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.
__________________
Wayner
.
I can't wait to see what I do next!...
.
Old 10-13-2016, 04:38 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Feb 2004
Location: UK
Posts: 2,231
Quote:
Originally Posted by tornik550 View Post
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.
Old 10-13-2016, 06:47 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Feb 2008
Posts: 98
Quote:
Originally Posted by chris_seven View Post
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.
Old 10-13-2016, 03:00 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
Join Date: Feb 2004
Location: UK
Posts: 2,231
Useful to know
Old 10-13-2016, 11:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Racer
 
winders's Avatar
 
Join Date: Oct 2010
Location: San Martin, CA
Posts: 3,687
The teeth shouldn't break off the ring gear like that. Did you recently replace it?
__________________
Scott Winders
PRC GTL #3
Old 10-14-2016, 03:12 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 07:43 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.